First Ride - Big Hesitation - Fuel?

[dave_a]

New to me: 1999 R1100R with 42K on the clock. Previous owner has done the 40K service (valves, fuel filter, fluids). Took my first real ride after paying the tax man for plates. Put the wife on the back and took an uneventful 75 mile ride. All normal running, including a burst or two on the interstate to 80-85. No prob's.

 

At the end of ride, decided to do full throttle acceleration run. Rolled on to full throttle in first. Somewhere around 5-6000 rpm the engine hesitated, on/off as if it was running out of fuel. No misfiring, just like the throttle was chopped or ignition cut. Return to lower throttle settings it resumed normal operation. So full load, max fuel demand, something's not right.

 

Haven't checked a thing yet - where to start gentlemen? My first Boxer, but have been riding for 40+ yrs. Fairly mechanically inclined.

Thanks in advance for the help. Dave

[dirtrider]

New to me: 1999 R1100R with 42K on the clock. Previous owner has done the 40K service (valves, fuel filter, fluids). Took my first real ride after paying the tax man for plates. Put the wife on the back and took an uneventful 75 mile ride. All normal running, including a burst or two on the interstate to 80-85. No prob's.

 

At the end of ride, decided to do full throttle acceleration run. Rolled on to full throttle in first. Somewhere around 5-6000 rpm the engine hesitated, on/off as if it was running out of fuel. No misfiring, just like the throttle was chopped or ignition cut. Return to lower throttle settings it resumed normal operation. So full load, max fuel demand, something's not right.

 

Haven't checked a thing yet - where to start gentlemen? My first Boxer, but have been riding for 40+ yrs. Fairly mechanically inclined.

 

 

Morning Dave

 

If it otherwise runs good under power the first thing to do is probably verify that the tachometer is accurate. Maybe you ran it up past fuel cut-off.

 

A high RPM problem that doesn't show up at lower engine RPM's or at low RPM high engine loading is very difficult to diagnose as you just can't run the engine at that point long enough to find the problem (so that usually leaves a lot of testing or guessing)

 

My personal next move would be to see how fast the bike runs out at sustained top speed for a reasonable distance (you might not feel comfortable doing this). If it will hold 125 mph (on GPS, not speedometer) then you probably don't have a fuel flow or ignition issue. On the other hand if it won't reach or hold a decent top speed (for a distance not just a burst then let off) then you know there is an issue somewhere.

 

Otherwise, start with new spark plugs that are properly gapped & then repeat the high RPM shift run-out.

 

If new spark plugs don't help then you are on to doing a fuel flow & fuel pressure test (or maybe a short-cut fuel return flow test).

 

It (also) might not hurt to check the air filter for signs of element swelling from water ingestion or from years of dirt.

 

 

 

 

 

 

[dave_a]

Dirtrider, questions:

 

1. How do you validate the tach's accuracy?

2. Do the plugs fire thru the same coil, so both plugs would shut down if one plug was bad?

3. The fuel filter is new, but brand unknown. Are there flow issues with aftermarket crap filters? Are there any other filters/screens downstream toward the injectors?

4. What could get screwed up in a fuel filter R&R?

5. I've read forums about a split hose in the fuel tank. How does that show as a running problem?

6. I've got a shop manual, I better start reading it. Fuel pump output?

 

I think my PO was well intentioned, but maybe ham fisted. I think I'll go after the "last thing he fixed": Fuel filter.

Dave

PS> I run out of talent at about 88mph. Sorry no top end runs. Plus it'll do it wfo in first!

Dave

 

 

[Mark K]

I wouldn't tear into anything just yet, Dave. It's possible you simply hit the rev limiter (not a bad thing). How sure are you it was around 6K? Also, was the cut-out at constant speed/rpm or was your plan to quickly flick through the gears when this happened?

[dave_a]

Mark, I don't believe I was near redline/fuel shutoff unless the tach is WAY off. The needle was around 11am: 4-6000 (I was looking for cars ahead). Redline's 7500 or around 2pm visually.

 

Anyway the cut out was pretty violent and had the wife on the back. Lots of helmet banging. I decided we'd keep the first ride positive. Went back to Mr. Conservative and all was fine.

 

I'll give it another ride soon and get more details.

Dave