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750 main jet size?

10K views 19 replies 3 participants last post by  nykuryu 
#1 ·
so as you know im running a 750 now. however its a 98' with 600 carbs. the power delivery feels great, front wheel lifts off the ground great, accel is great. now i dont have money for a dyno to see how well it is actually running but was wondering what the main jet sizes for maybe the 97' gsxr 750 are. google didnt reveal anything. i see alot about using 120ish sizes, if thats the case im already running 125's. but my real concern is she runs kinda warm, even on the highway. ranging from 188's to 200. scared its too lean maybe...? sorry Freak, i have to ask tho.
 
#2 ·
Well it have been HOT the last few days, What RPM range are you running when you see the 188-200 temps?

As for your jet size, putting a 750 sized jet in is not really the best option, It would be better then too lean, but but you would likely be on the rich side since you can not flow as much air as a 750 carbs does.

I would say look into the service manual for the jet size, maybe running a stock 750 sized jet with your 600 carbs and your mods? But you would need to do a plug check.

Also, what spark plugs are you running?

John
 
#4 ·
You could drop a heat range on the plug (cr10e) from the stock cr9e.
But, check the plugs, you might find that a bigger motor just makes more heat.

John
 
#6 ·
I have been running the 10EK for years. Love em... and the color is perfect.

John
 
#8 ·
Agreed. The EK has the better tip and is a tad longer. Works very well.

John
 
#11 ·
The Number is the temp and the letters tell you the type of plug as pictured above.
The higher the number the cooler the plug.

John
 
#13 ·
well update. i pulled the plugs, they looked VERY clean, looked almost brand new. i would say almost to the point of running too lean. but i felt it better safe then sorry i went ahead and bumped up to 128 mains. didnt run hot today at all. maybe 190 cruising on the highway, but i may attribute this to the pretty cool day we had today.
 
#14 ·
With the weather we had today, 190 is hot for freeway speeds. You should have been closer to the 180 mark.

I would give it a little time and pull the plugs to take a look. Remember you want tan, not white like it was a new plug.

Also, your main jet isnt really used much at cruising speed, it would be more in the needles, so you might want to shim the needle a bit or move the clip if you can.

John
 
#15 ·
the plugs looked used, not new, but not burnt either. i got to 190 from cruising behind a car. it was generally mid 180's. 190 was the hottest it got on the highway. when you the mains kick in? i cruise at 8-9k.

what size washers can i use for shimming. im not gonna buy a real kit.
 
#16 ·
The main would kick in at ruffly a little more then 1/2 throttle openings and more.

It isnt always about RPM so much as it is about how much you twist the tube.. :D

I think it is a #4 washer to shim it, but the carbed guys might have more info on that for you. It has been a long time since I did any shims on GSXR. I think back then I picked up an assorted washer kit from Radio shack and measured out a bunch to be the same thickness that would fit on the slide.

John
 
#17 ·
oh i thought the mains opperated at certain rpms. so i can cruise at 385483838383k and still be using the needles?

CALLING all carbs gurus. what washer do i use?
 
#18 ·
The slides work off vacuum to lift them. Well more like Negative pressure. So if you do not open the butterflies (turn the gas) then the pressure is = on both sides of the slide.

I dont know if you have an area where you can go to put the bike in 2nd gear and hold it wide open from like 6K to red line, then pull the clutch, shut it off and pull the plugs to see what they look like. That would tell you if the main is ok.

John
 
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