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General Tech Gas Boiling Still—a Thought

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KVH

KVH

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I’ve discovered that there is a material difference in the temperature of the gasoline in my front SU HS6 float bowl compared to the rear float bowl.

The front is showing 132° in mid afternoon driving, and the rear is showing 148 to 152°. I’m told that the boiling point for gasoline, especially with ethanol, is right about 150°.

I assume this is a material part of the problem I’ve been having with mid afternoon driving, idling at stoplights, etc.

In carefully checking the operation of the engine, I can see there is definitely a blast of hot air coming off the exhaust manifold, and which is directed by my fans, standard plus auxiliary, toward the rear of the engine compartment.

This must explain the difference.

I have a heat shield and I’ve tried applying some reflective insulating material. Neither has been helpful reducing the temperature of that rear float bowl.

A suggestion has been made that I put fabric heat shield over the steel shield that I already have. I just don’t know.

I am wondering whether anyone else has encountered this, and what other ideas you might have.
 
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I run premium. Is that a mistake?

I’m fairly certain upon further examination that most of the heat is bouncing off the firewall near the passenger foot well and coming up to “fry“ that rear float bowl.

I’m going to first try more flexible foil backed heat shield material in that location. The other alternative is that I Pull the carburetors yet again, remove the steel heat shield, and fabricate an extension of it in that same location, but, if I did that, I would then be blocking access to both the generator and the starter. I’d be removing the carburetors anytime I needed to access either one of them.
 
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Before you try to fix a problem you think exists, Try wrapping a wet rag around the float of #2 to cool it
temperalay to see if symptoms persist . I salute anyone in Az that drives a Tr in the summer.
Took the Mini out Wednesday in 96deg heat.The car was better of than we were!
Mad dog
 
Good idea MD that should help explain some of the theory of boiling fuel.

Up here in Washington with the cool weather my car is happiest in Fall. The idle is stronger and will hover around 700 rpm. Summer driving around here on a very hot day, I often need to push the gas pedal to the floor to let more air into the engine when trying to restart the car. If I do not hold the pedal to the floor when restarting, the engine will not catch. There are no accelerator pumps in the SUs so holding the pedal to floor only lets more air into the engine without more fuel. i think the boiling gas some how floods the engine

steve
 
Modern gasoline boils. This happens in everyone's car, whether they realize it or not. Occasionally the boiling can leave bubbles in places, like upward arching fuel lines, where they will slow or prevent fuel from passing. This was the problem in my Bugeye Sprite, and the cure was to move the fuel lines so they were routed continuously upward. That way, the vapors simply vented through the float-bowl vents instead of forming bubbles.

It's hard to give a specific boiling point for gasoline, since it is a mixture of substances.
 
Hi there.
Extending the shield might help. Instead of removing it to extend it, you could simply add a piece of bent metal over the ledge and extend it as close as you want to the firewall. You could simply screw it to the shield without taking the shield off. Easily remove for access to the starter. Just a thought.
Fern
 
Good ideas, but it’s complicated. I tried the wet towel but it was inconclusive.

I might extend that shield like Fern says, but after I blocked the heat blast from the lower exhaust manifold areas (replicating an extension) there’s still a heat blast, and that rear carb got hot again.

But my fuel line between my two carburetors, that 12 to 14 inch stretch, was even hotter, measuring almost 160°, which I find difficult to believe. Also unbelievable is that the portion of the fuel line that I insulated appears not to be any cooler. I’m going to remove the insulation on the theory that I’m actually making it worse.

See pic below. Triumph specifically designed the fuel line to hug the block, and then to hug the cylinder head, and to virtually touch the heater bypass hose, and then it comes in front of the engine. What a course!

Well, I think this issue is beat. The heat shield and extensions can only do so much, and with that fuel line where it is, the best I can do try to cool things down. I’ll keep experimenting.

Thx all.
 

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Hamish, another forum member on here ran a fuel line from the pump along the firewall to the rear float bowl. You just have to switch the fuel bowl lids around. This routing avoids the engine block and thermostat area heat. This is on a TR3 that he races but I cant see why it would not work on a 4A I would post a picture but cant find the post he once sent me when we were discussing fuel line heat issues and vaporization.
 
It sounds like you're not having enough fresh or at least outside air blowing over the carbs.
 
I added an auxiliary fan last week. It has helped only slightly. Yesterday, I expanded my heat shield to almost completely isolate the rear carburetor, which seems to be the one getting so hot. I’m going for a test drive in a few minutes. Hopefully, I won’t be towed back home.

FYI, I just bumped into an MG owner, who I saw parked in the shade at a convenience mart. We talked about vapor locks and stalling, and he told me that he found a great fix. He said he avoids driving between 11 AM and 3 PM during the summer months. I guess I could try that next. I won’t need to disassemble anything, and I won’t even need to buy any new parts.
 
Does anyone here recommend automatic transmission fluid in the carb dashpots? Instead of straight 20 weight oil?
 
Not very.

I’m still analyzing excessively hot fuel, mixture and performance issues.

Heavy oil in the dashpots apparently contributes to a richer running carburetor. 20 weight (and some say ATF) is an easier piston lift than heavier oil.

Maybe better a separate thread—
 
Hi All
I have been lurking on this post. My few (OK a lot) thoughts on this are that the fuel is boiling in the float bowls. This happened to me on the hottest days when stuck in stop & good traffic or long stop lights. If so,
  • Today's gas, although much higher quality, boils at a lower temp than 1960's gas
  • This is measured in Reid Vapor Pressure. The higher the RVP the easier it boils
  • Adding ethanol and removing lead have raised the RVP. Ethanol free gas is not available in CT (except for race fuel at ~$10/gal)
  • Octane does not affect RVP
  • But, I am told, different brands of gas can have different RVP (i.e. Exxon vs Chevron vs Shell, etc). Try switching brands
  • "Winter" blend fuel (sold here in CT from October to May) has increased RVP to improve cold weather starts. The gas compannies do this by adding more butane. If you don't drive many miles and have a tank of winter blend fuel in the car come June/July, it will spell trouble
  • I add 3oz of Marvel Mystery Oil at each fill up as a cylinder top lubricant but, am told it also lowers RVP
  • I have added float bowl "koozies" to my carbs, as available from Joe Curto (not on website, you have to call him)
  • I have added heat shield to my fuel lines
My car is stock with the original TR4A metal 4-blade fan. I do not want to mess with heat shields. If I suffer issues with boiling fuel (on the hottest days stuck in traffic) due to high under hood temps, I do two things: 1) I pop the TR4A hood/bonnet to give the hot air somewhere to vent, 2) pull my fast idle/choke knob and bring the idle up to 1200 RPM - I stop before the chokes engage. This move more air, speeds the water pump and also pushes more fuel so it has less time to absorb the heat. Once the car is back underway, I can easily reach around the windshield, lift the hood from the corner and drop to re-latch it.

This has resolved the issue for me in 99% cases. Next steps, if I ever want to keep going on this are: a) adding a TR6 engine driven fan (I have both the 8-blade yellow and 13-blade red) and b) rebuilding my distributor vacuum advance. I suspect my ignition timing is not advancing as it should at idle (when engine is under high vacuum). That leads to late ignition timing and increased exhaust manifold temp (and thus, increased under hood temps right at the carbs).

Sorry for the long post

Bob
 
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