ACV Revisited

I did the ACV mod by blocking the vacume port, reversing the diaphram and leaving the spring out. If you roll off the throttle from a high rpm run it pops like crazy when the revs get low, regardless of pilot screw position. I've got a 45 PJ installed. I figure the valve is shut with the diaphram reversed, so having the atmosphere port open shouldnt make a difference. Any ideas? Or anyone that has done the mod and had sucess?

My understanding is that the ACV richens the mixture when you close the throttle to prevent a backfire from lean mixtures.

If you close the ACV you may get a backfire. You may consider raising the needle(lower the clip)to richen your mixture, but I'm no expert on jetting.

I closed mine and did not get any backfire, but my altitude(6000ft minimum) makes everything I do irrelevant.

2 cents worth

With the diaphram reversed the ACV is OPEN all the time, you need to richen the pilot jet to get it right...

With the diaphram reversed the ACV is OPEN all the time, you need to richen the pilot jet to get it right...

with the diaphram reversed how would the acv be open?under normal conditions (not decel) diaphram nipple should press on valve opening it, allowing extra air into pj cuaseing it be lean. Let off the gas and the diaphram pulls away from the valve, closing it, letting less air into the pj cuasing it run richer during decel. I may be wrong but thats my understanding.

With the diaphram reversed the ACV is OPEN all the time, you need to richen the pilot jet to get it right...

with the diaphram reversed how would the acv be open?under normal conditions (not decel) diaphram nipple should press on valve opening it, allowing extra air into pj cuaseing it be lean. Let off the gas and the diaphram pulls away from the valve, closing it, letting less air into the pj cuasing it run richer during decel. I may be wrong but thats my understanding.

OK...the ACV purpose is to stop the backfiring on decel. The backfiring is caused by an excessively rich mixture in the throttle closed/high vacuum conditions. When this mixture hits the open air it burns, causing the explosions we hear. Tha ACV leans the mixture by allowing more air into the pilot circuit, thereby diluting the rich mix.

The nipple on the diaphram is pushed into the carb body by the spring, except under high-vacuum(closed throttle, elevated RPMs), when the spring pressure is overcome and the diaphram pulls the nipple out of the carb body and opens the passage for additional air to flow....

You have it backwards...... :cry:

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