I never posted the issue I was having on here but thought my results might be interesting to a few others.
I have a 780dp from Pro Systems that I ordered when I built my 406sb a few years back. This carb has performed flawlessly until now. I changed heads from Eddy e-techs to AFR's eliminators last year and the carb was still great. This winter I went to 1 3/4 headers with 3" pipe to a X and then the original 2 1/2 back from there. My old system was 1 5/8 headers to a H pipe , all 2 1/2" pipe. I also just completed a swap over to a m22 from a th350.
Anyway, last week I checked my timing and tried to adjust the idle/mix screws. Turning the screws in increased my idle rpm substantially and cleaned the idle up a bit. The problem was I couldn't lower the idle rpm with the idle screws. Both the primary and secondary were backed right out and still wouldn't lower the rpm enough. Richen up the mix screws and the idle would back down.
The pro-systems carb comes with the throttle blades drilled, both primary and secondary. I phone Patrick and asked if plugging the holes in the blades might help. He said it might but gave me a few other things to check first.
I tried his suggestions Saturday but nothing helped. I JBed the holes closed and let it dry until Sunday. I put the carb back together and bolted it on. I now have complete control again. I found this quite interesting that it worked. My initial reasoning for closing the holes in the butterflies was that maybe with the bigger exhaust it was breathing better and pulling too much fuel at an idle. I don't know, all I know is it worked.
I have a 780dp from Pro Systems that I ordered when I built my 406sb a few years back. This carb has performed flawlessly until now. I changed heads from Eddy e-techs to AFR's eliminators last year and the carb was still great. This winter I went to 1 3/4 headers with 3" pipe to a X and then the original 2 1/2 back from there. My old system was 1 5/8 headers to a H pipe , all 2 1/2" pipe. I also just completed a swap over to a m22 from a th350.
Anyway, last week I checked my timing and tried to adjust the idle/mix screws. Turning the screws in increased my idle rpm substantially and cleaned the idle up a bit. The problem was I couldn't lower the idle rpm with the idle screws. Both the primary and secondary were backed right out and still wouldn't lower the rpm enough. Richen up the mix screws and the idle would back down.
The pro-systems carb comes with the throttle blades drilled, both primary and secondary. I phone Patrick and asked if plugging the holes in the blades might help. He said it might but gave me a few other things to check first.
I tried his suggestions Saturday but nothing helped. I JBed the holes closed and let it dry until Sunday. I put the carb back together and bolted it on. I now have complete control again. I found this quite interesting that it worked. My initial reasoning for closing the holes in the butterflies was that maybe with the bigger exhaust it was breathing better and pulling too much fuel at an idle. I don't know, all I know is it worked.
