GSXR 750 38mm carbs

[pig]

Hi wondering if anybody can help me with this one I'm in the process of fitting a GSXR 750M lump in my MK1 600 bandit I've 2 sets of 38mm carbs off a GSXR 750 but they are slightly different, bodies & spacing match up but have different float bowls one set has all plastic breather tubes the other brass. floats are the same float bowls fit both sets are they the same carbs just off different years & are the parts inter changeable be nice if they are for spares

Also between No2 & No3 carbs there is a large rubber opening I assume is some sort of breather not on the 600 bandit carbs

Last one will the 600 fuel tap supply enough fuel to the carbs if I fit a T piece for the twin fuel lines

Any advice would be much appreciated thanks pig

[pig]

Sorted the set that's built in the picture are off a 91 the single carb with the drain bolt in the bottom is off a 90 all parts internal parts are the same part No's throttle bodies have different part N0's 91 part No's start 13201-18D30 to 13204-18-D30, 90 parts No's start 13201-17D30 to 13201- 13204-17D30.

I've measured everything up & the only difference I can see apart from the float bowls is the 90's have a brass  breather & the 91's have plastic

1990 GSXR 750 L

1991 GSXR 750 M

If there are any other differences please let me know but I'm assuming the throttle bodies are interchangeable as well.

Cheers pig

[se5itchy]

are you gonna use the b6 airbox ,will it even fit, i dont know if the angle of the carbs from horzontal coming out of the head is the same as b6. Either way if you do end up using pod type air filters, can you ppost what setup you use for the bs38's to make it work ?

cheers

tidy looking bike that

[pig]

Hi se5itchy

Thanks for the comments the 91 M carbs already set up with a stage 3 dynojet kit from when I had them in my chop, not using the air box just got a set of K&N RU-2922's twin ovals.

Cheers pig

[dago]

the brass bit in the photo is for the power jet fitted in the us market was connected to the float bowl with a rubber hose supplied extra fuel at full throttle,was banked off in the float bowl in the uk 

[pig]

Ah cheers that'll explain why the corresponding tube on the float bowl is blocked, I take it the plastic tube on the 91 carbs is the same, learn something new everyday :-)
Thanks pig

[se5itchy]

so wht size jets are you using ? what height is the needle ?

[pig]

There where set up for my GSXR chop off the top of my head 150 main jets ( dynojet size ) think its 2nd notch down on the dynojet needle & either 2 or 2 1/2 turns out on air screw. I was running different pipes on the chop though, so once I've got it running half decent I'll put it on a rolling road there's one about 10 miles from mine

[marcsalvisberg]

Mar 30, 2014 10:24:48 GMT dago said:

the brass bit in the photo is for the power jet fitted in the us market was connected to the float bowl with a rubber hose supplied extra fuel at full throttle,was banked off in the float bowl in the uk 

The USA, 38mm, "49 state" models, 90-92, came with "zero" sized power jets, too.
I think the Canadian ones came with activated powerjets (but the wrong size).

The power jet circuit is designed to deliver a more atomized fog of fuel and the power jet increments of change were finer for finer tuning.
The power jet circuit, as on the 750's 38s, delivered fuel due to airbox inlet air "vacuum". Without the airbox's restriction, the power jet circuit will not lift the fuel up the side tube. So - if running individual or dual filters, the pj circuit doesn't deliver any fuel.

In 1988, most AMA 750 Supersport teams were using dynojet jet kits. By the end of 91, hardly anybody was. The power jet circuit and smoothly tapered needles were track proven to be better performing.


The proper method of tuning the 38's with an airbox is as follows:

Special fine tuning for these carbs.

Use whatever main that make the bike pull the hardest at 9k-10k. Pay no attention to 12k and 13k.

That's the right main jet.

Adjust the needle for best full throttle 5k-7k power.

That's the right needle height (assuming you did the previous main jet test).

Adjust the float height for the best full throttle / 3k-4k power.

That's the right fuel level (assuming you did the previous main jet and needle testing)

Adjust the fuel screw for best idle and cruise (whatever it happens to be).

If you are 3.5x+ on the fuel screws, you should try a larger pilot jet. If 1.5x or less, you need to try a smaller pilot jet.

Adjust powerjet size for best power at 12k and 13k.

That's how we tuned them and won AMA Nationals.

When it's right for EC997 dyno and real world, and you run them on a dynojet style dyno, it will show an imaginary burble at about 10.25k.
It doesn't exist in the real world.

Nice to see people still practicing carburetor artwork!

Marc Salvisberg
FPT

[nightrider]

Apr 15, 2014 5:22:31 GMT marcsalvisberg said:

The proper method of tuning the 38's with an airbox is as follows:

Special fine tuning for these carbs.

Use whatever main that make the bike pull the hardest at 9k-10k. Pay no attention to 12k and 13k.

That's the right main jet.

Adjust the needle for best full throttle 5k-7k power.

That's the right needle height (assuming you did the previous main jet test).

Adjust the float height for the best full throttle / 3k-4k power.

That's the right fuel level (assuming you did the previous main jet and needle testing)

Adjust the fuel screw for best idle and cruise (whatever it happens to be).

If you are 3.5x+ on the fuel screws, you should try a larger pilot jet. If 1.5x or less, you need to try a smaller pilot jet.

Adjust powerjet size for best power at 12k and 13k.

+1