Carb issue

gphil

Member
Jan 9, 2011
274
4
18
USA Georgia
The guys on the other pages of this site helped me through a drive problem so now going to ask a question here. Carb has been changed to a 049 carb from Piston Bikes. I can get more info if needed. Runs great but seems to get fuel starvation. I also see bubbles coming up from the Carb in the clear fuel line. It drains well from the tank but cannot see why it seems to run dry. Stop wait a few and off I go. Have I missed something? gphil
 

2door

Moderator
Staff member
Sep 15, 2008
16,325
114
63
Littleton, Colorado
This sounds like a case of the fuel tank (cap) not venting. It works like putting your thumb over a soda straw. If the tank can't vent to the atmosphere there will be a vacuum created in the tank that will not allow fuel to flow out of it.

Try loosening the tank cap and ride your bike. If the problem goes away you've found the reason. I did a tutorial on this problem a while back. If I can find it I'll post a link.
The problem with non-venting caps is where the factory 'peened' the edge. The peen is supposed to distort the inner section and allow air to enter. Sometimes the peen is too low and the cap won't vent.

EDIT: Here's that link > http://motorbicycling.com/showthread.php?t=30967

Tom
 
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gphil

Member
Jan 9, 2011
274
4
18
USA Georgia
Having ridden this bike in the past although not too long each leg , I had no problem. I did think of that and took the cap off. Maybe this newer carb draws more , although doubt it. Also another change was a offset mainfold etc in order to get a filter on. Going out and see about the peen . Thanks 2-door. gphil
 

gphil

Member
Jan 9, 2011
274
4
18
USA Georgia
Just looked at the cap and it has a peen on one side and a little notch opposite side. Actually looks like your bad one according to the location of the peen. Is there any fix to that other than a new one? On next ride if it happens I will loosen it while riding and see what happens. Probably stop thing is tight. Thanks........... gphil
 

2door

Moderator
Staff member
Sep 15, 2008
16,325
114
63
Littleton, Colorado
Look very carefully at where the peen is and see if you can see a small gap between the inner and outer parts of the cap. As was said in that old thread, the peen is meant to distort the two parts and create a gap that serves as a passage for air to vent the tank. The gap is small but it doesn't need to be big. It simply needs to allow air to get into the tank to equalize the pressure.

Some folks drill a small hole in the cap but that usually leads to fuel leaks from vibration.
I have 'fixed' defective caps by simply making a new peen above the factory one and checked to see that the peen seperated the two, inner and out cap parts.

Or, you can order a new cap and hope it was made right from the factory.

Tom
 

twostrokejimmy

New Member
Feb 25, 2014
28
0
0
BELVIDERE, ILLINOIS
ahhhh YOU FOUND MY PROBLEM glad I read this one thanx darn bubbles it would start sputtering id pull over pull fuel line n wait a min then alls good so at work ill fix this lil issue this forums great
 

gphil

Member
Jan 9, 2011
274
4
18
USA Georgia
Upon checking my cap, it seems to have the peen where it is supposed to be. The inner portion is small and I may try to make it larger, needle nose or something. We will see if it stalls on the next run. Later guys gphil