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View Full Version : Exhaust/jetting help appreciated

oddnumber
31-10-2007, 09:39 AM
Hullo folks ...

I'm fed up with the dragstar sounding a bit feeble, so I'm after putting a set of Highway Hawk snake pipes on. So, I was wondering if a rejet would be required? If so, would it be just the mains or all three? One of the pipes is a slip on, one is full, if that makes any difference. Theres also no air mods done, its the standard intake.

As usual, thanks very much for the advice :)
motopat
09-11-2007, 10:52 PM
from what I know exhaust mods make a difference to the overall 'breathing' of the motor. Sticking a 'free-er flowing' pipe on will cause the exhaust gases to exit quicker and likely to cause the exhuast valves to run hotter if left standard. I have put a race can on my ZR-7 and not rejetted - after +9k miles the exhaust shims were past their tolerances on a 13k bike and were adjusted at a recent service. REallly you should re-jet. YOu may as well put a free-er flowing air filter on before too and set the thing up right with hours of dyno time too. Or just ride the thing. Up to you (my opinion).

I had an XR600R with uncorked (unblocked airfilter intake), free-flow filter and aftermarket pipe and only altered the mains (145 to 168?) and the difference was amazing.

(mains only do 2/3rds throttle open to fully open - so to get it set up right is going to take adjustment to needles and pilots)

I hope I'm not too wrong - just had some juice tonight. Think I'm still making sence and typed it OK :o
motopat
09-11-2007, 10:57 PM
I had an XR600R with uncorked (unblocked airfilter intake), free-flow filter and aftermarket pipe and only altered the mains (145 to 168?) and the difference was amazing.



I NOW THINK 168 was the biggest main I bought and I read / found out 165 suited best. It's all trial and error unless you know someone that has and therefore lots of dyno money.*

sorry for caps

* as a guide - if you close the throttle from fully wound open (not low revs :rolleyes: ) and the bike accelerates a little before winding down it's lean. You can tell from the seat of yer pants, apparantly. :cool: