When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
my L36 has a disabled heat riser and apparently blocked heat riser passages, as suspected by IR gun measurements. Intake stays at 80F for several minutes after startup and slow idle, and is no warmer at the choke coil base than elsewhere except the water neck. Thermostat seems to open at 160F. I've decided to go without the heat riser and leave the passages blocked to avoid heat issues.
Tradeoff is that the choke doesn't open fully, as the intake stays so cool so long. With choke connected, fast idle cam is engaged for a prolonged time, and the choke blade is still partially closed at 160 deg water temp. So I've disconnected the choke, but now warmup is tedious as the fast idle cam is deactivated with no choke. The choke rod length is to stock specs; 1.5 rod diameters above the hole in the linkage with blade held closed, rod pulled up.
Took out the choke coil. It appears to be the standard aftermarket replacement, looks new and shiny, stamped with a 7129 on the coil, 25 on the base.
Put it in water at varying temperatures. As you can see from the pics, the loop in the coil is well above the stop at 40F and 70F, which is the way it appears in Zip and other catalog pics. At 100F it's part way down, at 150F it's close to the bottom of the well.
This would seem as expected in a system with a functioning heat riser apparatus.
But for my application, I'd like it to reach full open at about 90F. When I saw the brass screw head holding the coil I had brief hope that it was adjustable. But it doesn't turn at all with moderate force. You can see I dinged it a bit.
Probably will try bending the rod so it's shorter and see if that'll do what I want, but if the coil could be shortened, it'd give a wider range of travel as the 40-70F range is hitting the open stop.
Has anybody worked with these coils to modify them? Can a new loop be easily formed with pliers? Is that done at a high temp? I'm sure it's possible to ruin a few trying.
I know I can get an electric choke and may eventually go that way. I won't go for a manual choke.
Last edited by red zed; Apr 8, 2022 at 12:52 PM.
Reason: added text
I've never messed with one of those choke coils, but for guys that want to block the heat riser I suggest just blocking the drivers side. The passage is still completely blocked, but the dead end passage from the pass. side to the block allows some exhaust gas to migrate up and might allow normal choke operation...certainly better than what you now have.
The heat riser may have been blocked with shims. Check carefully. Maybe you can pull one out. If the gasket has built in blocks then I think your best bet is to bit the bullet, remove the manifold and install conventional gaskets with open heat riser passages. Get some thin SS stock, no more than 10 thou, and fabricate a shim to install on the driver' side. Leave a tab on it so if it doesn't work out you can loosen the manifold bolts and pull out the shim with a pair of needle nose pliers.
can't tell at a glance about shims. Engine was recently painted before I took on stewardship.
Going to stick with the blocked passages. Classic tradeoff dilemma: hot rod maximum peak performance vs convenience/emissions. Duke is the one with the halo on this round!
Last edited by red zed; Apr 8, 2022 at 02:12 PM.
Reason: add text
I hate them, but about all you can do is put an electric choke on it and swap the thermostat for a 180 degree F . I have to run an electric choke on the 68RS as it has an Edlebrock C3B intake and there are no divorced choke provisions.
Just $.02 that the government hasn't stolen.
here's with the choke rod shortened 7/16" compared with stock. At 67F at the coil housing, choke is partially closed. At 100F, it's fully open. I'll see how that works. Still may need it a bit shorter as that part of the intake takes quite awhile to reach 100F even when ambient is 75F due to the cooling effect of the fuel vapor.
Amazing to see how much heat these ol' lumps of iron retain. Went for a short drive yesterday afternoon to heat it up. Immediately after shutoff, intake was 90F centrally, 160F at the water crossover. Temps slowly became uniform between different parts of the intake and heads. Four hours later was still 120F, six hours 110F, seven hours 100F. This morning still 67F with ambient 45F!
Bubba, why are you trying to re-engineer something that works so well, (just kidding about the Bubba part) :-)
Plug the hot slot just under the carburetor and use a functioning heat riser and in warm weather just wire it open. When the weather cools un-wire it, the heat is your friend in a cast iron intake manifold, and is just not there to make the choke open as heat helps vaporize the fuel mixture . The GM engineers knew what they were doing when these cars were designed, but I will say the ethonal fuel today can present problems with excess heat.
You will notice a huge difference in intake temps with just wiring the valve open in hot weather and still allow enough heat to rise and allow a functioning choke although it will open slower but you can use the factory adjustment on the choke coil rod. I am 100% with blocking the hot slot under the carburetor, on my 67 300hp cast iron intake I used 1/4" allen head plugs threaded in snug when flat with the manifold surface and still used the factory gasket sandwich.
I would also try to find non ethonal gas in your area but that may prove to be difficult.
So now I know more, which, admittedly, can be a dangerous situation. However, in keeping with my Bubba-ist philosophy, I'm gonna stick with what I started with for now, which is the defrocked heat riser, heat passages previously blocked at the intake gasket, with the only new mod being the 7/16" shortened choke rod. It worked well yesterday with a 50F startup and was able to come completely off the fast idle cam after three miles. Summer is coming, and there's no non-EtOH gasoline in these parts.
choke coil performance
