Hi guys. I have the opportunity to buy a 4 - 2 -1 Yoshimura exhaust for my 86 VFR 750. I have a K&N filter already. If I just bolt the pipes on wth the same jets will the performance suffer? Which part of the powerband would suffer? Anyone have some experience? Is it worth having these pipes compared to stock? Thanks
It's hard to tell where it will suffer. It will gain here here , but suffer there. If you know anyone with a dynomometer that has a air:fuel exhaust sniffer, you can jet the powercurve(botton, mid, & top ends). For starters, back out the fuel mixture screws to 3 -3.5 turns out fron lightly seated.Dynojet jet kits are really good for the slide springs.
Lean / Rich .. Hello: Well, what you have to worry about - think about - is whether or not the two mods, the exhaust plus the K&N, will cause the bike to run too lean with the OEM main jets. That, in short order, can fry the motor. The only way you really, really will know for sure is to dyno the bike - or - as has been stated, analyze the exhaust gasses. I am in the midst of downgrading a way too "heavy-handed" Dynojet Stage 2 kit installation; the bike was running too rich. I'm making sort of an "educated guess" as to my downgrade, but I really won't know until I get the bike back on the dyno. The Dynojet kits provide more flexibility in the carb mods. The jet needles are much more highly engineered than the OEM jet needles, and you have the option of raising or lowering the jet needle in relation to the needle jet/main jet. Gray Market
I have a Micron 4-2-1 race pipe on my VFR750f (87) and still stock jettings, no problem, runs fine. A littel less low end and much happyer on high revs, it makes the powerband more revy. Other than maybe california models I dont think you need to rejet, pretty fat jetting stock on 80 bikes.
