Problem

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lowrider

lowrider

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Jun 16, 2009
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Hi,

My bike isn't running right and I need all the help I can get.

Problem is the bike runs fine for about 1/4 of a mile.

then it bogs out and goes slow then it will pick up slowly the rpms and then back down again:-||.


if I kill it for a min and then restart it it runs fine for 1/4 mile.


what could cause this??

:-||
 
GearNut

GearNut

Active Member
Aug 19, 2009
5,104
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San Diego, Kaliforgnia
It sounds to me like your gas cap is vent is plugged up. If air cannot be let in as the fuel is consumed then it creates a vacuum inside the tank stopping the flow. It only needs an itty bitty air hole. The next time the bike acts up, pull over to the side of the road and loosen and tighten the gas cap. If that fixes the problem for the next 1/4 mile then you have found your problem.
 
lowrider

lowrider

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Jun 16, 2009
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GearNut said:
It sounds to me like your gas cap is vent is plugged up. If air cannot be let in as the fuel is consumed then it creates a vacuum inside the tank stopping the flow. It only needs an itty bitty air hole. The next time the bike acts up, pull over to the side of the road and loosen and tighten the gas cap. If that fixes the problem for the next 1/4 mile then you have found your problem.
Click to expand...

Thats not it I have a vent tube in there
 
2door

2door

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Staff member
Sep 15, 2008
16,302
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Littleton, Colorado
If you're certain you don't have a venting problem, and you're sure fuel is flowing well then I'll go with the heat related vacuum leak. Sounds like something is opening up with engine heat to me. Do a thorough check at the carburetor to intake and intake to cylinder.
Here's something I've discovered recently. For a long time many of us have suggested using a silicone gasket sealer to seal the carb to the intake. If you read the package of most of the silicone gasket sealers available it plainly states "not for use in contact with gasoline" One of my bikes developed similar air (vacuum) leak symptoms and when I pulled the carburetor off I found the silicone (Permatex Black) sealer I'd used had turned to goo and it was apparent it wasn't sealing correctly. I cleaned off the mess and used a gasket sealer compatible with gasoline, a sealer/adhesive called SealAll, and the problem went away. Just my observation.
Tom
 
lowrider

lowrider

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Jun 16, 2009
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2door said:
If you're certain you don't have a venting problem, and you're sure fuel is flowing well then I'll go with the heat related vacuum leak. Sounds like something is opening up with engine heat to me. Do a thorough check at the carburetor to intake and intake to cylinder.
Here's something I've discovered recently. For a long time many of us have suggested using a silicone gasket sealer to seal the carb to the intake. If you read the package of most of the silicone gasket sealers available it plainly states "not for use in contact with gasoline" One of my bikes developed similar air (vacuum) leak symptoms and when I pulled the carburetor off I found the silicone (Permatex Black) sealer I'd used had turned to goo and it was apparent it wasn't sealing correctly. I cleaned off the mess and used a gasket sealer compatible with gasoline, a sealer/adhesive called SealAll, and the problem went away. Just my observation.
Tom
Click to expand...
I chopped the bottom of the muffler off and im running it without an exhaust gasket

gasket blew so i made some from beer cans and then they blew then i found out a gasket isint necessary i don't think unless the distance from pipe to cylinder matters?

cut the cap off muffler due to it going slow last year and so i took the exhaust off and the slowness went away so i thought there may be some restriction in the pipe.

Now it just doesn't seem to want to work right. it used to go 40 when it was new then after the gasket thing it wouldn't go any faster then i could pedal it then it would just maintain. thought it was the plug and cap so i replaced them and it still does the same crap. works but goes slow and now it does the bog down thing.
 
2door

2door

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Sep 15, 2008
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Littleton, Colorado
If you've been running an open exhaust you've probably fried the motor. Especially with the exhaust not sealed to the cylinder properly. 2 cycle engines rely on exhaust back pressure to perform correctly. With no, or insufficient back pressure the engine will draw in excessive air through the exhaust port and create a lean running condition. I would be willing to bet you'd see evidence of this if you remove the head and cylinder and inspect the rings/piston/cylinder walls. There should also be a noticable decrease in compression but it would be a gradual thing, not something you'd see overnight.
In addition to potential engine damage running an open exhaust will most definately attract negative attention to motorized bicycles. Keep them muffled and your engine and the hobby will be better off

Tom
 
corgi1

corgi1

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Aug 13, 2009
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Did you have a catiletic converter muffler,u said that you cut the end off the muffler,right?
 
Cabinfever1977

Cabinfever1977

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Mar 23, 2009
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Put a muffler and gasket back on and just keep changing the gasket if it falls out or blows. Check the aircleaner filter, thats seems to be your problem, the engine wants more air.
 
lowrider

lowrider

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Jun 16, 2009
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I havent been running the exhaust open other than the cap i cut off. I guess it is the model with converter.

Remeber it was these symptoms that led me to pull the muffler not the other way around.

Ill try and pull the air filter out and see but i really doubt it helps any.

I guess for 150$ ill just buy a new kit and install it
 
corgi1

corgi1

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My thought is ,,,is the converter stopping up, like on a car ,and not getting through,blowing the gaskets,,,do u have an old style MB muffler to try,,,,It is bad for the motor to run w/out a long pipe or muffler of some type
 
lowrider

lowrider

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Jun 16, 2009
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corgi1 said:
My thought is ,,,is the converter stopping up, like on a car ,and not getting through,blowing the gaskets,,,do u have an old style MB muffler to try,,,,It is bad for the motor to run w/out a long pipe or muffler of some type
Click to expand...

It has always been ran with the muffler just had the cap cut off. I dont think its stopped up it started doing this at like 3 months old.


So instead of a little hole in the bottom of the muffler there is a large hole.


Not sure if thats a bad thing or not?
 
Last edited:
ferball

ferball

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Apr 8, 2010
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I could be way off, but has the electrical system been considered? I mean would it be possible that something is slowly draining the coil or impeding the magneto output so that the spark is weak and by turning it off it discharges what ever is causing the problem until the build up occurs again? It is just a thought. My background is computers and electronics not engines, but static build up and discharge can cause funny problems, not sure if such a thing happens on these engines but may be one of you gear heads on hear can take the concept and translate it to bike problems.
 
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