SUZUKI GSXR750 Carbs Mikuni

[mro]

MC carbs

From what little I've read.....and limited experiences
You'll want to get the mains dialed in first.
Then move to what ever is feeding the rpm stage below that etc..

Unfortunately have yet to find a manual that's specific to my hot rods carbs, but have found a few that are similar. All seem to agree to start at the top end of the RPM range and work down.

Get it up to speed (just under the problem rpm) for a mile or so and do the kill switch/ coast to a stop and check plugs to see if lean/rich.

Seems to be a little controversy on the merits of changing carbs on a stock engine. More info you have the better and looking forward to hearing your results.


mro

[underdog57]

re mc carbs

I did find one site that leaves the mains out and does the
jet needle first . its set to half way till they get the jet needle picked ...
They do the main next ....

I wonder if they do this on a dyno(rollers) . how else can they test under load with the mains off for the first setting ??

I'll dig that up , it was interesting ....they had some good descriptions of how the engine will react to lean or rich ...at the differant throttle positions ...

One reason I want to try the gsxr carbs is they are easier to get parts for . alhtough the stock carbs do pack a wallop ....

need to clean the plug collection I've aquired , should get a blaster ...

Something I'm really curious about is , how much does the needle jet/needle jet affect the mixure at idle , say if its worn or not set right . Can it throw the idle mixture off ...

Or I might have a problem with the idle mix screw and or orifice??

Think I'll call the bike Blacky till the carbs are sorted out ....
Will get the sudco book asap ...
Another guy does snow machine carbs . should be a lot of good info in that book too ..

Bob

[underdog57]

Originally posted by AlanB
Hi Underdog,

Good job!

Keep in touch!


AlanB

Hi Alan , You get credit . I would never of thought to try these .
Not sure if mine are gsxr 1100 or what . Have not narrowed down the year yet either . Roughly late 80's early 90's ...

They are needing something , but cant be to far off ...
Will keep you posted ..
Thanks

Bob

[mro]

Mine tune diffeent than CV's

Have you tried to get manual or gone to the manufacturers web site. Some times they have very detailed info on tuning/jets etc...

My flat slides jets come in to "play" depending on how far throttle is open, where as the CV's are determined by rpm/vacuum. (Flat slides also have a fuel pump so when you twist the grip it squirts a shot of fuel, instant responce )



mro

[underdog57]

http://www.psep.biz/store/carburetor_repair_manuals.htm
Am looking at these plus other sites ...

well 4:30 gets here quick so will call it a day

Bob

[underdog57]

aha , just refound this one ..
http://www.smellofdeath.com/lloydy/jetting.htm

My carbs may be worn , so am looking into what happens as jets get tired , especially jet needles ...
One set of original carbs seem to need one jet needle .
But I am not positive .
Want to try some experiments ...swap parts and compare ...

Bob

[underdog57]

Re: Mine tune diffeent than CV's

Originally posted by mro
Have you tried to get manual or gone to the manufacturers web site. Some times they have very detailed info on tuning/jets etc...

My flat slides jets come in to "play" depending on how far throttle is open, where as the CV's are determined by rpm/vacuum. (Flat slides also have a fuel pump so when you twist the grip it squirts a shot of fuel, instant responce )



mro

I was soooo close to buying a new set of Mikuni RS carbs .36MM
Adjustable width to fit our intakes ...dream ...
They have the accelerator pump also ...extra jets and a tuning manual ... ready available parts . $715.00 ...Will play with my abused parts first .
Want to just ride though , Yikes ...
Bob

[pggg]

Dog' if the emulsion tubes and/or needles are even a tiny bit worn, throw them in the trash, get new ones. Almost bet someone else has fiddled round in the carbs too, needles notched too high? also float level, may need to be set with carbs at an angle, at the point where the tang touches the valve pin, and no more. A gixxer manual would state for sure, pretty sure the float heights for those carbs is 14mm from memory, see even the latest CV carbs inside are copies of those original slingshot carbs, they probably didn't call them slingshots for nothing.. Good luck

[AlanB]

Hi Underdog,

My float heights are set to standard for the Suzuki; Can't remember the figures! I initially fitted bigger main jets and lifted the needles a notch for "safe" jetting; it was better than stock, but a bit "fluffy"

On the dyno, with a CO meter rigged, the jetting came back down to almost stock; I think the jets were one size bigger than stock, and needles are i/2 notch up from stock (Using a shim from a dyno-jet kit!) Pilot jet adjustment made more difference to how the bike ran than all the rest put together!

Can you post a pic of your carbs? I was told (on a GSXR forum) that the carbs I used were "Europe only" and never went to the 'States. Same poster said that the first bikes sold as the Slingshot in America had a modern version of CVs and later bikes used the 38mm slingshots....... I have no idea if he is correct!

If your carbs are the same as mine, I can give jet specs!

Best of luck,

AlanB

[underdog57]

Mik Slingshot

Take a look ,,,

















Gotta hit thye road , mains say 124 on them ...
The needle jets do look worn ...

Later

Bob

[AlanB]

Hi Underdog,

Those do look like mine! Did they come off a U.S. bike, or were they imported?

I took my dyno sheets down off the shop wall to try to scan them (too faded!) But I discovered that the operator has noted the carb specs for each run.

My memory tells me thay the jetting was close to stock, but the "Money run" has main jet 142, needles 1.5- your bike is unlikely to need exactly the same!

When the bike was dynoed it had the stock SG headers, with a pair of universal straight through "silencers"

I later changed to a four-into-one, and gained a low-speed "stumble" That got sorted by adjusting the pilots; no other changes were needed. Float heights are still standard.

Best of luck with them!

AlanB

[underdog57]

Hi Alan ,
I think they are USA carbs . An E-bay deal ...

Funny as every part looks the same when I took them apart .
Idle mix screws out 3 turns , and 2 and 3 cly running black .
It breaks down back firing at times mid range .
You can tell it wants to pull ....but not now ...
Need time to jet them ....correctly ..
Thanks for the extra imfo !!

This is a special and I jacked the gas tank up with a big socket temporarily ... Just plug the 1/4" / 6MM fuel lines on no problem ...
Not sure what clearance for the new valve to the air filter will be.
Looking at Pingle for a valve ...or can put a fitting plus inline valve
in...

Bob

[AlanB]

hi Underdog,

Interesting that these are USA carbs; I was told that these were not used there- perhaps there are State to state differences

If the carbs are all set equally, and 2/3 are different from 1/4 I would be suspicious of the coil; It is the usual link in those pairs!

You could try swapping coils (HT and LT cables) and see if the poor running swaps to 1/4(poor coil) or stays with 2/3 (carbs , or leads at advance/retard)

Stick with it; it is worthwhile!

I have been messing about today with a Standard tank (The BIG one!...6gal?) I like the look of it, but I don'd know if I can be bothered sorting out another set of petcocks!

AlanB

[xschop]

same ones

are these the same? ebay #160117577354

[underdog57]

Hi Alan ,
I was thinking of the coils too , but on the sets of original carbs.
those cylinders plugs look good ...
had a black number 3 and 4 plugs on one set and the other 82 xj carbs were good except #1 plug ....

And its got great top end with either of those carbs , just the 2k to 3k plug loading stumble ....

Wonder if the pick up coil wire moves to a differant position with the vacuum advance (gsxr carbs on). I stuck an old jet in the line ...
I dont hear the advance knocking , but want to look at it in operation ...

I'll try putting an inductive timing light on #2 and 3 plug wires and move the breaker plate by hand . can I do that?? will look it over ..

cant wait to try more stuff , plus the specs you have provided ...

Bob