1956 312 Y block heat riser

[Reg M]

I have a 56 T-Bird with a 312 Y block engine. On cold starts it spews a considerable amount of black smoke (enough to make a mess of my garage floor) On another forum it was suggested the heat riser is probably the culprit so I plan to replace it with a spacer which is readily available online. Here is my problem: it makes sense to me that there would be a gasket on each side of the spacer. I have also been advised the two gaskets are different but I have only been able to find one gasket. Can anyone shed any light on identifying the two gaskets? ie; part numbers etc? I am in Florida for another 3 weeks and want to get the parts to take home to Canada at the end of this month. Since the car is 2300 miles away I can't take it apart to see what I need. Thanks for any forthcoming info. By the way, I am new to the forum and this is my first post and in searching the forum for an answer to my question I saw a lot of good info indicating a high degree of knowledge and was also impressed by the lack of uncivilized responses which tend to be the norm on some forums.

 

[KULTULZ]

... it makes sense to me that there would be a gasket on each side of the spacer. I have also been advised the two gaskets are different but I have only been able to find one gasket. Can anyone shed any light on identifying the two gaskets? ie; part numbers etc?

It should take the same gasket - ORIGINAL FORD PART NUMBER C1SZ 9450-A (upper and lower)

 

[scicala]

Somebody explain to me how a heat riser causes black smoke.
Sounds confusing to me.

Sal

 

[Reg M]

I just assumed it had something to do with the exhaust being blocked due to the heat riser being frozen in the closed position. I know from experience that small marine diesels will discharge black smoke when carbon builds up on the exhaust elbow where the cooling water enters the exhaust but I don't know if a blockage has the same effect on a gas engine - I'm just going on what I was told by a member of another forum. I would really appreciate any info anybody can provide as to the cause of the black smoke. I just bought the car last Aug and have not had a chance to drive it very much due to knee surgery just after the purchase. I had a mechanic do a tune up on it and it seems to run great, lots of power, no sluggishness etc and the black smoke (more like soot actually) only happens on a cold start. There is one problem and I think that can be attributed to the heat riser and that is on a cold start I have to pump the gas pedal about 6 times before doing what the manual says and holding it down for a second then releasing it. If I don't pump the pedal it does not start anywhere as quick. I'm thinking the heat riser is stuck open rather than closed? I tend to agree with you that this is not the cause of the black soot.

 

[KULTULZ]

I had a mechanic do a tune up on it and it seems to run great, lots of power, no sluggishness etc and the black smoke (more like soot actually) only happens on a cold start. There is one problem and I think that can be attributed to the heat riser and that is on a cold start I have to pump the gas pedal about 6 times before doing what the manual says and holding it down for a second then releasing it. If I don't pump the pedal it does not start anywhere as quick.

It sounds more like the choke is not operating properly and when you pump the gas and she finally fires, carbon build-up blows. Is it at the tail pipes or under the hood? Do you see soot around the riser valve?

A properly adjusted automatic choke requires one initial full pedal depression and then take your foot away from it. The choke should do all the work for you.

You also may have engine heat soak after shutdown which will empty the fuel bowl causing hard starting. You pump it several times and gasoline falls out of suspension flooding the intake plenum and after a while, extreme carbon buildup.

 

[Reg M]

Good points. I did check to see if the choke butterfly in the carb is actually closed after pushing down the pedal for a second and it is closed so I'm thinking that eliminates the choke. When I get home I will check to see if the bowl is full prior to starting it. In answer to your question there is no sign of soot under the hood, it is all at the tail pipes. If there was any under the hood it would be easy to see as everything is in showroom condition under there. I did order the spacer to replace the heat riser as well as the two gaskets. Since I will only be running it in the warmer months I really don't need the heat riser and I'm pretty sure if the heat riser ins't a problem now it probably will be at some point in time.

 

[Reg M]

It should take the same gasket - ORIGINAL FORD PART NUMBER C1SZ 9450-A (upper and lower)

Thanks for that - I have ordered the spacer and two gaskets.

 

[dmsfrr]

Somebody explain to me how a heat riser causes black smoke.
Sounds confusing to me.

Sal

When the heat riser valve is closed the exhaust from that side of the engine is mostly forced thru the intake manifold crossover and out thru just one exhaust pipe on the other side of the engine. The 'extra' pressure blows out any soot or moisture buildup in the intake manifold crossover and that exhaust pipe.

I have a 56 T-Bird with a 312 Y block engine. On cold starts it spews a considerable amount of black smoke (enough to make a mess of my garage floor) ...

Black smoke and excess soot in the exhaust system is a problem that should be corrected with some good carburetor repair work and adjustment.
.

 

[scicala]

When the heat riser valve is closed the exhaust from that side of the engine is mostly forced thru the intake manifold crossover and out thru just one exhaust pipe on the other side of the engine. The 'extra' pressure blows out any soot or moisture buildup in the intake manifold crossover and that exhaust pipe.

Black smoke and excess soot in the exhaust system is a problem that should be corrected with some good carburetor repair work and adjustment.
.

I agree, that soot with condensation can blow out on a cold start, but that's not black smoke. Only thing that causes black smoke is too much fuel. Maybe an issue with the choke being set too tight or gummed up from a corroded choke hot air tube.

Sal

 

[Reg M]

When the heat riser valve is closed the exhaust from that side of the engine is mostly forced thru the intake manifold crossover and out thru just one exhaust pipe on the other side of the engine. The 'extra' pressure blows out any soot or moisture buildup in the intake manifold crossover and that exhaust pipe.

Black smoke and excess soot in the exhaust system is a problem that should be corrected with some good carburetor repair work and adjustment.
.

But I am getting black soot coming out both tailpipes, not just the left one. And it is about the same amount of soot on both sides. Perhaps if I put some of that carburetor cleaning stuff through it it may solve the problem?

 

[miker98038]

If you’re getting smoke out of both tail pipes, the exhaust heat riser isn’t stuck closed. Open maybe. On a cold engine you should be able to reach down and move it against the spring pressure.

I’d take another look at the choke adjustment. Not all mechanics are familiar with the peculiarities of the Holley teapot. Sal is one of the known experts on them.

 

[Reg M]

If you’re getting smoke out of both tail pipes, the exhaust heat riser isn’t stuck closed. Open maybe. On a cold engine you should be able to reach down and move it against the spring pressure.

I’d take another look at the choke adjustment. Not all mechanics are familiar with the peculiarities of the Holley teapot. Sal is one of the known experts on them.

Is Sal someone who is a member of this forum? If so, I am hoping he will jump in here. I'm having a hard time understanding how the choke can be out of adjustment when I actually removed the breather, pushed the pedal to the floor, held it for a second and released it, then, before turning the key I looked at the choke butterfly in the carburetor and saw that it was fully closed. I would think that, if it was out of adjustment, it would not be closed.

 

[dmsfrr]

The choke mechanism on the carburetor can be adjusted too rich or sticking closed or partially closed.

The main jets in the carb can also be too rich for your driving conditions or the carb can have other internal problems making the fuel/air mixture too rich, causing black soot and black smoke.
If the (original) hot air tube isn't functioning correctly the choke may not be releasing at all.

... Only thing that causes black smoke is too much fuel. Maybe an issue with the choke being set too tight or gummed up from a corroded choke hot air tube.
Sal

Photo example of an exhaust corroded choke mechanism.
.

 

[Reg M]

OK, seems there are a few things, seems nothing is ever straight forward. When I get back home I guess the first thing I need to do is take off the breather and see if the choke opens as the car warms up. If it doesn't then I need to check out the choke heat pipe. I'll also put a container of carburetor cleaner through it. Is there any particular procedure to check the choke heat pipe? I hope it doesn't involve removing the intake manifold.

 

[Reg M]

I read elsewhere online that worn valve guides could cause black smoke on a cold start but I don't think that could be the problem here as the whole drive train was rebuilt just a few years ago when the complete off frame resto was done. There is just not that many miles on it since the resto.

 

[dmsfrr]

I read elsewhere online that worn valve guides could cause black smoke on a cold start but I don't think that could be the problem here as the whole drive train was rebuilt just a few years ago when the complete off frame resto was done. There is just not that many miles on it since the resto.

Worn valve guides would usually cause blue/white smoke on startup, from oil getting in around the valve stems & their seals. Since you aren't getting that it's likely not a problem.

 

[miker98038]

Sorry, scicala in the above post is Sal. It’s been 20+ years since I had an early Holley. But auto chokes have pull off, fast idle, etc. settings and adjustments. It’s not just as simple as them going closed when cold and the throttle is pressed. If it’s running good warm, there’s a solution there. Base line settings might be a little off in Florida, you don’t have really cold weather.

 

[oldave57]

I really think the situation you are describing is fairly normal, depending on the ambient temperature and relative humidity. Both my current 57 with 312 and my previous 57 with 292 exhibited similar "black soot and water vapor" when the engine is started cold and left to idle a bit. Both these cars had dual exhausts with the heat riser blocked fully open. The discharge disappears after the engine and exhaust has warmed up. Moisture is a fairly normal by-product on cold start up and the "black suit" is most likely just the interior of the exhaust and mufflers being "washed out" with the moisture in the exhaust. If you are not losing coolant or engine oil and your engine runs well with no black or blue exhaust when warm, you are probably ok.

 

[KULTULZ]

Well, just to stir the pot and anger a few this morning ...

Excessive carbon buildup indicates an overly rich fuel curve, whether contributed to the choke system or fuel mixture (or weak IGN SYS). True the water (humidity) from combustion is going to carry the accumulated carbon out of the exhaust system, but that degree of carbon should not be there to start with, especially if it marks the garage floor.

Can you imagine the amount of carbons in the combustion chambers? Did the TECH that performed the tune-up mention the condition of the plugs that were removed? Were the correct heat range plugs installed? Is the ignition system still LOAD-O-MATIC?

There is a problem here. And the heat riser needs to be replaced/removed if not functioning properly.

 

[oldave57]

Well, just to stir the pot and anger a few this morning ...

Kultulz: No worries on the post. I always find your posts full of good information. I just thought some observations of similar symptoms sometimes come in handy.

On my two cars, the cold start up with moisture and some soot coming from the tailpipes (both sides since I have the heat risers blocked open) seem to happen only if I leave the car idled for an extended period on cold start and particularly if I rev the engine a bit. There is never any black smoke in my case, so if the OP has a lot of black smoke in addition to the water/soot, his case is not nearly the same. Another thing I should have mentioned is that both cars had a manual choke and I hardly ever need to choke to start during warmer weather.

Good luck to the OP with diagnosing and clearing up the issue. It would be great if you could post a follow-up with your solution.