SUZUKI GSXR750 Carbs Mikuni

[AlanB]

Hi Underdog,

Jet is a good idea! I have not reconnected the vac line because when we dynoed the bike, there was no extra power with the vac advance on or off, so I did not bother.

Nowadays I (and my mates!) are all older, and I am chasing H-Ds and Drifters, Not GSXRs and Ninjas, so I want to fit it back up to help the economy!

I had a quick look at the original vac take-off on the carb; It seems like the edge of the butterfly almost closes the port, presumably to prevent vac advance at idle; It might be worth checking thet vac advance does shut down at idle with your system?

AlanB

[underdog57]

Re: same ones

Originally posted by xschop
are these the same? ebay #160117577354

Those look similar , I have ben looking at a lot of parts lists and they get updated every now and then .
Nice price so far six hours to go ...
Good luck , I'd try them . 36MM and they will pop on with not much effort ...
I think mine are 88-92 but am still trying to figure that out ..

Bob

[pggg]

Regarding that notch in the XS butterfly, at idle position the butterfly covers the vac timing exit hole, but there's still a sliver of vacuum getting past the edge, the vac timing's still operating at idle , just dampened to be really smooth, but my ZRX carbs have the vac unit running off a carb boot thru a 0.5mm restricter in the hose, and idle & vac timing is still smooth, no difference at all, so that tricky little notch isn't really necessary

[AlanB]

hi PGGG

Thanks for that! Good to know it works!

AlanB

[underdog57]

The Vacuum must draw the timing retarded and at higher speed , loss of vacumm must let the plate go advanced ...
funny why they would restrict the vacuum at idle ..

All these details are great to know !!!
Thanks for clearing that up too Pggg

Bob

[pggg]

there's strong vacuum on the over- run decelerating, probably why they restricted at idle, yeah with the hose connected you gain another 15 deg of timing advance at high revs, and yeah, low rev vacuum drags the timing down to suit.

[AlanB]

Hi Guys,

Advance is quite complex, and does not work as most imagine;

Bobweights should advance timing as revs rise. Basically to allow the spark enough time to cause a bang when the piston is at the top of the stroke, the spark has to start a bit earlier at higher revs!

Vac advance is a bit more subtle, and adds extra advance when there is a high vacuum in the inlet system. When the throttle is open wide, and the engine is making power, there is little vacuum, and the system is at rest!

Vac advance helps economy, smoothness and refinement. It does not affect power or speed! Therefore, almost all cars have it, and almost no bikes.

Hope this helps!

AlanB

[underdog57]

I found out why I could not sync #2 and 3 .
Something was bent , the carbs are a little off on the mounting brackets .And/ Or the throttle shaft was bent . I loosened the brackets and twisted as the screws were tightened ...
Then I tweeked the throttle shaft a little , pliers tweak ...
They are looking in the middle of the adjustment screw now ...
Kinda odd ....

I think the throttle shaft was the problem . Could of been dropped ..

Bob

Need to know what family of needle jets this has , no marking on the needles ..

[petejw]

hey underdog,
how did u end up with the carb swap,
have u finished it yet, was just curious
how it turned out, as i was thinking of
doing the same.



pete

[underdog57]

Not Yet

Hi Pete ,
I mounted the carbs , was able to push the 1/4" fuel hose onto the petcock and carb fittings ...they are bigger on the carbs than stock xs ones..

The petcocks need to be changed ( thinking of Pingel) To clear the breathers .

I did synch them , but they need to be jetted , mains and mid are off ..
Have not had time to play with that yet , but did run it around town . Put a block temporarily under the rear of the gas tank ..for clearance ...

Alan B is the guy that got these to work .
Ckeck this out http://www.benefiscal.co.uk/forum/index.php?topic=851.0

I'm sure these will be great !!!
Plus being CV carbs should be very streetable ...

Bob

[Shuriken]

What are the latest updates on this project?

Ben

[underdog57]

Need to jet still , havent had time still . It idled , but mid and top end was gutless ...seemed lean on top end ...anf poppy/flubby at mid range .

I blocked the gas tank up and was able to put the poly gas line on the original petcock and over the bigger carb inlets . The original petcocks interfere with the air breathers though.

The carbs pop on with a bit of force , but not bad .

They did feel like the carbs wanted to pull good if you played with the throttle ...

I'm sure they will be great dialed in , and its a learning curve for me ....still cranking busy so not sure when I can try jetting or where tio get the jets , what style they are ect ...

Alanb has allready done this so sure its going to be great !!

Bob

[Shuriken]

Did you find out if these were slingshot 750 carbs, or regular gsxr-750 carbs? Any idea what year of carbs they are?

[underdog57]

I think the slingshot and gsxr carbs are the same carb but a term ..
The years change , mine are around 1988 to 1990 aprox.
I'll try to find out more ...
They might be gsxr 1100 carbs also ...
I can take and post a float bowl gasket , they have differant designs from what I found out so far ...
these are the 36MM ,

the 34's I have will not drop right in , the bowl gasket is a differant shape to id . And they are much smaller od where they get pushed on the carb boots , very sloppy fit . would need to be adapted ...

Bob

[81xsproject]

Again, the best resource I have found for this gixxer carb info is HERE