Uncontrollable revs !

[swampy]

Hey folks, I have a Nsr 125r, and it seems to be misbehaving. When I start it up the revs rise to over 5000 (no choke or throttle) they then die down a tad, however when I give it a rev once warmed up they stick at around 5000 again. I've checked the throttle slide, and that seems to be tickety boo. The only way I can control the revs is by applying the choke, which perversely drops the revs, however if I pull the choke out all the way, the bike stalls. I'm pretty sure the mixture/idle are set Ok. Having read other posts, i'm guessing it may be an air leak, but would appreciate some pointers. Thanks folks.
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"I hate to advocate drugs, alcohol, violence or insanity to anyone, but they've always worked for me." Hunter S Thompson
"Faster, faster, faster, until the thrill of speed overcomes the fear of death..." Hunter S Thompson

[stinkwheel]

As long as you are happy with the throttle action then it is almost definatley an air leak rount the inlet manifold area somewhere. If the engine revs up when you spray WD40 on the outside of this area that confirms it. I'd imagine there are a few gaskets, o-rings and bits of rubber involved with an NSR inlet manifold, one of these would most likley be at fault.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[mr jamez]

There is a single paper gasket for the inlet manifold, so it shouldn't be too hard to find the leak

[Kickstart]

Hi

The rubber manifold for the carb can crack which will lead to a major air leak.

Also the main bearing seals can fail resulting in this problem.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[loply]

Why would an air leak cause it to rev higher?

[Kickstart]

More air into the engine, just like when you open the throttle.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[swampy]

Cheers for the help so far guys, Ive checked over the manifold, and it looks ok. Keith where are the main bearings seals located ? Thanks...
____________________
"I hate to advocate drugs, alcohol, violence or insanity to anyone, but they've always worked for me." Hunter S Thompson
"Faster, faster, faster, until the thrill of speed overcomes the fear of death..." Hunter S Thompson

[Kickstart]

Hi

Around the ends of the crank. Not easy to see. On the o/s it will be under the clutch casing and obscured by the primary drive (although if this one goes the bike will use gearbox oil). The n/s one is under the ignition system.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[swampy]

Bugger, fair bit of stripping down involved then ! Better get me spanners out lol
____________________
"I hate to advocate drugs, alcohol, violence or insanity to anyone, but they've always worked for me." Hunter S Thompson
"Faster, faster, faster, until the thrill of speed overcomes the fear of death..." Hunter S Thompson

[Kickstart]

Hi

Be very certain that you have eliminated all the other possible causes first before you go to the extent of replacing those seals.

If it is a crankshaft seal then it is most likely the one under the ignition, and that should be fairly easy to replace without dropping the engine.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[ZRX61]

Sounds like the throttle cable isn't seated correctly in the carb.... no need to strip the engine as some people suggest just yet....

& from the way you describe it, it sounds like you may be operating the choke backasswards....

[swampy]

Okey doke, I think the throttle cable is ok as I can see the slide going up and down in response to turning the grip, and I assume that applying the choke lifts a slide in the carb, at least thats whats happening in my case. I cant start the bloody thing now, so I haven't had a chance to test anything out. Theres compression, and a spark, and when I pull the plug out it appears to be wet with petrol/oil, anyone have any ideas why it might not be starting that might be related to my previous problem ?? Cheers for the help so far guys.
____________________
"I hate to advocate drugs, alcohol, violence or insanity to anyone, but they've always worked for me." Hunter S Thompson
"Faster, faster, faster, until the thrill of speed overcomes the fear of death..." Hunter S Thompson

[ZRX61]

It's getting air from someplace.. the usual test is to spray WD40 around the carb boots & intake rubber manifold doohickies etc. If the revs increase you have a leak.. but you're already at 5000rpm...

[alains]

what says your petrol consumption ? i am thinking about the carb tank needle stocked or a bad level . also if do or undo the pilot screw , has this an effect ? set the pilot screw thight and undo 2 1/2 turns
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the worst day fishing is better than the best day working

[stinkwheel]

Ok, a silly one but I have seen it done. You put the throttle slide back in the right way round? the cutout should face the air filter.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[alains]

good shot , i've forget this one !
____________________
the worst day fishing is better than the best day working

[swampy]

Yeps the throttle slide is in the right way, there's a notch in it so it will only go one way round, will double check tomorrow though. Thanks for the thought though, I wouldn't be surprised if I've done something that stupid !
____________________
"I hate to advocate drugs, alcohol, violence or insanity to anyone, but they've always worked for me." Hunter S Thompson
"Faster, faster, faster, until the thrill of speed overcomes the fear of death..." Hunter S Thompson

[swampy]

Ok, well the plot thickens.... I took the carb apart today and gave it a thorough blasting with an air gun. I then checked the plug again, it turns out that this wasn't working (it was arcing between the bottom electrode and the chassis) Stuck another plug in, and she fired up. I then had the original problem of over revving, so I took your advice and gave the intake manifold a go over with Wd40, and about two sec later she stalled. Cue trying to start, and it cutting out when I gave it any throttle. I then noticed that the tank was a little low, and switched to reserve. Now she is running OK with no over revving. I'm not moaning but does anyone have any ideas why this might have solved the problem for the moment ??
____________________
"I hate to advocate drugs, alcohol, violence or insanity to anyone, but they've always worked for me." Hunter S Thompson
"Faster, faster, faster, until the thrill of speed overcomes the fear of death..." Hunter S Thompson

[alains]

you've certainly a dirty tank . make it empty , take off the tap , clean the filter . it happens also that water vapor condense in the tank or bad petrol services (when they got empty) . as water has more density than petrol it goes down in the bottom and more quickly in the carb . if you have filled it up , do this even it's bowring . in addition when it will be empty put a piece of clean clothe on an iron wire to clean all dusy & mud
____________________
the worst day fishing is better than the best day working

[alains]

i forgot (if you have not already do that) you must open the carb and clean the tank of water & mud
____________________
the worst day fishing is better than the best day working