F.I. Percolation

[Richard T.]

Both of my F.I. cars have started to suffer from fuel percolation in the spider after 20 miles or so of driving on a hot day. This results in a poor or no idle condition. If the weather is cool or it's the evening neither is affected. I drove my 57 to Carlisle last August and only had a minor problem while waiting at gate 3 after a 4 hour drive in high heat. Has the gasoline changed that much in the past year? I looked at Jerry Bramlett's web site and he reccomends 103 octane racing gas which is almost impossible for me to get.
I drive my cars quite a bit so would like to beat this problem without a second mortgage on my house. I'd like to hear from owners of F.I. cars relative to their experiance with this problem including solutions.
Both of my cars (57 & 62) have fresh and well maintained F.I. units with stock high compression motors. Rich

[Rob M.]

Re: F.I. Percolation

In the Netherlands we have expiriencing similar problems. The boiling temperature of todays gas is much lower than in those good old days... I little fan to blow/suck air under the plenium might be a solution...

greetings,
Rob.

[Joel F.]

Re: F.I. Percolation

Hi Richard,

Been having the same issue with my '62 for the past several years anytime weather is over 80* F. Someone here mentioned using a boat's bilge blower and some fresh air hose from the inlet to blow cool air(or cooler anyway) under the plenum. I've learned to live with the issue as embarrassing as it is. I tend to keep a foot on the gas, other on the brake when I'm at a light.

I have not and will not try the 103 octane thing. Too costly, too difficult to find, etc. FWIW, my uncle had a '58 FI car back in the early 60's. He said he had the same problem back then, but only on when the weather was in the upper 80's.

Joel

[Gary C.]

Re: F.I. Percolation

Someone recommended putting insulation between the spyder and base plate (intake manifold). Can't recall (CRS) but maybe John D will chip in with his 2 cents worth on this approach. Last year on the Boston Road Trip we had very little perculation problems with a '57 and the other FI cars on the tour. Gary....

[Joe M.]

Re: F.I. Percolation

Has anyone rigged up a way to check underhood temperatures while the car is being driven? Wonder what the differences among cars would be?

What would be the underhood temperature threshold for the percolation to occur?

Has anyone tried to pop their hood while driving to see if the problem goes away?

Drag races had a cool can set up to chill the incoming fuel, wonder if a derivation of one of these devices would work?

J

[Joel F.]

Re: F.I. Percolation

I've tried wrapping the fuel line from the fuel pump to the fuel meter in one of those wrap things sold by Jegs, etc and it had no measurable impact. I have also tried wrapping the spider in aluminum foil, again no impact.

From what I understand, Dale Pearman used to have some sort of plumbers insulation on his car's spider and it was supposedly ugly but effective.

IMHO, a cool can would not do much. Keeping a cool can cool in traffic would be next to impossible, and the fuel would need to be really cold to off set the heat absorbed in the fuel meter and especially the spider.

Joel

[Mike M.]

Re: F.I. Percolation

Nothing new, guys.
At the drag strip in the '50's, owners would leave the rear of the hood open, resting on the pins and a couple of guys made spacer blocks to improve ventilation.
On a cool overcast high humidity day they would run like "Gangbusters".
HaND

[Jerry G.]

Re: F.I. Percolation

I have had a couple of FI cars for over 35 years. The only thing that makes them reliable in hot weather is racing fuel . My problem is further exaperated by the elevation I live at,4800 feet. It's expensive but it has a boiling point that can deal with the FI quirky characteristics. There was extensive discussion on this issue a few years ago and it the vapor pressure of todays fuels. It is significantly lower than those of the 50's and 60's. It only hurts while your filling the car up, then go have fun.

[Mike M.]

Re: F.I. Percolation

I trust no one is trying to run an ethanol blend in these things, since alchohol has a sinificantly lower boiling point than gasoline.
HaND

[Duke W.]

Re: F.I. Percolation

Gasoline doesn't have a specific boiling point. It's made up of scores of hydrocarbon species that have boiling points ranging from about 100F to over 300F. Ethanol boils at about 170F.

A common vapor pressure characterization is the 10/90 points defined by the 10 percent point - the temperature where 10 percent of the components boil and the 90 percent point - the temperature where 90 percent of the components boil.

The 10 percent point of typical winter gasoline blends is lower than typical summer blends.

Duke

[Joel F.]

Re: F.I. Percolation

I trust no one is trying to run an ethanol blend in these things, since alchohol has a sinificantly lower boiling point than gasoline.
HaND

No choice around here Mike. Ethanol blended gasoline is the only thing that has been commonly available for years (aside from the odd race gas distributor).

[Bill W.]

Re: F.I. Percolation

I add a whole can of 104 octane booster to a tankfull on my 62 . It helps until the temp hits about 90+. Dale P had a insulator that fit under the spider that he said helped.....Bill

[Robert S.]

Re: F.I. Percolation

I did two things to my 60 that seemed to help. First, the air/fuel ratio was around 18:1. Got this adjusted to about 15:1. Then I removed the plenum and cut a piece of white cardboard (the kind that comes in shirts) that fit inside the doglegs with about 1/4 inch of clearance. Make 4 of these. Then, using spray adhesive, glue up a foil layer to cardboard to foil to cardboard, etc. until you have used up the four cardboard pieces and five pieces of foil. Leave the foil about 1/4 inch oversize and crimp the edges. Place this under the doghouse. It doesn't show much and seems to help. I also have the idle set at about 1200.

[Bruce B.]

Re: F.I. Percolation

I have heard that adding a quart or so of diesel fuel to a tank of gas helps raise the boiling point of the fuel. A friend of mine does it and it seems to help.
Any thoughts about this?

[John D.]

Re: F.I. Percolation

Rich, If I had a total solution to this much asked question I would be rich for sure. Sorry I did not read all the posts. Too late and I'm ready for bed.
But here is something to think about. Barry Holmes from our Pittsburgh Chapter really taught really stumpled onto a partial solution for the perculation problem on his 62FI car. Here is how Barry solved the problem using pump gas (don't know the octane). The REPRO FUEL LINE is the culprit big time. On a 62 for sure and probably a 59 to 61 the repro line isn't bent correctly and therefore it is dangerously close to the valve cover. This results in the line being sooo hot if you touched it in hot weather you would fry your hand. So Barry's solution was to cut off about a 1/2" off the line and reflare it where the line goes in the AC GF-90. This raised the line away from the valve cover.
#2. He put a one piece base gasket between the FI and the base plate.
End of problem. Now he does live in the sticks so I don't know how much city driving he does in bumper to bumper.
#3. Back in the summer of 62 old JD here went to the GM Training center in the Pittsburgh area. Took the United Delco courses. Anyhow the FI class was run by Paul Glagola. A student in class had a new 62 FI Corvette and he was complaining of the same complaint as you are. Paul had him bring the car into the class room. I watched the older guys (I was 18-19) remove the unit and Paul put a one piece base gasket on it. Those typically fit 57 to 59. Well that fixed the perc problem and the fellow quit the class. Seems that the Chev. Dealer had no fix. Not saying the one piece is the super fix but it helps a little. Big thing is to get rid of the heat Rich. Copy the street rodders. Add an electric fan to the front of the radiatior. Want an easy fix but it's illegal. (sshhh) RUN 100 low lead.
Anyhow I mentioned before about Zaroom's 62 black FI Car. Old Dale Pearman had the world's most ugly 62 FI unit but the damn thing ran like no tomorrow in any kind of weather. He had this God awful ugly green stuff on the individual spider lines. Insulated the crap out of the bottom of the base plate to plenum. Insulated the fuel lines and I don't know what else. He was running a 400 SB with a 62 FI and the car was reliable.
Insulation, fans, and better fuel. But it's only going to get worse guys. It will never be better. Prop the back of the hood open with wooden blocks like we used to do back in the late 60's.
Here is one I forgot. Commerical insulation-the kind they use before you put the roof shingles say if you are running a tin roof, etc. Put that stuff under the FI unit and watch the difference. It's like fancy aluminum foil. Don't know the trade name. JD