1981 gs750 carb problems

[bass5473]

Hello all kinda new to this so any info would be greatly apprciated. Ok I have a 1981 gs750e with BS32SS mikuni carbs. Bike was not running very well when first got it but after some coils plugs and petcock I think Im getting close. Bike is running ok but, when really get into it 3/4 throttle or above it would spit sputter and backfire soo I did some research and decided to check size of main jets. I pulled out 132.5 jets. I called local suzuki shop and they said stock is a 112.5 so I bought the smallest they had and went with 120's ( i do have aftermarket exhaust and air pods) but now bike runs worse than ever! Backfiring rally bad through exhaust and carbs! Please help!! Very frustrating! And yes, carbs have been off about 5 times and cleaned. Maybe air screw adjustment??

[hikermikem]

Well, I'm not a carb guy but I do know you will need much larger mains than the stock size if you're running pods & a pipe...

Tons of info here regarding re-jetting issues, woes, & problems - use the search function to see it all.

Many members here use a stage 3 Dynojet kit when in your situation, as it gets them very close to where they want to be. Perhaps a call to the Dynojet folks would be helpful.

Good luck,

Mike

[Larry D]

You don't have a carb problem, you have a jetting problem. I would suggest finding the stock airboxes and going back to the way it was designed.
On the other hand with some trial and error I'm sure the proper jetting can be found for your mods. I'm just thinking that putting it back to stock would be alot less headaches.

[tkent02]

Hello all kinda new to this so any info would be greatly apprciated. Ok I have a 1981 gs750e with BS32SS mikuni carbs. Bike was not running very well when first got it but after some coils plugs and petcock I think Im getting close. Bike is running ok but, when really get into it 3/4 throttle or above it would spit sputter and backfire soo I did some research and decided to check size of main jets. I pulled out 132.5 jets. I called local suzuki shop and they said stock is a 112.5 so I bought the smallest they had and went with 120's ( i do have aftermarket exhaust and air pods) but now bike runs worse than ever! Backfiring rally bad through exhaust and carbs! Please help!! Very frustrating! And yes, carbs have been off about 5 times and cleaned. Maybe air screw adjustment??

Sounds like you went from too rich, the spit sputter and backfire, to too lean. Probably you need a main jet somewhere between the two sizes. With CV carbs you need to get the main jet correct first, and then do the needle, pilot after.

this should get you started:

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

You DO NOT want to run your engine hard with too small main jets installed, it will burn it up.