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Discussion Starter · #1 · (Edited)
My FZR600 behaves funny on light throttle while cruising...and... also at low RPM under load at anything but light throttle.

From 2700-3100rpm the bike does not want to go. If you give it really really super light throttle on level ground, where the motor is not loaded at all, its okay, you can get through those RPMs, but any load at all and it bucks rapidly through this RPM range and the RPMs dont really climb because you're getting like equal deceleration and acceleration rapidly. And if you're going up a hill or something, it literally won't accelerate at all and you have to quickly downshift or burn the clutch to get the RPMs above 3100, or you're boned. The more the load, the harder it bucks. At 3100 it snaps back to normal. It feels more load dependent and happens everywhere in the throttle during these RPMs. Even wide open throttle in first gear you go nowhere.

Then cruising at the lightest possible throttle input, say 1/16" of turn on the throttle, it runs normal. But give it just a little more, an 1/8" of turn, and it starts sounding like its misfiring and power drops off. Until you get to 1/4" of throttle and beyond where its better.

First off, I have cleaned the carbs but I haven't synced them, and I made no adjustments to air/fuel settings on them. Just cleaned. The idle jets are so tiny they could clog very easily. But none of mine were totally clogged when I opened them up and it was soft stuff in there, I was able to simply blow through them and remove it. Cleaning had no noticeable effect on this behavior, and it has always idled perfect and pulls hard everywhere else.

I've also been Google searching for a year now and I have seen other people with this specific model of bike having each if the aforementioned problems, but none of the threads had a solution.

Obviously it feels like its a fuel problem, but after going through the carbs with no change I'm looking elsewhere. Could this be something with the coils? Or maybe yamaha just screwed up a bit with the ignition tuning on this bike since I'm guessing the electronic ignition was a somewhat new thing in 1989. Maybe they're all just like this.

Anyone got any ideas?

Wheel Tire Sky Plant Fuel tank
 

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My FZR600 behaves funny on light throttle while cruising...and... also at low RPM under load at anything but light throttle.

From 2700-3100rpm the bike does not want to go. If you give it really really super light throttle on level ground, where the motor is not loaded at all, its okay, you can get through those RPMs, but any load at all and it bucks rapidly through this RPM range and the RPMs dont really climb because you're getting like equal deceleration and acceleration rapidly. And if you're going up a hill or something, it literally won't accelerate at all and you have to quickly downshift or burn the clutch to get the RPMs above 3100, or you're boned. The more the load, the harder it bucks. At 3100 it snaps back to normal. It feels more load dependent and happens everywhere in the throttle during these RPMs. Even wide open throttle in first gear you go nowhere.

Then cruising at the lightest possible throttle input, say 1/16" of turn on the throttle, it runs normal. But give it just a little more, an 1/8" of turn, and it starts sounding like its misfiring and power drops off. Until you get to 1/4" of throttle and beyond where its better.

First off, I have cleaned the carbs but I haven't synced them, and I made no adjustments to air/fuel settings on them. Just cleaned. The idle jets are so tiny they could clog very easily. But none of mine were totally clogged when I opened them up and it was soft stuff in there, I was able to simply blow through them and remove it. Cleaning had no noticeable effect on this behavior, and it has always idled perfect and pulls hard everywhere else.

I've also been Google searching for a year now and I have seen other people with this specific model of bike having each if the aforementioned problems, but none of the threads had a solution.

Obviously it feels like its a fuel problem, but after going through the carbs with no change I'm looking elsewhere. Could this be something with the coils? Or maybe yamaha just screwed up a bit with the ignition tuning on this bike since I'm guessing the electronic ignition was a somewhat new thing in 1989. Maybe they're all just like this.

Anyone got any ideas?

Sounds like a weak fuel pump...
(its not a pressure pump but is a volume pump) So I sense you have problems filling the fuel bowls fas enough.

Is it priming when the key is turned on? its a few clicks, getting quieter as it goes, then stops when slight pressure is detected.
 

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Discussion Starter · #5 ·
Plug caps and wires, did you post this before or is it deja vu or a glitch in the matrix
I haven't looked at the plugs or the wires yet. I think the wires are actually one piece with the coils and they're $130 a piece, bike takes two of them.

I think its a glitch.

Sounds like a weak fuel pump...
(its not a pressure pump but is a volume pump) So I sense you have problems filling the fuel bowls fas enough.

Is it priming when the key is turned on? its a few click, getting quieter as it goes, then stops when slight pressure is detected.
It clicks like it should and quickly builds pressure and stops.

I dont think its a fuel pump because it springs to life above and below 2700-3100 and 80% of the throttle range it pulls as hard as it should. If it can supply sufficient fuel at wide open throttle at 10,000rpm then it should be good at low RPM or light throttle cruising.

The bike is rideable it just has these really annoying hiccups.
 

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Ok, agreed... pull the plugs and check the conditions..

Also check the coils , place an inline spark tester, and revit to the problem rpm range and see if spark is lost.


typically when electrical componets go, they just go. my 89 3HE runs flawsley btw...
 

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Discussion Starter · #8 ·
Maybe the the coils are sort of programmed to click over and deliver a larger shock at 2700-3100rpm, and because my magneto isn't spinning fast enough at those speeds, or is somehow on the fritz, or generally just insufficient for this bike.
 

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Discussion Starter · #9 ·
Ok, agreed... pull the plugs and check the conditions..

Also check the coils , place an inline spark tester, and revit to the problem rpm range and see if spark is lost.


typically when electrical componets go, they just go. my 89 3HE runs flawsley btw...
The problem is it doesn't misfire or do anything abnormal when you rev it. It has to be under load.
 

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Well I have had a inline 4 give bucking issues when they were out of sync. one cylinder gets proper fuel, the next gets verry little, and in sucession the 4 fight each other causing a bucking, like it has turets!

But this is an all rpms issue.....not just the lower mid range rpm's like your having
 

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That is how ignition misfires occur under load and more often than not plug wires or extensions that connect to the plugs. Could have a carbon track in one or more of the extensions. Definetly stick with the ignition system. You could also take a spray bottle of water and spay the plug boots with engine running in a dark garage or out side at night and see if you see arcing -spark jumping to ground.
 

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Discussion Starter · #13 · (Edited)
I have some video that demonstrates the issue. It looks more subtle in the video than it really is because its a very quiet bike (ignore the womp womp womp sound of the loose 20+ year old chain)

At 19 seconds and 28 seconds


I will look at the R6 coils.
 

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The tach is a good diagnostic tool if it jumps erratically when the issue occurs it is an ignition problem It's difficult to tell with the video but thought I could see the tack jump? a tach that gradually falls off is a fuel issue still thank your looking at ignition though.
 

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Maybe they're all just like this.
Something is not right. When everything is working correctly those bikes run nice and smooth.

Maybe the the coils are sort of programmed to click over and deliver a larger shock at 2700-3100rpm, and because my magneto isn't spinning fast enough at those speeds, or is somehow on the fritz, or generally just insufficient for this bike.
Your bike has a battery powered type ignition system. In the most basic terms that means the coils get power from the battery just as does the lights and everything else using electrical power. Of course the battery is constantly being charged / supplied voltage by the charging system but everything is powered by the battery. The coils supply a spark and function the same at any speed, idle to top speed. Because the bike runs good at high, and most RPM's there is no reason to believe the coils are giving trouble. I don't think bad plug caps would cause the problem you're having because it only acts up at around ~3000 RPM.

Even though you just cleaned the carburetors...
I'm thinking you may still have partially plugged slow speed ports (passages) inside the carburetor bodies. Also / and / or maybe crud in the jet block assembly along with what Yamaha calls the main nozzle. (Functions the same as an emulsion tube on the more 'straight forward' type carbs that do not use a jet block assembly).
But,
You should set the carb synch. Out of synch will effect idle and slow speed running. After handling the carburetors the synch is almost certainly off.

S F

Edit:
FYI ... When re-installing the brass cap looking thing (has a hex nut type area at one end) that is straight down from, and inline with the jet needle in the jet block be VERY careful not to over tighten. They break easily.
 

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Sounds like something is still clogged or not right in the carbs in the low speed jets, fuel bowl levels, etc, once it gets on the main jets it's running OK but in the transition it's starving for gas. If it didn't run better when you got the RPM up at higher power settings I'd be suspecting the fuel pump but since it seems to be OK under higher power settings I think the fuel is getting there OK as you said as well.
 

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Discussion Starter · #17 ·
Sounds like something is still clogged or not right in the carbs in the low speed jets, fuel bowl levels, etc, once it gets on the main jets it's running OK but in the transition it's starving for gas. If it didn't run better when you got the RPM up at higher power settings I'd be suspecting the fuel pump but since it seems to be OK under higher power settings I think the fuel is getting there OK as you said as well.
That has 100% been my assumption as well, but the jets were clear.

My other thought is that its possible it's overfueling because the jets are worn or too big. I suppose it's possible this bike could have been jetted for a different exhaust, although I doubt it.

Plus, if it was something with the carbs, why would others be experiencing identical symptoms? The odds seem low on that.

The first post doesn't describe the problem as clearly as he does a few posts in. Symptoms are identical.

 

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I had issues between 2k and 4.5k prms on mine, the carbs are a flat slide down draft. the bowls are essentially at an angle, a carb has to have the jet circuits fully submerged in fuel to allow proper atomization. under acceleration (mine) was stumbling/hesitating at the mentioned rpm ranges, but was fine above or below.

two resons I found. 1 coils were weak on spark output., I made the plug gap smaller, and this helpd. but did not fix totally. So I replaced the coils with some newer but used coils off a 1998 yzf R6. 2 was the float heights, were a little on the low side. compared to the factory specs. which any carb bike manufacturer dows not give a definitave setting, So I set the floats a slight higher than it was. this combined with the coils made it run like a top and screams in all rpm ranges.

No way am I saying this is your fix, but weak spark combined with improper fuel atomization was my issues and are now history.
 

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I have some video that demonstrates the issue. It looks more subtle in the video than it really is because its a very quiet bike (ignore the womp womp womp sound of the loose 20+ year old chain)

At 19 seconds and 28 seconds


I will look at the R6 coils.
Ok I watched the video
the womp womp womp sound was scary. almost as much as the traffic.
 
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