Even more carb problems!! Yay!

[gunnervirus]

Hello again,

Well, I finally gave up on the holley carb. I went back to the quadrajet, and am now having a bit more problems. The car is still running rich. It'll start up, but black smoke pours out the tailpipe. I found a good deal on a MSD setup, billet distributor and box fairly cheap. That helped, but it's still fouling the plugs. I think the problem is in the carb.

Any ideas?

Thanks for all the help,
Ben

 

[Freddie's Buick]

Is it electronic?

 

[gunnervirus]

no, it's a 79.

Could it have been messed up when in storage?

Ben

 

[Freddie's Buick]

It's the power valve. Probably sticks. If it's never been rebuilt then that's the problem. If it has been rebuilt, it's still the power valve. There is no info anywere in the planet on it's adjustment. My sources say about 2 1/2 to 3 1/2 turns out. The further out, the more rich.

If it's never been rebuilt, it's a good idea to turn it in as far as it would go and record the number of turns. From 1974 to 1979 most Q-Jets had a power enrichment valve that was very tricky to adjust and very problematic. Prior to '75 the Q-Jet's had a better power valve with good response. The later years were as I said, very tricky.

How good are you with Q-Jets? If you are a novice, get the Doug Roe book and I'll do my best to walk you thru understanding the rebuilding process. Holly's are much more involved. The only easy ones were the two barrel Hollys. The Q-Jet is much easier to fix then the Hollys. Especially the pre-electronic ones.

Note: To adjust the power valve a special tool is needed which is no longer available. If you have a grinder with a thin cut off wheel and a 6-inch 9/32 diameter aluminum rod, cut a slit at the end of the rod. This is a great substitute.

First adjust the mixture control needles according to specs. Next, adjust the power adjustment valve. Remember to record the number of turns out first by turning it in as far as it would go as I mentioned before, (never tight), just like the needles.

Or, you can go in one or two turns on the power valve and take it for a spin. If after several differant adjustments she's still too rich. Rip it apart and rebuild, the valve sticks.

 

[gunnervirus]

thanks for the info,

I pulled the carb top off today, and adjusted it all the way in, then went one more turn out on the mixture screws. The power valve's nice and springy. It's better, but still rich...

The plugs are fouled again, so I'll pick up some plugs and a timing light when I go to work tomorrow. I want to make sure I don't have a dead cylinder.

With all the talk about running wider plug gaps when running an MSD box, I guess I'll give it a shot and bump the gap up to 45.

Thanks for the help,
Ben

 

[b4black]

The power valve on a Turbo carb is plumbed externally. Do you have it plumbed right? Without vacuum sucking it closed, it will be open on start up and be very rich.

 

[gunnervirus]

Yeah, it's sourced to the manifold with a check valve in line.

Ben

 

[gunnervirus]

update:

I change to a set of Champion copper plugs gapped @ 60. Adjusted the timing, did a compression test (came out good), and put a bit of Marvel Mystery Oil in the tank. Results: It idles cleaner... the smoke is gone, but when given gas, it still smokes a bit. I leaned out the mixture screws a bit more, same results. I'm happy that it's running better.

Question, should the choke be hooked up to a switched 12 volt source? I think that might be part of the problem.

The old motor's carb had a choke that operated off of hot coolant. Could I just tap the ignition wire?

Thanks,
Ben

 

[Buicksandrail]

You definitely need the choke hooked up to a 12 volt source. I am not sure if the ignition lead would be the best place to tap in to. That could be your entire problem. The choke may be always on. You could do a quick check to see if the choke is on or off. Just remove the air cleaner and note the position of the choke plate. If it is closed the choke is on, if it is open (straight up and down) then the choke is off.

You need to ascertain if the choke is working properly before you can move forward on the richness problem.

Make sure that your inline check valve to the power enrichment valve is in the correct position. The power enrichment valve should never see pressure, only vaccuum.

Good luck,

Trent