Bike Starts Right Up Runs 100 Yards Dies.

CalKustoms · May 15, 2013

My basic 2 stroke bike starts right up and will run for about 100 yard before she dies. After that she will not start back up for a few minutes. But after a few she will start right up with no prob run 100 yards and die. I will start her up run her at high rpm while clutched and she will just die after a little. It runs around the same amount of time before she dies leading me to think it is a fuel clog. Spark is ok. Maybe the pin controlled by the carb float is getting stuck? Any advise?
Thank you

maniac57 · May 15, 2013

Next time it dies, remove the fuel cap and see if it fixes problem. Some caps do not vent correctly and need a small hole drilled in the cap to prevent vacuum locking.

crassius · May 16, 2013

saw this once - guy mixed his fuel, then poured into the tank from the can that had the straight gas in it by mistake - ran, then quit just like that

biknut · May 16, 2013

Your gas cap isn't properly vented.

bairdco · May 16, 2013

is your fuel petcock on?

pull the fuel line off and turn the petcock on and make sure it's flowing.

if it is, blow through the fuel line to make sure it's not clogged.

if you have an in line fuel filter, make sure it's installed the right way. some only flow one way.

if all that's clear, pull the carb apart and blow the jet out with carb cleaner, and spray all the holes to make sure nothing's clogged.

allen standley · May 16, 2013

Don't mess around ...Drill a 1/6 or smaller hole in the top of your fuel tank cap. Built a dozen bikes, done it to em all.

CalKustoms · May 16, 2013

After rebuilding the carb and checking the line, I came to the conclusion it was not a fuel problem.
However I did find the problem. It was a small head gasket leak. I guess when the motor warmed up the gasses thinned out and I would lose compression. Or it was taking in air through the leak. Either way it was killing the motor. Once cooled down the motor would start back up because it was cool.
So to test it. I let it cool and tightened the head down and it has been running fine since. I need a new gasket because the leak is not completely fixed. But she does not die anymore after multiple tests.
Thank you to everyone who took the time to post.

bairdco · May 16, 2013

glad ya figured it out...

a small leak will eventually get bigger. it can also cause a hotspot, with the hot gases building up at the leak, which can lead to piston siezure, etc.

one thing you should definitely do is remove the head and re-deck the surface.

you need a piece of glass with a piece of wet sandpaper taped to it. use a circular motion and sand the mounting surface of the head down till it's shiny all around.

this gets rid of any warpage or defects to make a perfectly flat surface.

the head gasket might be cleaned up and re-used, depending on how bad it is. sometimes they burn through, then you definitely need a new one.

allen standley · May 20, 2013

Well theyah! And yes bairdco is dead on about the re-decking the surface. Correct me if wrong I believe this is also called "Lapping the Head/Jug"

2door · May 20, 2013

Gas cap venting: Here's a good thread on the subject and a reason why some don't vent> http://motorbicycling.com/showthread.php?t=30967 See post #6

allen standley said:
Well theyah! And yes bairdco is dead on about the re-decking the surface. Correct me if wrong I believe this is also called "Lapping the Head/Jug"

Lapping is the correct term and there are several good posts here showing the process in detail. Use the search feature, keywords 'lapping cylinder head'

Tom

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Bike Starts Right Up Runs 100 Yards Dies.

CalKustoms

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maniac57

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biknut

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bairdco

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allen standley

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CalKustoms

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bairdco

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