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Hello all. I’m new to the forum and am looking for some help with an apparent carburetion issue. I have combed through the internet but haven’t found a solution
I purchased a 1980 Suzuki GS850G in 2020. I took the top end apart to fix an oil leak, which was the start of a five-year project. After reboring for oversize pistons, fixing a frozen clutch, and a dozen other issues, it was nearly done, but I could not get it to run well under load.
The bike has Mikuni BS32SS carburetors, aftermarket electronic ignition, and I just verified that the timing is good. The bike is at sea level now; I have tried stock jets (115 main and 40 pilot), 117.5/42.5 and 120/45 jet combinations with all mixture screw adjustment settings, but it still ran poorly under load. I’m presently running 117.5/42.5 and it idles well but bogs with throttle and generally runs much worse. We noticed that with throttle, the slides jiggle up and down rapidly and don’t open uniformly. Often they drop back down to the closed position even when throttle is applied. It seems like this is a likely culprit for the lean performance above idle, but I cant figure out the cause.
The diaphragms look good. The problem is uniform across all four carbs. If I close off the vacuum port on the intake-side of the carb and lift the slide with my finger, it stays up until I release the port, which seems like another indication of a good diaphragm. The hole on the bottom of the slide that appears to go through to the diaphragm is patent. The butterfly moves with the throttle as expected.
I have rebuilt the carbs several times. Compression is good. The floats are set correctly, and I replaced the carb gaskets using a quality carb rebuild kit. The bike has new coils and wires, and fairly new plugs.
Any suggestions would be welcome.
Thank you.
I purchased a 1980 Suzuki GS850G in 2020. I took the top end apart to fix an oil leak, which was the start of a five-year project. After reboring for oversize pistons, fixing a frozen clutch, and a dozen other issues, it was nearly done, but I could not get it to run well under load.
The bike has Mikuni BS32SS carburetors, aftermarket electronic ignition, and I just verified that the timing is good. The bike is at sea level now; I have tried stock jets (115 main and 40 pilot), 117.5/42.5 and 120/45 jet combinations with all mixture screw adjustment settings, but it still ran poorly under load. I’m presently running 117.5/42.5 and it idles well but bogs with throttle and generally runs much worse. We noticed that with throttle, the slides jiggle up and down rapidly and don’t open uniformly. Often they drop back down to the closed position even when throttle is applied. It seems like this is a likely culprit for the lean performance above idle, but I cant figure out the cause.
The diaphragms look good. The problem is uniform across all four carbs. If I close off the vacuum port on the intake-side of the carb and lift the slide with my finger, it stays up until I release the port, which seems like another indication of a good diaphragm. The hole on the bottom of the slide that appears to go through to the diaphragm is patent. The butterfly moves with the throttle as expected.
I have rebuilt the carbs several times. Compression is good. The floats are set correctly, and I replaced the carb gaskets using a quality carb rebuild kit. The bike has new coils and wires, and fairly new plugs.
Any suggestions would be welcome.
Thank you.
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