rs34 mikuni

[rotty]

I was wondering if anyone out there can help me out.I have a 84 gs 750.I have a aftermarket header and rs34's.The book says to use 115 main jets.That seems kind of small.I was thinking of going with the 120's.The carbs were shipped with 125's.Has anyone used these carbs on a motor like mine ?.if you have what main jets did you find work the best?.

Bill

 

[rapidray]

Bill, if your motor is stock cams & pistons, you are going to have fun jetting it. I had an 85 700 with 29 round slides that ran REALLY good but it took awhile to jet. I truly believe the 34s are too big for a stock, non GSXR, 750. Ray.

 

[rotty]

I made some calls to some bike shops and the place i bought the carbs from.They all said the 34's would work best.They all use those carbs on their bikes??.Now i am worried

Thanks for the info.

Bill

 

[gearhead13]

Oh, rs-34 flatslides, ok. Run the bike, get a seat of the pants feel, check the plugs.
I found this site might be helpful:
http://www.braigasen.com/Mikuni_jetting_chart_four_stroke.htm

 

[don_gibb6512]

No worries, you're fine with the 34's. I've got an 80 GS1100E with those carbs and 117.5 mains that pull like a freight train. Needle is at the 3rd from top, air/fuel screws at 1.5 out. Pilot's are 17.5 The stock 125 mains are probably too much for your motor for sure.

The Mikuni manual calls for the air/fuel screws (Pilot fuel screws) to be 1/4 - 1/2 turns out. I turned mine in 1/4 turn so they're now 1 1/4 turns out. I'm still fine tuning the Pilot circuit so I'll post again with what I end up with on that.

Haven't had this bike on a Dyno yet but it's running pretty good like this. I have a Kerker 4-1, K&N Pods, Dyna coils and the coil relay mod (a must). Stock engine setup otherwise.

I wouldn't jump to the 120 mains from the 115. Go one step to the 117.5 if you have to first and then if that's not enough go to the 120's. In general, that's the trick for changing jet sizes. One size at a time and make only ONE change of anything at a time regardless. It can be a long and tiresome process but it's worth it in the long run.

What you should do before anything else is get the bike warmed up, run it to where you can open it up without getting busted by the cops and do a full throttle run for a few seconds and then pull the clutch in and hit the kill switch. Do this where you can safely pull over and stop and then check the plugs. If they're white, you're too lean and need to increase the mains for sure. The mains can affect anything from about 1/4 turn throttle on up but they're really in the game after 1/2 turn throttle.

Good luck and keep us updated.

Don

 

[don_gibb6512]

Ahhh, my ADD kicked in again and I was reading that as if you already were running 115 mains. Sorry about that. If your plugs are black and sooted at WFO or it's just bogging down and doesn't seem like there's as much power as it should have, then drop down to 120's and see how that works. If it's still that way, drop down to the 117.5.

HTH.

 

[rotty]

Thanks for your advice.I will go out and buy some 117.5 and try them.I am going to get dyna coils as well.

I will give the 117 a try.Thanks again for your help.

Bill

 

[don_gibb6512]

Thanks for your advice.I will go out and buy some 117.5 and try them.I am going to get dyna coils as well.

I will give the 117 a try.Thanks again for your help.

Bill

Don't forget the coil relay mod. Chances are 100% that you're not getting 12v to your coils like you should be and that will make a HUGE difference.

 

[jetta90]

Great discussion here guys. Doing some carb head scratching myself on my 1984 GS750E lately.
Running stock carbs BS32SS in this case where in a previous life the bike had a header and pods I think. Carb jets were changed then, but now back to original exhaust and filter and running rich.
I found this that was a good read.......................

http://www.iwt.com.au/mikunicarb.htm

and this might have bits of interest....................

http://www.mikuni.com/fs-carburetor.html

Lets keep this discussion going. Let the information and tips flow.

 

[rotty]

Thanks for the links.They are both helpful.

Bill