Pulled carb......Carbon Carbon Carbon everywhere..

I pulled the AFB off my 65 to rebuild and noticed a few things. The heat passages in the intake were completely clogged with carbon. The aluminum heat shield above the gasket was actually burned through directly above the holes in the intake manifold. Inside the carb the choke housing was also plugged...but I hear that is pretty common. I can see that the car still have a heat riser valve on the passenger side, but have no idea if it is operational. I am in the process of completely tearing down the motor for cleaning, detail and just general maint and just broke all the exhaust manifold bolts lose(didn't break a single one thank god). Will pull the manifolds in a day or two and have a look at the valve.

What should I look for? Is it safe to assume that if the flapper is stuck closed or even not 100% open, this will push exhaust back up into the carb at all times?

I pulled the AFB off my 65 to rebuild and noticed a few things. The heat passages in the intake were completely clogged with carbon. The aluminum heat shield above the gasket was actually burned through directly above the holes in the intake manifold. Inside the carb the choke housing was also plugged...but I hear that is pretty common. I can see that the car still have a heat riser valve on the passenger side, but have no idea if it is operational. I am in the process of completely tearing down the motor for cleaning, detail and just general maint and just broke all the exhaust manifold bolts lose(didn't break a single one thank god). Will pull the manifolds in a day or two and have a look at the valve.

What should I look for? Is it safe to assume that if the flapper is stuck closed or even not 100% open, this will push exhaust back up into the carb at all times?

Yes, the function of the heat riser when closed is to force hot exhaust gas thru the intake manifold and out the exhaust on the side opposite the heat riser. If the valve is stuck closed this could deposit extra carbon with time.

I would also take a real good look at the carb as a rich running situation will also contribute to excessive carbon buildup.

Good luck,

Tom Mooney

This is my 2 cents worth from the viewpoint of being in the car repair business since 1975. The choke that uses a hot air tube coming

off the exhaust manifold was an engineering faux pas and is nothing but trouble to maintain. If it was my car I would remove the hot air choke tube, leave the ports in your intake clogged and install an electric choke kit on the carburetor. One thing to keep in mind is that when they put

exhaust ports under the carb back in the 60's people were not running alcohol laced fuel which has a different vaporization rate. GM realized it was

a bad design and quit cooking the carb with exhaust in 1968. I've got an electric choke on my Riviera that was installed by the original owner and

I was thrilled to discover that had already been done to my car. As for the heat riser valve, I would do away with it completely. I haven't had one on my GTO since 1974 and it runs great cold. Since you live in Tampa ,Florida, the last thing you need on your car is a heat riser that causes problems. It might make sense to have one in Fargo, North Dakota but not Florida.

If you are concerned about appearances at shows, leave the choke heat tube on but install a plug in the end of it to block flow.

Sure enough...the heat riser valve was seized and about 80% shut. I was able to break it free with a torch and open the valve. It is still tight as hell so will prob stay open for the next 50 years. Or I just may invite mr grinder to the party and remove the flap completely.

I know what you mean about electric chokes. Used one on my 70 GS and it worked just fine here in FL. I'm trying to go for the original look on the riv so will have to see what to do with the choke. Being that the heat riser will never close I should not see any exhaust under the carb. I rebuilt the afb so the vac source for the choke should be working. I will hook it all up and see how well it works.

Amazing that with the heat riser 80% shut the car still ran pretty well before I took it all apart.

Unless you block off the passages in the manifold or in the head or on the block itself, you'll still get some heat to the base of the carb. Contact Russ Martin in Grass Valley, CA to find out the proper way / place to block off that exhaust heat.

Ed

Ed, I dont want to block of the heat to the head and manifold as I think that would cause issues. Filling the holes under the carb is another matter. I would like to do that and stop the exhaust from cuming up directly under the AFB. Have heard of folks using JB weld to do this and apparently it holds up to 600F and last forever. If I get them holes filled, I am guessing I wont need that heat shield and can just run a regular gasket?

Since you live in Tampa, you MAY get by with the electric choke (and you may not).

Electric chokes work better with cars with manual transmissions where you can slip the clutch if necessary in city traffic until the engine warms.

We have replaced numerous electric chokes WITH MANUAL CHOKES for folks with auto transmissions and A/M intakes with no provisions for the heat choke. Why? The electric choke is timed; it doesn't care about temperature, it goes off in a certain time. Older cars with auto transmissions get about 3 blocks from the house, stop at a stop sign, stall, and will NOT refire for about 30 minutes. So you sit in the middle of the street with looking sheepish because your "old junker" won't start, or call for a tow truck.

Again, the fact you live in Tampa may save you for local driving, just don't consider touring the country with the car.

Jon.

I am going to use the factory setup on this car. But I had an electric choke on a 70 GS with no issues in FL. If you let the car warm up before driving the 3 blocks, I dont see any reason why it would stall. And if it does, and will not re-fire, I would think there are other issues.

What are your thoughts on plugging the holes under the carb?

If you're going to plug the holes, plug them at the source. No need to let that hot air and corrosive gas up into any place it's not going to be used. Russ Martin will sell you the proper plugs for doing this. He, Tom Telesco, and Carmen Faso are the gurus when it comes to building / rebuilding the nailhead engines.

http://nailheadbuick.com/

Ed

I am going to use the factory setup on this car. But I had an electric choke on a 70 GS with no issues in FL. If you let the car warm up before driving the 3 blocks, I dont see any reason why it would stall. And if it does, and will not re-fire, I would think there are other issues.

What are your thoughts on plugging the holes under the carb?

You said the magic words "let the car warm up before driving".

If you warm the engine for several minutes, then you wouldn't have issues. Most simply get in the car, start it, and go......and stall.

As far as plugging the holes under the carb, again, since you live in Florida, you would probably get away with it.

On the other hand, some fairly intelligent graduate engineers designed the system. And it is very easy to cut the stainless baffle IF one is not available.

To cut the baffle:

Acquire a piece of sheet stainless about 0.030 (often a junk sink from a restaurant can be found at a salvage store for a little of nothing).

Acquire a couple of pieces of 3/8 inch plywood about 1 foot square.

Put the piece of stainless between the two pieces of plywood.

Bolt the two pieces of plywood together with bolts around the perimeter of the square

Draw the outline of the baffle on the top piece of plywood, and cut it out, using hole saws, sabre saws, what ever. If you use a sabre saw, expect to break a bit or two; the stainless is HARD!

The reason for using the plywood is the plywood will keep the stainless flat.

By the way, I learned the lesson of the stalling with the electric choke on my wife's car!

Jon.

Yes Jon that is a fact. Driving off without a warmup even here in FL would not be good. Those AFB shields are available.

Yes Jon that is a fact. Driving off without a warmup even here in FL would not be good. Those AFB shields are available.

I am certainly glad someone made this shield available. Years ago, I documented some 180 different shields (not all for Carter), and only a handful were available. That is when I devised the method described above. It works! But if one is available, certainly much easier than trying to make one.

Jon.

You said the magic words "let the car warm up before driving".

If you warm the engine for several minutes, then you wouldn't have issues. Most simply get in the car, start it, and go......and stall.

As far as plugging the holes under the carb, again, since you live in Florida, you would probably get away with it.

On the other hand, some fairly intelligent graduate engineers designed the system. And it is very easy to cut the stainless baffle IF one is not available.

To cut the baffle:

Acquire a piece of sheet stainless about 0.030 (often a junk sink from a restaurant can be found at a salvage store for a little of nothing).

Acquire a couple of pieces of 3/8 inch plywood about 1 foot square.

Put the piece of stainless between the two pieces of plywood.

Bolt the two pieces of plywood together with bolts around the perimeter of the square

Draw the outline of the baffle on the top piece of plywood, and cut it out, using hole saws, sabre saws, what ever. If you use a sabre saw, expect to break a bit or two; the stainless is HARD!

The reason for using the plywood is the plywood will keep the stainless flat.

By the way, I learned the lesson of the stalling with the electric choke on my wife's car!

Jon.

My Riviera has an electric choke and I just get in it and drive. I don't warm it up even 10 seconds....no problems in Winter or Summer. If

your car is stalling, the electric choke is not the reason...they work fine.