HarleyTechTalk

I just picked up a new to me 1980 sportster. I rode the bike 40 miles home and it was doing good till about 3 mile from home and it started to spit and sputter. I'd pull the clutch in and give it a rev and it would rev up but as soon as I would let the clutch out it would bog down. It shut off on me a few times but I managed to get it restarted and back home. I let it set for a few days and took it out for a ride down the road a mile or so and it started to do the same thing. Any idea's on what could be causing this? Guy had told me he just had the carb rebuilt. the plugs and wires look to be new. the bike starts up and idles fine. It does have short laf pipes which I plan on changing out at some point down the road.
 

So I did some reading at lunch and was reading about improper gas cap venting. I noticed that when I got the bike hope I wanted to check the fuel and when I removed the gas cap it made a sound like I was opening a bottle of pop. could that be whats causing the stumbling?

Pressure or suction?

Screw in cap or cam lock?

I have seen aftermarket tanks with the vent line soldered closed.

Pressure is often seen due to fuel expansion.

Suction is NEVER good.

Burnout  its a cam lock cap and stock tank. I'm not sure I just know it made a fizzing sound like opening a coke bottle. I'm going to drain the gas and remove the petcock and see what it looks like. probably try to find a new gas cap.

Known as.............vapor lock.

looks like you might want a VTwin 38-7004?

going to try and get a new cap today. I did drain the tank and replace the petcock. the old one was dirty. I checked the plugs and they were dirty also so that's on my list for today also. I had it running last night and it seems to be running real rich so i'm going to try to lean it out a bit. Thanks for your help Burnout.

A friend  had same  problem , he  cracked  open  the  cap and  it was  fine . Needed  a vented cap.

Quote from: Panzer on July 10, 2019, 06:01:35 PM
Known as.............vapor lock.

That is not what vapor lock is...

Vapor lock is when the fuel in the lines turns to vapor.