HI guys,

When I ease off throttle to 5.5k, I get a bucking, almost jack-hammer effect in the power delivery. It is not a hesitating, bogging but rather fast on-off-on kind of bucking or judder. Andy, I know we are not to discuss jetting here, but I do not think this is a jetting setting issue per se for two reasons: first, the bike accelerates up through the rev range to redline just fine, no stumbling, bogging, or the like; it is only when I am cruising along in traffic say and have to come off throttle at 5.5k that I get this...actually it happens less noticeably also at 7k, if that tells you anything. The other reason I don't think it is jetting settings is the bike started doing this with my having made no jetting changes whatsoever. It MAY have started after I had some AV gas sitting in the tank for a couple weeks because I wasn't able to ride, but I am not at all sure that is when it started....

So NSR Gurus, can you give me any idea what this could be or what I might do to remedy the situation? I am sort of riding around it now, but it is not as it should be...or was. Thanks for any help.
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-Jim
'93 MC21

So what other mods have you done? It will help a lot with diagnostics.

You may have a jetting issue, or the needle shape may not be right. Your jetting may be correct for wide open throttle, not for cruising at a light constant throttle.

If you had stale fuel sitting for a while, clean out your carbs.

Mods, which have been in place for years, are just wire splice (m-max) and Tyga pipes (stock airbox).
Jetting was done years ago on a dyno, worked fine for years, and hasn't been changed, which is the reason I am thinking it is not jetting settings. I guess I will try cleaning the carbs, though I've personally never done it and don't really know what I am looking for....never a good combination in my limited mechanical experience. Probably a lame question, but is there any way the carb gaskets or float settings could cause this or would I basically be looking only for residue or blockages of some kind....don't have access to compressed air. Thanks.
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-Jim
'93 MC21

So if you had it set up well for years and suddenly has not performed well I would guess it is either bad fuel, plugs fouled (stale fuel can foul plugs), gummed carbs, battery issue or another mechanical problem.

Start with the easiest first and confirm battery condition, change your plugs and flush out the fuel (include draining carbs). Then I'd worry about cleaning the carbs.

Yes, I totally agree with starting with easiest first. Though it did go from running fine to not, I neglected to say that I have been living with this for a while, during which I have changed the plugs and gone through many tanks of gas. So we can probably rule those out. Although I keep the battery on a tender, checking my notes, I see that it is 8 years old! I'll definitely start there, as it should be changed even if it is not the culprit. Would be so nice if it turns out to be something so simple. If not, will explore the gummed carb idea. thanks!
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-Jim
'93 MC21

Jim, I'm hurt that you didn't email me first.

I had a similar issue and I remember it being electrically related. What I can't remember is what it was! Check battery, plug/coil connections, and coil pickups. Do you have a lightened flywheel on your bike?

Scott, I DID think of you first, of course, but I figured you were busy and that I'd give you a break and bug the entire NSR world instead. Going to start with replacing the battery, given that it is 8 years old. Stock flywheel. Fingers crossed it is the battery. If it is not that, be forewarned, I am going to you with the carbs.
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-Jim
'93 MC21

Hiya
I have this too but goes away when I change down??????? I just thought it was the bike telling me "You're in the worng gear you twit!"

Well, my bike bad-mouths me regularly enough, but I really don't think this is one of those times. It didn't used to do this and I don't think my riding has changed in years.
_________________
-Jim
'93 MC21

I have a similar current issue on my TZR and I've been told it could be a TPS related, throttle position sensor. I haven't had time to attack that issue as yet and I also don't know if the nsr has a TPS?

Yes, it does have a TPS. Argghh, I don't know exactly how to troubleshoot that possibility though. I'll have to root around the search function. Thanks for the suggestion.
_________________
-Jim
'93 MC21

So putting in a new battery did not fix the problem, but given that it was 8 years old, probably good to change out. So still getting a juddering or bucking at around 5k and also 7k if ease off throttle to get there, no problem at all if just reving up through the full rpm range.

If it is a TPS issue, wouldn't there be a problem going up through the rev range too? If it is a carb issue, could the float settings cause such symptoms?

Thanks for any help.
_________________
-Jim
'93 MC21

I was thinking about this on the weekend. In summer I never had this issue. It is now the middle of winter and it has appeared. On teh weekend I couldn't get the bike to warm up (it was about 8 degrees on the ride) and the problem seemed worse than normal on the trailing throttle. Got me thinking tune and dare I say it that word beginning with J that I'm not allowed to use..........

Extremely difficult to diagnose something like this remotely, but I would be looking at the electrical system.

It sounds to me like you're dropping the spark on at least one coil. Try hooking a volt meter up to the coils, taping it to the top triple, and seeing if the display drops out at 5500rpm as you ride. It's unusual for a TPS to cause problems, although not unknown. However, rolling on and off the throttle appears to allow the motor to pass through the bad zone, so I suspect it's not the TPS.

If nothing has changed since the last perfect ride, and the last ride wasn't that long ago, then it's not going to be jetting.

The biggest problem is what you describe as bucking, someone else may describe as a judder, and someone else may describe as a misfire. Only slow, simple, logical methodical steps will diagnose this.

Start by eliminating the fuel. Drain/clean the tank and carbs, and refill with fresh fuel... whatever fuel you always use! If that's an AVGAS mix, then use fresh AVGAS mix, if it's 95/97/98/100, us that! Eliminate all variables.

Clean/replace the air filter. Replace the plugs and caps, shortening the HT leads 5mm before fitting the new caps. Check the LT terminals on the ignition coils and at the pulser coils, and the condition of the wiring from the pulsers. There was a good post by Dave Ett on checking the coils a couple of months ago. If it's still misfiring, then go through the harness, checking and cleaning all the connections and earth/ground points. Try your PGM on another bike (always preferable to trying a new PGM on your own!). That's all the easy stuff!

After that it gets expensive, and I'd be doing leak and compression tests. Bad compression, broken/worn ring(s), and duff crank seals can all cause the misfire too.

Again, it sounds like you're dropping a spark, but it's almost impossible to diagnose remotely. All you can do is work your way through the systems (fuel/electrical/mechanical) methodically.
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Andy.
NSR-WORLD.COM

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well, Andy, as I have said on more than one occasion, if you would just open a shop in Southern California, we could solve the remote diagnosis problem! But as I have yet to
hit the lottery and have no magic wand with which to fly you out, thanks for your many expert thoughts. At my usual rate, this should keep me busy for a very, very long time. I hate electrical problems!

Thanks!
_________________
-Jim
'93 MC21