Honda NH80 Aero/Lead Scooter    
Whether your scooter is simply a travel appliance or an escape pod used to fight the gravitational pull of the "daily grind" I am hoping this page will offer something useful, if not entertaining. The information contained in this page is a record of my experience and  not  that of a trained mechanic or  even a rational person .  "If  its not broken don't fix it" is a methodology that I have often had trouble following. I enjoy taking things apart and seeing how they work .  If in doubt a Honda factory trained  mechanic is usually availiable within scooting range. Nevertheless the following journal will , I hope, contain information valuable to any Honda NH 80 owner.  Certainly more info than I'd been able to find on any other site. Duplicating my efforts does not guarantee the same results and should only be attempted by a qualified scooter mechanic or someone crazy enough like myself who is willing to sacrifice a perfectly good scooter to answer the eternal question "what if...".        April/2002

  Having completed my Elite LX scooter to the point it was rideable, I decided to visit the local wrecker.  I spotted a scooter sitting under a batch of used motorcycle gas tanks and a bit of digging revealed a 1984 Honda Aero 80 (NH80) .  A quick look at the engine revealed a two stroke with a close resemblance to my Elite 50 although this engine was substantially larger. The engine turned over and even ran! Included with the price was also a newly upholstered seat. How could I resist? After gathering some information from the local library I concentrated on tearing down the bike to clean and do a mental inventory of what needs fixing and or replacing right away. First a picture of the cleaned up and painted scooter. 

1984 nh80 Aero


Facts of Life:

The following is  information from the factory service manual for an 85 NH80. 

Dimensions          Overal Length 1,715 mm / 67.5 inches

Overal width 680 mm / 26.7 inches

Overal height 1.050 mm / 41.3 inches

Wheelbase 1,185 mm / 46.6 inches

Seat height 745 mm / 29.3 inches

Ground clearance 110 mm / 4.3 inches

Dry weight  77 kg / 170

Curb weight 82 kg / 180.8 lb
Frame Gross vehicle weight rating 234 kg / 520 lb

Vehicle capacity load 152 kg / 335 lb

Front tire size 3.50-10-4PR

Rear tire size 3.50-10-4PR

Front tire pressure 21 psi, 1.5 kg/cm2 ,150 kPa

Rear tire pressure up to 90 kg 
or 200 lbs load
24 psi, 1.75 kg/cm2, 175 kPa

Rear tire pressure up to vehicle capacity load (152 kg / 335 lbs) 32 psi, 2.25 kg/cm2, 225 kPa

Fuel Capacity 4.8 litre, 1.1 Imp gal, 1.2 US gal
Engine Type Air cooled two stroke

Cylinder arrangement single cylinder (15 deg from vertical)

Bore x Stroke 48 x 44 mm

Displacement 80 cc (4.88 cu in)

Compression ratio 6.8:1

Transmission oil  0.09 litre 10W-40W Honda 4-stroke oil or equivalent 

Oil tank  1.2 litre of two stroke (2T) oil

Lubrication system oil injection from remote oil tank

Cylinder pressure 142-200 psi
port timing Intake open and close reed valve controlled

Exhaust open 80 deg BBDC

Exhaust close 80 deg ABDC

Scavenge open 55 deg BBDC

Scavenge close 55 deg ABDC

Exhaust duration 160 degrees

Scavenge duration 110 degrees
Carburetion Carburetor type, size  round slide,
 16 mm venturi

Model # PB54E

Air screw fixed range

float level 8.5 mm
Tune-up specs
drive belt width 13.5 mm minimum
roller weight size 18 mm diameter (17.4 minimum)
cylinder compression 142-200 psi
spark plug type (NGK)
standard BPR6HSA
below 41F, 5C
High Speed              

turn signal bulbs 1156

 Service manuals and owner manuals are available online from Helm inc. Service manuals  are invaluable for maintaining or resurrecting a scooter and will save you a great deal of money in repair /maintenance costs.

Scooter Disassembly:

    Even if all you wanted to do was change  the spark plug, its necessary to know how to remove the side panels. The following diagram shows the side panel (both right and left have the same attachment points) sequence of removal. First, remove the phillips head screw (#1 in drawing). The rest of the attachment points are push or pull fit but it helps to do them in sequence. exploded view of body panelsNext gently  remove the tabs (#2) from the corresponding slots in the rear body panel. The attachment points shown as # 3 are two finger shaped extrusions. They fit into corresponding holes in the frame. The only thing preventing you from pulling the panel straight out are the tabs (A) resting in slots (B) in the side panel. Make sure the seat is up and gently pry the topmost #3 out. Then rotate the panel clockwise so that the tabs(A) come out of the corresponding slots(B) and then you can pull the bottom #3 out and the panel will be removed.  You'll now be able to do some fairly routine maintenance like changing the spark plug, removing and cleaning the air filter and gazing in awe at all the mysterious hoses emanating from the carburetor.

    The front battery cover is straightforward by comparison. There are some concealed brackets (#4) which are bolted to the frame  I missed first time around. The battery itself can be accessed by the door at front  however if you are going to remove the exhaust, work on the oil pump, the removal of the battery cover helps. Once the cover is removed you'll also have access to the starter solenoid which is housed in the battery tray. The gas line attachment to the gas tank  is also accessible.  The battery is mounted in a plastic tray which is attached to the frame by three bolts. Once the tray is removed, you'll see what appears to be a number of "inspection" holes in the frame.  Some of these holes allow you to get a socket on to the nuts holding the exhaust in place. Much easier than having to grope with a wrench.  

    I removed the left hand engine case cover to inspect the belt and clutch. While I hadn't intended to do any major work until later, the scooter was accelerating poorly and only reaching a top speed of about 50 km/hour. It felt as though the clutch was slipping as engine revs would rise but the scooter would not accelerate unless you increased the throttle very slowly.  Sure enough, the belt measured 10 mm wide compared to the new measurement of 14.0 mm. There was black "dust" all over the engine case from the worn belt .  The clutch is fine and has lots of wear left so I'll just replace the belt for now.

    I had to remove the left rear body panel ( 1 phillips head screw), the black plastic rear floorboard/battery cover ( two bolts with 10 mm head, one nut with 10 mm head and two bolts with 8 mm heads) and the left hand metal floorboard support (two bolts with 12 mm heads and one with 10 mm head) to remove the engine side cover. The kickstart lever was also removed . In order to remove the nuts holding the clutch housing and the front pulley housing I used the "universal holder" that I made for use on my Elite and detailed on the Elite  page. Before removing the case from the engine, I used masking tape to hold the bolts  so I would know which holes in the case they had come from. There are a variety of bolt lengths and you should take some steps to identify which bolts go in which holes before you remove the side case.  One area where problems could occur is at the kickstart shaft. When the side case is removed, the kickstart shaft should stay with the motor. I had to remove the case after re-assembly as I had pulled off the case with the shaft attached and all sorts of springs/ pins/ gears had to be re-assembled by the "this must go here" approach which should be avoided at all costs unless you derive satisfaction from solving puzzles. I mis-matched the gear mesh the first time and had to take it apart again. A large gear puller would have allowed me to separate the side case without disturbing the kickstart assembly.  Purchasing a workshop manual ahead of time wouldn't be such a bad idea.

    After replacing the belt with a 726 mm x 15 mm x 30 version,  the top speed was much better.   Acceleration was not that "brisk" although the engine seemed to have good bottom end power. The top gearing was achieved at a very low engine speed and I can understand how lightening the weights in the front moveable pulley would be of benefit to acceleration. As I understand it, the ideal is to keep the motor at top speed all the time and to have the variomatic drive adjust the "gearing" according to the driving demands (acceleration, hills, cruising).

 I ended up stripping the bike down and sanded a few areas where the paint was loose or rust had started. I brushed them with black enamel. I sanded the wheel rims and brushed them with silver enamel. The tank was rusty on the inside so I had to drain it, remove it and clean it. Being "economically impaired" I filled the tank with some sharp edged pebbles and started shaking. I mean shaking and shaking until my arms felt rubbery.  Otherwise a radiator repair shop should be able to boil the tank to remove any scale. The idea is to remove the rust before starting the scooter and having all that rust work its way through the fuel system. The fuel filter was replaced. The carburetor was removed , then inspected and cleaned thoroughly. The airfilter was also removed and cleaned.
         Oil was checked and replaced, both in the autolube tank as well as the final drive. A new spark plug was installed. The exhaust system was removed, wire brushed and painted with "barbecue" paint.  I charged the battery and checked the connections weren't too corroded.
    I also took off the various peeling decals from the body parts and repainted them with a silver spray bomb. I used laquer as I wanted silver otherwise I probably would have used an enamel for a solid colour. The panels were wet sanded, then primered and then coated with the finish coat. Follow the instructions on the side of the container and all should go well. I removed the wheels/brake drums and checked for brake wear/cleanliness although Honda has break wear indicators mounted externally. Have someone squeeze the brakes and then checkout the front/rear brake arm that moves. The brake arm should have a small arrow on it and a corresponding line on the brake drum. When the arrow and line match up, its time to replace the brakes.
I removed those two silly large plastic things mounted on the front suspension swing arms that hold the front axle.
I also applied much "black gold" polish to all the black plastic body parts. They were turning kind of whitish but cleaned up nicely. The polish can be found at any auto parts/department store ~ find one meant for the black body parts on a car such as bumpers,window trim etc.    

 Performance Improvements:

  The warning at the top of the page is especially applicable to any changes you decide to make. While I'm hoping to obtain the "greased lightning effect" from my scooter, I'm at all times aware that any changes could indeed reduce the lifespan, reliability and resale value.  The safe and sensible method of obtaining a faster scooter is to go out and buy another larger, faster more expensive scooter. Even if you decide to keep yours "stock", the following  will at least make you familiar with the various parts and why you should keep the stock parts in good shape. The primary performance increase is to ensure all the stock pieces are in good operating condition. Even if you want to improve the performance of your scooter, make sure all the stock pieces are in good shape first. That would include drive belt, Variable pulley weights, brake shoes, tires (overall shape and day to day pressure), air filter, fuel filter and final drive oil and that would just be the short list.  

    Simply tuning the motor to equal that of a comparable motocross or street bike of the period would result in substantial improvements in both acceleration and top speed. The frame and running gear on the 80 are the same size as larger scooters in Hondas line-up and considerably beefier than an Elite 125 I have. In my opinion a 25% increase in power wouldn't be overstressing the frame or motor. 

Honda Aero NH80 manifold and TM24 Mikuni carburetor If your stock carburetor/auto choke is acting up, think about a replacement carburetor slightly larger than the 16mm stock Keihin. To give you an idea of the size , Japanese suppliers sell a 24 mm carburetor kit for the Lead 90 , the modern day equivalent of the Aero. Consider that stock 80cc motocrossers use 24 to 28 mm carbs. Local motorcycle shops or internet retailers  sell carburetors like the VM20 mikuni with a manual choke that would substantially increase your motors breathing ability (over 50% increase in area of venturi).  The Mikuni VM20 and VM22 carbs come with a flange mounting like the stock keihin although the flange width on the mikunis is wider than the stock manifold so an adapter is going to have to be made or, alternatively, material ground from the carbs flange mount to allow it to fit. The stock manifold has a 19mm throat so anything larger will need some grinding. The Keihins throat is offset to the centerline between the mounting bolts whereas the mikunis throat is the same centerline as the mounting bolts. An adaptor made out of aluminum or some grinding of the manifold would be required to match the manifold opening with the carburetor mouth. Shown in the picture at top is a TM24 Mikuni carb adapted to an Aero NH80 manifold. At least two of the tubes need to be plugged.
I recently ordered some parts from Steve at
 VT cycles in hawaii and he said he had a bolt-on replacement for both the Aero 80 carb and the reed valve which would give the Aero 80 similar breathing to the Honda CR80, Hondas racing dirtbike. Steve had this to say:
"I have a carb set up for the Aero 80 scooters.  A big dual reed, chrome CT intake manifold w/ a OKO 21mm carb (or 24mm) and an adjustable throttle cable.  These are the PWK "D-slide" Keihin type carbs, so you can get these jets from mostly any bike shop. It has a manual choke, but they are the pull the knob on top of the carb type. Not the remote cable type."
  VT cycles also has the Metrakit 19 and 21mm carburetor kits (dellorto carb)  with a cable choke. With the aero 80 bodywork you'll need some way of remotely actuating the choke.

Shown at right is the dual reed manifold and a 50cc scooter manifold of similar size to the Aero 80 manifold . This is much better than just a big bore carb as the manifold incorporates two reeds rather than the Aero 80s one reed. The unit bolts right on to the Aero 80.

malossi carb21mm carburetor for Aero NH80 Scooter Another altenative is one of the aftermarket carb kits offered for the 94 and up 50cc Honda Dio. The manifold from a 1997 SK50 I have has the same distance between the mounting holes as the Aero 80. Kits from 19 mm to 21 mm are offered from European manufacturers (Polini, Malossi) as well as the Spanish Amal carb either bolts right on to the stock intake manifold or to an adapter that bolts to the stock manifold.  The photo at left shows the generic Malossi carb kit. Most scooter performance retailers will offer a 19 or 21mm kit for the Dio bolt pattern.
Consider that even a 19mm carburetor has 43% more venturi area than the stock Aero 16mm carburetor. 

    You could also tune the engine for increased RPM if top speed was that much a concern or for more torque if acceleration was the prime consideration. A good site to visit for two stroke tuning tips is Macdizzy's site.  Besides offering a lot of good advice it also has numerous links to other tuning web sites.

The Honda uses a reed valve in the intake system to control the flow of gas/air mixture into the crankcase. The reed valve housing is located between the intake manifold and the crankcase . The stock reeds are metal. Boyesen, who make reed valves that offer performance increases in bottom end power, offer a reed valve (part # 740) for the Lead 80 which should fit the Honda Aero. I sent Boyesen a diagram of my reed valve and they confirmed The Lead 80 model (#740) will fit the Aero 80.  The Aero 80 reed valve is identical in overall size to the 50cc Honda "Elites" however it has two petals whereas the Elites I'm familiar with have three petal reeds.  The bolt pattern and gasket shape for the reed valve body is identical to the 50 cc Elite. The 50cc Elite has a three petal reed whereas the Aero 80 has a two petal valve reed. So its possible to swap the mounting block and a carbon fiber reed valve from the 50 onto the Aero 80. The carbon fiber reeds perform better at higher RPM as they resist "fluttering". For low to mid RPM (the stock range of the Honda) the Boyesen reeds are the best as, being more flexible than the stock or carbon reeds, they'll supply more fuel .

  The advance in the ignition (14 degrees) isn't as advanced as the NH125 (16 deg) or my Elite 50 (17 deg).  I do know that the wiring setup (connectors, colour of wires, etc ) on the aero 80 is identical to the setup on my 50 Elite scooter. I had switched over a performance cdi unit for the Elite 50  but I couldn't feel any difference in performance on a stock aero 80.. The cdi unit works in conjunction with all the other electrical components and substituting just one piece from another system does not guarantee the system as a whole will function properly.  Definitely a "you're on your own" item. For some insight into how to advance the ignition timing using the stock CDI, vist this page.  

Modifications I've done so far:

 I've also increased the size of the main jet and have managed to get rid of the bogging I was getting after 3/4 throttle where increasing the throttle actually slowed the bike down. The acceleration improved as well as the top speed which has increased to over 70 km/hour (44 mph) and that was on a fairly short stretch. I haven't had a chance to wind it out yet. I'm including below a list of number drill sizes and their corresponding jet sizes for those who wish to use number drills available at hobby shops to increase the main jet size. What worked for me may not work for you as jetting can vary by season, altitude, humidity etc so you'll have to figure out what works best for your scooter in your area.

    Number Drill Size  Imperial measurement  Metric measurement
     #65      0.0350 inch      0.889 mm
     #64      0.0360 "      0.914 mm
     #63      0.0370 "      0.940 mm
     #62      0.0380 "      0.965 mm
     #61      0.0390 "      0.990 mm

I have checked the mileage after two tankfulls and I'm getting about 100 miles per imperial gallon which would be about 80 miles per US gallon. If you drove your scooter sensibly you could get a lot better mileage. You have to figure anybody who tries to "hop up" a scooter probably isn't what you'd call sensible so use my mileage figures only as a general guide.

Jan 2001 update ~  I've measured the port timing for Exhaust and transfer ports. The timing is fairly conservative (Exhaust~160 degrees, Intake~114 degrees) and by raising the cylinder 1.5 mm  and raising the exhaust port an extra millimeter you would wind up with 180 deg Exhaust/130 deg transfer. This would result in an engine capable of higher RPM. It would also reduce bottom end torque although fitting the Boyesen reed should help in that department. The piston has at least 0.076 mm clearance which is way over the recommended clearance (0.050 mm) and the rings are 3 times the maximum. Time for a new piston. The top of the cylinder liner walls are as thin as 3 mm thick in one spot  so a  practical piston size would be about 50 mm leaving a minimum 2 mm cylinder wall.  Wristpin size is 12 mm, the same size as the 1994 and later Elite 50cc. Compression height appears to be 25 mm and overall height of the piston is 48 mm to the shoulder.

A 50 mm piston would give  86.4 cc displacement, a 51 mm 90 cc. This is unknown territory and issues such as piston compression height, piston length, ring pin position and the profile of the piston top would all have to be taken into account to determine what pistons could be suitable. My particular cylinder wall was 6 mm thick in places but the bore was off centre.

A european catalog for Wiseco pistons (an aftermarket supplier) listed their 1984 Honda CR80R piston as being suitable for a "Lead 80" scooter.  My Aero has almost a 1 inch wide boost port; substantially more than the total .820 inch spacing on the 1984 CR80 piston.  The earlier cr80s (1983 model # 493) wiseco piston has almost an inch between the pins so its the one I eventually installed. They come in sizes from 49.5 mm to 51.5 mm and wiseco pistons should be availiable through your local motorcycle dealer. After buying the piston I visited my local machine shop who bored the cylinder to match the piston.

January, 2003~  The wiseco cr80 piston is in the scooter and it works great! I had to buy a cr80 wristpin as well because the aero 80 wristpin was too long and wouldn't allow me to fit the pin locating circlips into the piston.  I had removed about 1/16 inch or about 2 mm off the stock head and so the compression is higher. Cylinder pressure is 160 psi.  The engine really wants to rev and I've re-installed the stock weights. I haven't been driving it anywhere that I could open it up yet but 70 km/h is easily obtainable even on mild hills. Acceleration is better than before but still not as good as I'd want. The engine revs and then the variable pulley kicks up and the engine bogs down until it increases speed again. Just another reminder that increasing engine power is only one part of the equation for increased speed and acceleration. The engine is still being "broken in" and I'm using ordinary two stroke oil (Yamalube) to ensure the piston rings and cylinder wall get properly seated. Once I've got 500 km on the scooter I'll switch to synthetic oil and maybe try switching cdi units around to see what works best. I've switched the license plate from my Helix and am having a blast riding the 80. It is such a good scooter for the city. Its nimble and light and can turn on a dime. I have to admit I also like the sound of the tiny two stroke motor revving high which was an invitation for speeding tickets on the Helix in the city. The Aero also corners so much better than the Helix on residential streets and can be flicked around obstacles like potholes, careening bicyclists, agressive pedestrians etc. Now if I can just get it accelerating off the line as quickly I'll have the perfect scooter for the city.  

Nh80 cylinderHonda NH80 cylinder with 1983 CR80 piston Pictured at left is a Wiseco model # 493 1983 Honda CR80 piston (50.25 mm) in the Aero 80 cylinder. The pencil marks on top of the piston represent the ring locating pins position on the piston. Notice that they are barely wider than the boost port opening.  Fitting the cylinder should be done with care to ensure the rings don't get hung up in the port; a recipe for disaster. Displacement increases to 88cc with this piston. Only time will tell if this option works. If your local machine shop can weld up the boost port to narrow it down, that would be a sensible option.

The Aero 80 wristpin is too long for the CR80 piston so you'll have to buy a CR80 wristpin  to mount the piston. Always use new circlips and insert a new wristpin/gudgeon bearing as long as you have the motor apart.

  PostMortem: I sold the Aero in February 2003  and the owner used it for everday transportation racking up 1000 km a month until May when the piston seized. I disassembled the motor and discovered that there was no oil being pumped to the motor as the oil tank line had become clogged after the owner had added a "miracle additive" to the oil to increase mileage, power etc etc etc.  A stock cylinder was substituted and the oil tank drained and the filter cleaned. Its now up and running again.  As a result of the above I can't offer any long term results from the piston swap. It  worked well up until the oil feed became clogged so it had a few thousand kilometers which is well past the point where I would have expected  a failure to happen if  the psiton wasn't suited to the motor. Certainly this brings up the point of NOT using oil additives. If you want  a clean burning low friction type of oil use a quality two stroke synthetic oil meant for oil injection systems. I use Bel-Ray S7 on my scooters but there are many others ( Motul etc) that would fit the bill.  The scooter was being run on the cheapest  two stroke oil from a discount auto store  so that would  not have led to a lengthy life in any case. Its cheaper to buy quality oil than rebuilding a motor and if you can't afford synthetic , Bel-ray and Motul also make quality low smoke formula conventional oils for oil injected scooters.

The good news is that I've located another Aero "basket case" to work on and should have an Aero to ride again soon. If I venture into any other projects on this new scooter I'll be sure to add them to this page.

For those interested in building an expansion chamber type exhaust, Ian Williams Tuning has a software design package for tuning two stroke motors called MOTA.  If you follow the link to MOTA page you'll see they also offer  a free design utility for expansion chambers that you can use for stock motors.  As an example, below is a diagram of a pipe based on the stock NH80 cylinder with a 7500 RPM limt (top diagram) as well as a pipe based on the stock 6500 RPM . While the program gives a diagram of a straight pipe, the reality  is that you'd have to do a lot of bending, welding and cutting to fit the expansion chamber to the Aero.  A muffler would have to be added to the end to make it so you didn't attract the attention of the local authorities when you fired the motor up.

 Expansion chambers typically have an RPM "range" in which they work best. The best way to describe it is you are motoring along and all of a sudden it feels like a strong wind pushing from behind. It's purpose is to stuff more air fuel mixture into the cylinder. In an 80cc cylinder it might stuff as much as 120cc of air/fuel effectively "supercharging" the motor.  Check out this wikipedia page for a good graphic display of an expansion chamber at work.

In the designs  below I used a  factor called BMEP (brake mean effective power) at a value of 8.0 to have a broader power range suitable for everyday riding.

 GP racers with a value of 12.0 BMEP at maximum power would have a very small "power band" unsuitable for daily driving.  As well as the expansion chamber, the carburetor size may need to be increased.
nh80 expansion chambers
 The NH80 motor was also used by Peugeot when Honda bought shares in the company back in the 1980's. The Peugeot motor evolved (as did the Honda NH series) to the 100cc motor used in the Peugeot 100cc scooters produced from the 1990's. The following picture is of a variety of tuned exhausts produced for the 90cc Honda and 100 cc Peugeots .  Although similar looking, each will give the motor different characteristics in power delivery (and noise) for day to day driving.  The arrow pipe looks like the only one that might fit without cutting due to the limited space between cylinder and frame in the earlier NH80s. The later NH90 and 100 had tubular frames with much more room for the header to bend .
Expansion Chambers

July, 2006   

    Phil wrote the following about modifications he'd one to his Aero 80:

"I currently own a Honda Aero 80 I have done some mods to . Most effective was the cr80r exhaust.  I had to fold it twice to get it on the bike but it fits. I also have the VTcycles 24mm carb kit. With these parts the scoot is a bit soft off the line but at 40mph (65Kmh) the pipe wakes up and the scoot rockets to the pin on the speedo; I would guess 55-60mph (90-100Kmh), before reason and the knowlege that this has 40mph brakes shuts me down. I am in the process of doing an overbore with a pro-x 50mm kit and I like your shim under the bore idea. I might use it for mine (see if I can hit 80mph (125Kmh)."

    Lee, an Aero 80 owner and aircraft mechanic, wrote to say he gets 42 to 43 mph and 90+mpg on his scooter and that his Aero doesn't suffer from that same bogging at full throttle that myself and other aero 80 owners complain of. Lee reminded me I'd failed to mention the importance of using a quality two stroke oil. He uses mobil 1 two stroke oil for the motor and mobil gear oil for the final drive. I have used Motul synthetic and am now using Bel-ray synthetic in all of my two stroke scooters and Lee is right to point out the economy and increased performance of using a good quality oil. As far as the gear oil, the reference I have states the aero 80 takes 90cc of SAE 10W- 30 SE oil. The oils are items you should pick up at a motorcycle shop. Make sure its especially formulated for two strokes with oil injection.
    Lee mentions the only modification he has used is to switch the stock foam air cleaner element with a aftermarket oil saturated foam element. You should be able to find this foam at any motorcycle shop. They sell it in sheets usually and you'd have to form it to fit the stock Honda "sock" shaped element. Uni-Filter make a clamp-on Pod type foam airfilter in several sizes.

Chris, another Honda Aero owner whose web page is listed below, wrote to tell me of some changes he made to his aero which seemed to have increased the speed substantially . He Said:

   " I find an average top speed on mine of 40-43 MPH (64 -69 km/h).  I was able to smooth out the ports on mine with a dremel (just hacking as I am not sure how to properly do it).  I find that despite many carb cleanings and experimentation and the installation of a foam air filter in place of the box, the highest throttle position bogs down the motor (dougnote: see comments on jetting above).   I think what got me the extra MPH over yours was the addition of the foam air breather.  I also smoothed the exhaust header ridge with the dremel.
    My average mileage is 50 MPG, which sucks compared to a 1982 Yamaha XJ550 Maxim that I have that gets closer to 60 MPG.  Then again the Honda is usually at full throttle.
    I can crank to over 50 ( 80 km/h) downhill if I keep the throttle at 7/8.  Any higher will cause it to stutter and go slower. I also removed 2 of the weights in the variator to allow it to get some RPMs before going into a "higher gear."  This helps up hills somewhat.
    I have 3000 miles now, with my longest trip being over 250 miles with my wife and camping gear!  We drove from CT to VT and back on Mt and back roads.  The scoot drove perfectly, but the suspension sucks and the seat has a nasty hard spot in the middle. "

An Australian correspondent owns a three wheeled NH80 converted for wheelchair use and wrote to say he had been tinkering to increase hill climbing ability. As mentioned above the NH80 drive seems to be tuned so that the engine does not freely rev throughout acceleration. Honda undoubtedly wanted to preserve gas mileage figures so the weights seem to push the variable pulley into a higher gear early on to keep the engine revs low and increasing gas mileage.  Lightening the roller weights will have the effect of keeping the motor revving higher and staying in "lower  gear" longer which would increase acceleration and hill climbing ability somewhat. What the Australian correspondent did was to do a simple modification to the rear pulley spring. Higher tension springs at the rear pulley will have the same effect as lighter roller weights in the front pulley.  After disassembling the rear pulley he installed a shim between the spring and the driven pulley. I tried this myself and found a Lambretta 150 piston ring fit perfectly in the cup where the spring is seated. The difference is huge and the engine revs freely now. The piston ring was, I think, 2mm thick ( 57mm bore) and I'd like to experiment with a thinner ring. If you live in a hilly area or carry two people frequently this may suit you just fine although you will find gas mileage is decreased.

Dan Wrote:

Last time we chatted my brother was just finishing installing an aftermarket reed cage, intake manifold and 24mm OKO carb. It's the same unit shown on your website but I'm not sure where it was purchased because he got it from another NH80 and didn't think to ask where he got it.

At the same time my brother installed this he also installed a new engine (his oil injection failed when the cable snapped so his original cylinder was toast) and this new engine had a high compression dirtbike piston that is supposedly around 85cc. I believe I compression tested this bike at 150-170psi.

Anyways, he got it running with the jets the previous owner has tossed in the carb (but never ran it) which was a 107 main jet and we didn't check the slow jet. It ran pretty good with that jet and topped out around 70km/hr. Stock he would cruise at about 65km/hr and it suffered from the common cutting out at full throttle etc. After about 100kms of riding like that his top speed had been dramatically dropping and he was down to 15km/hr. A new plug temporarily got it running okay again but it was obvious that it was running way too rich.

We tried using the stock jet (88) but we couldn't get it started so we ordered some new Keihin jets in between 88 and 107 which were 95 and 102. We tried the 95 Jet first and it started up easily and it's been all sunshine and roses ever since. He's put several hundred kms on it since then and accelerates much better than stock and blows away by 1983 Yamaha Beluga which is also an 80cc 2-stroke. His top speed has also risen to 75km/hr from the stock top speed of 65km/hr. As well, it runs so much's a little hard to start (you need to use the choke) and it cuts out slightly off the line but from 5km/hr and up it runs like a champ. There's no cutting out like the stock carb and it accelerates obviously better than stock. The other day he (200lbs) and his friend (200lbs) were riding double and were still way way faster than my stock 1983 Yamaha Beluga 80cc 2-stroke.

Anyways, I just thought I'd let you know our final results and what the jetting was. It's possible the larger, high compression piston and the porting the previous owner did have affected it's jetting needs but 95 should be a pretty good starting point for anyone with this setup.

Cheers, Dan

Check out Dan's Beluga 80 forum for some tips about restoring and modifying the 80's yamaha 80cc scooter at

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