63 L75 Overheated Fuel

[Joseph S.]

Looking for some help.
I have been dealing with what seems to be boiling fuel issue on my 63 L75 Coupe. Car runs great until I shut down and restart on hot ( around 85-90 degree ) days. First symptom is extreme bogging ( accelerator pump becomes inoperative) and then stalling. Engine is not overheating, and cooling water temps get no higher than 180-200 degrees.
Heat riser valve is open and I have plugged exhaust circulation holes under the carburetor. Stock fuel system, AFB carb (performed same before and after rebuild) and carb mounting configuration (carb, ss plate, phenolic pad, gasket, manifold). Base ignition timing about 8 degrees w/VAC disconnected.

Once carb cools accelerator pump goes back to work and idle returns to normal and all is well.

After shutting down on a hot day, you can hear and see boiling fuel at the accelerator pump nozzles. I am running 93 octane pump fuel, I realize avgas or racing fuel have a higher boiling point but I'd like to use the car for road rallies and that limits my flexibility.

Is there a better (I use a standard aftermarket) phenolic pad?? Any suggestions, very frustrating.
Joe

[Duke W.]

Re: 63 L75 Overheated Fuel

It sounds like your configuration is correct, but you said the insulator is aftermarket. So how does is differ from the OE type? The heat riser should be wired open. If functional it may not be full open at idle speed, which is why it should be wired open.

What's the number on the VAC bracket, and does it meet spec?

There have been several threads on insulating the fuel lines, so try an archive search. The input line to the pump passes very close to the exhaust manifold and at idle fuel flow is low so a lot of heat is picked up... also after shutdown. The percolation issue is common, but your's seems more severe than most.

Take some temp readings with an IR gun on the carb body and post.

Duke

[Joseph S.]

Re: 63 L75 Overheated Fuel

Insulator is a repro from one of the major parts suppliers. Not sure if anyone knows of any with better heat insulating qualities. Heat riser is open.

VAC was a 201 15 ( which I think was original) and functioned to spec. Began opening about 8"- fully open at 15-16". In any case I changed to a B26 which begins pulling at about 6-7 and fully open by 12-13". Motor actually ran better (idle vac in 16" range). I also adjusted base timing to 8-9 degrees which resulted in total idle timing @700rpm (with VAC connected) at 26-27 degrees.

After a short 12 mile drive (temps were in the low 80's today) all operated fine only temps were relatively cool with no sun load.
On completion of drive engine temps as follows:

Thermostat housing - 182 degrees ( have seen this over 200 on hot days)
Fuel line - inlet fitting to carb - 130 degrees
fuel line -fuel filter - 135 degrees
fuel line - inlet fitting to filter - 130 degrees

front carb body- 145 degrees
intake manifold (measured in front of carb) 210 degrees

I had no issues, but I didn't drive long account cooler temps - However some of these temps concern me especially the carb body. Since ethanol percolates at less than 180 degrees - It seems to be running pretty close on a moderate day.

Not sure if anyone has data on carb temps. I may try to insulate fuel pump to filter line and recheck on a warmer day.
In any case when the weather warms up I'll take temps again, I'm sure I still have the issue.

Any input appreciated, Joe

[Richard M.]

Re: 63 L75 Overheated Fuel

Joe, I had similar L71 issues. Heat soak etc.

We insulated fuel line from under battery tray to fuel pump. This was a side pipe car which made it even worse. You don't have added non stock sidepipes do you?

We split insulation lengthwise and fit it over the line and tie wrapped it. It helped, but BB manifolds are closer to hard lines than SB but it could help. Definitely add from pump to filter, and maybe filter to carb.

Rich

[Joseph S.]

Re: 63 L75 Overheated Fuel

Thanks Rich,
Car has rear exit exhaust. I have ordered velcro wrap insulation for the filter to fuel pump line in the front of the block. In addition I also ordered a wood laminate carb spacer (said to insulate much better than the hard rubber phenolic pad I am currently using) from Edelbrock. I will try each individually and take temps, hopefully this brings things into a workable range.
If not, I'll work on the tank to pump fuel line in the engine compartment. I have also been told I should consider blocking the exhaust at the head to intake manifold ports. More to come.
Joe

[Duke W.]

Re: 63 L75 Overheated Fuel

Insulator is a repro from one of the major parts suppliers. Not sure if anyone knows of any with better heat insulating qualities. Heat riser is open.

VAC was a 201 15 ( which I think was original) and functioned to spec. Began opening about 8"- fully open at 15-16". In any case I changed to a B26 which begins pulling at about 6-7 and fully open by 12-13". Motor actually ran better (idle vac in 16" range). I also adjusted base timing to 8-9 degrees which resulted in total idle timing @700rpm (with VAC connected) at 26-27 degrees.

After a short 12 mile drive (temps were in the low 80's today) all operated fine only temps were relatively cool with no sun load.
On completion of drive engine temps as follows:

Thermostat housing - 182 degrees ( have seen this over 200 on hot days)
Fuel line - inlet fitting to carb - 130 degrees
fuel line -fuel filter - 135 degrees
fuel line - inlet fitting to filter - 130 degrees

front carb body- 145 degrees
intake manifold (measured in front of carb) 210 degrees

I had no issues, but I didn't drive long account cooler temps - However some of these temps concern me especially the carb body. Since ethanol percolates at less than 180 degrees - It seems to be running pretty close on a moderate day.

Not sure if anyone has data on carb temps. I may try to insulate fuel pump to filter line and recheck on a warmer day.
In any case when the weather warms up I'll take temps again, I'm sure I still have the issue.

Any input appreciated, Joe

Good info! Everything appears to be close to OE spec and temp readings are similar to most others I've seen that have no owner added insulating sleeves on the fuel pipes. The 210 is probably because that area of the manifold is right above the heat riser passage, and even with the valve wired open exhaust gas is free to flow back and forth.

Tell us more about your driving environment. Altitude? Brand and PON of the pump gas you use.

Was your measured idle vacuum of 16" Hg measured at 700 with the VAC connected?

Duke

[Joseph S.]

Re: 63 L75 Overheated Fuel

Live and drive the car in central Texas. Altitude around 900 MSL.

I have tried many brands of pump gas- the last addition was Valero 93 PON. I have used Bothe Shell and Mobile 93 POH with the same result. I have used 91 in the past with no obvious detonation issues.

Measured idle vacuum was at 700 rpm with the VAC connected.

thanks Joe

[Joseph S.]

Re: 63 L75 Overheated Fuel

Follow up from my prior notes: -50-75mile drive, 3 stops, 90 degree ambient
Temps post drive- 140 degrees- fuel line, pump to filter, 145-150 degrees- filter, 150+degrees fuel line, filter to carb.

Although better, lost accelerator pump (engine hesitates badly) after second stop. No stalling and drivable but needs a lot of improvement.
Will attempt to insulate fuel line to filter and check again.
Joe

[Frank D.]

Re: 63 L75 Overheated Fuel

For my WCFB on my base motor 63 I used "dashman's" 1/4" phenolic spacer, but he makes AFB and Holley versions as well:

https://www.dashman.net/search.php?q=555phenolic+spacers+afb&submit=Search

He makes 1/2" versions too but hood clearance will no doubt be an issue with those.
I don't know if its been mentioned but the fuel pump to carb line passes close to the passenger side head, I've seen it touching on some cars, so make sure that is pulled away from that head at least a 1/4"; I also insulated that line. Even with my base motor I ran 14* initial timing on Lars recommendation; I don't know if your factory 8* makes a difference but that is way conservative.

I also blocked off the intake manifold heat riser passages with fuel injection gaskets to stop the heat from entering the manifold and getting under the carb at all. Blocking the holes under the carb helps but you still have exhaust heat roiling around under the carb. In the pic you can see that heat is hot enough to fry paint off before it even gets to the carb.

Some friends drive with the hood propped open claiming increased air flow helps the issue, I was never comfortable doing that.
This issue is more than just aggravating, have your classic car stumble in traffic around Orlando and you might just have some moron rear end you.

[Ken R.]

Re: 63 L75 Overheated Fuel

Have you tried any gas w/o ethanol? Walmart/Murphy here as 87 non ethanol, but not sure if any higher octane. Some in the past some have had a can with ice in it installed around the inlet gas piping.

[Mark E.]

Re: 63 L75 Overheated Fuel

Hi Joe,

You've already received some great advice. I always learn from this forum.

Here's what I would do, in sequence:

1. Adjust timing
2. Wire open the heat riser and make sure the exhaust isn't plugged up (it happens)
3. Replace the intake gaskets to block the heat riser passage.
4. Install a lower temperature thermostat. Go to 180 if 195 is installed. I use 160.
5. Insulate the fuel line.

My 1970 454 runs well in Texas heat so there's hope for your '63.

[Bill B.]

Re: 63 L75 Overheated Fuel

Joe, What Mark (and everyone else) said!

I had the same issue and obtained a phenolic 1/2" spacer for mine, which improved a bit, but did not eliminate the issue completely on my very heat transferring aluminum manifold. Had a stock 1/4" gasket there before. I also purchased the insulated fuel fuel line shields but did not install as of yet for summertime driving. I got an approximate 3 ft strip of 3/8" line Velcro wrap and a 3 ft strip of 1/2" to 1.25" line wrap by Design Engineering from Amazon. The wider one is needed for the "Y" block and Holley carb inlet areas, as well as fuel pump flanges and the rubber hose from frame to pump.

I suspect my issue is in the fuel line itself as big time vapor lock would occur upon shutdown, therefore suspecting the fuel pump was not pumping during restart due to boiling issues. BTW - I was already running a 160 deg thermostat and had bypassed the heat-riser valve with a blank spacer. The riser valve replacement fortunately did not seem to affect the warm-up time for the thermostatic choke to fully open. (I don't plan to drive it in the colder winter months anyway)

I do caution, however, that if you completely block the heat riser passages at the head/intake manifold interface, the choke may not fully open or be very slow to open even though the engine is warm and not needing the choking assistance to run efficiently. If taking the complete blocking approach, you may want to adjust the choke for a leaner situation so that you don't over-enrichen and inadvertently foul the plugs.

[Frank D.]

Re: 63 L75 Overheated Fuel

I hope we aren't conflating two different issues, which may, or may not, occur in tandem. Vapor lock is when the fuel at the pump has turned to vapor and the pump cannot compress it enough to pump it, there are various ways to deal with it, one is by installing an electric booster pump near the gas tank, but that has some downsides and is a temporary fix. (see picture). This allows fuel to be "pushed" electrically through the line from a relatively cool location instead of being mechanically "pulled" from a hot fuel pump at the engine.

Heat soak (from percolation) had fuel dribbling down the carb throat to the point that after 20-40 minutes there is a pool of raw fuel sitting on the intake runners so the driver, upon restart, is basically cranking a flooded car (and so flooded car start techniques apply). This condition usually abates after an hour as the fuel evaporates. This condition can be independent of vapor lock.

[Bob W.]

Re: 63 L75 Overheated Fuel

Frank, that is a nice size electric pump, what brand is it?

Thanks BOB

[Frank D.]

Re: 63 L75 Overheated Fuel

The trick is to find one of these pumps that won't have too much pressure; this is the unit:

https://www.amazon.com/SUNDELY-Unive.../dp/B010R12MA2

Currently unavailable but the same part is rebranded under several names:
https://www.amazon.com/Electric-4-5-...7W3DRZ41&psc=1

It is operated with an LED switch near the driver's knee at the center console. I installed it as an emergency stopgap if vapor lock should occur when I'm in traffic. Too many tail gaters and modern roads in my area don't have shoulders. A problem that was a minor nuisance in yeas past can get you killed nowadays.

Before I solved the vapor lock issue though means listed above this method got me out of a couple of bad situations. Its also great to prefill carb bows if the car has sat for weeks and very unobtrusive.

HOWEVER, two important caveats since this pushes fuel THROUGH the factory mechanical pump.

1) If the mechanical pump gets a blown diaphragm and you don't notice it, this pump will put raw gas in your crankcase and

2) if you are in a rollover crash there is no oil pressure shutoff switch, the electric pump will continue to pump fuel if its powered even if the engine is not running. (It is possible to add such a switch)

So this workaround is relegated to short-term, emergency use.