1962 fuelie runs rough when hot

[Jerry N.]

I have a 1962 fuelie that starts fine, runs fine, but when the car gets warmed up, it runs rough and the idle hunts between 200 and 500 rpm. It has no issues until you get it warmed up, and it is very noticeable when you drive some and then shut the car off, and if you restart it in 5 minutes, the rough idle starts back. I have 93 octane gas, add max lead, and add lucas injector cleaner. When the car is hot and you take your foot off the gas and shove in the clutch, the engine dies.

Any suggestions would be helpful.
Thanks, Jerry Nutt

[Jim L.]

Re: 1962 fuelie runs rough when hot

I have a 1962 fuelie that starts fine, runs fine, but when the car gets warmed up, it runs rough and the idle hunts between 200 and 500 rpm.

Welcome to the wonderful world of Rochester fuel injection. The behavior you are describing is typical and well known to anyone who has ever lived with a fuelie for any length of time. The cause is fuel percolation in the spider and nozzle lines.

What can you do about it? All of the following will help, but none are a cure:

1. Keep the engine cool. By this, I mean keep the cooling system in top condition and run a low temperature engine thermostat, say 160 degrees

2. Drive with the hood popped open at the rear to vent hot air

3. Keep moving. Seriously. Once the engine is under load propelling the car, the fuel in the nozzle lines becomes pressurized and the percolation instantly stops.

4. Be sure the ignition timing is spot on. Late timing will cause an engine to run hotter, which aggravates the problem.

5. Be sure the air/fuel mixture provided by the injector is right. A lean mixture will cause an engine to run hotter.

5a. Set your idle mixture richer than optimum, however. This will reduce the exhaust gas temperature slightly and lessen (but not eliminate) the tendency for the rough running.

One "cure" that isn't legal for street use is to use either aviation fuel or racing gas. Both of these fuels have properties that make them less prone to percolation in the old FI units.

Good luck with your '62.

Jim

[Don H.]

Re: 1962 fuelie runs rough when hot

Jim is right on. The best fix he mentioned is AV gas. I have used it in my '60 for 20 years and works great, especially hot starts. Don H.

[Mike E.]

Re: 1962 fuelie runs rough when hot

Save your money on injector cleaner--that is designed for a very different style of injector, and does nothing for the old continuous flow 57-65 injectors.

[Dan H.]

Re: 1962 fuelie runs rough when hot

Double check if it has a cranking signal valve, must be 'tight'. Also vacuum leaks at the main diaphram control line will make it die when stopped/idle. I'm running unleaded 91 octane California junk gas without additives, but I do have a 160 thermostsat. I do run a coolant additive in addition to antifreeze, will run 180 in 90+ weather. It's a 64 FI Coupe but they'll all similar critters!
Dan

[John D.]

Re: 1962 fuelie runs rough when hot

Jerry, If you are not showing your car try a one piece base gasket between the FI and the base plate. It's about 1/8" thick and is a great insulator for heat. Now if your 62 has a syphon breaker solenoid kit on it this one piece gasket will help keep it cooler. The gasket takes the place of the 4 individual leg gaskets. Originally the one pc gasket was used on just 57 to 59 but today it's a big help for the 60-62. You will notice the ports on the gasket are a tad too small for the 62 plenum but so what. Won't hurt a thing unless you are racing.
Insulate the fuel line from the engine fuel pump up to the filter. Make sure the repro line is not hugging the valve cover which really heats things up.
Dale Pearman probably had the only 62 in his days that would run in 100 degree weather. He was quite proud of his engine compartment. But the FI was uglier than sin in that Dale insulated the crap out of everything. The spider fuel lines, under the planum, all the fuel lines, and he also had a fan under the hood.
I almost forgot. A big time cure is to put a fan in the hose on the pass side. The big heater hose. Then duc the air from the fan to under the FI. Hook it up on a bubba toggle switch. Makes a world of difference. And only takes a few minutes to put the car back to original.
As Jim Lockwood said switch to some better fuel. Ethanol is the pits for our cars. Even though we have some good viton parts today to help out the truth of the matter is the driveablily suffers from that crap.
Rumor has it that farmers are growing less and less corn and maybe the ethanol might go by the wayside. Now that is just internet chatter so don't count on it.
100LL will make your car run like the old days when we had 260 Sunoco.
Don't put any additives in the 100LL please as it doesn't need it. Problem is that it's not street legal but don't tell anyone. My 63, the LWC loves 100LL. Good luck, JD

Old Dennis Clark (very old) once said the big time cure for the heat soak is to remove the hood and put it in the attic.

[Dennis C.]

1962 fuelie runs rough when hot

And, "the hood in the attic" cure is so reasonably priced...

[Jim L.]

Re: 1962 fuelie runs rough when hot

Old Dennis Clark (very old) once said the big time cure for the heat soak is to remove the hood and put it in the attic.

I'll second this advice, even though it was offered sort of tongue in cheek.

My bride and I once drove my injected '60 from CA to Steamboat Springs CO (and back, thank you) for a regional. We would open the hood immediately upon stopping the engine for any reason.... be it a rest stop, gas, or food.

That let cool air reach the FI unit and for the hot restart, we didn't even have to open the throttle.... just turn the key.

It sure looked strange at a restaurant though: Open the hood.... go inside.

Jim

[John D.]

Re: 1962 fuelie runs rough when hot

Hi Jim, You know this problem is nothing new. Problem is though its getting worse and I don't foresee the issue going away. I can remember when I was in the restaurant business for 20 years or so. I drove a 63 340 HP (original engine)saddle/saddle car with a fake fuel unit on it and a fiberglass air cleaner. I drove that car almost every day to work as it made it fun. Or I drove my 80 Corvette. You would be surprised how many cases of liquor you can put in a split window coupe. Anyhow so often when I stopped in hot weather the 63 would be hard to start. And when it did I had to keep goosing the gas pedal to get cold fuel in it. When I went to my hangout I opened the hood sometimes. Then the car would start instantly and run perfect. Now that was 25- 30 years ago!!! It's the heat and the crap fuel and of course the condition of the fuel unit has something to do with it. Keep up the good work. John

[Ian G.]

Re: 1962 fuelie runs rough when hot

Another member suggested attaching a baffle under the aluminum intake, like on cast iron carb intakes. The idea is to shield the underside from hot oil spray. Is this worth the time and effort?

[Richard S.]

Re: 1962 fuelie runs rough when hot

jerry; i had my fuel injection unit rebuilt by jim lockwood a couple months ago.living in southern calif, our weather is similar to you in florida. although mines a 64 unit, i drained out all the old collant,refilled with distilled water a couple cans of water wetter and a 160 degree t-stat. car barely gets over the 160 degree mark on gauge. done alot of stop and go driving along with freeway driving. you shouldn't need anti-freeze in florida and cars run cooler on straight water.good luck.richard

[Jim L.]

Re: 1962 fuelie runs rough when hot

Another member suggested attaching a baffle under the aluminum intake, like on cast iron carb intakes. The idea is to shield the underside from hot oil spray. Is this worth the time and effort?

I doubt that anyone here has done a controlled experiment that would conclusively answer your question. Intuitively, it probably wouldn't hurt, it might help, but it won't be The Solution to The Problem.

The Problem is fundamental to the design of Rochester Fuel Injection: The fuel pressure at the nozzles at idle is very low, a few tenths of a PSI, and this makes it easy for the fuel to percolate.

The connection between fuel pressure and percolation is easy to visualize if you think about how the boiling point of water is lower at high elevations, where atmospheric pressure is reduced, compared to its boiling point at sea level.

Fuel behaves similarly ( but not identically) Raise the fuel pressure and the "boiling point" (*1), if you will, instantly rises . If it rises above the fuel temperature, percolation stops.

You can test this statement easily enough. Next time you do a hot restart with your fuelie, and the engine is running roughly, IMMEDIATELY start driving. The percolation will instantly stop and the engine will run smoothly. Why? Because as soon as you put the engine under load, the fuel pressure increases sufficiently to raise the "boiling point" of the fuel above its then-current temperature.

So, solving The Problem would involve either finding a way to always keep the fuel temperature below its "boiling point", or redesigining the unit to increase the general operating pressure of the fuel delivery system.

Using 100LL Avgas or virtually any racing gas covers up The Problem because both have "boiling points" that are higher than that of motor fuel and generally high enough to not percolate in the nozzle lines.

Well, that was a long answer to a short question. Shutting up now....

Jim


*1 Motor fuels do not have one single boiling point since they are a blend of liquids each with a different boiling point.

[Dan H.]

Re: 1962 fuelie runs rough when hot

jerry; i had my fuel injection unit rebuilt by jim lockwood a couple months ago.living in southern calif, our weather is similar to you in florida. although mines a 64 unit, i drained out all the old collant,refilled with distilled water a couple cans of water wetter and a 160 degree t-stat. car barely gets over the 160 degree mark on gauge. done alot of stop and go driving along with freeway driving. you shouldn't need anti-freeze in florida and cars run cooler on straight water.good luck.richard

Richard, totally agree on the water wetter idea. I also use it and the difference was amazing, just enough to keep the 64 running cool enough to be a pleasure to drive. 160 t-stat also in the mix! It will still run a little rough when first hot started but does fire instantly and drives off smoothly as Jim says. The '380' units are very nice when dailed in, I have the 'improved' spider/check valve I got from John D. I'm running plain pump gas now, got 21 mpg on trip to Bend Oregon right past Death Valley. Can't afford Av. gas, no air ports in Death Valley.
Dan

[Tom P.]

Re: 1962 fuelie runs rough when hot

The problem is also getting worse and worse with the unit on my 56.
When it is cold, it runs better than GM designed it, but once it heats up, ESPECIALLY with the hood closed, it just goes to crap. Keeping the idle up helps. When it starts to run poorly, purging it with the throttle 2-3 times helps. Once moving down the road its fine.
I'm convinced that the prime problem is crap gas. I'm out at the airport all the time and I never remember to take a couple of 5gal cans with me. DUH!

[John D.]

Re: 1962 fuelie runs rough when hot

Tell me more about the "water wetter" please. Never heard of such a thing in SW corner of PA.
Now I can typically tell if an old poc FI unit is from the hot climates as the base plates are all eaten up from corrosion as you folks don't use anti-freeze. I used to run a coolant in my BB's in the old days. White milky stuff which had a lubricant in it. Is water wetter the same? Is this a trade name? Thanx, JD

Just googled Water Wetter. I am impressed and will order a case. Why did it take so long for this to come to light to us poor folks who are in the sticks. Thanks very much. JD