rough running when gas gets low in tank

[portdave]

This has happenned to me at least twice now. When I get to about 70 miles on a tank of gas it starts acting like it is starving for fuel. (I normally get about 105 before I have to put it to reserve) First time it happenned I limped it home and took the car to work. Next day I went out and put it on prime and it started up. Felt better. Moved petcock to normal position. Filled up the tank and it was fine.

Yesterday morning it happenned again. About 71 miles on the tank and it acts like I am reserve level. Stopped by and filled up but it still felt like it was starving for fuel and running rough. Drove car again to work.

Tonight I get home from work and go out to start bike. Put it on and listened to it flow for a few seconds. Pulled up on choke. Started up great. Then about 8 seconds later it was running rough again and now I can't get it running right.

I pulled off the fuel line, hooked up extra line and the petcock is operating properly. Flowed into a container freely on prime and properly on normal position when I sucked on the vacuum line.

I checked spark on all four wires with an extra plug.

I dropped the float bowl on number one and it looks clean. These carbs were fully taken apart and rebuilt about a year ago. Orings etc.

Not sure what to check next.

I did rebuild the petcock about 5 tankfuls ago.

I ride this bike about 4 times a week to work.

I also checked the gas cap thinking maybe it wasn't venting properly. Blew some cleaner through the holes and it flowed okay. Then I blew it out with air.

Any suggestions?

Thanks.

[Steve]

Any chance you have a fuel filter in the line?

.

[chuck hahn]

points and condensors? heating up condensors and they are acting sporadic when hot???

[Steve]

points and condensors? heating up condensors and they are acting sporadic when hot???

If the 70 miles were all in one shot, I might (sort of) agree with you, but I happen to know that Dave does not live that far from work.

.

[chuck hahn]

Well i dont know that!!! I have had old cars act like that when the condensors were getting ready to crap out..then again at a short distance maybe they are weak enough to act up anyways..just fishing here of course. And i am assuming the ignition is stock.

[portdave]

Thanks Chuck but I have a dyna ignition on it. I am pretty sure it is not electrical but something might be off on it. Congrats on moving. Glad you made it safe.

Steve, I don't have filter on the line.

And all of these are short trips of no more than 30 minutes or so. Happenned both times with about the same amount of fuel which made me think it was somehow related to the flow of fuel but I am not sure....

[chef1366]

I'd say either the petcock is malfunctioning or the fuel tank isn't venting properly. Remove the gas cap when running poorly and see if that remedies it. If not I'd just by a new petcock.

[Dave8338]

Short trips??? Start stop at low RPMs... check your battery voltage next time it happens.

[Steve]

Steve, I don't have filter on the line.
....

Dang. I was hoping that you had one that was just restrictive enough that half a tank of fuel was not enough pressure to push it through.

.

[portdave]

I'd say either the petcock is malfunctioning or the fuel tank isn't venting properly. Remove the gas cap when running poorly and see if that remedies it. If not I'd just by a new petcock.

Chef,

Thanks. I am thinking I may just get a new petcock and cap. I am gonna drain all the gas out too... I started wondering about too much water in the gas too....lovely corn

Steve,

Good try. I will give you a call soon.

Dave,

Battery is really good but I will double check next time it happens. Right now I can't even get it to run right on a full tank. I just put it on the trickle charger. Will double check charging.

Thanks all.

[atb1998]

Fuel filter inside of fuel tank on top of petcock clogging from debris in tank.?

[portdave]

Well I got it running again. I took the petcock out of the tank and there was some debris as mentioned by atb. I fully disassembled the petcock and soaked it in carb cleaner. I had just rebuilt it not too long ago so it wasn't too bad. I did get some tank cleaner and swished that around all day. Got some stuff out. Also dropped the bowls on all the carbs and pulled the float valves. Cleaned the pilot jets.

The carbs had been fully cleaned about 9 months ago.

Got it running again strong tonight so only time will tell. I am gonna get another petcock and gas cap on my next order anyway.

Thanks for all the help and I will let you know what develops.