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#1 Poor top end performance after big bore kit
- Join Date
- Jan 2012
- Location
- Norwich
- Posts
- 408
06-04-2012, 09:38 PMIt's been a week since I installed my big bore kit and I am now having some engine problems; normal use is fine but under hard acceleration, speeds above 50mph or at WOT I get what I think are missfires and I cannot go above 55mph whereas I could do 65 - 70 with my 125 cylinder. I'm hoping that it's just because the piston rings aren't seated yet but I fear that it could be something more serious. I have upjetted the carb a bit but I couldn't feel much difference.
Can someone help me out please?Sinnis Max II (QM125-2V), K157FMI engine (technically a K162FMJ now), 115 main jet, 40 pilot jet, cone air filter, 150cc big bore kit, 17 tooth front sprocket, 30mm carburettor, alarm with remote start, HID spotlights, performance CDI.
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#2 Re: Poor top end performance after big bore kit06-05-2012, 02:09 AM
High rpm miss usually shows a rich mixture do a plug chop and see what the plug looks like
It should be light tan
any shade of black is rich
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#3 Re: Poor top end performance after big bore kit
- Join Date
- Jan 2012
- Location
- Norwich
- Posts
- 408
06-05-2012, 08:29 AMI tried that but the spark plug was white so I upjetted it.
Sinnis Max II (QM125-2V), K157FMI engine (technically a K162FMJ now), 115 main jet, 40 pilot jet, cone air filter, 150cc big bore kit, 17 tooth front sprocket, 30mm carburettor, alarm with remote start, HID spotlights, performance CDI.
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#4 Re: Poor top end performance after big bore kit
- Join Date
- Aug 2011
- Location
- texas
- Posts
- 266
06-05-2012, 04:04 PMcheck fuel filter and perhaps take a screw driver with ya next time you ride to tune your fuel mix screw (if have one) , be prepaired to stop often in is leaner out is richer , back it out 2 turns n go for a ride and tune 1/2 a turn at a time untill get no more performance increase then back it up 1/2 a turn
here is a quick test to see if she's lean , tape up your air filter leaving only 1/4 uncovered , go ride if it runs better she's lean and you need to mess with fuel mix / jetting (although your main 110 seems quite large enough so I asume just fuel mix is off )
you may also wanna peek at your valve adjustments again if backing out the mix screw (or taping up the air filter) doesnt show immediate benifits
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#5 Re: Poor top end performance after big bore kit
- Join Date
- Jan 2012
- Location
- Norwich
- Posts
- 408
06-05-2012, 04:15 PMI forgot to update that, I now have a 115 main jet. I only have problems at high throttle positions and the air/fuel mixture screw only affects low throttle positions so I don't think that will make any difference, however I will try covering my air filter that's actually not a bad idea. I noticed that the o-ring on my carb where it connects to the cylinder head is a bit damaged and I could see a gap so maybe it was leaking which would explain the problem, I have put some RTV sealant on it to seal it up but I haven't tested it yet, I'll also check the valve clearences tomorrow once my engine has cooled. If it's still running badly I'll get a compression tester to see if I have a gasket leak or something.
Sinnis Max II (QM125-2V), K157FMI engine (technically a K162FMJ now), 115 main jet, 40 pilot jet, cone air filter, 150cc big bore kit, 17 tooth front sprocket, 30mm carburettor, alarm with remote start, HID spotlights, performance CDI.
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#6 Re: Poor top end performance after big bore kit
- Join Date
- Jan 2012
- Location
- Norwich
- Posts
- 408
06-07-2012, 09:12 AMOk I've got it sorted it! Luckily it was a bad seal at the carb. It's running fine now and the engine runs a lot cooler too.
Sinnis Max II (QM125-2V), K157FMI engine (technically a K162FMJ now), 115 main jet, 40 pilot jet, cone air filter, 150cc big bore kit, 17 tooth front sprocket, 30mm carburettor, alarm with remote start, HID spotlights, performance CDI.
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#7 Re: Poor top end performance after big bore kit
- Join Date
- Aug 2011
- Location
- texas
- Posts
- 266
06-07-2012, 09:59 PMya when I saw the post on leaking manifold I knew you had found your problem
just lucky u didnt hole something running THAT lean
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#8 Re: Poor top end performance after big bore kit
- Join Date
- Jan 2012
- Location
- Norwich
- Posts
- 408
06-07-2012, 10:27 PMSinnis Max II (QM125-2V), K157FMI engine (technically a K162FMJ now), 115 main jet, 40 pilot jet, cone air filter, 150cc big bore kit, 17 tooth front sprocket, 30mm carburettor, alarm with remote start, HID spotlights, performance CDI.
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