[Wbulk]

Jhiarsak, you are so close that I have to l give it to you. Winner, winner, winner!!!!!

Here is what I found. The last day I drove it the problem was still there so I took the carb apart for the umpteenth time. I decided I was going to study every single detail of the gaskets, the metering block, and the power valves and circuits. I checked the power valves again and they tested good. But that was the logical area. Somehow it had to be staying open at times. So, I next followed the vacuum passage and tried to blow air through it. A little air, but there was the anti-backfire valve. So I removed the throttle blade plate from the main body to get to it and tried again. Not conclusive, so I put a hose over the bottom vacuum port for the Mighty Vac and I could get about 5-7" of vacuum as I pumped the handle and it would drop slowly. I then would shake the plate and test it again. This time I was only able to get a few inches of vacuum and it would drop right off. I should be getting no vacuum with my gauge so the port would have no restriction to the power valve.

I then got on the phone with Quick Fuel tech support and discussed the issue. It was suggested I try and push the ball down. I have some micro drill bits so I found one small enough to go in the hole. It was solid. There was no spring against the ball. With no spring the vacuum pulls the ball down to an un machined end of the hole that cuts off most or not all of the vacuum. No or not enough vacuum and the spring pressure holds the power valve open. I am thinking since the bottom of the hole is just drilled and not intended to seal vacuum, over a period of steady state cruise it would build up enough vacuum from closed to fully open and all points in between, causing the AFR to go back and forth.

So, Jhirasak you were right with the restriction in the vacuum port. Good job.

Quick Fuel is sending me a new anti-backfire valve and gaskets. Who would have thought the valve would be installed without a spring during the manufacture. Consider if you have any carb with a anti-backfire valve and it fails to work and you have no wide band hooked up you may not know you have this problem for some time.