I am doing a restoration on a 1955 Cadillac Eldorado convertible with a 331 cu. in. motor equipped with two Rochester 4GC carbs. Someone rebuilt the motor a few years ago and removed the choke stove pipes. I have an original Cadillac shop manual for the car but there is no picture showing the choke stove connected to the carburetors. However, the manual clearly states that exhaust heat is used to open the chokes by applying vacuum to the bimetal housing and drawing heated air through a nipple on the bottom of the housing. My recollection is that GM used a couple of different choke stove systems in the 50?s and 60?s to provide heat to the bimetal contained in the choke housing. One was to take it directly off the exhaust manifold and the other was to extract it from the intake manifold crossover (Pontiac?s maybe?). I can?t tell by looking at the manifolds which system was used. There is no heat riser valve sandwiched between the exhaust manifold and exhaust pipe which could have suggested that hot gases were directed to the intake crossover (I can see the crossover runner in the intake manifold), but the exhaust system was replaced and it is possible that the shop didn?t replace the often troublesome heat riser valve. The presence of a crossover tells me that there probably should be a heat riser valve regardless of whether or not the chokes were tied to the crossover because its one of its functions was to warm the carburetor base during cold starts. Furthermore, unused fittings on the intake manifold read a strong vacuum as does the nipple on the bimetal housing (the source of vacuum to the housing are internal passages in the Rochester 4GC). The exhaust manifold on the right side (passenger side) has a block off plate situated on top just before the exit flange. It?s possible that the exhaust manifold was replaced with one from a manual choke / non-Eldorado that didn?t require a choke stove. I?m wondering if a choke stove fit into the area of the block-off plate in the exhaust manifold. I can?t find any pictures on the web or in the shop manual that would help. Does anyone recall how this car?s choke stove was configured?
For such an unusual question you’ll have more luck at a classic Caddy forum:
Thanks for the tip! What a relief - I thought everyone but me knew how the '55 Caddy Eldorado choke stove worked
I believe there was a flared metal tube that screwed on to the threaded nipple on the choke housing. at the other end of that tube was a flange that bolted over a recess in the intake manifold (Some older actually had the tube pass through the exaust manifold sort of like a heat exchanger) warm air from that recess went up the tube relaxing a bi-metal coil so that vacuum from the choke housings internal passage from the carb. body could actually “pull off” the choke. This vacuum will also pull warm air up the stove pipe.
Try these sites:
Good advice. All I know is the one on my 59 Pontiac was a real pain and never did work right. I should have done what the mechanic told me to do and put a manual choke on it and life would have been a lot simpler.
Thanks for all the links PvtPublic. They were great and added more information. I’ve searched the web for hours and hours and have read lots and lots but still can’t find a picture of the passenger side of an assembled 1955 Eldorado motor. As the saying goes, “a picture is worth a thousand words”. All the text at hobbyist sites, and even the Cadillac service manual, explains how the choke system functions, but none describe the location of the heat exchanger used for the choke stove. I found it interesting that one of your links stated that the heat riser in the '55 was only used for only one year and is very hard to find. That explains the absence of it in the car I am restoring. The shop that did the replacement exhaust system must have given up and deleted it. There isn’t a place on the intake where a flanged heat exchanger would fit. I’ve seen repro’s of that type and it definitely wouldn’t fit the '55 Caddy (mid-60’s Pontiac used them too). Based on your recollection that some cars used a heat exchanger in the exhaust manifold, I’m becoming increasingly convinced that one might have fit where the block-off plate is situated in this Caddy’s exhaust manifold. It would be pretty simple to fabricate one if that is the case, but it would lose its stock appearance. I’d still like to find a picture of the passenger side of the Elky motor so I can see the routing of the heat pipe to be sure. Thanks again for all your help!
I bet only ONE CARB had a working choke, and that the stove is in the passenger side exhaust manifold. The steel tube connecting the carb choke housing to the manifold stove would have been covered with fiberglass or asbestos insulation. There is a vacuum choke pull-off built into the back of the choke housing.
The cover on the choke stove was a tin stamping and they rusted out quickly, rendering the choke useless…You will have to fabricate a heavier one to replace the block-off plate someone made for yours, which does nothing…