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Need help with Lean running issue

Mike T

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Two weeks ago I had an electrical short with the heated grips on '95 R1100RS with 19K miles. About 6 wires melted together in the harness. I've repaired the wires and all seems fine except the bike runs poorly when warm between 3000 and 4500 RPM. It idles fine and runs better at higher RPMs. It feels like the bike isn't getting enough gas and it also surges more than it used to between 3000 and 4500 RPMs.


Here's what I've done so far:


-replaced air filter

-replaced spark plugs (old ones had carbon on them)

-Drained and replaced gas

-Checked gas filter (you can blow throug it easily)

-Checked fuel pressure at idle (50 psi)

-Replaced HES

-Checked TPS voltage (.385)

-Put 1/2 bottle of Tectron in gas

-Gave it an Italian Tune Up.

-Turned off Techlusion 259 (same problem only worse)

-Adjusted the TBs using Twin Max (helped a little)

-Checked spark plug wires with bike running at night (no flashes noted)



What else shoud I check? The bike ran fine prior to the electrical mishap. O2 sensor?

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Mike, you might try re-setting the Motronic.. Pull the # 5 fuse for about 5 minutes then re-install the fuse.. Maybe that short in the wires scrambled the Motronic's memory..


If that doesn't help, try tracking the TPS voltage on both the low throttle wiper & 1/2-full throttle full range wiper.. Use an annalog voltmeter as most digital's don't update fast enough to find a hole or dip in the TPS voltage..



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Could also be a battery problem.


I just had my Blackbird cook its gel battery due to an out of spec voltage regulator. Performance had seemed soft for the last week or so, lacking torque in the mid range. I was getting ready to change the plugs. Now, that bike has an excess of HP so soft performance is still pretty good and the plug change is a PITA so I was putting it off. Did a 600 mile day on Saturday and on the last gas stop before the hotel, no start, just a click. Battery voltage using the diagnostic screen GPS was fair at 12.4 volts but the battery wouldn't put out any current. Voltage dropped to nothing as soon as I hit the starter. A new battery from O'Reiley auto parts solved the problem and performance was back as well.


Put a voltmeter on your battery and carefully observe the voltage drop when cranking the engine over. A healthy battery should stay above 10 volts.

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I'll check the Battery voltage. I was planning on buying a new one for next year anyway. I did reset the CPU (fuse 5) with no change. I also checked the timing with a timing light and the 'S' was showing in the timing window.


I ordered an Analog Voltmeter to check the TPS throttle ranges.


Thaks for the input so far.

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I had one other thought on what the problem might be. I installed some quick disconnects that turned out to be pieces of crap. They would not seal properly due to the O-Rings coming dislodged so I took them off and put on new Napa 5/16" fuel hose.


Do you think it's possible one of those little O-rings could have come off and gone into the fuel line??


If it did would it be stuck in the Pressure regulator?


My pressure is a bit high at 50 psi. Would a stuck O-ring cause increased pressure?

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Well, it would be pretty tough for the O-ring to reach down those little lines to the fuel pressure regulator. It could be partially blocking one though.


When you measured the fuel pressure did you do it with gauge mounted in a tee in the line or dead head the pump into the gauge. The former is the proper technique. I like to do it with the engine running as well to be sure there is adequate flow under at least some load.


Ideally, you would mount the gauge into a tee in the line, go and ride the bike and observe the fuel pressure as you undergo the acceleration that is causing the problem. If fuel pressure drops, I would bet on a clogged fuel filter, despite the fact that you can blow through it. Air is not liquid gas and you can't produce anywhere near the pressure needed to simulate flow.

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Thanks for the response Ed. I did use a T set up to test the fuel pressure. I attached one end of the T on the tank outlet hose (bottom one) and then hooked the other end of the T with hose into the plastic intake hose. I did run the bike but did not go for a ride. I'll do the ride thing this weekend as the problem seems to be getting worse (which I would expect if it were a fuel delivery problem vs an electrical issue).


One other piece of info is that when the bike had the short problem in the heated grips, it was actually fuse 6 (fuel pump) that blew. Is it possible for a pump to be partially wounded and not perform at steady, lower RPMs and work OK at idel and higher RPMs? (Yep, as you said, go for a ride with the pressure gage attached and see). Thanks

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