I need some help with a carb swap, it's a '63 GMC pickup, 305v6, SM-420 4sp, Pertronix ignition. I'm replacing the Stromberg WWC with a Holley 4412 500 cfm 2 barrel, (see http://www.6066gmcguy.org/holley.htm for more info) It's a used carb and I went thru it to clean and install new Holley gaskets, a 125-35 power valve and check the jet size, #73. It looks to be in good condition. After a bit of fiddling I got it to start, I had to advance the timing (along with a new battery and new plugs). I got it running now, but it's pouring black smoke out the exhaust. After it warmed up I retarded the timing closer to where it was. No amount of fiddling seems to reduce the smoke. Motor pulls about 15" of vacuum at idle , ~800rpm. It's my first Holley, so any tips on baseline tuning and how to lean out the idle would be much appreciated. Thanks!
Turn the air idial screw or adjuster in while its running till it starts to die , Then out till it starts to die , then back in , somewhere in the middle should do it .Turn the screw slow. make sure the flot is ajusted right .
At first the float was about 1/4" below the sight hole, I adjusted it and began messing with the idle screws, nothing much happened, then I checked the float level again and it was so full it came out the adjust screw on top of the bowl. I'll readjust that in the AM. Would an over-full float bowl cause a way-rich idle condition? Thanks
Aside from the float setting, is the powervalve stuck open? Also 73's are the stock jets but did someone drill them out? My experiance with these is that they are a little rich "out of the box" for some engines. I've run them on 302's, 305's, and 350's on the street. The smaller and more stock engines I usually ended up downsizing the main jets 2 or 3 numbers. On my tweeked 350, I added a K+N circle track air filter, and it leaned it out a bit, with no other changes. This add on required some surgery to clear the choke linkage, as they are normally used on chokeless carbs. Hope this helps.
Aha! In on the air screws is lean, out is rich. Set them to 1 turn out, reset the float, no longer spewing out... started right up. Set timing, tweaked air screws, running like a champ. I'll probably try leaner main jets, they say 1 jet size is roughly 4.5% more or less fuel. Thanks for the help
I told you lol I wouldnt change the jets unless you have to . drive it a little and check the plugs ,dont just set the air screws one turn out thats an old wives tall . turn it in till it starts to die then out till it starts to die then in the middle somwhere its easy you have to get the hang of it. you can tell buy the way its running . simple is better somtimes
The Jalopy Journal
