[Jimbobeast]

Stock 1970 RAIV engine with the exception of Rhoades lifters, rebuilt carb (I got the kit specific for this carb and carefully disassembled, cleaned and reassembled q-jet). Dwell at 30, timing set to 12 BTC with 650 idle and vacuum advance plugged (I disconnected the TCS system for tuning). Engine starts up and runns/accelerates fine but there is a 300 rpm slow surge at idle. Vacuum advance reconnected and seems to be working, 11 inches idle vacuum.
I sprayed Brake-Klean all around intake and carb - no change. All vacuum lines are new and tight.
Surging seems to smooth out if I restrict air a little and the exhaust smells lean. I get no adjustment at idle mix screws (all the way in, engine still runs).
The manual suggested an incorrect float adjustment (should be 9/32" from top of casting), so I removed and disassembled the carb. All looked well. My float adjustment was correct, but the bowl was only 1/4 filled with gas, so I bent the float arm to give a little more fuel in bowl. I will put it all back together tomorrow and fire her up. Any thoughts?

[steve25]

If all was well before you dove into rebuilding the carb, then there your issue lies!
Turning in the idle mixture screws should stall the motor out.
Are you 100% sure the throttle plate gasket to throttle body gasket was the right one?

Many kits come with two different ones.

[Jimbobeast]

Great points.
Unfortunately I disassembled this car over 25 years ago and it was not running then, so I have no history of this carb. Similarly the entire engine was rebuilt, so the problem may lie anywhere.
My neighbor, Steve is a drag racer and used Q-jets back in the day. He, too suggested the throttle plate gasket may not be correct.
I don't remember where I got the rebuild kit earlier this year. I believe it was suggested on this forum and it was specific for this motor/car. I will search that info out.

[Kenth]

What carb-#?
M/T or A/T?
Nozzle drip at idle speed? (750 rpm in D for A/T or 1050 rpm for M/T).

BTW, factory initial timing is set at 15° BTDC.

[Jimbobeast]

I'll get carb number later today.
Manual Transmission
I don't know what nozzle drip is, but I'm guessing a shot of penicillin will take care of it.
How do I know if the throttle gasket is the correct one for this carb?

I carefully removed the carb and kept everything level, fuel filter attached. Does this look like the correct fuel level?

[67drake]

Originally Posted by Jimbobeast

I'll get carb number later today.
Manual Transmission
I don't know what nozzle drip is, but I'm guessing a shot of penicillin will take care of it.
How do I know if the throttle gasket is the correct one for this carb?

I carefully removed the carb and kept everything level, fuel filter attached. Does this look like the correct fuel level?

I hav no idea. Why don’t you measure the float level instead?

[JSchmitz]

Look at the bottom of the primary throttle blades. There's a transfer slot in the front of the venturis. If you have the throttle open too far it will be transitioned to the main metering circuit. Then the idle mixture screws will do nothing. Or you could have the float level too high and it's dripping from the boosters.

[Jimbobeast]

At a measured float level of 9/32" the fuel in the bowl was at the level in the photo.

When you say float level too high, do you mean it is measured at less than 9/32'?

[JSchmitz]

Originally Posted by Jimbobeast

At a measured float level of 9/32" the fuel in the bowl was at the level in the photo.

When you say float level too high, do you mean it is measured at less than 9/32'?

Observing the fuel left in the bowl means nothing. Float level of 9/32" should be good. That's if it's measured properly. Kinda tricky on a Q-Jet. You have to hold down the pivot rod and pull up lightly on the float. The needle and seat could be defective also. This could cause the fuel level to be high even if the float is set properly.

[george kujanski]

Unquestionably, with the idle mix screws closed, the engine should not run. Since it is, there is fuel being supplied somewhere.

George

[Cliff R]

Seating the idle screws completely may not kill the engine as some transfer slot is still exposed to supply idle fuel to it. It may also be getting some idle fuel from the main nozzles (nozzle drip).

Either way that's not really alarming but you should have some control with the mixture screws and be alble to lean up/slow down the engine when turing them in. If nothing changes at all you have either not enough idle fuel and getting nozzle drip, or you have too much idle fuel and its getting plenty from what little transfer shot is exposed.

Either way it needs some help someplace.....

[steve25]

If I understand what he posted correctly he said he choked. It off some and the idle got better.
To me then that would indicate a lean condition.

[Kenth]

I would set initial timing (15°) and idle rpm´s (1050) to factory specs to start with.
Here is the correct style bowl gasket for 1970 RA Qjets.

[Gary H]

What power piston spring did you put in the carb? The ram air IV cam doesn't create much vacuum in a 400 and the wrong spring may be causing the issue. You may also want to check and make sure you have strong enough distributor springs to keep the weights closed when at idle. If someone has monkey'd with them over the years and replaced them with an aftermarket set, then your idle can be all over the place.

[Jimbobeast]

Carb # 07040263
Gasket seems correct and identical to your photo.

The carb rebuild kit I obtained was specific for this engine/carb. Let us assume that the carb is clean and all jets/rods/floats, etc are functioning correctly. I have just set the float level to the factory spec 9/32".
The carb functions perfectly off idle. What else could be causing the lean condition (I say lean because the exhaust smells lean and the idle smooths out when air flow is slightly restricted).

Also please understand that this will be a show car, never raced and probably driven minimally. I want it to run strong but absolute peak performance, while desired, is not as essential as running well and smooth (think 70 series tires as the limiting factor).

Also, please try to keep suggestions as simple as possible. I have SOME knowledge and skills in 1970 GTO restoration but not like you guys. I just bought Cliff's book to help me out.

Thanks again

[steve25]

Some graph / visual help.

[steve25]

Once you get the metering rods loaded into the primary jets confirm that the power piston travels down and back up nice and smooth.

Also check that the air horn gasket when placed on the main body does not restrict the movement of the metering rods.

Many times I found that I needed to trim some of the gasket around them with single edge razor to get that free movement.

[Jimbobeast]

Metering rods move freely, as does the power piston.
The float level was set at factory spec 9/32" from the casting when it was surging. I adjusted the float up to 7/32" and re-assembled the whole shebang. The only potential issue I discovered was this ? port on the base of the carb (see pointer in photo) that was uncovered by the current carb base gasket. What does this do? I had another base gasket that covered this area. I put the carb back in the car with the second base gasket and no more surging. Also the engine now stumbles when I close the mixture screws. The timing was set at 15 BTDC all along (I mis-typed). Idle is at 1050, pulling 12 inches of vacuum. The exhaust smells LESS lean (or maybe it's my imagination).
I'm calling this a win-win. Time for an adult beverage.

[steve25]

Yes, nice work so cheers!

[Cliff R]

The 7040263 is set up really lean on the primary side and will not work well on this new fuel. Typical complaints are hesitation/stumble/bog coming off idle and often "surging" at light cruise.

It's the "grocery getter" model in 1970, and yours is a Service Replacement.

To work well on a RAIV engine with a real RAIV cam in it and stock compression it's going to need some help in several areas. The RAIV carburetors in 1970 were built from different main components and set up for the much larger camshaft.

You can still make that one work OK, contact me at the shop if you want the real fix for it. It would take too many pages here to go over all of it.

I would also avoid using "black" gaskets to assemble the carb. They are "skinned" and dubbed as non-stick, but after a few good heat cycles they stick to the casting and baseplate like super glue requiring hours of tedious removal with a razor blade.

You will also need to upgrade to the high flow N/S assembly and I'd upgrade the accl pump at the same time since the top is going to have to be off of it to modify the idle system and upgrade the jets and metering rods, PP spring, etc......