Cag Motor Vibration Areating fuel at high RPM

old motorbike

old motorbike

New Member
Having trouble with a pocket engine build bike, dying at higher rpms.
Can see the air bubbles out the input line then. Had same problem on China girl engine also.
In process of remote mounting the carb from engine to test possible solution.
Used the regular float carb that came with the engine and also a pumper type that did the same.
Making manifolds now, so I will be back in a few days.
 
Here's a tip that I use on model airplane engines to prevent fuel foaming/air in lines: 1/2 squart of armor all per gallon of fuel stops fuel foaming caused by vibration. Will eventually buidl up on glow and/or spark plugs but not a huge issue. not sue if vibration/foaming is what is causing your issue.
 
i had a similar problem i removed the rubber from the frame that i used to try to keep vibration down and everything was good. my opinion is that these things need to be mounted as rigid as possible so all the vibration isnt just in the motor but evenly distrubuted through the whole bike its worth a try it worked for me. PEACE OUT RAT BIKEdnut
 
Improper Fuel Tank Venting can also cause this. Make sure you can get air into your fuel tank. Tank Vacuum can cause this. Make sure your gas cap is venting properly.
 
Drewd,
Explain that armor-all recipe again, don't quite get it, some basics of why it works too, I'm kinda slow tonight.

Mac
 
Thanks all for the replies. I'm still not sure of the total problem.
Engine is solid mounted.
I have:
1. Opened up fuel outlet and took out shutoff valve.
2. Added bigger fuel filter and lines.
3. Moved float level.
4. Slightly enlarged jet by .002"
5. Tried a pulse performance carb and different manifold and air cleaner
6. Checked reeds.
7. Different gasolines @32:1

Installed old carb., remote mounted with rubber hose yesterday.

1. Initially it started ok and ran the most it ever reved in 1st gear (shift kit)
even though it was sluggish and still ran like it had a rev limiter.
2. Then on the return trip in upper gears it died out and only would only
re-start 3 times. Then no start.
3. Had plenty of fuel. Spark plug was just light gray.
4. Took off fuel connect hose and had a few drops of fuel in it. Wanted
to see if it was loaded up?
5. Gave up for now.
Could even be weak, intermittent spark????
 

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your extension between carb & case will beef your bottom but kill your top end. Try a conventional carb mounting?
 
So far I've tried 2 other carbs.
All have different results.
Also changed plug and coil (no difference)
Cut down intake tube (about to 2 ") and have an unknown new motorscooter carb.
it runs the best so far.
All the tests with the rubber intake will rev high but take an eternity to get there and seem real lean at all ranges.
The stock carb won't run once engine is warmed, but ok cold.
The current carb is a Micuni?, without an air filter which will also cause it to be lean. It runs best, but real sluggish in all ranges. Responds to choking on acceleration, but not top end.
Engine feels (although cleaner revving) like it has a rev limiter at about 6-7K with all carbs and about 5-6K, direct mounted.

My thoughts now are maybe the engine was a defect the way the ports are timed as it has always died at top end from new?

A friend has an identical motor in a pocket bike and it runs circles around mine and revs to the sky with similar carb.
 
Norman said:
when it starts and runs fine when cold then dies when warmed up and won't restart. that kind of tells me you have an ignition problem most likely the cdi coil.
Click to expand...

That's what my thoughts were, but after changing new coil & plug (no cdi box on this), Still the same

Changed the stock carb over to the mikuni, it ran also when hot, but just real lean. I trimmed the needle down a few thousandths and its running and starting better, still lean at top. Not dying though.
 
old motorbike said:
Thanks all for the replies. I'm still not sure of the total problem.
Engine is solid mounted.
I have:
1. Opened up fuel outlet and took out shutoff valve.
2. Added bigger fuel filter and lines.
3. Moved float level.
4. Slightly enlarged jet by .002"
5. Tried a pulse performance carb and different manifold and air cleaner
6. Checked reeds.
7. Different gasolines @32:1

Installed old carb., remote mounted with rubber hose yesterday.

1. Initially it started ok and ran the most it ever reved in 1st gear (shift kit)
even though it was sluggish and still ran like it had a rev limiter.
2. Then on the return trip in upper gears it died out and only would only
re-start 3 times. Then no start.
3. Had plenty of fuel. Spark plug was just light gray.
4. Took off fuel connect hose and had a few drops of fuel in it. Wanted
to see if it was loaded up?
5. Gave up for now.
Could even be weak, intermittent spark????
Click to expand...

did you ever get it running at top perf again? I just put on a manic mechanic head and am having the same issues. may go back to stock head and see if that solve things
 
Check the reeds. I had a problem with one that drove me NUTS! would run but not rev without dying. tried everything no joy until I threw a new reed block at it just for giggles...WOW! Night and day difference! Runs like a scalded dog after new reed. Pure luck...still have no idea why reeds would affect it like this. China engines...go figger.
 
maniac57 said:
Check the reeds. I had a problem with one that drove me NUTS! would run but not rev without dying. tried everything no joy until I threw a new reed block at it just for giggles...WOW! Night and day difference! Runs like a scalded dog after new reed. Pure luck...still have no idea why reeds would affect it like this. China engines...go figger.
Click to expand...

Reeds on a china girl? Wha?!!?
 
I had similar bogging issues on my 3 Cags & a Subaru Robin EH035 4 stroke.
The Cags all needed the gas cap opened up with a motorcross dirtbike breather tube.
Haven't had any trouble since. Just a few bucks on ebay & a small drill bit...
-Lowracer-
 
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