Re: Allan in NE-carb photo

Posted by Ron in Nebr on November 25, 2004 at 08:57:30 from (65.169.97.23):

In Reply to: Re: Allan in NE-carb photo posted by Allan in NE on November 25, 2004 at 05:11:03:

Hi Allan, happy Turkey Day!
From looking at both his carb pics, it appears to me that the actuating rod for the pump is indeed in place. Most likely, as you mentioned, it needs a new pump plunger.
There's usually some adjustments to be made on these pumps. I always had the best luck with the actuating rod in the top hole(nearest the pivot point) on the "rocker" assembly. This'll give it the fastest response.
A very critical measurement on these is how far the pump plunger itself sticks up above the main body of the carb. The pump plunger is what the little "S" shaped link is hooked to on the rear of the pump pivot "rocker" assembly.
If the plunger is too high, it will uncover a slot in the main pump well that's used to feed fuel to the pump, and it won't give any pump shot until it moves low enough to cover this slot back up. There should be a measurement for this in the original instructions that came with the carb. If not, there'll be one in the carb kit that you have to buy to get the new plunger.

A quick check he can perform is, with the engine OFF, looking down the primaries, move the throttle shaft slightly. There should IMMEDIATELY, with even the slightest throttle movement, be two good streams of fuel shooting out, one above each primary throttle venturi. If you can move the throttle and there isn't fuel squirting out in the venturis, OR it takes several degrees of throttle movement before the fuel starts to squirt, OR the fuel just kinda trickles out and doesnt come out in two good streams, it will result in the symptoms described.

As a side note, and maybe I'm thinking of something else here, on the AFB's I've been around, at least the "Competition Series 750 AFB" that I had, there was an air valve plate above the secondarys. This was controlled by a counterbalance weight. This would only open when the engine airflow demands overcame the counterbalance weight. You could "tune" on it by grinding some off the weight, or adding weight to slow it down. Anyway, I don't see any such air valve plate above the secondarys in these pics. Maybe the 600 AFB's didn't have them? But if it's supposed to be there, and for whatever reason it's gone now, it'll sure cause those same symptoms as the secondarys open up before the engine is ready for them.

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