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I rebuilt my carb this weekend with the kit from MWM. The kit came with two springs for the metering rod and pump diaphragms. However, neither spring matched the length or spring rate of the springs that were already in my carb.

The spring for the pump was considerably shorter but stiffer and the spring for the metering rod was a tad shorter and also stiffer. Anybody else run into this?

I just kept the springs that were in there instead of swapping them out as they appeared to be in good shape. I suppose a shorter, stiffer spring might give the same result as a longer, softer spring once compressed.

Conversely your springs were considerably longer and softer!

Actually we've seen many different sizes and shapes over the years. The ones in the kit work. But if you carb had no problem before the rebuild with the accelerator pump or metering rod diaphragms then it certainly won't hurt to use your old springs. On the other hand since they are easy enough to change with carb installed why not try your old set for a few weeks then swap in the new set and see if you realize any change in performance.

wesk wrote:Conversely your springs were considerably longer and softer!

Actually we've seen many different sizes and shapes over the years. The ones in the kit work. But if you carb had no problem before the rebuild with the accelerator pump or metering rod diaphragms then it certainly won't hurt to use your old springs. On the other hand since they are easy enough to change with carb installed why not try your old set for a few weeks then swap in the new set and see if you realize any change in performance.

I think that's what I'll do. It didn't seem to have a flat spot off idle prior to the rebuild, so I would guess the springs were working fine. If I notice any problems, I'll swap them out.

The other thing I noticed was that the ball and weight were missing when I disassembled it. It seems like it was running really rich, not sure if that was related.

They are very easily lost during dis-assembly and often overlooked even at assembly. Their effect on mixture issues has been discussed on other threads.

Yes the carb will run rich if they are not there. It will allow fuel to pull over into the venturi at road speeds.