My buddy has a 69 Chevy Stepside with a 454 in it and it has a 750 Double Pumper and it has 850 Metering blocks front and rear. He is fouling spark plugs all the time and was wondering if that could be the problem.

Here are the paticulars on the carb.

750 Double Pumper
850 Metering Blocks
6.5 Power Valve in the front
76 Jets in the front
Blocked power valve in the back
86 Jets in the rear
Idles with about 10-12 inches of vacuum in gear

Idle mixture screws acting wierd as well. Turn the left drivers side all the way in and it still runs. Then proceed to the other side and do the same and it slows down a little. Usually my experience tells me it should shut the motor off.

The back metering idle screws don't do anything. I presume that is because the power valve is blocked off.

The truck runs like a raped ape when you stomp as long as the plugs are clean. It has somewhere around a .580 lift hydraulic roller as well plus a Team G intake sitting on 840 square port heads with closed chambers.

Truck has run 12.50's at a 107 mph at the track. Anyways is that carb a bad combo? I was telling him to just pick up some old 750 Metering Blocks and try them.

6 sizes too big on the primary side to start with

Find the correct blocks. All metering through the blocks is wrong. The metering is set up for a carb with a very poor signal at the booster(850) You can't just bolt 4 sided idle circuit blocks onto a non 4 sided and have it work.

I will have to let him know about that Mike. The guy that he got the carb off of says it worked great. HAHAHAHAHA!!!!! I did not think those 850 metering blocks were right.

It could also be getting fuel from the throttle blades being open too much, pulling from the transfer slots. This will cause the rough idle and the problems with lack of response from the idle mixture screws. It's a common tuning mistake, too. Back off the idle speed screw until it's not touching the lever. Then start with it open 1 turn, try to tune the idle mixture. If it won't run, turn idle speed up a little at a time until it will, then set the mixture screws. If the motor has a big cam, you might need to drill the primaries. It's a common tuning procedure. The main problem is, no two engines are alike, so the carb might've run fine with his old combo, but not your buddie's combo. It needs to be tuned. I had a friend who used to manage a speed shop back in the 80's, he'd have 1 or 2 brand new 750 Holley carbs returned every week, people cursing them because it didn't run like a champ straight out of the box. :rolleyes: No effort taken to tune them. A good book on the subject will help alot. Learn the different circuits and how they work with each other, and you'll be surprised how simple they can be to tune properly. FWIW, I took a friend's car from 14's to 12.42@108 with just carb and ignition tuning. It was a fresh combo, and he couldn't get it tuned right.