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recommended needle shim modification?

G

gkoeber

Forum Newbie
Hi - new here but have been lurking and searching forum for weeks.

few details - bike is a 1982 GS750T running a stock airbox \ when i overhauled the carbs i found the main jets were 92.5 I live in NJ so I knew I had to replace them as the bike was running very lean..... replaced all the o-rings thanks to Nessim's o- ring kit.

I have recently installed a Delkevic 4 into 1 exhaust and rejetted my main jets to 115 bike runs great except between 5500 and 6000 RPMs which leads me to believe i will need to lift (enrichen) my needles to correct issue, and according to this very helpful link i found in one of the threads searching for answers.


So my question is is there a starting \ recommend height? i see in the rebuild BS-CV Carburetor Rebuild Tutorial the picture shows the plastic spacer needs to be modified (Pic one shows thickness of 2.47) Pic two shows the plastic spacer was reduced to 1.72mm - so curious if that is a starting point or recommendation? I know every situation is different but was wondering if there is a guide or starting point before I mod my plastic shims? I did purchase needle shims from Jets R Us 10 of the .5 shims but again before I start replacing the plastic spacer with shims was wondering if there is any guide or insight that can be shared?

Thanks in advance

garret
 
I'm surprised you had to go up that many steps with a stock airbox if you are using stock jets (Dynojet jets measure up differently)..

Usually with only a 4:1 you need to go up 5 sometime only 2.5, the airbox is what makes the biggest difference.

Are you sure you don't have airbox leaks? Have you replaced the carb boot o-rings?

What happens at 5500-6000? It might also be running rich & that's where it finally starts to clear. Have you done plug chops?
 
Maybe it's not running right on top because it's too rich? As Dan mentions, it should only take a size or maybe two larger on the main, assuming the airbox is installed.
 
Thanks for the responses...

Yes, the stock airbox is installed and connected and the rubber boots have been replaced on airbox side and carburetor sides as the older ones were very hard and inflexible.

According to the Suzuki Manual Specs the main jet should have been 112.5 so I went up to the 115's based on recommendation from Delkevic, and I bought Mikuni jets from JetsRUs to ensure it was a Mikuni jet.

"What happens at 5500-6000? It might also be running rich & that's where it finally starts to clear. Have you done plug chops?"

I have not done a plug chop yet.

The stumble or flat spot is right at 5500 then clears and runs fine at 6k and above - as I believe at this rpm it is all the main jet and no longer related to the needle position.

The needles are the ones that require the special snap ring tool and the spacer is a plastic disc vs dynajets which would allow me to adjust the circlip position.

your insights are greatly appreciated.
 
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