View Full Version : Question about tuning for an OLD Kerker exhaust on an RC30

06-12-2009, 09:15 AM
I just found a beautifully well-kept Kerker 4-into-one race exhaust for a 1989 VFR750R - Rc30.

Are there any records which could indicate if or how the bike would have to be jetted for the road or the track?

The exhaust has a (removable) baffle in it. With the baffle left in, I don't know how much more free flowing it might be than the stock one. What would be the symptoms of a bike that needs to be re-jetted?



06-12-2009, 09:51 AM
Sorry, no specs for your RC30, cool bike though!

Leave the core in.

Jetting issues would be noticeable by general poor performance, hard starting, hesitation, stumbling both on the throttle as well as steady throttle. Popping on decel.

I would do some internet searching on 'RC30 Jet specs' you'll find something.

06-12-2009, 10:02 AM
Thanks - I'll let you know how it comes out.

06-12-2009, 10:12 AM
Please do, and go ride the snot out of that thing.

06-12-2009, 06:44 PM
I tuned my bike using the procedure from one of the jet kit manufacturers: Factory Pro. The procedure has several steps and requires a starting point that is not skipped. The procedure will take several hours of changing jets, testing, recording and doing it again and again.

For those interested in fine tuning their bikes, here's a link to Factory Pro's CV carb tuning procedure (http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html) and one to what I did on my 2000 ZX-9r (http://www.zxforums.com/forums/zx-9r-forum/5014-how-fix-carb-stumble-2000-9r-s-2.html#post136060).

In a nutshell, I found that on my Supertrapp equipped bike (http://forums.supertrapp.com/showthread.php?p=1642), jetting 2-4% richer and/or raising the jet needle 0.75mm, makes for the best results. I mean, 2-4% richer than whatever the manufacturer recommends for your bike's stock setup, compensating for altitude (like I did). For instance, Kawi recommends 8% leaner main jets for operation above 4,000.' So instead of running the 152 mains as they recommend, I run 155/158s. OMFG!! I can't believe this is the same bike I purchased 9 months ago. :D:D:D