High Performance Honda Scooters    

The following  are excerpts from several E-mail exchanges with Frank about modifications he'd done to his Elite 250. Franks modifications require an intimate knowledge of engine tuning and would not be suitable for novice mechanics or those hoping to retain the reliability of the stock engine.
     Also included is an e-mail from an Italian correspondent about an article that appeared in an Italian scootering magazine about modifying the 250 cc Honda Helix motor.

    Both these e-mails demonstrate the tuning possibilities for Honda four stroke scooter motors and are commonly found modifications to the Honda single cylinder SOHC "XL/XR" range of dirtbikes.

"In my 1990 Elite motor, I currently use:
1: Malossi aftermarket pulley and weights
2: hi-performance reground cam and performance valve springs
3: shaved head to give 10.75 compression
4: 34 mm carb
5: Ported and polished head.
6: +4 degrees over stock ignition advance
(295cc overbore and 11.5 :1 piston will be next)

Since I have had no advice on what to do to increase the power in this engine, I did the above modifications from my experience with 4 strokes ( I am a 2 stroke performance guy) and would like some feedback from others who have modified similar engines, (Helix, Foresight, Elite, etc.).

1: Malossi aftermarket pulley and weights
I modified the original one. (the stock elite 250 is VERY BAD makes belt ride 1/2 way up to start and not fully open.  I just put on the Malossi foresight one with 6x 18 gram Malossi weights. Foresight pulley works with a little shaving on the diameter. Malossi sells a kevlar belt, but it is too long for the elite 250.

 

The following are Malossi part #s:
 

~5111226 Multivar 2000 Foresight .250 cc  fits with shaving
    1/8 in off diameter
~66 9917.M0 ^6 Htroll D.23 x18mm ,18 grams  pulley comes with
    these weights
~66 9917.U0 ^6 Htroll D.23 x18mm ,25 grams
~66 9917.Z0 ^6 Htroll D.23 x18mm ,27 grams

2: hi-performance cam and valve springs- The stock cam was reground from "webcam" in California  909-369-5144 $130.00 + price of a new cam from Honda ($45.00 cheap).  Lift on the stock cam is .310, on the performance cam .365.
 

	Stock Cam (lift .310)	Reground cam (lift .365)
intake duration	220 degrees	250 degrees
exhaust duration	220 degrees	250 degrees
intake open	0- TDC	15 deg  BTDC
intake closed	40 deg ABDC	55 deg ABDC
exhaust open	35 deg BBDC	50 deg BBDC
exhaust closed	5 deg ATDC	20 deg ATDC

The springs are custom made. Inner and outer springs, shortened valve guides and titanium collars for $130.00 (Regrind was $110.00) Jury is out on the springs though unless you use very high rpm. I had 2 springs break.
3: shaved head 2 mm to give 10.75:1 compression

4: 34 mm carb  Older 34mm Mikuni from a junk yard. I stayed with the CV type for smoothness .

5: Port and polished head.Ported and polished considerably.  The exhaust seems to be very restrictive.

6: Advanced ignition +4 degreesWelded a tab on the flywheel for the electronic Pickup to "hit it sooner"( 3/16" long)

Results:  bottom end makes wheelies and burn outs and top speed went from 70 or so to 85+. I do not use the Elite 250 motor on a stock bike or helix, so I guess to expect 10-15 mph more. (295cc overbore and 11.5 :1 piston will be next) Still waiting for the Malossi piston and bore (foresight) that was supposed to be available in March 2000 but delayed until Sept. 2000. Very nice popup piston that adds compression to 11:1.  It is for a foresight, but head gasket is the same as the 1990 Elite 250 ." (note : the 1989 and newer Elites had a horizontal cylinder as opposed to the upright cylinder on earlier Elites)

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I received an E-mail providing this translation of an article from an Italian scooter magazine about an Italian product that could be bought complete, saving the labour intensive and head scratching labour required by Franks modifications. For that privilege, a premium cost has to be paid but the results sound interesting for those with more money than time. The e-mail  also mentions some useful information for those who want a bit better suspension dampening:

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Hello Doug,
Just checked out your  web site on Honda Elites and all. As you mentioned performance mods I thought you might be interested in an article from the Italian scooter mag (issue 68) which I've translated . You might also like to know that Hagon, who make good shocks for the Helix (cheaper than rebuildable Bitubo's and with excellent tech.support), are at http://www.hagon-shocks.co.uk (on my Helix I use front Bitubo, rear Hagon)

Cheers
S...

Translated article

" ...the 2 Roman technicians have worked on obtaining a compromise between
performance and reliability, as befits a road going vehicle, and it's based on
the standard Honda. The stroke is the same, but the cylinder has been
lowered to obtain a C.R. of 11.5 to 1 (geometric value). The piston crown
has also been turned down to make sure the squish band is right for the
lowered cylinder, and two pockets have been milled into the crown to avoid
valve interference at high revs due to the new camshaft. The piston -
cylinder clearance is in the order of 0.02 mm...

The original cam has been reprofiled. Lift is up by 1.2 mm for both valves,
and the phase diagram for this asymmetric cam  is 55 - 20, 28 - 53
(degrees), with a value for the 'lobe centre' of 113 deg. obtained with a
valve play of 0.2 mm for both inlet and exhaust, as opposed to the 0.08 and
0.13 of the original.

The head, which is supplied already assembled, is the part that has been
most heavily modified in order to optimise gas flow... The valve seats have
been enlarged by 1.5 mm, the tracts enlarged and smoothed (with fine
sanding). The exhaust collector has been enlarged to aid evacuation of spend
gas with the larger tracts. The valve guides have also been
modified/replaced (?) (the original text says 'reassembled!) in line with
the other modifications, and the gaskets are also new, including the head
gasket, made especially for this kit by Spesso.

The chain tensioner support has also been modified to ensure more accurate
tensioning with the lowered cylinder.
2 main jets (for the standard carb) are also supplied with the kit, for
summer/winter use, to optimise carburation..."

Max power is said to be 28 bhp and max revs 8500, 1500 above the standard
motor ( they claim reliability is unaffected). The tester rode a bike with
the 11" Hexagon rear wheel and a Bettella Varimax variator, which comes with
a 'revolutionary' spring slider to 'aid spring operation' (that's a thrust
bearing to the rest of us). The bike is also fitted with Hagon shocks

The tester enthuses about the progressive  and impressive power delivery and
max speed of 140 kph 'in favourable conditions'.

Yours for 1,500,000 lire from Ma.Za  tel: 0039066623468 (Italy)

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I downloaded the automatic scooter catalogue from Scooter Center Koln's website and have listed a sampling of parts for the 250cc Hondas. Most parts should fit the CH250 Elite/Spacy with the exception of the exhaust and shocks which are different on the Helix.  As these scooters grow older and require rebuilding, it makes sense to look at the alternatives,  both in aftermarket parts and engine tuners in your area.
 

And finally some figures for those trying to figure what engine displacement can be gotten from what bore size. The stock CH/CN250 is 244 cc with a 72 mm bore and 60 mm stroke. The piston sizes listed are availiable from wiseco (piston manufacturers) and are designed for other Honda (XR250/TRX300/)  2 valve SOHC motors with a 17 mm wristpin, the same as the Elite 250. Whether or not the other dimensions (compression height of piston, machined valve pockets etc) are compatible with the 250 cc Honda scooter motor is something you'd have to check out if interested. Wiseco offers "high compression" pistons for those who have increased duration cams that want to keep the stock compression ratio. Increasing the bore will automatically increase cylinder pressure if the stock cam is used or restore cylinder pressure if a modified duration camshaft is used. As mentioned by Frank previously, Malossi offer a 77 mm big bore "Foresight" piston however another reader, Steve, indicates its not a simple replacement.
 
 

Cylinder Bore	Displacement  (with stock 60 mm stroke)
73mm	251cc
75mm	265cc
77mm	279cc
78mm	286cc
80mm	302cc

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