Big honkin' tire chirping miss on my R1 - Updated symptoms

[Tim K]

'99 R1 race bike, pretty new to me.

This thing ran rich, but otherwise fine on the first couple of track days. On the last one of last season, it developed a profoundly scary miss. It would cut out so hard it would break the rear tire loose. I discovered I'd ridden an entire session with the choke on, so I assumed I had fouled the plugs.

Fast forward to today, I re-jetted it back to stock settings (it had been fooled with), cleaned the carbs, and changed the plugs. On a very short test ride in the neighborhood, it was doing the same thing again.

I can't even get out of 1st here in the neighborhood, but rolling on from 3K I get a pretty big stumble at 4 or 5K.

Things that might be important:
K&N filter
Yosh can and some sort of aftermarket pipes, maybe also Yosh.
Jetted for stock, but I live at 8,500ft. The track where I run it (HPR) is at 5,500ft. The test ride was at 8,500.

I am hoping it's a fueling issue that will go away with proper operating temps and lower elevation, but now I'm worried it's ignition related.

Dang, the next track day is this Sunday!

Any help will be appreciated.


Post Chicane track day update:

I thought I was going to the track with the problem solved, and on the first session, about midway through it started again. Basher kindly looked at it with me and we checked a bunch of electrical connections, thinking it might be an ignition issue. On the second session, the problem continued, but I noticed that if I didn't run it at WOT and shift at redline down the straight, it ran well through the rest of the course.

Once I figured that out, I was able to ride it without issue unless I wound it up on the straight. Every time I did that, it would give me those big misses for 1/2 to 3/4 of a lap.

This now has me suspicious of fueling again. I don't know enough to know if this is a symptom of to large or too small a main jet.

On the plus side, I got a lot of experience riding with the rear end loose. Backed it in a couple of time inadvertently when the rear let go at an inopportune moment. Yippee.

[rybo]

I've been thinking about this - is the miss ALWAYS at the same point in the rev range?

You just had the carbs apart and changed some jets back to stock - did you also synchronize the carbs when it went back together?

That's where I'm starting....

[Tim K]

I've been thinking about this - is the miss ALWAYS at the same point in the rev range?

You just had the carbs apart and changed some jets back to stock - did you also synchronize the carbs when it went back together?

That's where I'm starting....

Don't know if it's always in the same spot. Will have to check. I did not synchronize the carbs, I actually forgot about it.

[TFOGGuys]

Sync is really only important in the lower RPM ranges and throttle openings. At WFO it is largely irrelevant. If the bike bogs under load, and backing out of the throttle cleans it up, you are likely too rich. 4-5K is where the slides are beginning to rise, so the issue likely rests with the slide needle setting. Does it have the original needles (nonadjustable) or aftermarket (multiple grooves and circlip)?

[Bueller]

What do you mean by stock jetting? Did you go back to sea level jetting?

[Tim K]

It doesn't bog so much as miss hard. It's a sudden and short duration jerk, then it continues to run normally past it. It almost feels like the ignition shutting off for a split second.

Needles are aftermarket, set pretty lean.

It has the stock jets for sea level. The previous owner had 3 or 4 sizes larger in it.

[TFOGGuys]

Any idea who's needles? I can give you a reasonably close jetting combo with the Dynojet stuff...

Also, if it's more throttle position sensitive than rpm dependent, it might be worth checking the TPS, as the R1s use that for ignition mapping...


Edit: Dynojet settings for 6K feet: Needle clip 4th groove from the top, main jet with K&N and full system 134-136 (Dynojet jets, OEM numbers don't cross accurately), idles screws 21/2 to 3 1/2 turns out from gently seated.

Updated to reflect the info for the correct year :banghead:

[Tim K]

Dynojet needles. If i recall, the clips are one from the top. I'll go ride it and try to get a better idea when it does it.


Edited to add:

I rode it again, a bit more extensively this time. I think it just wasn't warmed up because it did it once when I first rolled out and then not again. It still feels a bit rich, but I'm thinking coming down 3,000ft in elevation might take care of that.

False alarm, I guess. Feeling pretty stupid now...

[Tim K]

Original post was updated.

[Bueller]

Main jets way too big if you jetted sea level, you are fuel fouling the plugs.

Just my opinion.

[Tim K]

That would make some sense to me except for the fact that the first couple of times I rode it, it did not have this problem. At that time, the jets were even larger than they are now.

Any other input?

[brennahm]

Any chance you ever notice the dash when the stumble occurs?

Unlikely, but perhaps you're having a problem with the ignition switch/wiring. Does the dash flicker when the bike cuts out? ANY other weirdness in conjunction with stumble?

[Tim K]

Not that I've noticed, but I try not to look at the dash on the track. Good idea, though. I'll try it in the neighborhood and see if I can make it happen.

[jplracing]

So I am a little confused. Are you saying that it is happening at a specific RPM or at a specific throttle position

If this is a race bike and has had race fuel in the tank for any length of time, it is possible that the fuel pump has gone bad

Had this happen on a previous bike. Basically the bike will idle fine however once you open the throttle to a certain point the bike starts lurching and won't rev...this can feel like the ignition is "missing"

If this is the case, Bart at Faster has had some success in disassembling the fuel pumps and cleaning them.

[Tim K]

So I am a little confused. Are you saying that it is happening at a specific RPM or at a specific throttle position

If this is a race bike and has had race fuel in the tank for any length of time, it is possible that the fuel pump has gone bad

Had this happen on a previous bike. Basically the bike will idle fine however once you open the throttle to a certain point the bike starts lurching and won't rev...this can feel like the ignition is "missing"

If this is the case, Bart at Faster has had some success in disassembling the fuel pumps and cleaning them.

It only happens after running the back straight at HPR at WOT, shifting at redline. If I don't do that, it's fine. I guess I'm saying it seems to be a combination of RPM and throttle position. I can't find another combination that causes the problem.

I think it might not be the pump. It runs the straight fine, no lurch or lag. It's the mile or two after that when I get the cut-out of power.

[TFOGGuys]

It only happens after running the back straight at HPR at WOT, shifting at redline. If I don't do that, it's fine. I guess I'm saying it seems to be a combination of RPM and throttle position. I can't find another combination that causes the problem.

I think it might not be the pump. It runs the straight fine, no lurch or lag. It's the mile or two after that when I get the cut-out of power.

Tank venting issue? If the vent in the cap won't allow air in as fast as you're pumping fuel out, then a partial vacuum may form, reducing fuel flow until the pressure equalizes.

Just a thought...

[Tim K]

Tank venting issue? If the vent in the cap won't allow air in as fast as you're pumping fuel out, then a partial vacuum may form, reducing fuel flow until the pressure equalizes.

Just a thought...

Very interesting...