Need jetting baseline please - RS34s on modded GS1000

[80GS1000]

Need some wisdom from the GSR collective mind about carb jetting if you would be so kind.

Got a set of some Mikuni RS34s smoothbores for my GS1000, which has a Wiseco 1100 cc piston kit and a set of .395 lift Web Cams. Stock unported head (with the '80 34mm intakes), 4-2-1 header with a Yoshi muffler. Carb intake boots are new as are the intake o-rings. Elevation is 4500 feet.

The carbs came stock jetted with 130 mains, 17.5 pilots, and the clip on the 3rd spot on the needle. Accelerator pump on all 4 carbs is on as you can see fuel squirted into the carb throat when you twist the throttle.

When I first fired it up, it seemed pig rich (lotsa black smoke which smelled like fuel) - so I went down to 127.5s. Same deal. Getting it to idle is a pain. When you roll on the throttle, it bogs badly to the point it wants to stall. If you can goose the throttle past the bog, it'll rev up and then the RPMs will "hang". Adding choke at this point drops the RPMs - so am I lean on the pilot and fat on the needle/mains?

So before spending lots of $$$ on jets, what's the next step? Also gotta learn how to tune the accelerator pumps on these beasties.

Thanks!

 

[67fire]

I am currently running the 110 mains on mine with 29 mm Smoothbores.
I am at 4,500-9,000 feet with all of the same modifications if that helps.
I can send you a couple of sets of the larger jets to try if you would like.
I'm pretty sure that I have 115's and 112.5's. I have to check.

Eric

 

[Guest]

130 mains
17.5 pilots
Get it jetted without the pump first.
http://www.carbparts.com/mikuni/mikuni_rs_standard_tuning_specif.htm

 

[rapidray]

Have you adjusted the mixture screws correctly yet? That's the FIRST thing you do! Ray.

 

[80GS1000]

Have you adjusted the mixture screws correctly yet? That's the FIRST thing you do! Ray.

What's the correct procedure to do that?

Also how do you turn off the accelerator pump?

 

[russr33]

130 mains
17.5 pilots
Get it jetted without the pump first.
http://www.carbparts.com/mikuni/mikuni_rs_standard_tuning_specif.htm

Chef he is asking about RS34's and not RS36's (I know the 36's of mine you have are 130 mains and 17.5 pilots). Should the mains and jetting be the same?

 

[80GS1000]

Chef he is asking about RS34's and not RS36's (I know the 36's of mine you have are 130 mains and 17.5 pilots). Should the mains and jetting be the same?

The 34s came jetted the same as the 36s (130 mains) but it's jetted far too fat like that - I still smell like gas from trying to rev it up in the garage. :lol:

 

[Guest]

The mixture screws are in near the motor by the float bowl. Start at a 1/2 turn out.
You can remove the accel pump rod by pulling up on the plastic spring loaded piece that pushes down on it and pull it out. There is also a screw adjustment that you can screw clockwise and it will turn the lever away from the pump rod. There is another adjustment on top of the #2 carb that inhibits how far down the rod is pushed. These adjustments are very important when doing your final adjustments to get rid of the bog at accel.
If you want me to rebuild these I just did a set of 36s for Russ.

 

[80GS1000]

Making progress...

OK, so the mixture screws were all turned 3 (!) turns out. After a bit of messing with those screws and the idle speed screw the best, steady idle is at 3/4 turns out on all 4. I also removed the accelerator pump rod to take the accel pump out of the picture during this tuning process.

If you open up the throttle quickly off idle to 1/4 - 1/2 throttle, it'll bog and then stall. How do you fix this?

Now if you roll on the throttle slowly, it'll rev up nicely into the upper rev range but black smoke comes out of the pipe once it gets onto the needle/main. So we're rich on the mains at 127.5....

 

[Guest]

You don't want to hit the throttle hard w/out the accel pump. A nice easy pull on the throttle will suffice.
3/4 sounds closer than 3

Probably too snowy to do plug chops.
Are you blowing smoke at wot? oops read all your post
What are the plugs saying?
What notch is the needle at. I'd try the third notch down or lean it one notch (one notch up) but this is redundant until you get the main dialed in. Black smoke still pulling is close. Try a 122.5

 

[80GS1000]

You don't want to hit the throttle hard w/out the accel pump. A nice easy pull on the throttle will suffice.
3/4 sounds closer than 3

Probably too snowy to do plug chops.
Are you blowing smoke at wot? oops read all your post
What are the plugs saying?
What notch is the needle at. I'd try the third notch down or lean it one notch (one notch up) but this is redundant until you get the main dialed in. Black smoke still pulling is close. Try a 122.5

Yep, blowing smoke from 1/4 to WOT. The RPMs hang up when you blip the throttle instead of returning to normal idle RPMs immediately which makes me think the pilot's a little lean? Yeah, a bit cold to do plug chops. Needles are on the 3rd notch down IIRC. I bought some 117.5 mains and 20 pilots so those are going in next based off don_gibb6512's advice in this thread. Sound reasonable?

Correctly tuned, will these carbs rev as cleanly from idle to WOT as the stock CVs?

 

[Guest]

I don't think the pilot is lean. Did you install a P/P throttle?
I hope the 117.5 isn't too lean. But at your altitude it may be alright.
I'd lean the needle and put in some 122.5s.
Do you have access to main jets?

 

[80GS1000]

I am currently running the 110 mains on mine with 29 mm Smoothbores.
I am at 4,500-9,000 feet with all of the same modifications if that helps.
I can send you a couple of sets of the larger jets to try if you would like.
I'm pretty sure that I have 115's and 112.5's. I have to check.

Eric

Thanks for the help guys.

Pulled the 127.5 main jets tonight and installed some 117.5s. It runs much better than with the 127.5s but there's still some black smoke past 1/4 throttle. Throttle response is much better with leaning it out - no more hanging idle either surprisingly. Gotta rig up a push pull throttle with a GSXR kill switch I guess. I didn't mess with moving the needle up or down.

Do you think the flow difference between 29 and 34 mm smoothbores necessitates bigger mains or should I grab some 110s and be done with it? The next step is to go 115, 112.5, or 110.

 

[67fire]

Send me your address and I will send you the 115's and 112.5's to try out.
If you like them, just replace them at a later date.

Eric

 

[Guest]

I find it hard to believe that you'd run mains that small with those big cams.

 

[srsupertrap]

I looked at the Sudco site and the RS34 & VM29's share the same main jet style which are the big round N100/604 main. The RS34 use a VM 28/486 pilot jet while the VM29 uses a VM22/210 pilot jet . . . could you possible have mixed jets which may explain why its running so rich with all those hi perf mods you have?

I am higher up in altitude (5250 Ft) than you and have similar GS1000/1085, Andrews street cams, 4/1, but running VM29's and my main is several sizes larger than 117.5.

 

[67fire]

I find it hard to believe that you'd run mains that small with those big cams.

We can pull the carbs off and you can have a look when you come up to Bruce's.
I have the Andrews .394/.394 in it currently.

Eric

 

[Guest]

We can pull the carbs off and you can have a look when you come up to Bruce's.

Eric

I was talking about Paul.
I'm sure yours is jetted just right.

 

[KEITH KRAUSE]

Dark exhaust at 1/4 throttle + is most likely the jet needle too rich.
I assume the bike is at normal operating temps when testing? Not familiar with these carbs. Are the float levels set correctly? Air jets clear and correct size? Other than the main jet, pilot jet and jet needle position, do you KNOW all the remaining parts are correct and in good condition?

 

[80GS1000]

Thanks for the help guys.

Did a bit of c-c-cold 38 degree road testing / plug chops tonight with fresh Chevron juice/new plugs and 117.5 mains are too lean. Plugs were white and throttle response/acceleration was improved across the board by pulling out the choke. Next step...120 or 122.5 mains?