still no top end..

Alright,

I have a 1978 Honda Hobbit PA50II. I have:

Kreemed the tank

cleaned the carb

replaced the air filter

replaced the muffler

replaced the spark plug

and my ped still bogs out at full throttle. When wide open the ped will have a burst of speed and then slow down, then a burst a speed etc.

I have had this problem for over a year and have tried everything. I haven't opened the engine itself for fear I might break seals and fuck up stuff. Could my problem have to do w/ a loss of compression or some engine problem?

thnx,

-B

Re: still no top end..

The problem sounds more like something to do with a variating air:fuel mixture. When mixture ratio is good, there's lots of power. But if something alters that mix ratio, power drops off.

If fuel flow into the engine is variable, and it is flooding or running out of fuel at top speed, the engine can surge like that. Another possibility is variable air flow due to an air leak of some kind. Both air and fuel flow must be steady.

But air / vacuum leaks will be noticed at all speeds. So if i had to guess at it, the problem would be inadequate fuel flow at top speed.

As fuel flow slows, the mixture gets lean.. A lean mix is hot and powerful and there's a burst of power while it runs out of gas.. then the engine slows until more fuel is available.

:

Try an experiment ..

There is something near 25ccs of fuel in the float bowl (a bit less than one fluid ounce).

At top speed and after a sudden burst of speed, reach down and turn off the petcock. Then kill-switch the engine and coast to a stop.

Then disconnect the fuel inlet hose from the carburetor.

Next drain the float bowl and measure how much fuel was in the bowl when you killed the ignition.. (Drain screw access is through the pedal sprocket.)

If there was very little fuel in the bowl when you killed the engine, the bowl is not refilling fast enough to meet the demands of the engine.

Re: still no top end..

I have seen to many Mopeds damaged by inexperienced people thinking they can do somthing way out of their legue. There is not much to see in the bottom end of the engine, I am shure unless the engine is a reed valve engine your problem is not in the bottom end. You did the right thing to not pull it apart, besides it's a big undertaking that is rarely nessecary. Sounds like a air breather problem try to run the engine with the air filtre off see what happens. Just don't want you to make more problems for yourself, I have seen irriparable damage on Peds to many times. GOOD LUCK

Re: still no top end..

thnx guys I'll try these out

-B

Re: still no top end..

Yes.........it's probably not refilling the float bowl fast enough at full throttle.

This could be a clogged (in-tank) filter above the petcock, or a clogged gas cap vent.

I worked on a Honda Express once that had a lever on the gas cap which you set to `vent'. BUT........if you over-twisted it past `vent' just a little, it lost all venting to the gas tank.

I am wondering if your gas cap has quit venting here or your petcock,in-tank filter has plugged.. don-ohio (:^)

Re: still no top end..

I thought of the gas cap.....All I found was a hole under a big rubber o ring I thought was a vent, it seems clear.

Also when this happens I always get a throaty studder sound when it bogs out. My air filter/box/hoses seem clear, but I feel like it has too much air or not enough.

me confused

-B

Re: still no top end..

Jason Luther /

my hobbit did the same thing. i was running too rich at top speed, so the only way to 'fix' the problem was to pull the air cleaner out 1/2". now it runs great. i would give that a shot just to see if you are in fact running too rich or too lean.

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