cruiser
Well-Known Member
Thanks, Rusty!
Poor hot idle caused by ethanol gas? Whaddya think?
- Thread starter cruiser
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Sho nuff.
slantsixdan
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The correct spacer for '73-up Holley 1920-1945-6145 carbs is a Walker G847.
slantsixdan
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Interesting. Top of the page you linked sez (added check marks are mine, to indicate applicable to the Slant-6):
WARNING
This product is not recommended for the use on:
1. Intakes with heat crossovers (√) and EGR values in the intake.
2. Straight 4-6-8 cylinder motors where the exhaust and intake overlap (√).
3. Some castiron intakes (√) have had an issue also
REASON: The polycore is an excellent insulation but it cannot take the extreme heat that the exhaust creates. This causes it to get soft or melt.
cruiser
Well-Known Member
Thanks, Dan.
I saw that but decided to try it nonetheless. It was cheap enough and it did help. I didn't notice that it got soft or melted and I ran it just shy of a year.
A trick that I have used in the past for carb heat insulation when you do not have room for a spacer or do not want to use a spacer:
- drill out the carb mounting holes to 7/16"
- use some insulation over mounting bolts/studs. Heat shrink, or some spark plug lead sheathing often works well
- fit the carb base gasket. Use fibre washers under a plain washer on the mounting bolts/studs
- do not fully tighten
- move the carb around until none of the fasteners touch the body. Then tighten.
- no metal to metal contact to transfer heat. might not be as good as a spacer, but better than nothing.
- drill out the carb mounting holes to 7/16"
- use some insulation over mounting bolts/studs. Heat shrink, or some spark plug lead sheathing often works well
- fit the carb base gasket. Use fibre washers under a plain washer on the mounting bolts/studs
- do not fully tighten
- move the carb around until none of the fasteners touch the body. Then tighten.
- no metal to metal contact to transfer heat. might not be as good as a spacer, but better than nothing.
I see you list your location as "cent IL". Where in central IL are you getting non alcoholic gas? Around Kankakee, I can't find it.
I have a similar problem on my Australian built AP5 Valiant. I have changed the ECG valve. plugs points Put a kit through the carby, changed the manifold gasket. Checked all of the vacuum hoses. Runs fine at start up. Shut it down after about 10 miles restart it and it just doesnt want to idle. It seems to be sucking air from somewhere but I have no idea from where.
James Clews
Well-Known Member
I remember my dad saying back in the sixties that those Holley single barrels on AP5s were garbage and would not idle. He used to change them to a carter single barrel!
I have been using a product called Carb Defender in ethanol gas for many years. The hygroscopic nature of the ethanol, combined with the fact that left sitting any real length of time our vented carbs will allow the gas to evaporate faster than the ethanol, further concentrating the ethanol and attached H2O in the carb will really do a number on the small spaces (metering) of the carb and causes slowly worsening issues over time. In my understanding, Carb Defender attaches to the ethanol (yeah, I'm not a chemist) so it doesn't bind with the water. What I know is that my carbs using 10% ethanol on 4 old cars run really well and I have seen a bunch of carb horror stories without such measures. I started using it after Herb McCandles recommended it at one of his Carlisle workshops.
Back when almost all cars had carbs and vented gas systems, the gas companies put stabalizer in the gas, but with almost all gas cars having sealed systems they don't bother to do that because those cars don't need it.
Back when almost all cars had carbs and vented gas systems, the gas companies put stabalizer in the gas, but with almost all gas cars having sealed systems they don't bother to do that because those cars don't need it.
slantsixdan
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Another poor-hot-idle countermeasure: install a hot-idle compensator. About a decade before these started being built into (some) carburetors, Rochester Carburetor offered one configured as a universal aftermarket accessory. They called it the CarbAIRator and it worked just like the inbuilt kind, except it's adjustable. They show up on Feebay from time to time, such as this one. Thread on a female pipe thread to hose barb adapter and tee it into your carburetor's choke pull-off hose.
chinze57
Push Button tranny and a Slant 6 that'll never die
You're dealing with vaporlock in the heat. It was not an uncommon issue before fuel injection, especially on hotter days. Yes, ethanol gas could be contributing to it, because it has a lower boiling point than non-ethanol, it's not likely to be your entire issue. As others suggested, doing the fuel line mod is probably a good idea. I did it when I rebuilt my slant and swapped carbs, and had significantly less heat transfer into the fuel line during a drive.
Getting rid of heat is a big issue, your issue is at idle, and the radiator fan doesn't spin as fast at idle, meaning less air moving across it, and less cooling. That contributes to vaporlock at idle, as the heat of every component in the engine bay will steadily rise the longer you idle.
If you can get no ethanol gas, you might as well. It has a higher energy density (potentially more mpg), and doesn't have the tendency to build up water if it sits for a bit.
Edit: Ethanol has only 2/3 of the energy of gasoline, which translates to some fuel efficiency loss.
Getting rid of heat is a big issue, your issue is at idle, and the radiator fan doesn't spin as fast at idle, meaning less air moving across it, and less cooling. That contributes to vaporlock at idle, as the heat of every component in the engine bay will steadily rise the longer you idle.
If you can get no ethanol gas, you might as well. It has a higher energy density (potentially more mpg), and doesn't have the tendency to build up water if it sits for a bit.
Edit: Ethanol has only 2/3 of the energy of gasoline, which translates to some fuel efficiency loss.
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They are built into some Carter AFB carburetors. Right between the secondary venturi all the way in the rear.
cruiser
Well-Known Member
Thanks, Chinze. This whole vapor lock issue is puzzling to me. Chrysler had decades of experience designing fuel systems when my car was built in the fall of 1973. Didn't they think about hot idling issues? They sold millions of vehicles and a helluva lot of slant six engines in hot environments, so they should have designed this issue out of the final products that they sold. How could they still have these vapor lock problems after all these years and billions of miles on their cars?
Rat Bastid
Dunamis Metron
Gasoline isn’t the same today as it was in 1973. Put a return line on it.
slantsixdan
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You are not experiencing vapour lock. If you were, the car would stall. 'Vapour lock' is not a catch-all term for heat-related fuel system hassles; it means only one thing: a big vapour bubble encompassing both sides of the fuel pump, caused by excess heat transfer to the fuel line. There is no liquid fuel available at the inlet of the fuel pump, so there is no liquid fuel pumped to the outlet, so the engine won't run. Not a match for your symptoms.
What you are trying to solve with heat shields and fuel line reroutes and suchlike is percolation, the fuel boiling in the carburetor (and/or in the pump-to-carb line) which results in an overly-rich mixture reaching the cylinders, causing rough running.
You can also "buy" your engine some additional leeway for dealing with less-than-perfect carburetion by following the tune-up parts and technique suggestions in this post, and by upgrading the ignition system.
Why do problems like this exist? it's true that today's gasoline is different to the stuff available in 1974—in most ways, today's gasoline is quite a lot better, but carbureted-engine driveability is not today's top priority in gasoline formulation, because most vehicles do not have carburetors. But leaving that aside, driveability of even a brand-new 1974 carbureted car was imperfect at very tip-top best. Take a look at this 1973 Chrysler video—12 minutes of what to do about poor starting:
Exactly none of this is of any concern with fuel injection; just hop in, turn the key, and drive off. It's not just starting; the same applies in pretty much all other conditions—idle, acceleration, cruise, etc.
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slantsixdan
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True. '70-'71 Carter BBSs and '70-'72 Holley 1920s, too, and a big variety of other carbs. But they were also one of the first items on the chopping block when Chrysler went on their penny-pinching rounds.
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