heat risers FYI

Mike Stevens

PCS Member
FYI in case your coach has a heat riser. You may want to check on the availibility of a replacement soon. I have been looking for one for my 61 MM. One parts store told me they had been deleted by the maker. 2 other stores told me they are getting very hard to find. One lived up to that statement by not being able to get one even though they had a part number. The other has one ordered but is telling me it may take a few days to arrive. Any time I can not get an ordered part the next day I get worried. All of our local stores seem to be able to get an ordered part the next day.
Mike
 
They help the engine come up to temperature quicker in the winter. If yours is a warm weather car, then it isn't needed.
Some people cut the flapper out of the heat riser, and weld the external parts in place so it appears correct, even though it does nothing as a result of the modification. If the spring that holds the heat riser open should fail, then by design the heat riser should move to the open position, however, this isn't always the case.
If your car is running hot, and getting poor gas mileage, then check the heat riser. When the heat riser is closed, it directs the exhaust through the passages below the carburetor in the intake manifold to the left side of the engine, and out the left exhaust manifold. This warms the base of the carburetor, and helps to move the choke to the off position sooner.

 
Thanks for the explination on this. I wonder if thats whats wrong with my Eureka Pontiac. The car runs great until it gets real warm then it kinda runs like crap. The hotter it is the worse it is. I have had the carb gone through with no results. The funeral home before me must have had the same problem because it had a aftermarket carb on it when I got it.
 
If they installed a Holley with forward and rearward mounted float bowls the problem may be fuel percolation. Actually boiling the fuel out of the bowls.

One fix is blocked heat riser intake gaskets. But if you have a manifold heat choke you will have to either convert it to a manual or an electric choke.

One other fix would be to get some flat stock aluminum, street sign or a little thinner and using the carburetor base gasket as a template cut out to match the plenum opening. Then mount the insulator to the intake and trim as necessary to clear the various linkages and vacuum fittings on the manifold.
Remount with new carburetor base gaskets on both sides.

Also, make sure that none of your fuel lines touch any water hoses or the engine block. Heat transfer from these also will cause the fuel to boil.

While I'm no engineer, IMO the new fuel "blends" are more prone to vapor locking in carburetor equipped vehicles.

GM used to make shields for both Holley and Quadrajet carburetor equipped engines in the early 1970's in the original Chevrolet Power Book. They have been discontinued for at least twenty years though IIRC.
 
John,

The Pontiac you are having problems with. Is this the '85 in your profile?

If so, did anyone get creative and "modify" the computer system on this car or was the carburetor replaced with another one for a computer equipped car?

And is the eighth letter of the VIN a "L", a "H" or a "Y"?

You might check to see if your EGR valve is sticking open also.
 
Also, If memory serves me correctly there is no heat riser as such on a 1985.
They had what was called a EFE Valve. It was similar to a heat riser but instead of the bi-metallic spring on the heat riser the flapper valve was controlled via a vacuum diaphragm that mounted adjacent to the valve cover on the right side of the engine connected to the valve by a rod. The vacuum was controlled by a vacuum signal but from what component I have forgotten.

(Hey, it's been a LOOONG time since I needed parts for one of those!)
 
Yes its the 85 Pontiac. It has the chevy 305. it now has an edelbrock on it, when we put an oem carb on it it from a nice running 85 Caprice with same engine, made no difference, so put the edelbrock back on. I will just let my mechanic worry about it, he can figure anything out. Thanks for the possible causes though. It isnt bad enough that you cant drive it, it just runs rough and is hard to start when hot. I drove it to Flint a couple years ago like this. Dont know the vin without looking it up.
 
more heat riser info

My new heat riser arrived today. One parts store took the time to make phone calls after getting nowhere on the computer. They had a good number from the book under the counter.
The new item came from Canada. Are you reading this Darren?
Listed for 1956 through 1965. (Mine was ordered for a 65 429) 56-65 covers the Cadillac engines of 365, 390, and 429 cubic inches.
Here is the info from the side of the box.
Graywerks by atp
made in Canada
part no. 105007
heat riser
Canalizacion vertical del calo
Canalisation verticale de la c
bar code number 740993038481
42B appears in the lower right hand corner of this label
With shipping the part was less than $50. great deal I think.
If you coach has a heat riser you might want to consider getting one for the
shelf while they are availible. The cast iron does not hold up forever. My last one came off in 3 pieces. Probably from old age and heat.
My 61 M-M may get on the road by April yet!
Mike
 
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parts store

My riser came from the local KOI-Kentucky Ohio and Indiana parts store. This store was formerly Main Auto Parts. A Springfield institution since long before I knew cars had four wheels. It was merged with Springfield Tire and Battery. STB was started in Spingfield in 1923. They sold more than tires and batteries.
I would think with the box info in the other tag here that anyone should be able to track down a heat riser if needed. You have a good number for your parts house to cross reference.
When I need an exhaust gasket kit I order one for a 67 Eldorado. Works every time. The parts store computers seem to drop a year every new year. They still list 67 parts here. A lot of 61 and 62 stuff has been dropped as they think there is no demand I guess.
I fit the new part to my exhaust manifold this afternoon. It fits just fine.
If you find a part that covers several years of our cars don't be shy about posting it here for all to see.
Mike
 
back into the dumbing down of the world now. parts housed forces to go computer and the computer just drops good number because they are old. I though the advantage of the computer was it's storage capacity?? we still go to the book here also.
 
A word of warning

I had a horrible experience 2 years ago involving the heat riser on my '54 Eureka hearse. The engine had prevously been rebuilt and running great, then it suddenly started having white smoke come out the exhaust. Turns out BOTH heads had small cracks in them due to escessive heat being sent to the manifold because the heat riser counterweight was catching on a nearby bolt head and not fully opening. It was an expensive fix! Fortunately both heads welded fine and the problem has gone away. Make sure your heat riser is FULLY opening, and that "open" should be the default position if it's rusty and not freely pivoting.
 
If you are not going to be using the car in extremely cold weather, you are better off cutting the butterfly flap out of the valve, so no matter what position it is in, it can't do damage to the engine.
 
this was one of those things that compounded the problems we had driving the 68 home. the heat riser had rusted in a semi closed/open position. you could drive it around town all day and not notice anything. but with a steady run down the road the forcing of half the gases across the base of the carburetor quickly ate threw the improperly installed base gasket. of course this did not show till I slowed down for the first fill of the trip. Paul's fix makes sure it won't happened again. but now we have that cold run stumble that the heat riser use to take care of. better take some numbers down to the parts store and see about replacing it.
 
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