Poor hot idle caused by ethanol gas? Whaddya think?

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cruiser

cruiser

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Hi Guys/Gals: I could use your advice on a lagging problem with my car. I have a very stock 1974 Duster with the stock rebuilt Holley 1945 carb. Stock, correctly sized base spacer gasket. The idle speed and mixture are correctly adjusted, and the timing is set to 10 degrees before. New plugs/wires and nearly everything else under the hood. When I cold start the car, for example after sitting all night in 40 degrees in the garage, she fires right up and goes to high idle. Kicking it down one minute later, it settles into a very nice curb idle. Things are different in the summer. After a hot drive on a 90 degree day, the car chugs (misfires) a bit at idle. Sometimes, it dies at idle when it's really hot outside, and it has a rough idle when stopped at a red light. I cannot find anything mechanically wrong with the car, or with any of the underhood settings and adjustments. I know that the carb is sitting on top of the hot exhaust manifold, but I think it should still idle smoothly without misfiring or dying out at idle after a hot day drive. Is it possible that the fuel that I'm using (87 octane unleaded, 15% ethanol) isn't good enough to keep the engine idling smoothly? What do you think would happen if I used ethanol free 91 octane gas? Would this prevent misfiring at idle? The engine seems to run just fine at highway speeds. Please weigh in with your opinion. Slant Six Dan: Any thoughts on your part? Thanks everyone!
 
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I have no experience with E fuel in our old cars, but I can tell you this: it has no place being in a metal carburetor.
I keep E10 in the shop for parts washing because it is cheaper.
A few years back I left some in a container overnight, very mild weather. Next morning there water drops in the base of the container because E fuel is hygroscopic. At first I thought there had been water residue in the container BEFORE I put the E10 in it. Carefully cleaned the container & left it overnight again with E10 in it. Sure enough, water in it next morning.

The E fuel might have formed water in your carb &/or corrosion which is blocking jets/passages.
 
Ethanol boils at 173 degrees, guaranteed its hotter than that under your hood on a summer day.
The fuel is probably boiling in the bowl and lines.
we have been fighting this on a driven to the track an hour away race car for 2 seasons.
it will pull for the full 1/4 if it sits and cools off with the hood up for an hour or so, but will fold up at the top of 1st gear like it's running out of gas if you try to hot lap it.

If you can get ethanol free 91 i would try that for a few tanks as a test..
 
Have you considered the EGR valve or the EGR Amplifier? A small amount of vacuum applied to the EGR valve could be leaning out the fuel mixture sufficiently to cause the conditions you describe.
 
Hemi Dude said:
Have you considered the EGR valve or the EGR Amplifier? A small amount of vacuum applied to the EGR valve could be leaning out the fuel mixture sufficiently to cause the conditions you describe.
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I removed the EGR valve, amplifier and associated tubing several years ago so I don't think that's the cause. Thanks for replying, though. I'll keep working on a solution.
 
motorpirate said:
Ethanol boils at 173 degrees, guaranteed its hotter than that under your hood on a summer day.
The fuel is probably boiling in the bowl and lines.
we have been fighting this on a driven to the track an hour away race car for 2 seasons.
it will pull for the full 1/4 if it sits and cools off with the hood up for an hour or so, but will fold up at the top of 1st gear like it's running out of gas if you try to hot lap it.

If you can get ethanol free 91 i would try that for a few tanks as a test..
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Yeah, will run a few tanks of premium ethanol free gas through as an experiment. Thanks.
 
Google "Slant 6 fuel line relocation" see if anything comes up.
There was a post on Slant 6 .org.
Or contact member Slant Six Dan
 
Have you rerouted the fuel line from the stock location?

When I first got my 64 on the road I used all the stock components which was fine for awhile. Then I noticed symptoms of heat soak when summer came. I did the @slantsixdan reroute of the fuel line over the valve cover.and it's been fibe ever since.
 
Install a return after the fuel pump as they did on all 80's mopars using a fuel filter with a return built in with an extra nipple on the side. You will have to run a 1/4 inch line back to the tank.

They sell a fuel pick up with a return outlet or you can use a awl and punch a hole in the tank at the top. Once you poke a hole make it larger using a tapered punch so the metal is bent inward to the size needed for a 1/8 pipe tap. Tap the hole just enough to get the 1/8 threaded barbed nipple started. You will now have a return liked used on all 80's model carbureted engines to deal with this issue .

I have done this to several cars with a fuel boiling problem.

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On the car above we ran 1971 fuel lines and used the vapor line for the return. The sending unit had two lines for a return
 
cruiser said:
the fuel that I'm using (87 octane unleaded, 15% ethanol)
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That's a very high concentration; even some newer cars gag on it. Can you get 10% instead?

Do the fuel line mod (I just linked above) and make sure your manifold heat control valve and thermostatic air cleaner are both intact and working correctly. You might very well wind up making a carburetor heat shield; here is a dimensional drawing of the late-'70s/early-'80s factory item (and more info here . As you can see, it has pass-thru cutouts for the throttle cable and kickdown linkage, access for the middle manifold nut, etc. Originally made of 1/16" pressed asbestos; you'd want to make it out of a modern heat-shielding gasket material—just do asbestos you can.

cruiser said:
What do you think would happen if I used ethanol free 91 octane gas?
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Well…give it a try and see for yourself! If your only options are 15% ethanol regular or 0% ethanol high-test, you might experiment with mixing those two to arrive at a blend that gives acceptable idle/driveability without draining your wallet too fast.
 
How is it some of us can run 10 or 15% ethanol and not have these issues?

If you are going to run pump gas you MUST change the way you think and make the changes necessary to deal with it.

Pump gas is now formulated for EFI so carb tuning needs to be addressed.

If pump gas has ANY alcohol in it you need to think about getting heat out of the system. Whatever that takes.

The first thing is you have to at least reduce the heat applied to the carb by the exhaust crossover. That’s number one.

Of course, if you can’t change the boosters in your carb, you have to be careful about taking too much heat out. You’ll know if you do because the engine will burn more fuel, make less power and the plugs will look lean even though you are feeding fuel to the engine like a mother.

So you have to be careful and thoughtful about what changes you make.

Maybe you just buy a Cool Carb spacer and that drops the carb temperature enough to clean up the issue(s) you are having.

That’s the only carb heat reducer I’ve seen that actually works.

So think it through. You have to get some heat out of the carb.

How you do that and what other changes you have to make take some serious thought.
 
You are 460 miles south of me, and only a little lower in elevation.
In 1994, I got me a 1980 Volare and only sold it about a year ago The slanty in it, since 87E10 came to town, always started/ran perfectly on it, year round ; 87E10 is not your problem.
My slanty had a Carbon canister but the vent-line rusted out. and yes it had an EGR. I installed an older solid lifter cam engine into it before I ever drove it, on account of I got the near-mint car with a blown engine for $100. It turns out that the rearend was also blown, but I did not know it, lol.
IMO:
87E10 is Not the ogre everybody likes to say it is. I have been running it in my carb'd 367 68 Barracuda since 1999. Granted the entire fuel system was brand new that year. Late this year, October, I fired it up and took her for a spin, on fresh 87E10.
IMO:
your problem is a rich condition. Take a couple of plugs out and look.
So then, if I am right, you just gotta figure out why. That could be simple or it could be ridiculously hard to figure out.
 
Simple enough to verify. Run the tank almost empty, then fill up with non ethanol gas.
 
Could run an electric with a T at the Inlet with a slight return restriction and have it constantly recirculating so it stays cool. My Mazda has this system. It also turns the fuel over through the filter so your tank will self clean of rust over time. I never had an issue with the plastic filters on the cold side of a slant but the glass ones are not impact resistant.
 
Just my $.02. You may have to adjust the carb from summer to winter etc. Just do some air fuel screws turns when it acts up. The air density is different summer to winter. You may also want to change jets but I'd tweak the AF screws first. Note how many turns so you can put it back where it was etc.
 
I put a spacer under my edelbrock caus ethe gas was boiling off when I shut it down and it would long crank on startup...:thumbsup:
 
Badvert65 said:
Here is a 1/2 inch spacer specific to a slant six one barrel.
one barrel spacer
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This is not a good idea. It'll screw up your throttle linkage—adjustable if you have a cable-type throttle linkage, but not if you have a rotating-rod type—and it'll screw up your choke (can sorta fix by custom-making a longer choke pushrod) and it'll screw up your automatic transmission kickdown linkage (maybe fixable partway or all the way if you're lucky, but often it's not).
 
slantsixdan said:
This is not a good idea. It'll screw up your throttle linkage—adjustable if you have a cable-type throttle linkage, but not if you have a rotating-rod type—and it'll screw up your choke (can sorta fix by custom-making a longer choke pushrod) and it'll screw up your automatic transmission kickdown linkage (maybe fixable partway or all the way if you're lucky, but often it's not).
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Dan, do you have a link to the correct spacer that you can recommend?
 
I used one of these on my 170 when I still had it in Vixen. It worked well. Scroll down to the one for the Ford 1 barrel and that's what I used.

www.coolcarb.com

Order Products

Heat Shield & Spacers come in standard thickness of .155. Most style Heat Shield & Spacers as listed below also available with a thickness of .232. Colors may vary. Limited time only!!...
www.coolcarb.com
 
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