Choke Mechaninsm Choking...

[MercuryMarc]

My car runs great after tune-ups but then it gets rough after a while-
eventually stalls like crazy after cold starts. I bought a replacement
1 bbl carb for my 1969 200 six and tried to install it - it would crank
well and fire a little but would not start. So I put back on the carb I
had just removed, and noted that the choke tube was very sooty. I
cleaned out the choke tube and scraped some soot from the inlet hole on
the choke itself. I then jammed the other end of the choke tube
securely back into the manifold. Now the car purrs like a kitten!

I wonder if my problem could have been caused by a dirty choke tube or
mechanism.

Any thoughts?

Marc in SF
63 Comet Custom Ragtop, 69 200 six/C4 tranny
Pretronix ingniton/coil
http://mercurycomet.net

 

[addo]

There might be a hole burned in the stove pipe. Soot suggests it.

 

[MercuryMarc]

Thanks for the stovepipe tip- I have had some trouble getting it to sit tightly into the manifold - once I heard a sound (like a machine gun) beneath my hood and the tube had popped out of the hole in the manifold. Any way to seal it snugly?

Thanks-
Marc in SF
63 Comet Ragtop with 69 200 six/C4 tranny
http://mercurycomet.net

 

[Anonymous]

What do you mean by stovepipe? Are you talking about the heat riser tube that comes up from the exhaust manifold?

-Dan in Atlanta

 

[MercuryMarc]

Yes - the stovepipe also is called the heat riser or choke tubing I believe. Anyway, I picked up a spary can of carb cleaner and a bottle of fuel/carb cleaner additive, so hopefully the car will run much better after I clean the carb, choke, and heat riser.

Marc

 

[addo]

It's supposed to be a closed loop, but can burn out, letting exhaust gases into the carb. If the manifold section is sound but comes loose, perhaps some kind of "pinning" with brazing spelter and manifold putty could help. That's about the best guess I can muster.

Regards, Adam.

 

[MercuryMarc]

I may have this all wrong- are exhaust gasses supposed to be routed into the choke? My heat riser/choke tube/stovepipe is a hollow tube (like a straw) with exhaust gasses piped into the choke. Is the end that fits into the choke part of the carb supposed to be a closed end of the tube?

I am confused. Sorry for all the questions and I appreciate all the help from the forum.

Marc in SF
63 Comet Ragtop, 69 200 ci six/C4 tranny
http://mercurycomet.net

 

[Anonymous]

No, the exhaust gases themselves should not flow through the choke. The way the heat riser tube works is that air going through the choke is first warmed by passing through the exhaust manifold. In the exhaust manifold the exhaust gasses pass from right to left, looking at the engine from the front, and then enter your exhaust pipes and exit the vehicle. The heat riser tube air passes from underneath the exhaust manifold up through the manifold into the heat riser tube and then into the choke mechanism. The exhaust heats the exhaust manifold and thus when the air enters the exhaust manifold from underneath it is warmed up before it gets to the choke. The heat riser tube runs from the a hole made for it between cylinders 3 & 4 in the exhaust manifold to the choke.

Since exhaust gases are not supposed to enter the choke, if you see soot then there is an exhaust leak and you likely have a busted manifold. If you hear a bab-bap-bap exhaust sound only when you remove the heat riser tube from the hole then you definitely have a busted exhaust manifold.

I recently had the same situation and I ended up switching to headers. I tried using JB Weld to seal off the choke tube but it went away under the extreme heat from the exhaust gas. You could try the 2500 F epoxy from Aremco if you want, it might work. You can buy a new exhaust manifold for about $100 before shipping, If you want them powder coated that is another $100. I for headers from Clifford for $327 shipped and paid another $30 for some high temperature epoxy to affix my port divider in the head. I like the upgrade and for the first time in a long tim I don't have an exhaust leak.

-Dan in Atlanta

 

[MercuryMarc]

Well- you guys are right, as usual. I checked out my choke tube carefully and it is sooty at the junction at the exhaust manifold. The tube passing through the exhaust manifold (is that the stove pipe?) must be broken, inside the manifold itself, alllowing exhaust gasses into my choke (no wonder it is choking!). I think I should just go ahead and replace the manifold. Thanks again.

Marc in SF
63 Comet Ragtop, 69 200 ci/C4 tranny
http://mercurycomet.net

 

[addo]

Depends how much a stickler you are. Firstly in SF you won't ever need a lot of choke compared to other places. Secondly, if you can seal the hole for the stove pipe, just adapt a copper loop of tubing from the carb, wrapped around the manifold and back into the choke housing. Even properly flared for the connections, this could well turn out cheaper than a new manifold, and without breaking that seal against the head.

 

[MercuryMarc]

I like the idea of the "external stove pipe" using tubing. That will give me time to consider a new exhaust manifold and maybe paint/coat it prior to installation.

Since I think I have a hloe in the inside portion of the heat riser, I'd have to seal the manifold tube openings on both the upper and lower sides of the manifold, correct?

Many thanks-
Marc in SF
63 Comet Convert, 69 200 ci six/C4 Tranny
http://mercurycomet.net

 

[ludwig]

I got a salvage header for 90 bucks her in the SFValley. The divider between 3 and 4 exhuast ports is hollow and the wall cracked and mushroomed inward, leaving a hole to the heat riser.
I tapped the heat riser holes and screwed 2 short bolts in it to plug it top and bottom. Be careful though because the metal is brittle and punky from age and heat.
I got an aftermarket heat riser which is just a little arch top, sheet metal fitting that looks like a miniature quonset hut. It clamps to the manifold pipe and a tube runs from there to the choke heat inlet. It is a standard item at speed shops or can be ordered. I got two, just in case. The best part is that you will still need something like this for your tuned headers since they are only pipe and have no other fittings. Just hook it up on the new pipe too.

 

[addo]

To seal the old hole, you might get away with a bolt/nut and some soft copper washers. A little of one of the manifold repair putties (POR Fireseal 2000 is probably one of the more advertised) under the sealing surfaces would be the finishing touch. I'm trying to present a solution that doesn't require the manifold off at the present, even for a repair.

Regards, Adam.

 

[Anonymous]

This is common in metro areas where MTBE was used in the 1980-99 timeframe in the gas. It corrodes away the tube inside the exhaust manifold that is supposed to allow cool, filtered air from the air cleaner to run thru a heated tube (inside the manifold) and into the carb's choke housing.

I fixed up my Fairmont by wrapping 6 turns of soft 1/4" copper tubing around the exhaust manifold (outside), right where it joins the exhaust pipe. Then I covered the tubing with some heat wrap to help speed up the transfer of heat. This all fits underneath the warm-air "stove" that heats up the air on cold mornings for the air filter.

The result is a choke that stays on a little longer than the original one did, because the incoming choke air is not quite as warm, but mine also has the electric choke, so it only has to reach 60 degrees for the electric part to start working and fully open the choke.

If you do not have the electric assist, the tube-wrap method will require considerably more heat ransfer to get good choke opening response. In that case, consider fabricating and mounting a small sheet metal (stainless) cover over the spot inside the exhaust manifold where the old heater coil USED to be, then seal the edges with high-temp epoxy (Mustang Six knows the right stuff). Then it will work better, more like stock.

The last option is to install a manual choke, which, in the end, saves the most gas..

 

[MercuryMarc]

Thanks for all the great suggestions. I found some manifold repair filler at NAPA and plugged the top hole of the exhaust manifold stove pipe. It looks like the lower opening has already been plugged with a bolt! So I think that a previous owner had the same problem but just plugged the bottom and routed the exhaust into the choke.
For now I have strapped an aluminum tube to the exhaust mainold (about an 8 inch section from the area below the carb up to the front of the engine). Still runs rough at the start though. I wonder if the choke is really messed up with soot. I did spray carb cleaner into it and black stuff drained out.

Marc

 

[ludwig]

Take the black cap off, making sure you remember which way it is mounted, and clean up all that stuff with a spray cleaner and make sure the pull off lever and everything are working properly. Then put it back together again.

 

[MercuryMarc]

Yikes-
The inside of the choke mechanism looked like a dirty ashtray! I removed the front choke plate and gasket and exposed the choke coil spring chamber. The entire mechanism was entirely filled with soot. I sprayed it with carb cleaner and scrubbed it with a toothbush, and removed all the soot. I have it all back together (hopefully in the correct position). I think this may have been a big part of my cold start problem - I think the choke spring was packed with crud and the choke plate neither fully opened nor closed. Looks much more mobile now.
I will keep you posted - thanks again for the great advice!
Marc in SF
63 Comet Ragtop,, 69 200 six/C4 tranny, Pertronix ignition/Flame thrower coil, aluminum racing radiatior, temperature triggered electric fan, external tranny cooler, Fuzzy dice (Orange)
http://mercurycomet.net