The Stovebolt Site Forums The Shop Area Engine Shop overactive heat riser

I have a '58 Apache 1/2 ton with a bone stock 283. After the engine warms up thoroughly the truck will not run smoothly at a constant cruising speed. Decelerating, and accelerating will smooth it out, but once it tries to run at a constant speed the truck bucks violently. It will not idle smoothly once it reaches running temp.
It has new points, plugs, condensor, rotor, distributor cap.
I've had the original 2-barrel rebuilt. I've had a remanufactured 2-barrel carter, and a remanufactured Rochester on it and it acts the same way
with all three......
It 's also hard to start, after shutting it off for a few minutes while at running temp. When I look down the throat of the carb, I can see fuel boiling into the carb. I believe the exhaust crossover in the intake manifold is overactive. I thought the butterfly was stuck closed, so I pulled the exhaust flange, and the rod is still there, but the butterfly is altogether gone.



I'm thinking that when I put the intake manifold on I may have left off a baffle, or the intake gasket didn't have a baffle, or the baffle rusted away in the 15 years since I built the engine. It's been doing this for a few years.

Have any of you guys had this problem before?

Thanks in advance guys.

-kevin

the hard starting when hot can be the starter getting too hot, although it sounds like the float bowl may be boiling dry ... the only baffle on the manifold is a plate on the underside held by small push in rivets - not sure that would have an effect on heat, but being right under the carb it might - don't have one handy to look at ... more likely the missing butterfly is allowing too much exhaust thru the manifold, I'd fix that for starters

Bill

Thanks for the input, and sorry for posting in the wrong place. I did search for past posts on this subject to no avail.

I have a new heat riser on order, but it can't be diverting the exhaust through the intake if it is totally missing the butterfly. It only diverts when partially or fully closed.

The starter cranks over just as quickly when at running temp.
The float valve opens when the bowl boils over and replentishes the fuel until residual pressure is relieved in the line between the fuel pump and the carb. This floods the engine, thus the hard start when at running temp. At least this is what I believe is causing the symptom. Just trying to get to the cause.
I can't figure out why the intake gets so intensely hot at the bypass. I fully expected the butterfly to be stuck in a closed position, not entirely missing. The paint burned off that area long ago, and maybe that's normal. I built the engine so many years ago, but maybe I left out a restricter plate in the intake, or maybe it eroded over time. Since this issue only reared it's ugly head in the last few years.
Thanks again for the suggestions.

I assume you're using the original Rochester 2-BBL carburetor? Pull the carb, and see if you've got an exhaust leak where the heat riser passage goes around the carburetor base. Those older Rochesters used to be notorious for burning away part of the cast iron carb base, and sucking up raw exhaust gas from the heat riser passage, which actually ran exhaust gas against the base of the carb under a thin stainless steel isolation plate. The symptoms were exactly what you're describing- - -rough idle, and a very hot intake manifold heat riser passage from the constant flow of exhaust gas pulled in by manifold vacuum.
Jerry

Thanks much.... I never would have thought of that.
Mama always said, it's not what you know, it's who you know.

A bit of trivia....
Hot Rod Lincoln was recorded by Johnny Bond in response to a previous song called Hot Rod Race. Hence the opening line of the song.

"Me and that Mercury was neck and neck!" Good song! Arkie Shebley recorded the original version of Hot Rod Race, including some very non-PC language in places.

The original Hot Rod Lincoln was a real car, a stretched-frame Model A coupe with a Lincoln Zephyr V-12 in it. There's a website dedicated to it, and the guy who sang the song and used the car as part of his road tour.
Jerry

KD, does the motor start up fine from cold with that butterfly burned off? My second riser is again rusted immobile, so when I get the money for a new exhaust system I want to just do without it. I'm not even sure if mine is rusted closed or open, though the truck runs fine.

Yes it runs normally until it warms up. I have read that the butterfly remains normally closed, so your's should be wide open.

It wasn't leaking there, but I read somewhere that the hot rodders used to shove wads of aluminum foil into the small ports beneath the carb. So I rolled up a piece, and blocked the straight passage under the carb. It seems to warm up normally, and no more bucking. Even in overdrive.
It's not a proper fix, but it's going to get me better mileage, and it's a great feeling having corrected this after dealing with it for so long.
Thanks for the advice guys!