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No power past 4000 rpm, need help

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Old Dec 19, 2019 | 09:48 AM
  #1  
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No power past 4000 rpm, need help

Good day all,

I'm just wondering if anyone has experienced/knows what could be the root cause of the following:

Bike doesn't accelerate past about 4000 rpm. I twisted the throttle but bike doesn't respond to it at all.

Everything is stock.

​​​
Old Dec 20, 2019 | 03:20 PM
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Originally Posted by Aetherza
Good day all,

I'm just wondering if anyone has experienced/knows what could be the root cause of the following:

Bike doesn't accelerate past about 4000 rpm. I twisted the throttle but bike doesn't respond to it at all.

Everything is stock.

​​​
Not nearly enough information to make many comments. Did this just start after riding it yesterday, or last year? What, if anything, have you done since it ran correctly and now? If I were to take a WAG, I might say it's having a TPS problem...

Last edited by YMRacing; Dec 20, 2019 at 03:23 PM.
Old Dec 21, 2019 | 01:12 AM
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Bike was second-hand so I don't have much knowledge on changes made by the previous owner, however what we did was clean the carbs, adjust the air-mixture screw (2 1/4 turns out) as it was set all the way in. I checked the TPS and it is showing a reading of 958 ohms on the multimeter. Another symptom, that could perhaps be relevant, is I noticed a fluttering on one of the carb slides when I take the airbox off and rev her while in neutral. The diaphragm doesn't seem torn. I apologise for the lack of information. I have read on forums of someone with a situation where the bike misfires at 7.5k rpm. The advice on this was the cam timing could be out by 180 degrees. Could this also possibly be the case in my situation?

It is also important to note that we rode her very briefly after buying her, thereafter she was standing for a long while as we did cosmetic changes such as replacing the speedometer, replace the radiators, replace the forks, brakes and front wheel.
Old Dec 21, 2019 | 04:37 AM
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We?
Old Dec 21, 2019 | 04:42 AM
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We refers to my father-in-law and myself.
Old Dec 21, 2019 | 07:36 AM
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Outstanding and welcome to the forum.
Old Dec 21, 2019 | 08:51 AM
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Try cleaning the carbs thoroughly again.

How how was it sitting around and did previous owner mention anying about it poor running / attempt any carb 'tuning'. Is airfilter standard and in good condition. Sparkplugs and caps all good? vacuum hose fitted correctly and secure?

CV Carb Tuning Procedures
Old Dec 23, 2019 | 04:47 AM
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Originally Posted by Wicky
Try cleaning the carbs thoroughly again.

How how was it sitting around and did previous owner mention anying about it poor running / attempt any carb 'tuning'. Is airfilter standard and in good condition. Sparkplugs and caps all good? vacuum hose fitted correctly and secure?

CV Carb Tuning Procedures
It was sitting for about 3 months

The previous owner didn't mention anything about any work done. Air filter is stock. I wouldn't say the filter is in excellent condition but it doesn't look broken or torn. Spark plugs are all good. Both coils are good too. The vacuum hose is indeed connected securely to the connector located behind the petcock.

I will follow the attached link to clean my carbs again and keep you updated.

Thanks for the assistance. Have a fantastic festive season
​​​
Old Dec 24, 2019 | 12:28 PM
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simple things first, vac line on the right spigot? vac lines fitted to inlet stubs ok and no leaks ? has the previous owner fitted mccts instead of the autos? that woiuld explain the 180 out tho thats normallly about 6k.
Old Dec 26, 2019 | 06:03 AM
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As the carbs were just worked on....... It remove them and check to the vacuum valve diaphragms to be seated correctly, no tears, cracks holes, the spring seated correctly. And then all other carb related things done in normal fashion.
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