1995 r100rt fuel issues

[burhead]

I am working on a bike for my wifes uncle. He is from out of town and his bike is stranded with me. The bike runs great but has a loss of power at 1/8th throttle. He was on his way here and started to run low on gas so he switched to reserve and stopped for fuel when he could. This is when the problem started. Several other people have messed with the bike in the last month before it landed with me. His son was the first to try and he owns a 79 r100 so he knows a bit about them. He noticed a cracked spark plug wire so he swapped in a spare and installed new plugs. He also cleaned the carbs and found a cracked diaphragm so he replaced that. No change in running condition. He then swapped the tank with petcocks and fuel lines to his 79 and it ran just fine. He then passed the bike on to a retired bmw mechanic to deal with. The carbs were cleaned and checked once again. The mechanic also synced the carbs and said it was running as good as he could get it to. The bike ran fine for a few miles and then the power loss appeared again. Now it is my turn. I pulled the plugs and noticed they were black. Then I ran the bike for a few minutes holding the throttle steady at around 1/8th throttle, right where the stutter is happening. I then pulled the plugs and found the left plug to be black and the right plug was white. I then tore into the right carb and pulled the pilot jet. I shot some air through the orifice in the carb body and ran a small wire through the jet. I noticed some crap in the slide area after blowing compressed air through the orifice. I thought I had it whipped. Not so it still studders. So what am I missing? I am thinking maybe the float is bad and messing with the fuel level in that carb. Is that a common issue with these bikes? Any help is greatly appreciated. The uncle is coming back to town this weekend and I hope to have this bike fixed for him.

[SteveD]

Welcommen.

Could be the float. Do both choke levers shut off all the way?

Have you swapped the spark plug leads/caps to the other side?

[ME 109]

He then swapped the tank with petcocks and fuel lines to his 79 and it ran just fine.

This comment would normally create interest, but I can't see how it can affect one carb and not the other.

More information regarding idle and higher rpm behavior is needed to help diagnose.

First thing I'm thinking is slide needle positions.

[burhead]

The tank and fuel lines were only swapped to check for fuel flow issues. As for needle position, I will check them but they shouldn't be the culprit. Bike was running great when he left Kansas and started running bad somewhere along the way. I will try swapping spark plug leads. Any idea what the resistance value should be on them? Both choke levers are unhooked to make sure they weren't the issue.

[ME 109]

The tank and fuel lines were only swapped to check for fuel flow issues.

Ah, the fuel ran fine, not the motor.

Leads are 5 ohm iirc.

So does the motor idle ok?
Will it rev to 4-6,000 ?

A white plug is no good, a black plug is no good.

Run the motor, make it "studder", turn fuel taps off, turn motor off, check level in float bowls.
If it idles ok, and runs ok at more revs than 1/8, it aint float levels.

[SteveD]

If it idles ok, and runs ok at more revs than 1/8, it aint float levels.

If it runs ok at higher revs but then starts to struggle, might be floats that aren't adjusted correctly. it's not running at higher revs though.
If it idles ok it won't be heavy floats.
Could there be a blockage on the white plug side? The revs are too low for a main jet blockage, but maybe somewhere in the transition circuit?
Is the air filter blocked somehow? Is the fuel cap venting?
What's fuel flow like from the tank? You say it started after filling up after reaching reserve, but the bike worked better with a different tank and taps. Blocked tap maybe?

The bike ran fine for a few miles and then the power loss appeared again.

Could this be a heat related issue..ignition somehow?

[Jean]

If it was running OK before he bought fuel, I'd drain the tank and put some fuel in that you know is good.
A similar thing happened to me coming from Huntsville back to South Carolina...Worked on the carbs...then decided it was after I refuled.
Drained the tank... drained the carbs...replaced the filters...filled-in NEW gas I KNEW was good.
No more problems.

[SteveD]

If it was running OK before he bought fuel, I'd drain the tank and put some fuel in that you know is good.
A similar thing happened to me coming from Huntsville back to South Carolina...Worked on the carbs...then decided it was after I refuled.
Drained the tank... drained the carbs...replaced the filters...filled-in NEW gas I KNEW was good.
No more problems.

Yep. He's done that...different tank and taps and hoses..it recurred when the original stuff went back on.

..swapped the tank with petcocks and fuel lines to his 79 and it ran just fine.

Even if there was a unilateral blockage the crossover should account for that.

[burhead]

Ok a little clarification. The tank, petcocks, and fuel lines from the ill running bike were swapped to another bike and the other bike exhibited no issues so I would assume fuel is flowing well. I wanted to swap the carbs from the good bike but they are larger so that idea is out. The bike idles fine and runs out ok. You actually have to hold it in that one specific range to get it to act up. The tank has new fuel in it. I stopped at the BMW dealer to find a new pilot and o ring. The dealer thinks it is something in the transition circuit. So the carbs will come off tonight for a good soaking while I wait for parts. If the problem persists I will swap the carbs from one side to the other and see if the problem moves to the other side. Thanks for all the input so far. Her uncle is pretty desperate to get the bike on the road and doesn't have a lot of spare change laying around. I normally wouldn't get into the middle of a situation like this but I feel his pain and I actually like the guy so doing what I can to get him back on two wheels.

[ME 109]

Next question.

Is it just one carb, or both? Stand behind the bike and get someone to slowly bring it to the breakdown. You will hear if one side or both drop out.