multifaceted acceleration/running too rich/etc. Q

Sorry for the long title...

I've been searching trought the forums for a while now and can't seem to pinpoint an answer to my problem.

So, here's the story.

Got an 86 maxi with the 70cc kit from steve's moped (head, 15mm amal carb, manifold, biturbo).

when i got the moped home, the acceleration was terrible, like 0-15 in 20 seconds, and that was with pushing it with my feet to get off the line. I made sure the exhaust was tight, cleaned the carb, new plug, etc. Little better acceleration then, but not by much. Also, the acceleration was much better when the engine was cold and became worse as the engine heated up. However, the acceleration between 15 and 20 was great. no problems getting up to top speed from there (top speed about 40). When i open the throttle from a stand still, the engine sounds like it bogs, and if i don't push with my feet, i feel like i wouldn't move at all.

Got rid of the biturbo for a tecno estoril. Much better acceleration, but still not much off the line. the acceleration was improved, but it still accelerated better when cold.

I was having some trouble with the engine flooding and difficult starts. I took the plug put and it was soaked, and there was oil/unburnt gas leaking from around the exhaust port still.

I had the person i bought the ped from come take a look at it. He said it was probably a float or jet problem with the carb. So, i replaced the carb completely and decided to fix the other one and sell it.

I put the new carb on, and I'm still having the same acceleration issues. Could a problem be that the manifold is tilted back toward the engine such that the carb is not level then the bike is level? The carb sits at about a 20 degree angle above the horizontal.

Haven't done a compression test yet, but that's my next step.

Sorry for such a long post, but any advice would be GREATLY appreciated.



Re: multifaceted acceleration/running too rich/etc

oh yeah, I was getting TERRIBLE gas mileage too. I went through 2 gallons in about 70 or 80 miles.

Re: multifaceted acceleration/running too rich/etc

I have the same problem with my yamaha U7E 1972 my spark plug was all dry and black and wen I run it for about more then 2 miles in full speed it going really like a crap (when it cold it go to 43 mph and after a little run the top speed is like 22 mph and when I pull the throttle a little bit more it begin to make '' pow pow '' and the engine shut up and then I try to start it IT start but when you gave it throttle the engine shut and I'm not able to find the problem too

Re: multifaceted acceleration/running too rich/etc

sounds pretty much normal .. Buy a modified bike and guess at what's wrong with it.. Personally i'd try going with a smaller carb to improve low end power and throttle response while sacrificing a minor amount of top end.

As far as i know a carb's bowl should always be level. The float seeks a certain level. Tilt the bowl and the level can be way off. The level of fuel in the bowl determines how fuel is metered into the carb's diffferent systems. But sometimes an aftermarket carb just won't fit that way.

Anyway a tilted carb could cause all sorts of weirdness if it's tilt causes an inacurate float level.

the bike's been extensively modified.. there may be hidden problems as a result of failed attempts at more power.. the problems you describe and the solutions may go beyond normal tuning and into the realm of the engine components themselves.

Without a good running bike to set a baseline, and then modifying and testing one thing at a time, you can end up with a bike like yours. It may have satified the previous owner but your idea of "performance" (good acceleration, good MPG) and his (max power output / max top speed) are different.

Re: multifaceted acceleration/running too rich/etc

but mine is stock and it's doing the same thing that Charles one

Re: multifaceted acceleration/running too rich/etc

you have a 70cc, 5HP, 3-speed scooter..

Try this Yamaha U7E discussion group.

or try scooterbbs

Re: multifaceted acceleration/running too rich/etc

THe person i got the bike from said this was abnormal. He said acceleration was much better when he had it. We are working together to get the bike running right, but i still need more advice.

Thanks for the input, though.


Re: multifaceted acceleration/running too rich/etc

I'm glad you're working together on it.. i was wondering if before selling the bike he swapped any parts and kept the ones he wanted to keep.. ask if he shaved the head, modified cylinder ports, changed intake manifolds or carbs .. ask if the air intake system and jetting is identical to the way it was set up when it ran right..

You did nothing to the bike when you got it home? and yet it seems evident that something is different.

Re: multifaceted acceleration/running too rich/etc


Re: multifaceted acceleration/running too rich/etc

How is the idle? Does it idle really high and the idle screw does nothing? I know I had similar issues when i was leaking air at the head gasket. Ran great until warm then it was a slug off the line to about 15-20 then the power kicked back in.

Run the bike and check for airleaks by spraying carb cleaner around your head gasket and intake manifold. If the bike dies then you have an airleak.

You should really put your stock carb and air filter back on and start trouble shooting from there.

Frustrated, and don't know what to do...

Idle is good. I can adjust it right where i want it with the combination of the idle speed and air mixture screw.

i'm seriously comtemplating just getting a 70cc reed valve kit (recomendations??) and starting over. OR, I can send my engine to smitty and have him re-work with what's already there... Either way, about the same price...


Re: Frustrated, and don't know what to do...

any more thoughts?


Re: Frustrated, and don't know what to do...

well consider the source Steves sells Brand new bikes that dont even run all the time lol but seriously it sounds like a jet problem

Re: Frustrated, and don't know what to do...

it's a brand new carb, though... i thought it was a jet problem at first too..


Re: Frustrated, and don't know what to do...

Jason Luther /

how is your trans fluid level? type f fluid in there? dont just send it off somewhere to have more performance stuff done to it, something obviously isnt right.

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