Splutter splutter :(

[Chealsie]

My bike (suzuki gp100) has been losing performance recently, the compression is 150psi and i have just replaced the plug, cleaned the filter etc. etc.

I cant get the bike to rev past 8k revs, and it only really has power between 6-8k, its kinda like the clock stops at 8k but it doesnt.
Even from neutral you can only rev it to 7-8k and it sounds rough.
(redline is 9-11k)

While revving and riding, it often feels a bit spluttery and hesitant. Like i have to rev past a certain point and then it goes again.

I understand this may indicate running rich? BUT i have the original main jet in, and a non-original replacement exhaust, which i understand to be a gianelli or micron, cannot remember.

Any one experienced this before?
Thanks, C.
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Chealsie Dagger!

[rotax81]

air filter ok?

exhaust port in the barrel clean?
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ZX636C6F road. ZX636C1H track. ZX7R redundant. ZX0.5R minimoto as ornament.
Audi A4 Avant 1.9TDi and VW Transporter 2.5TDi 888 Special (no mot and tax lol)

[Chealsie]

I had the air filter out and cleaned the other day, it had a few tiny bits of leaves on it so i cleaned it all up and put it back in the box (box was clean too)
And the exhaust port (do you mean the short section where you can see the piston and rings though when the exhaust is off) if so, then ive havent checked but would this be a major influence on it? If so, ill take the exhaust off and clean it. What would be the best way to do this?
Thanks, Chealsie
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Chealsie Dagger!

[ms51ves3]

You have exactly the same problem as me. Performance exhaust on the bike (mine's a Giannelli) and it will not rev past 8,000rpm. Does your start losing power around 7,000-7,500 and then creep up to 8,000rpm?

I re-jetted mine as it was still running the standard jet (went from a 120 to a 130) but it still won't rev past 8,000rpm. Did improve the performance slightly and I can do 60mph bolt upright. Previously it would struggle to do 55mph.

[rotax81]

depends if it ran fine before the exhaust was fitted.
depending on the engine an exhaust can be a nightmare to set up. some are that radical that they need a lot of barrel and carb mods to make them work properly.
i had a new one fitted some years ago, i tried everything to get it right to no avail.
i went back to the shop and asked what other people do he said.
you will need to tune the barrel and get a bigger carb to make the exhaust work properly. as it was a new bike under warranty
i sold it and put the original one back on.
looking back at it the exhaust must have been designed at an infants school as the expansion chamber was way too big for a 171cc bike
____________________
ZX636C6F road. ZX636C1H track. ZX7R redundant. ZX0.5R minimoto as ornament.
Audi A4 Avant 1.9TDi and VW Transporter 2.5TDi 888 Special (no mot and tax lol)

[Chealsie]

aha, ms51ves3 - you know what i mean then and the frustration especially when you only have 100ccs and your not using them all
I think i may source an original exhaust, try it out for performance (and any performance loss) and ill get back to you on it if you like.
Thanks rotax, it came with this exhaust so i dont know any different, although it is suspect know. from your experience aswell, it may seem some bike just dont like perfomance exhausts on standard-ish engines.

Will report back
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Chealsie Dagger!

[Chealsie]

hmm, just been looking at exhausts, ive found a nice shiny standard one to replace my battered aftermarket one.
But one question before i do buy it, would there be a notable performance loss in going to a standard exhaust from a performance exhaust. Bearing in mind, the bike is totally standard apart from the exhaust itself?

Thanks, Chealsie.
____________________
Chealsie Dagger!

[rotax81]

you normally lose a bit of umph at the top end of the revs but gain some mid range with a standard one.
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ZX636C6F road. ZX636C1H track. ZX7R redundant. ZX0.5R minimoto as ornament.
Audi A4 Avant 1.9TDi and VW Transporter 2.5TDi 888 Special (no mot and tax lol)

[stinkwheel]

It isn't your exhaust being wrong. It isn't your carb jetting.

If it was running fine before and now it isn't, unless someone has sneaked in and either changed the exhaust of jets, these are not the problem.

By all means give the carb a clean too but it probably isn't this either.

It could be a coked up exhaust or dirty air filter as has been suggested.

It is most likely to be an electrical problem. Chech all aspects of the ignition electrics. If it has a points ignition clean them, check the gap and timing, replace the condenser and points if they seem at all dodgy. Then go on to the plug cap, HT lead and coil.

90% of fuelling problems are electrical. People always suggest carbs because they understand how they work. The more you work on bikes, the more you realise this is just wishful thinking
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“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.

[ms51ves3]