i am stumped

linnix13

linnix13

Member
ok this is not technically a mb, but its one of my other toys, and i have seen these engines on bicycles before. it is a 49cc chinese piston port 2 stroke, they are usually red, anyways the engine was running perfect until it just died right out. i took it home, rebuilt the carb(diaphragm carb) and made sure its proper. still no luck, i put the carb and manifold from my engine bicycle onto it. i know the carb works, i fueled it up. held the primer down, and it still wont run, however get this. if i pour a little fuel into the carb it will start right up! i can rev it or it will idle fine, but it dies very shortly afterwords, even if i rev it up, its only running on the prime, but i know the carb works. i even tried another little diaphragm carb and its the same, so the problem isnt the carb, im stumped. any input would be graciously accepted
 
diceman2004 said:
pop the fuel hose off at the carb and see if gas is comming though the line . sounds like the filter is plugged .
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its not fuel, i have tried three carbs and they are all getting fuel, on both the diaphragm carbs the return line spurts fuel, and on the grav fed float carb the over flow leaks, so it has fuel, its like the engine doesnt have "suction" or something
 
If you pour gas into the carb and it runs, then your carb is not passing gas.

It doesn't matter if the fuel pumps out the overflow or not.
 
yeah i knew it was fuel related, but i tried 3 carbs. they work, i know they do. and the grav fed carb does too. so is there anything else that could cause this?
 
As stated by Mike B, crank your engine around with thumb over intake port, if it sucks it will draw fuel/air.

1.
Check your fuel flow rate with the fuel line placed in a container. Remove the tank fuel cap. Open the petcock and see if there is good fuel delievery.

2.
Make sure your carborator is secure and that your intake manifold is on tight with no air leaks at the engine or carb mount.

3.
Make sure you have fresh gas that is properly mixed!

4.
Re-assemble all components and check everything.

5.
Fire it up!

Trouble Check:

A: Remove carb filter and make sure choke is open.

B: Hand choke carb with palm of hand and see it the engine starts. (Choke once with hand - dont flood the poor beast.)

C: Is the exhaust restricted?????? It happens.

D: If all else fails you might want to consult someone who is ASE - Ask Someone Else (That's a joke :)

--------> One of these things are a miss if you are still having issues as you discribed. Best of luck and please keep us informed or feel free to bounce ideas off of us. Cheers!

broke-and-hungry-albums-my-builds-picture2901-felt-build-1-build-process-dry.jpg
 
well it does suck my finger, no reeds, its piston port, and everything is in good shape. so it should run! it just died out in operation a few days ago. at wot. but nothing is damaged. and like i said if i pour gas into it. it runs! perfect, for a few seconds, then it dies. i will troubleshoot it more tomorrow but i have never come across anything this confusing
 
You said that this engine had sat for some time, are you sure the carb has not "veniered" (ie: gas evaporated out of the float bowl leaving behind "gookie" oil and clogging the main jet).
 
You could have the dreaded crankcase leak.

But if it won't fire with a carb with the choke full on I still think you have blocked passages.

How do you know that 2 carbs are good?
 
Barnfresh said:
Where does the pulse line to the carb come from, crank case or intake manifold?
Click to expand...

That's what I was thinking of.
If it is a port that passes through the typical plastic manifold that these little engines use, it is all too easy to get the gasket backwards and block off said port.
Also, these teeny diaphragm carbs are very sensitive to the smallest debris getting inside them. That is why the fuel filters are made of a tightly woven felt material. The felt traps the smallest of small debris, much smaller that one would think.
 
thanks for the info guys. gearnut is right, its a small hole in the intake manifold. however i made sure the gaskets are on right and nothing is blocking the pulse hole, i know the 2 carbs work because i have a 33cc variant of the same engine and the carb runs on the engine fine, also i attached my bicycle carburetor to the little engine and its grav fed, so it shouldnt even need any pulses?
 
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