[cranky bill]

I have a Proform 750 Race Series carb that's decided to drive me nuts. After changing metering block and float bowl gaskets, I cannot get it to draw fuel through the idle circuits. The lowest I can get it to idle down to is 1400-1500 rpm. This was after switching back to the original gaskets. They weren't bad. I had simply done enough jet changes, I felt fresh gaskets wouldn't hurt. Timing is bang on, at 36 total. I have blown out every air bleed and fuel passage in the base and metering blocks, set the throttle blades at the proper initial setting. The idle, as it is, is fairly rich, but that's the only way I can get it to "idle" at all. Below the 1400-1500 threshold, the only way to keep it running is to jiggle the throttle enough to spill some fuel from the accel pumps, but then it will simply run out of fuel after a few seconds. ?????

 

[crazees#2]

Did you change baseplate gasket?

 

[cranky bill]

Did you change baseplate gasket?

Nope. Baseplate has never been off. The worst of this is that it was fine when I put it away for the winter. While I was waiting for some parts, I put new gaskets in, realized there was a lot more than meets the eye there, put the old ones back on. Now I cannot find the idle. Should idle about 1000. 900 in gear. Nope.

 

[wingnutks]

Did you make sure and clean out front and rear transfer slots on the main body?

 

[fastfox420n/a]

sounds like a gasket misalignment issue to me

 

[cranky bill]

sounds like a gasket misalignment issue to me

I've never really thought about that. Now, it may be possible that the gasket for the secondary block has been moved to the front, and vice versa. They have the alignment pins, but could it be something as simple as that? The carb has no residue or deposits. It literally looks brand new. Float level's good, just a hair above half way up the sight glass. Given the simplicity of these carbs, I know it's something simple, but damned if I can find it. I will try moving gaskets front to back tonight and see what transpires. I'm waiting for new gaskets to show up. The old ones aren't in bad shape, but the new ones had to come from across the border as there were none in Canada. (Proform #67220)

 

[cranky bill]

Did you make sure and clean out front and rear transfer slots on the main body?

Yeah, I've blown about 2 whole cans of brakekleen through every orifice in this carb.

 

[wingnutks]

Make sure the gasket isnt covering the transfer slot hole front or rear. can also check for some vaccum leaks.

 

[slowtrain]

Not sure of all details involved, but if you're running a plastic carb spacer, check to make sure you didn't crack it when tightening the carb back down.

 

[juiced coupe 78]

Did you change anything else.

I got a AED carb kit one time and the car wouldn't hardly run after freshening the carb. Turns out that the mixture screws in the AED kit had a longer tapper than the Holley ones. Swapped them back and everything was fine.

 

[cranky bill]

No other changes but gaskets. It has to be a gasket issue, related to transfer slots or air bleeds. (Although I am tempted to stick the shop vac nozzle to one of the valve cover breather holes, and use that to rule out a vacuum leak on the intake gaskets. Even though I have no reason to believe there is one there, as my intake has been tweaked to fit perfectly.)

 

[xlcr77]

Are you SURE you have the correct metering block gaskets? Is it a 2 or 3 circuit carb? Do you have the correct circuit number gasket?

 

[cranky bill]

Are you SURE you have the correct metering block gaskets? Is it a 2 or 3 circuit carb? Do you have the correct circuit number gasket?

That I'm sure of. I went back to the ones that have been on the carb since new. Now, you've thrown a new one at me. 2 or 3 circuit? Educate me. I did swap the metering block gaskets last night- primary to secondary, and vice versa. They're exactly the same, but maybe they'd taken a "set". Who knows at this point? While it was apart, I made sure air moved through every orifice in the main body and the metering blocks. All good. I made no changes to the throttle positions, and the primaries are right at where they're supposed to be, and the secondaries have at least double the amount of transfer slot showing as what they should have.

 

[wingnutks]

Vacuum nipple cracked or fell off?

 

[cranky bill]

Vacuum nipple cracked or fell off?

Well, the nipples LOOK fine, and it's not like the carb's ever been dropped or mishandled. However, it wouldn't kill a guy to run a nice little bead of silicone around where they go into the base.

 

[xlcr77]

That I'm sure of. I went back to the ones that have been on the carb since new. Now, you've thrown a new one at me. 2 or 3 circuit? Educate me. I did swap the metering block gaskets last night- primary to secondary, and vice versa. They're exactly the same, but maybe they'd taken a "set". Who knows at this point? While it was apart, I made sure air moved through every orifice in the main body and the metering blocks. All good. I made no changes to the throttle positions, and the primaries are right at where they're supposed to be, and the secondaries have at least double the amount of transfer slot showing as what they should have.

If you have 2 air bleeds per "barrel", you have a 2 circuit carb, If you have 3 air bleeds per, you have a 3 circuit carburetor. The metering block gaskets are different from 2 circuit to 3 circuit. As long as the new metering block gaskets match the hole size and hole positioning as the old ones, you should be good. As far as the "set" you speak of, I have used some pretty ratty metering block gaskets in a pinch, and never had a problem.
Do you run a power valve? If so, make sure it's good.
Are both primary and secondary blades about the same angle when at idle?
Air bleeds clean?
Idle mixture screws set at 1.5 to 2 turns out, and their seats are clean.

 

[xlcr77]

Something I thought of, I have a Pro Systems dominator, and they recommend the float settings (levels) to be 1/3 up in the glass window. If you go over 1/3, like 1/2 up, the fuel spills over into the venturies.
If the only thing you changed is the gaskets, it's got to be in them.

 

[bigblockmark]

3 circuit metering block gaskets will work on 2 circuit metering blocks but not the other way around. Neither will affect idle circuit.

 

[crazees#2]

How are the gaskets/seals around the mixture screws?

 

[cranky bill]

How are the gaskets/seals around the mixture screws?

Hmmm. I would have to say there's nothing I would call a 'seal' at the mixture screws. I have not physically removed the mixture screws and blown them out. Now, thinking back to last summer, this all really started when I towed to the track and forgot to put a towel over the carb. Drove through an ugly wind/rain storm, and had to disassemble the carb and blow out the air bleeds just to get it to run. I've never pulled the mixture screws and blown out that circuit from the screw side.