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Carb Jet Sizes for GS550 with Kerker

cloudbreakmd

cloudbreakmd

Forum Mentor
Past Site Supporter
The bike I just bought has a 4-1 Kerker. The PO told me that the bike would backfire a bit. What jets do i need to change and out and to what sizes? Also what are the adjustments for the carbs after installation?
 
Backfiring is caused by an exhaust air leak, when you close the throttle the pressure in the exhaust drops and it sucks in oxygen rich air, which is perfect for combustion, you have a heat source, un-burnt fuel, and oxygen.
There mat be a minor jetting issue but sealing the exhaust up is your first priority.
Dink
 
I thought improper jetting would do the same. I had the bike running briefly the other day and the exhuast sounded fine. I ordered rebukld kits and had planned on installing them but they are the stock jet sizes (as are the one in the carbs now).

Are you suggesting that the manifold gaskets need replacement?
 
It is possible that "some" backfiring could be caused by fuel leakage in the carbs, BUT for it to burn in the exhaust it must get an oxygen supply, oxygen is consumed in combustion, hence there must be a leakage oxygen source,so yes replace the gaskets.
Dink
 
I aways been told to go up one jet size on my pilot jet that should fix your jetting problems
 
depends on how crazy you want to go... with a 4 into 1 and stock airbox you can get away with the stock jets as you are going to draw much if any extra air into the engine.

On my '83 GS550E the stage three jet kit came with 114 and 118 mains... I forget the pilots currently though... when it's cool and the air is pretty dense the 114 mains and 3rd from the bottom on the needles (sometimes 3 and a half) works awesome...

For an 80 model I think Nerobro was using 122 mains... though you'd need to ask...
 
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