Upping performance

Well, I finally got my moped legal to drive.. cost me about $315 bucks for title, plates, insurance, tax, and whatnot. And so, I've been able to continue my twiddling.. This is what I've done so far to my moped: cleaned out carburetor real good, fixed float bowl leak, changed air filter element, took out exhaust baffle, hooked up a timing light and set timing really good, put in spark plug with proper gap and heat range, cleaned and set points, cleaned carbon deposits in combustion chamber and on top of piston, and cleaned out the fuel tank. While performance has improved somewhat from what it originally was, it still tops out at 29-31 mph and the accelleration still sucks (though not as bad as before). I dont care so much about top speed, but it'd be really cool to be able to accellerate faster (LOT of stop signs in my town (and i already got a ticket for rolling through a stop)). It seems the only things i could do now would be to: A) get a 15mm dellorto carb (its a 12mm gurtner now), B) buy a leo vinci performance exhaust, or C) change the rear sprocket to a couple teeth higher. C I dont want to do because I'd rather not sacrifice my top speed. A and B will cost money though (of which im not in abundant supply). How much performance could i expect to gain from getting a nice exhaust (considering that i already removed the baffle from the stock exhaust) or larger carb? If I'm going to be paying 98 bucks for a new carb or over 100 for a new exhaust, I want a very noticable power increase. Is this too much to ask for? or am i stuck with no accelleration? Also, are there any other ways i could increase performance that i havent thought of? thanks.

- Michael

RE: Upping performance

Have you tried adjusting the carb? I mean the fuel/air screw on it. And are you sure the compression in the cylinder is good? Anyway, installing a performance exhaust will be fine, but if you install a larger carb the engine will reach its best performance at higher RPMs, which means that you will have to open the throttle wider to feel the pickup and power. Carbs with smaller diameter make the engine more powerful at low and medium RPMs -- in some cases you can even start moving without opening the trottle at all, just engaging the clutch slowly. So, it's up to you to choose.

RE: Upping performance

Well my carb doesn't have a fuel/air mixture screw..only an idle screw..but i have fooled around with fuel/air mix by taping up and untaping holes on my airbox. and the compression is good..new piston rings and such.. thanks for the suggestions though.

I missed one thing

One more thing that I've forgotten to mention is the throttle needle. This needle also affects the mixture quality. It usually has several pinholes, so you may try adjusting the needle using these holes.



RE: I missed one thing

If you want more power you should:

- Advance the ignition as far as possible. Every little bit the ignition is set too late will cost a bit of power. Setting the ignition too early will cause the engine too run very poorly and the engine will make a "pinking" sound so set the ignition a tiny little bit later than that.

- Increse the compression ratio. You can do this by grinding down the cylinderhead. Do this with polishingpaste on a glass plate.

- A 15mm carb will really get you some extra power. My bike originally had a 12mm Keihin carb, it gave power at about 4500 rpm. I've now got a 20mm Keihin (off a Honda CB125!) and this gives power at 7500 rpm and higher. So that 15mm will give power at about 6000 rpm I think but you really wont lose much power at low revs.

- Set the clutch to engage at higher revs. At higher revs you'll have more power and so you'll accelerate faster. You can do this by mounting stronger springs, they'll only cost a few dollars. If you've got a manual clutch just let go of it slower.

- If you have to pay over $100 for a Leovinci racing exhaust you're being ripped off. In Holland (where I live) those pipes cost about F130.-, that's $60.

RE: I missed one thing

Gary Trezza /

I'm having a similar problem on my '75 Puch. I've done virtually everything you've done, and installed a much bigger jet. I also installed the BiTurbo exhaust. The high end is great- I do about 37 MPH now, but it did nothing for accelleration (except for a short mid-range "burst"). I've gone 4 sizes larger on the carb jet to try to get more bottom "punch" and hill climbing power, but little improvement. If you've already removed the exhaust baffle, the H.P. exhaust will do nothing for you, don't waste your $$. I will look next at compression, as I'm about out of ideas myself. Let me know if you hit on something. Thanks, Gary

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