bog under low rpm load, WOT fine

Burns Hudson /

I just got a kit and carb and all that jazz, PHBG.

With the wheel off the ground, the rev up is great

With any load at all, it barely moves at any throttle position

If I scoot it along by foot or down a small hill, eventually I can get going under motor power and once the pipe kicks in I am doing 40+ uphill.

Idles great, but is sputtering gas out of the filter side, the whole inside of the carb looks to be completely saturated in gas when it is running

I have adjusted the mixture screw, but it doesn't seem to change any of the symptoms. I dropped the needle all the way down (clip at top, leanest it can get)

Is this a pilot jet problem, or is there something I am overlooking?

The jetting is all stock for the carb, I didn't see any numbers on any of the jets. (edited)

Re: bog under low rpm load, WOT fine

THIS IS MOST LIKELY A COMPRESSION PROBLEM. RINGS BROKEN OR IMPROPERLY SET IN, HEAD NOT TIGHT ETC. COULD BE TIMING AND JETTING ALSO, MIXTURE SCREW AFFECTS LITTLE, TRY PLAYING WITH SOME OTHER MAIN JETS AND SEE WHAT CHANGES.

THE "with the wheel off the ground, the rev up is great

With any load at all, it barely moves at any throttle position" SYMPTOMS HEAVILY POINT TOWARDS COMPRESSION THOUGH.

Re: bog under low rpm load, WOT fine

Burns Hudson /

but once I get moving, it is a torque monster. I wouldn't think it would have much power at any rpm if the compression was bad

Re: bog under low rpm load, WOT fine

what kind of air filter do you have?

When you get moving, can you max it out?

If so what does your plug look like?

double check leaks, do it again, then again.

make sure your timing is not too advanced or retarded.

Your main jet does influence your idle some, but the idle jet could be a bigger problem.

Also (if you are new to phbgs)...check the wiki, it has a picture of what I'm talking about, and a relevant step by step walk through.

Your main jet isn't really used until 1/4 throttle (or later).

Anything below that is the idle jet.

If you have solved all other problems, and everything is in check, you might need to downjet your idle jet.

Note: I've built more bikes than I can count and seldom do I have to change the idle jet, but everything is different.

Re: bog under low rpm load, WOT fine

Down jet..tune your carb..

Re: bog under low rpm load, WOT fine

♣Slew Foot♣ /

an ehaust leak would rob you of low end too

Re: bog under low rpm load, WOT fine

Burns Hudson /

Thanks guys, I will check for air leaks again and tighten up my exhaust some more.

Then if I still have the problem, I will downjet the idle and main significantly to see if that changes anything, then if it does I will jet back to stock and buy a range of jets and work my way slowly down.

My carb is crazy sputtering gas out - I smelled like I dipped my pants in gas when I stopped working yesterday, so I am guessing that it is carb-related.

Re: bog under low rpm load, WOT fine

Burns Hudson /

I think my reed valve is the problem. See this thread: https://www.mopedarmy.com/forums/read.php?6,2738672

I will buy a new one, because if it fixes it, its cheaper than going crazy jetting, if it doesn't fix it then its still good to have a nice new one.

Thanks for the help

Re: bog under low rpm load, WOT fine

If you have a broken/warped reed valve you wouldn't be getting above 20mph :/

FIXED, read to know how

Burns Hudson /

Sorry to revive the thread, just so anyone searching later can know what I did to fix it:

Turns out that I had some big headgasket leaks and some minor basegasket leaks. I replaced the headgasket, basegasket, and intake gaskets all with 'thick' gaskets from treats (I'm after reliable transportation, not a race machine) and now I have 110psi with the stock a35 head and no leaks anywhere that I can find.

I also replaced the reed block because I decided to go all out, I do think that was some of the problem, because now the carb is not backfiring gas out of itself and I can only feel air being sucked in, none pushed out.

It now pulls hard through the low rpms and is a rocket at high rpms. (edited)

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