Gs1000 with mikuni rs36 carbs

[Terrorshark]

Ok so I'll start out with the basics.
Motor is stock from what I understand.
Im at altitude.
Main jet is 120
pilot is 17.5
screws are 1 turn out
needle is 2nd slot from the top
k&n filters
dynatek ignition that is timed correctly and has strong spark.

leakdown test is air tight at TDC
compression is just over 120 on all cylinders

plugs are reading rich.

Ive played with needle in every setting
gone from a pilot jet starting at 10 all the way to 17.5

high rpm the bike revs and is killer.
Under 4K it stumbles and if you chop the throttle it kills it.
Plugs are black but not super sooty.
#4 is always a little wet. #4 cylinder reads 120 compression with no leaks found in leakdown test.

Any help on this would be fantastic as I'm beating my head against the wall with this one.

 

[Doug]

At first blush I'd say lean it on the mains. I was in Colorado but 8300' but would have no recollection of what jetting I ran on a street bike.

After rejetting carbs several times I had forgotten how it ran to begin with. Once you go to the track you can get numbers for comparisons. Does Bandimere still tolerate bikes? He hated us when I was there.

Have you recently oiled the K & N filters - I assume you have pods. It doesn't take much oil to restrict air flow. Try running around for twenty minutes with the air cleaners off.

 

[steve murdoch]

Hopefully it is not the stock bore because everything have read over the years says the 36 mm would be too big for a 1000.
Despite what Mikuni says.
One of many threads here.
http://www.thegsresources.com/_foru...d-for-easy-cruising&highlight=rs36+and+gs1000

 

[pano]

I have had RS34s and RS36s on my Katana 1000 with K&N filters with a Kerker 4-1 w/2 inch diameter baffle and both ran great. Unfortunately I do not remember the settings. I did buy both carb sets used and the bike ran decent just mounting them although I did make slight needle adjustments.

stock bore and my plugs were never black. I think I am about 800 ft above sea level.

 

[pano]

The 36s seemed to have a tad more response WOT at speed. I don't recall too much difference at lower speeds. The 34s went on first and were replaced with when I had a float bowl support mount issue. I bought the 34s off EBay and multiple float bowl mounts were epoxied. I noticed only after the bike began to run funny. The gas had eaten the epoxy and threw the bowls off. I have since repaired the mounts with a POR product and hope to reinstall them this summer. The 36s are on my 1100. I don't even think I adjusted them when I swapped them. Come to think of it, maybe the 36s did run a little rich on the 1000. I seem to recall thinking the 1100 would run leaner.

 

[GregT]

When you say "chop the throttle" do you mean shut or jerk it open ?

If it dies when you give it a handful try pulling the accelerator pump rod out - ie disabling the pump.
That's contrary to everything I know about RS's - but it sounds very rich at small throttle openings.

 

[rapidray]

FIRST, did you ever vacuum sync the carbs yet???
Ray.

 

[Terrorshark]

Carbs are synched.
And yes the bike dies when I give it hard throttle.
Just dropped the mains from 120 to 115 and it's worse.
I feel like I've played with the accelerator pump in every possible way and it's still giving me issues.
I'm starting to feel that the carbs are too big for the motor.
It's a friends bike so I'm not sure how it ever really ran before.

 

[Guest]

A long time ago I had a similar experience on a big bore, lumpy cam GS1000

put some VM29's on and ........... problem solved

at the time I was convinced it was too much carb for a road bike ...... fine on the strip though

 

[GregT]

Carbs are synched.
And yes the bike dies when I give it hard throttle.
Just dropped the mains from 120 to 115 and it's worse.
I feel like I've played with the accelerator pump in every possible way and it's still giving me issues.
I'm starting to feel that the carbs are too big for the motor.
It's a friends bike so I'm not sure how it ever really ran before.

Ok now we have some hard facts. Snap the throttle open and it dies, ease it open and it will reluctantly come up - yes ?
Given they're 36's the airflow is relatively slow giving a poor signal at the throats, so it's going to need bigger idle jets to get the fuel it needs.
Running 17.5's currently ? Try bigger - say 22.5 or 25. Go back to your 120 mains too.
Leave the pump operational.

 

[pano]

This has a chart with starting settings for the RS carbs based on engine size. I have a paper coy of this manual.
http://mototh.com/files/other/carburetors/Mikuni-rs-manual.pdf

shows a 130 main and 17.5 pilot.

 

[bobgroger]

o-rings under intake manifolds replaced? 120psi is a bit low, IIRC 128 is low limit. Is that at WFO throttle?

 

[DohcBikes]

Valve clearance?

Carbs are too big but shouldnt be THAT bad

 

[Terrorshark]

Something I didn't think if before but had me thinking. Ow.
The intake boots are definitely much larger than the port into the head. They are aftermarket mikuni boots part number m-vm34-200. Definitely much larger than the stock intake. Possibly screwing with airflow too much and not enough vaporizing of fuel?

 

[TxGSrider]

Since you said going down on the main jets made it worse, why not try going up and see if it gets better. Pano said it came with 130 mains, so put them in and see if it improves.