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Post by gsforster on Jul 3, 2015 1:15:09 GMT
Hi all,
I started fixing up this bike for a good friend, and among the many things I did to it including valve check and adjust, carb cleaning and float level verification, spark plug replacment. It has a Vance & Hines Superssport 4 into 1 exhaust. The thing pulls smooth and strong like a rocket at mid and high range rpm, but cannot pull through a low end "falls on it's face" flat spot between 2-3000 rpm as in city stop and go stuff. The more throttle applied the worse the flat spot. Nothing I have done adjustment wise to the carbs has made any difference. I am pretty sure the jetting is all stock. I suspect this exhaust system that is on it is reducing the low rpm scavenging effect and not allowing enough intake speed through the carbs to pull in fuel. Should there be some sort of restrictor or venturi that goes into this exhuast system to help with this, or am I even on the right track or out in the weeds somewhere? I contacted V&H but did not get much help - I guess the product is 30 years old and the rep probably doesnt have knowledge of it.
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Post by Graham on Jul 3, 2015 12:08:44 GMT
It's a fairly safe bet to say the exhaust is causing the problem. Unfortunately the solution isn't an easy one. You could spend many many hours experimenting with jets & needle settings only to disguise the problem slightly but not solve it completely. There are members on here who know more about this than others. General opinion is that primaries that are any bigger than stock will cause this problem. Counteracting it is not easy with the FZ. Maybe someone could invent some kind of valve in the exhaust to compensate?.. .
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Post by gsforster on Jul 3, 2015 14:08:35 GMT
I think what I need to do is find a complete stock exhaust to try on there. The flat spot is so bad the bike is just about unrideable in everyday traffic. Thanks for the reply
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Post by welshbanjo on Jul 23, 2015 22:09:55 GMT
you could try a stage 1 jet kit, dynojet kit, if memory serves me right, had to fit one on my cb900 with open filters and yoshimura exhaust, years ago,
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Post by welshbanjo on Jul 23, 2015 22:10:30 GMT
error ops
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