1960 - Hard start when hot

[Joe M.]

Just took my 1960 into the shop and mechanic discovered that the gasoline is boiling in the carb when the engine is shut down. He has seen this one other time and he had to remove the intake manif and clean out the build up to open up the passages that supply hot air to the carb. He believes it has to do with the 10% ethanol in our N. TX gas supply. I wonder if it would be better to block off the passages that provide the heated air under the carb?

[Stuart F.]

Re: 1960 - Hard start when hot

Joe;

It is always a good idea to keep the exhaust crossover passages clear and, along with the heat riser butterfly, operating properly. However, the problem you describe is not likely to be caused by this source of heat being interupted. If that were the case, it would be a driveability problem specially when cold. The engine might stumble and hesitate, but overtheating the fuel (boiling) and causing hard hot starts is not a likely symptom.

I am dealing with a similar "severe" fuel boiling problem after shut down here in Florida in my 63 with a Carter AFB. It is so bad that with the air cleaner off, I can see a strong heavy stream of fuel pouring out of either my Accelerator pump nozzles or the main jet tubes in the Venturis (depending on which carb I have on the engine. Yes, it happens with two different carbs). I have had several threads going on this problem and have received lots of helpful ideas, but nothing I've tried to date has stopped the problem. The main factor that has changed is the fuel here in Florida. There used to be only certain brands thaat had the ethynol, now they all do as of a few months back. I have experimented with numerous changes and continue to do so, but at a more calculated pace. I had severe fuel dilution of my oil to the point where my local Auto Parts store has refused my drain oil, and before I changed it last week, I could smell it on the dipstick and the normal 15W dripped like water. The other danger is potential Hydraulic Lock which can ruin an engine big time.

Make sure your mechanic knows what he is doing and not just playing around and charging you for his guessing and tinkering.

Stu Fox

[John H.]

Re: 1960 - Hard start when hot

He has seen this one other time and he had to remove the intake manif and clean out the build up to open up the passages that supply hot air to the carb. I wonder if it would be better to block off the passages that provide the heated air under the carb?

The absolute LAST thing you want to do is to improve the flow of hot air through the manifold passage to the carb base; you want to STOP it. When you do so, be sure to wire the heat riser valve open or replace it with an F.I. spacer.

[Stuart F.]

Re: 1960 - Hard start when hot

I guess John has said it better than I: the fix your mechanic is proposing is the LAST thing you would want to do to address your problem, in fact it will only make it worse. All things being equal, you would want all your original systems functioning as they were originally designed to do, but things have changed - specifically with the fuel. I would like to see one of our Magazine Writers tackle this problem straight on, because "Houston we have a big Problem!" Certain models and certain years are worse than others, including mine; the 63 L-76 SHP (340 hp) engine.

I have compiled lots of notes and posts from the members, done lots of experiments and, if someone else doesn't tackle this issue, I may call out my 23 years of Tech Writing experience to document it.

Stu Fox

[Steven B.]

Re: 1960 - Hard start when hot

Joe, I live about 100 miles east of Dallas and south of Mount Vernon. I have not had this problem, yet, but others in the area have. One of them told me tonight that when he uses gas with ethanol the problem is pronounced and his fuel mileage decreases. When he uses non-ethanol fuel the problem is not present and his mileage increases. He said he now uses Exxon, no more gas from Brookshires. I can't attest one way or the other.

Steve

[Jack H.]

Re: 1960 - Hard start when hot

The fuel mileage issue should come as no surprize. If I remember my college chemistry correctly, gasoline has an energy content of 25K-cal/mole while alcohol weighs in around 18K-cal/mole.

Energy is the ability to do work, so if vehicle speed is held constant, you'd expect to consume about 20% more E85 than you would gasoline on the same trip. Hence, a rational economic consumer would therefore demand paying 20% less for E85 than for gasoline.

Now, with typical pump gas containing only 10-12% ethanol vs. E85's 85% content, that 20% reduction in fuel consumption drops DRAMATICALLY and you'd expect the loss to weigh in at about 3%...

[Wayne P.]

Re: 1960 - Hard start when hot

Had a similar problem recently. Make sure your fuel pressure isn't too high. Most of these old carbs can't handle more than 5-6 lbs. Mine measured over 7 lb.

[Phil D.]

Re: 1960 - Hard start when hot

Rather than start a new thread, I thought I'd just add my question to this one since I'm having the same problem in the same region of the country as the OP. In the last few weeks, my 69 base engine has had a couple of episodes where it won't start again until it has cooled off substantially. I removed the air cleaner and observed bubbles from a vent tube in the top center of the carburetor. The temp gauge always reads normal and there are no signs of overheating. The heat riser valve was replaced with a spacer so that is not an issue. I didn't build this engine so I'm wondering if there are block-off plates installed or not or mabe there was and they've burned through. Is there a way to tell without removing the intake? Would a IR thermometer register a significant temp difference between points on the intake manifold or would it read fairly even across the top of the motor regardless?

[Bruce B.]

Re: 1960 - Hard start when hot

If your mechanic removes the intake have him get Fel Pro intake set which should include a set of sheetmetal plates to block the crossover passages.
Install them and the carb base should remail cooler.
In addition there is a phenolic plate available which goes under the carb and insulates it from the intake manifold.

If you use the phenolic plate be sure to check air cleaner stud clearence to the hood bottom.

[Timothy B.]

Re: 1960 - Hard start when hot

Phil,

I am not sure there is a hot slot in the intake manifold under the carburetor in 1969. Do some checking to find out, others here may give some guidence there. Also, check the gasket arrangement (sandwich) under the carburetor because if there is a stainless heat shield under the carburetor it may be burnt through letting exhaust heat through to the aluminum carburetor cooking it.

The gasoline is a issue and has been discussed here many times so careful attention to inital timing and engine tune are important.

[Mike M.]

Re: 1960 - Hard start when hot

I have a '71 Olds 442 (455ci stock engine) that had this same percolation problem. I first tried a phenolic plate (beware of carb to hood clearance issues-but very thin phenolic plates are available) but the problem continued. I then bought some small plates (from Mondello) to block off the heat riser ports. This finally fixed the problem. I have been on 2 2000 mile trips in terrible summer heat with no issues. Good luck.

[Philip P.]

Re: 1960 - Hard start when hot

My 1960 had a similar problem when using ethanol gas not to bad but it did start a little hard, we went on a trip and used only non ethanol fuel and I did not notice the problem. My heat riser ports were blocked off.
Phil

[Phil D.]

Re: 1960 - Hard start when hot

I don't know what I'm going to find when I take it apart, but went ahead and ordered a set of gaskets with the block-offs and will just plan to go ahead and change them. Fingers crossed.

[John D.]

Re: 1960 - Hard start when hot

Joe and others. Try to avoid ethanol by searching your state/area for the stations that sell gas without ethanol. Google: pure-gas.org

In Texas there are about 93 stations that sell ethanol-free gas. Now I did not study which ones had higher octane fuel.
As of Feb 2012 my state of PA has about 18 ethanol free stations. Problem is most of them only have it in 87 octane.
Try the boat docks also as the boating industry is suffering big time as the ethanol is attacking the fiberglass tanks.
You poor guys with the big tank Corvettes are in trouble. The ethanol is losing up the gel coat and completely clogging the fuel system. Whew!!!!

Try insulating the fuel line from the engine fuel pump to the carb or FI unit. That helps. A former DB member by the name of "Dipstick" suggested removing the hood and putting in the attic.
Since ethanol boils at a lower temperature you have to do something about the heat under the hood. It's only going to get worse my friends.
Rebuilt your carbs with a kit for ethanol. Do the same for your 57 to 65 fuel injection. Don't forget to rebuild your engine fuel pump with a kit for alky also. And throw away those correct looking fuel hose from the engine fuel pump to the main fuel line and replace them with ones that will withstand ethanol. Readily available at most auto stores for a buck or so.
Jack Humphrey said a mouth full though.
If you have a late model car try putting some ethanol free fuel in it and watch that baby scream to life.
Those of you that have a steel gas tank are looking pretty good now you know. The guys with the big tanks are suffering. Answer for them is to use FI Art's favorite fuel which is 100LL. JD

[Mike M.]

Re: 1960 - Hard start when hot

The percolation problem on my Olds manifested itself when the car was allowed to sit for 30-90 minutes after being driven for a in hot temperatures (it would crank and start if not allowed to sit very long). When you would try to crank it the gas would come shooting out (like a fountain!) of a vent on top of the carb and would actually flood into the front 2 barrels of the carb killing the engine. Then it woud not pump any new gas into the carb. I first thought it was the fuel pump, then the gas lines, on and on, lots of $ trying to fix the problem. When I actually saw the gas fountain I knew then it was purely a heat realted issue. The phenolic plate and especially the blocking of the heat riser ports fixed this particular problem.