'63 problems after carb cleaning

[Guest buickriv63]

Hello!

I found out a leak at the bottom of the intake manifold and fixed it. After that I thought it was a smart move to clean up the carburetor as well. Well, it wasn't.

Now the idle is gone. The exhaust pulses with a lot of pressure and I have to keep high idle RPM's just to keep it going. Also the car shudders badly at idle and even worse when I try to move it.

Starts pretty easily and sounds a lot healthier in higher RPM's than idling.

There's a thick stainless steel heat shield sandwiched between two fiber gaskets at the bottom of the carb. Is that OK?

So, what should I check first? I didn't touch the timing or anything ignition related.

[Jim Cannon]

Hello!

I found out a leak at the bottom of the intake manifold and fixed it. After that I thought it was a smart move to clean up the carburetor as well. Well, it wasn't.

Now the idle is gone. The exhaust pulses with a lot of pressure and I have to keep high idle RPM's just to keep it going. Also the car shudders badly at idle and even worse when I try to move it.

Starts pretty easily and sounds a lot healthier in higher RPM's than idling.

There's a thick stainless steel heat shield sandwiched between two fiber gaskets at the bottom of the carb. Is that OK?

So, what should I check first? I didn't touch the timing or anything ignition related.

The stainless steel heat shield is required. I am glad to hear you have one.

This sounds like a major vacuum leak. You probably disconnected the vacuum hose at the rear of the carb that runs to the PCV valve. Check that for tight fit. Perhaps replace that rubber hose with a new one to ensure tight seal.

How much did you take the carb apart to clean it? Just remove from car, clean the outside, and return it as a unit? Or disassemble to clean inside?

Is this the original Carter AFB carb on this engine or a replacement aftermarket carb (like and Edelbrock)?

Is it possible that you bumped the distributor and changed the ignition timing?

Did you need to remove any of the high voltage wires that run from the distributor to the spark plugs and then replace them?

[Guest buickriv63]

I took the carb (Carter AFB) out and cleaned it insideout with solvent and pressurized air. I did only minimum disassembling in order to clean the unit and also tried not to bend the floats etc.

I checked the timing with a light and it's not changed. I didn't replace any of the ignition wires, I only removed the coil wire and put it back securely.

Edited September 23, 2012 by buickriv63 (see edit history)

[Guest buickriv63]

More information about the idle problem: I figured that I have to keep the idle RPM screw all out and it still idles too high. Also opening the mixture screws didn't have any significant effect on the idle quality. I could even open those screws so that they almost fell out and the engine RPM's stayed almost the same. At higher RPM's the engine sounded like there's no serious issue. I Hope this helps in diagnosing the problem.

[Guest JDagg]

I am having a similar problem with my 65 Riv. the motor was recently totally rebuilt at a performance machine shop, after driving a few weeks, I detected some problems which I believed was related to the carb. since it had not been touched, so I had my carb. professionally rebuilt, they ran it and sent me a video, so I believe that its good. I drove it to a garage to have it tuned up, that was a week ago and now it has all gone down the tubes. I runs rough at low idle, but seems fine when the engine is throttled up. They haven't driven it yet though. A fuel flow regulating device was put in line between the filter and carb. and turned down to 3 psi at the advise of the Carb. overhaul people (new filter by the way) No backfiring now, but seems to still be blowing fuel out the exhaust, (but still idles rough). They switched out the distributor with a new one, still no difference, They now think the front two cylinders are what is causing the problem and believe it tied to a cam issue. The vacumm gauge is indicating a rapid flutter on either side of 14 inches. All new hoses and components. Only one metal gasket on the carb. thought there were supposed to be more though. Sorry for rambling but I am at wits end. Had the car since 1970 and am the second owner.

[Jim Cannon]

More information about the idle problem: I figured that I have to keep the idle RPM screw all out and it still idles too high. Also opening the mixture screws didn't have any significant effect on the idle quality. I could even open those screws so that they almost fell out and the engine RPM's stayed almost the same. At higher RPM's the engine sounded like there's no serious issue. I Hope this helps in diagnosing the problem.

I still think you have a vacuum leak. When you run the RPM up, the mixture depends more on running jets and less on idle circuit jets, and the air coming in is not enough to mess up running.

There is a temperature compensating bimetallic spring on the top of the carb. Check it's condition and seal. When the engine is running poorly, try pressing gently down on the sealing button to see if that improves it.

Did you get both of the little aluminum pistons into the top of the carb, along with the metering rods that connect to them?

Did you try temporarily removing and capping where the PCV valve hose connects to the carb?

[Guest buickriv63]

Jim, I think you nailed it again. Started the engine and sprayed carb cleaner around intake manifold. Immidiate change in RPM and idle quality. So, I have to fix that in order to get to carb problems (if there's any).

Is it possible to use the old intake manifold gasket? It seemed visually OK. How about some sealant adhesive (silicon?) to make sure it's airtight?

Thanks everybody so far, especially Jim.

[Jim Cannon]

Is it possible to use the old intake manifold gasket? It seemed visually OK. How about some sealant adhesive (silicon?) to make sure it's airtight?

Normally I would say "yes, you can" but you are already having a vacuum leak problem, which tells me maybe you can not use it again.

Some sealant could offer a short-term fix, but a new gasket is a better long-term solution.

[Guest buickriv63]

Hello again.

Idle problem fixed. I replaced the old intake manifold gasket and now it's purring nicely. Also fixed the leak in the bottom of the manifold (exhaust passages). Made quite a difference in the engine noise levels!

Again, thank you Jim for helping me out.

[alini]

You can buy a sheet of gasket material and make your own, just use the old ones and trace the pattern on the new paper and cut them out with a razor blade. This way you dont buy a whole gasket kit or wait for new parts to arrive.

[Guest Steeleco]

Hello again.

Idle problem fixed. I replaced the old intake manifold gasket and now it's purring nicely. Also fixed the leak in the bottom of the manifold (exhaust passages). Made quite a difference in the engine noise levels!

Again, thank you Jim for helping me out.

Hello Pasi, Please tell me about the leak at the bottom of the manifold (exhaust passages), what exactly was leaking and how do you get to it or find it and fix it. Thanks alot!

[Guest buickriv63]

Hello Pasi, Please tell me about the leak at the bottom of the manifold (exhaust passages), what exactly was leaking and how do you get to it or find it and fix it. Thanks alot!

Hello Steele.

I found the leak just listening to the engine. It started to sound noisy especially right after startup. I used a piece of garden hose to listen the engine. I just pushed the end of the hose under the intake manifold keeping the other end to my ear and the source of leak was obvious.

The leak was at that round plug under the manifold. I took the manifold out, cleaned the surroundings of the hole with a wire brush and solvent. Then I just used a epoxy heat resistant repair putty to seal the hole. Then I made a round stainless steel plate (same size as the original plug) and glued it with heat resistant silicon on the top of the patch I made.

I have to say that this garden hose is very efficient tool to find out leaks. Yesterday I found a exhaust manifold gasket leak with that hose. Just to make sure I did a right diagnose I put the other end of the hose next to my nose and was able to smell the exhaust gasses through the hose.

I'm not sure this intake manifold fix being a very durable repair, but let's give it a try.

[Jim Cannon]

Hello Steele.

I found the leak just listening to the engine. It started to sound noisy especially right after startup. I used a piece of garden hose to listen the engine. I just pushed the end of the hose under the intake manifold keeping the other end to my ear and the source of leak was obvious.

The leak was at that round plug under the manifold. I took the manifold out, cleaned the surroundings of the hole with a wire brush and solvent. Then I just used a epoxy heat resistant repair putty to seal the hole. Then I made a round stainless steel plate (same size as the original plug) and glued it with heat resistant silicon on the top of the patch I made.

I have to say that this garden hose is very efficient tool to find out leaks. Yesterday I found a exhaust manifold gasket leak with that hose. Just to make sure I did a right diagnose I put the other end of the hose next to my nose and was able to smell the exhaust gasses through the hose.

I'm not sure this intake manifold fix being a very durable repair, but let's give it a try.

Good job!

This is a common place for intake manifolds to fail.

Look in the shop manual. You will find the description of an exhaust passage that is cast into the base of the intake manifold. It is there to create a hot spot at the bottom of the manifold where the intake air flows down, to improve cold weather performance. The passage is only supposed to have a lot of exhaust gases flowing through it then the heat riser flapper valve (in the exhaust manifold on the passenger side) is closed on a cold engine. Once that flapper opens, the majority of the exhaust gases are supposed to go through the exhaust pipes.