fuel problem

arnoldsq · Post by **arnoldsq** » Thu Sep 16, 2021 8:53 pm

im a little confused at the 82 interstate that I just finished rebuilding. On tuesday night I was able to run it synching the carbs "they were barley off" no issues. I would say it ran for a total of 2 hours on tuesday between breaks and different projects. Carb sync made it so she starts without choke just needs a minute to warm enough to drive. Tonight I drove down to the local school to use their parking lot to test a bit, and after a while she started stumbling and only staying running if I was giving throttle. I stopped and switched to reserve thinking it fuel was reading 1/4 maybe its running to low for the pickup.

When I started back up she only ran at 1K RPM at full throttle. now here is the part that gets me. when I pulled the choke out just a hair she took off to at least 3K immediately and ran perfect the rest of the ride. I wouldn't think its the carbs since its running perfect and pulling hard most of the time, but im at a loss. The fuel filter has only been on there a few months, I had run a few gallons through a sacrificial filter after deducting the tank to be sure I didnt have debris.

DenverWinger · Post by **DenverWinger** » Fri Sep 17, 2021 7:48 am

This sounds like a resurrection after sitting a while.

You cleaned out the fuel tank but how much gunk and crud and debris do suppose was in the fuel pump, it might've broke loose and got pumped into the carbs....

arnoldsq · Post by **arnoldsq** » Fri Sep 17, 2021 9:38 am

you know I never really thought about the pump. I did pull it apart and wipe they diaphragm down but that was it. It was a bike that sat for 10 years that I just got back running. Im hoping to get a few weeks on her before the winter weather starts setting in.

The only other thing I can even think of is the fuel cap. I may be looking at this wrong, but if it went back to normal operation after bumping carb on and off could that have pushed enough vacuum in the system to overcome a bubble? I spent the night searching the forum for similar instances but didnt see anything other than freshly rebuilt carbs causing the issue.

LAB3 · Post by **LAB3** » Fri Sep 17, 2021 12:00 pm

Start with your basics. Fuel filters are cheap, checking to see if the petcock is allowing the gas to flow through is only going to cost you some time and as for the fuel cap, you should not hear any air rushing in when you take it off. Sounds like you already know how to clean up the fuel pump and the only other thing I'd add is make sure the fuel lines aren't clogged.

arnoldsq · Post by **arnoldsq** » Fri Sep 17, 2021 1:09 pm

Well I started it after lunch. Looks like I have a bigger problem. It did pull air when I opened the fuel tank. But the 4th cylinder stopped firing. I’ll check for spark after work.

arnoldsq · Post by **arnoldsq** » Fri Sep 17, 2021 2:02 pm

I had a few extra minutes on the way out and decided to pull the plug. it is wet with fuel and the cylinder had a decent puff of fuel shoot out when I turned it over. im starting to think I jacked up the sync tuesday and caused all my own problems.

Im going to start tonight with manually setting the carbs again with a needle. That should make sure im not completely out of sorts.

arnoldsq · Post by **arnoldsq** » Fri Sep 17, 2021 7:51 pm

Cylinder 4 and we have a stuck linkage.

arnoldsq · Post by **arnoldsq** » Sat Sep 18, 2021 7:30 pm

Now that I reset that adjustment and got it set I can now idle correctly with the fuel cap off. I currently have the cap soaking in vinegar and might toss it in the ultrasonic overnight.

After I ran it last night I shut the fuel off and today when I opened it I heard a large gasp of air.

If the cleaning doesn’t work I’ll start looking for a replacement option.

YouTube · Post by **WingAdmin** » Mon Sep 20, 2021 1:37 pm

arnoldsq wrote: ↑Sat Sep 18, 2021 7:30 pm Now that I reset that adjustment and got it set I can now idle correctly with the fuel cap off. I currently have the cap soaking in vinegar and might toss it in the ultrasonic overnight.

After I ran it last night I shut the fuel off and today when I opened it I heard a large gasp of air.

If the cleaning doesn’t work I’ll start looking for a replacement option.

You may well hear a pressure change (air escaping or going in) when you remove the cap. There is a valve in the cap that will allow excess pressure to escape or air to replace excess vacuum - but it doesn't mean ALL pressure - only when the pressure differential gets to a certain amount does the valve open. So it's entirely possible that there was some pressure differential, but not enough to trigger the valve to open - and that pressure equalization is what you heard when you opened the cap.

arnoldsq · Post by **arnoldsq** » Mon Sep 20, 2021 2:09 pm

Thanks for the tip. I did put it in the ultrasonic for an hour and got a bunch of gunk out. if nothing else its much cleaner now.

With that linkage not stuck fully closed, it made a huge difference. I drove around town in the 20 to 40MPH area for about 20 minutes and she ran good. I did find the next issue to work, but I haven't started into that one yet. Basically for the first 1/4 throttle it is great, but if you really get on it starts bogging. Sounds like you are in to high of a gear. its a new air filter so air should be good. Could be the plugs fouled from the previous mistake, and could be the fuel filter. Will start with the filter and work my way around. We had 70MPH winds yesterday so I couldnt do much.

arnoldsq · Post by **arnoldsq** » Wed Oct 06, 2021 1:01 pm

to post an update, its not the gas cap. I just cleaned and checked over the carbs again and reinstalled them. I also just did a neon coil swap with new plugs and wires. I don't have the filter box on yet so I was able to watch the 4th cylinder stop firing and start pushing fuel vapor back through the air box.
tell me if I am wrong here, but isn't the only way for that to happen is the intake valve stuck open?

MattMcCoy · Post by **MattMcCoy** » Wed Oct 06, 2021 2:36 pm

Have you tried compression and leak-down tests?

arnoldsq · Post by **arnoldsq** » Wed Oct 06, 2021 4:33 pm

Not yet. I need to order the tools

LAB3 · Post by **LAB3** » Wed Oct 06, 2021 4:42 pm

arnoldsq wrote: ↑Wed Oct 06, 2021 4:33 pm Not yet. I need to order the tools

You might be able to borrow what you need from an auto parts store, many of the big chain stores offer use of them for free.

arnoldsq · Post by **arnoldsq** » Wed Oct 06, 2021 5:30 pm

good point. might try that tomorrow. The further I look at this bike the more problems I find. I took the valve cover off to make sure it was actually moving and not stuck. The bottom right bolt was broken off in the head. ive never been in there so it came that way from previous owner. just finished drilling it out.

arnoldsq · Post by **arnoldsq** » Thu Oct 07, 2021 10:53 pm

I didn’t make it to the auto parts store tonight with parent teacher conferences, but timing is off. That will be a lunch time project tomorrow. Hopefully it didn’t contact.

DenverWinger · Post by **DenverWinger** » Fri Oct 08, 2021 6:30 am

Yup, off a cog in bottom photo. No contact. These will run "ok" one cog off but won't run "right". BTDT

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