HarleyTechTalk

Technical Forums => Iron Head => Topic started by: Crawler on July 10, 2019, 05:13:55 AM

Title: first iron head and have some questions
Post by: Crawler on July 10, 2019, 05:13:55 AM
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.
 
Title: Re: first iron head and have some questions
Post by: Crawler on July 10, 2019, 11:13:48 AM
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?
Title: Re: first iron head and have some questions
Post by: Burnout on July 10, 2019, 11:33:38 AM
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.
Title: Re: first iron head and have some questions
Post by: Crawler on July 10, 2019, 12:26:49 PM
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.
Title: Re: first iron head and have some questions
Post by: Panzer on July 10, 2019, 06:01:35 PM
Known as.............vapor lock.
Title: Re: first iron head and have some questions
Post by: Burnout on July 10, 2019, 08:50:56 PM
looks like you might want a VTwin 38-7004?
Title: Re: first iron head and have some questions
Post by: Crawler on July 11, 2019, 07:12:35 AM
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.
Title: Re: first iron head and have some questions
Post by: bobrk1 on April 04, 2021, 04:58:50 AM
A friend  had same  problem , he  cracked  open  the  cap and  it was  fine . Needed  a vented cap.
Title: Re: first iron head and have some questions
Post by: Dan89flstc on April 07, 2021, 05:59:37 AM
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.