Another carb question GSXR mikuni radial slide carbs

Hello all, again I have a question regarding these carbs. I followed the
advice provided here and recleaned them thoroughly. Now when trying to start
the bike using the choke, fuel flows out the overflow (drain plugs are
tight) of 2 of the carbs. Once it's running they no longer piss fuel and
once the engine catches up and burns the excess fuel off it runs fine.. I
pulled them rechecked everything and all seems as it should be.I am
concerned however that I may have been over zealous when turning the pilot
jets/screws in before counting the turn outs.. If I tightened them too hard
(not forced in but very very snug) could I have damaged them and could this
be part of the reason I'm getting so much fuel at startup with the choke
on?? Also, a common starting point seems to be 1 1/2 turns out, is this a
rule of thumb or just that, a starting point that should be experimented
with?

TIA!

Tom B

 

Either your floats are adjusted incorrectly, or the fuel shut off
needle valves are sticking when you first start cranking the engine. If
you have a vacuum-operated petcock, it opens and the carbs flood
because of the incorrectly adjusted floats or stuck needle valves...

There is a tiny fuel filter mounted above the fuel shut off needle
valve that should catch debris coming out of the gas tank

The standard float setting dimension, withthe carbs upside down on the
bench is 17 millimeters plus or minus 1 millimeter from the carb gasket
surface to the top of the float valve actuator tab...

Yes, you could have damaged the pilot screws by overtightening them,
but if you take them all out and compare them, you'd be able to see if
the thin tapered tip of one of the screws was broken off. But this
would not make the
carburetor overflows "piss" gasoline...

The nominal range of turns out on Mikuni radial flat slides is 1/4 to
1/2 turns out from lightly seated...

The standard idle jet for all Mikuni radial flat slides is #17.5

Mikuni made various radial flat slide kits for different model where
the multi-carb assemblies had different center to center dimensions...

The carb sizes were 34mm, 36mm, 38mm and 40mm...

Look for a kit number etched onto the carburetor body or an aluminum
tag..

The kit numbers that fit Suzukis were:

RS34-D21-K fits 1988 GSX-600, all GSXR-750's, all GS-750's #115 main
jet

RS36-D3-K fits 1988 GSX-600 #120 main jet

RS36-D9-K fits GSX-600 GSXR-750, GSXR-1100, GS-1000, GS-1100, GS-1150,
has leftside cable drum #120 main jets on 600's and 760's; #130 main
jets on the big engines...

RS38-D19-K fits GSXR-750 GSXR-1100, GS-1000, GS-1100, GS-1150 #135 main
jets

RS-38-D29-K fits GSXR-750, GSXR-1100, GS-1000, GS-1100, GS-1150, has
leftside cable drum #135 main jets

RS-40-D1-K fits GSXR, GS-series RACE ONLY #140 main jets
RS-40-D7-K fits GSXR, GS-series RACE ONLY has left side cable drum #140
main jets

If you need more tuning information on Mikuni RS series radial flat
slides, I have the Sudco Mikuni carburetor, parts, and tuning manual
here...

 

took them off and cleaned them yet again, float levels were all fine as were
the needle valves
its no longer pissing fuel at startup...gremlins maybe?

phew, I took them out as well and they all seem fine.

I did that and it definately starts better.

I may yet take you up on that offer! Although at this point carbs are not my
favorite item to work on. After following all of the above advice, I then
swapped in a set of new plugs (3rd set I've cooked and yet to ride a
kilometre!) and it fired right up, idles nice...except...the number 2 carb
pops intermittently, (backfires through the carb), till the engine gets hot
then it stops, also that pipe, # 2 will glow red hot till the engine is hot
and then when the backfiring stops the pipe cools to about the same temp as
the rest, thoughts/diagnosis on this??

thanks again for all the invaluable advice!

Tom B

 

Gum and varnish on the fuel shut off needles and the needle seats will
cause the
float bowls to overflow. A bit of varnish so small I needed a
magnifying glass to see it kept the needle valve from seating in my
Kawasaki's carb...

I don't know what you mean by "cooking" a set of plugs. Copper core
spark plugs are resistant to heat cycling, unlike the old steel core
spark plugs that would start misfiring when thye were overheated and
never work well after cooling off again...

Are the plugs all black with dry soot, or all black with wet oily soot,
or wet and brown?

A cylinder that spits back through the carbs may have an intake valve
that doesn't seat properly because it's adjusted too tight, or has a
weak valve spring (4-valve per cylinder engines usually have incredibly
weak springs)or the that cylinder might have a leaky valve guide oil
seal and oil leaking past the valve guide oil seal may have carbonized
on the valve head, stopping it from
seating properly...

OTOH, a header pipe that glows red indicates that fuel is still burning
in the
pipe, and that points toward a very rich mixture in that cylinder, so
maybe the
carburetor isn't adjusted right or the float is still sticking or the
fuel shut off needle valve is sticking...

On a typical carburetor, there is a fuel drain screw attached to a
spigot that has a little rubber overflow hose on it. You can check the
operating fuel level
by replacing the rubber hose with a short length of clear plastic
tubing and holding it up alongside the float bowl gasket surface and
opening the drain screw. The fuel level in the plastic tube should rise
no higher than the float bowl gasket surface while the engine is
running...

The parts diagram for Mikuni RS flat slide carbs show that all four
float bowls are interconnected by short ruber hoses. This seems to me
to be a way to keep all four carbs getting fuel even if one float valve
sticks...

But, it looks like if you want to check the float bowl fuel level,
you'd have to disconnect the hose between the #1 and #2 carbs and put a
clear plastic tube on each float bowl to do the float fuel level check
I described above...