Join Date: Jul 2009
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83 Suzuki SP100 Carb
I'm new to the forum and have come seeking help for a 1983 Suzuki SP100 that I bought for my son. a few years ago.
The bike was in good overal condition except for the carb. The bike would not idle at all. It just reved right up when started.
I removed the carb for inspection and discovered that the pilot screw threads are stripped out of the carb body. I tried making a repair using JB weld and rethreading it. But it didnt hold so I went to a local Suzuki dealer and since the carb was no longer available they sold me a Mikuni VM-20 flange mount carb. The carb seems to be very similar in size to the OEM carb.
I have adapted the card to the bike and now the bike starts right up and idles fine. I thought I had it whipped unitl I rode the bike and found that the thing now surges teriibly. It will run fine unitl I start giving it throttle and then the engine kind of drops out, like it is starved for gas. Then it will come back and go fine for a few seconds and then fall off again. It just keeps doing this surging.
I compared the OEM carb needle with the new carb needle and the OEM was much thinner. I swapped the OEM needle into the new carb and it seemed to improve but the problem persists.
I have done a lot of looking on the internet and it seems to point to the carb needing to be rejetted. But this is where I get confused and am hoping someone with experience would be willing to advise me.
Is the surging behavior indicitive of a lean condition when under half to full throttle?
I am pretty handy mechanically but this is the first time I've worked with Mikuni VM type carb and am at a loss as what to do.
Any help or advice will be very much appreciated.