General Tech Gas Boiling Still—a Thought

[KVH]

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

Love long posts! Thanks. Always good to learn. About the vacuum advance, yes, I need to check mine. Symptoms are all the same. I feel I’m dialing this stuff in step by step.

 

[RJS]

Cool! Yes my distributor is original to the car. The rubber diaphragm in the vac advance unit supposedly hardens over time (ie 60 years) and no longer flexes/advances as originally designed.

Bob

 

[PDIGIO_6x3]

I'm in Florida guys. I've been experiencing an issue which I believe is the same thing, very hot carbs. I have 3 ZS and I don't know if this is the issue or not. I have a Pacesetter header, wrapped. It definitely runs cooler than the stock cast iron manifold. However, it's been in the 90's here. Yesterday I took the car out for about 15-20 miles, one way trip to the barber shop. He changed his hours, so the trip was nothing but a joy ride. Anyway, about halfway there, the car started to sputter, like starving for gas. I'm pretty sure it's the same issue. Can any of you describe what the symptoms of the boiling gas would show? I can tell you that after shutting the car down for less than 5 minutes, it was fine for about 3 miles, then it started with the same miss, and sputter. It was certainly hot enough to believe this could be the cause. If you can, let me know if this is what you've experienced because it would be a first for me.

 

[poolboy]

I live in SW Mississippi about 75 miles due North of New Orleans...It's hot from May until October so I've dealt with fuel percolation in the ZS carbs float chambers from the get go.
As long as the car is moving forward with enough air flow and the constant replenishing of the gas in the float chamber, there is no 'boiling' or percolation going on. so I doubt that's what made your engine sputter while you were driving.
Percolation occurs when the air flow under the hood in the engine compartment stops and the fuel in the carbs float chamber stagnates and the heat from the exhaust,manifold and header rise up upon the float chamber.
That usually happens in high ambient temperatures when the car is parked or prolonged idling following a complete engine warm up or a nice drive in the heat. The engine will be hard to start within the first 10 or 15 minutes and when it does start it may sputter until all the hot gas in the float chamber has been displaced with relatively cooler fresh gas from the fuel pump.
If it happens to you again when you are driving, reach back and open the gas tank cap and leave it loose,see if that helps.
Otherwise if you are really dealing with percolation, you need to protect the float chambers from the manifold heat.
I solved the problem with a heat shield that I layered with heat insulation material in order to make the heat shield effective...without the insulation, the heat shield didn't do much to prevent percolation.

You might also if you haven't consider an electric fan to keep the air moving when you are just sitting at idle.

 

[PDIGIO_6x3]

thank you Poolboy. I don't know what to make of it. I think a heat shield couldn't do anything but help, so I'll be looking at that for sure. The symptoms feel like there's a bad ground to the coil if I can give you an idea of the cutting out and sputtering I'm experiencing. Again, it only seems to happen during a really hot drive. Maybe there could be an issue with the Pertronix I just put in about two months ago.

 

[RJS]

Agree with Poolboy. If occurring while driving, likely not fuel percolation. Electric resistance increases exponentially with temp. I'd suspect a weak link in your ignition. I had a similar issue several years ago that started intermittent (like you) - exacerbated by heat or heavy load (i.e. climbing a big hill. It turned out to be a faulty low tension lead to the coil (over time engine vibration weakened the joint from the wire to the spade connector). Clipped the wire, new spade connector...$-0- fix!

Bob

 

[PDIGIO_6x3]

Thanks Bob. I’ll have a look through the connections.

 

[AndreL]

This thread has many great suggestions.
I attributed my issue more with vaporization in the line,
as I could drive 3 city blocks away from the last stop, before it would stall out.
After implementing some of the remedies, I installed an auxiliary free flow 2.5/4 lbs/ft electric pump.
By raising the pressure of a fluid, it also raises the boiling point. Bowls are still at atmospheric pressure.
I use it on start up, on the hwy, but mainly in stop & go traffic. Otherwise I use mechanical pump only.
After stalling out due to fuel starvation ~10 times, this has been working out good.
When I feel hesitation in fuel delivery, I flick the pump on & the response is noticeable.

Rock Auto & GM dealer sell the same after-market part they promote as genuine AC Delco.
The first pump died after ~2hrs of use, spread over 1 year.
I made a shackle w rubber mounts to attach to the frame.
I'm no expert, if there are flaws in my theory, feel free to point them out.

 

[KVH]

But you have to be careful not to raise the fuel pressure so high that you encounter flooding in the fuel bowls and overpowering the needles, correct? My Triumph manual suggests a maximum of 2.5 psi.

 

[PDIGIO_6x3]

After reading some the known symptoms for the "boiling gas", I have to believe I'm looking more of a possible electrical issue. The main reason being that my car does not stall at a red light or shut down in heavy traffic. It just starts to cut out or sputter under load during straight out driving. I think I'm going to look beyond a fuel problem for now, but I am going to get a heat shield in at some point. I think that can only be beneficial if nothing else.

 

[KVH]

To me, if your sputtering is under load while driving at higher rpm’s, that would suggest— or at least I’d want to rule out— a carburetor or pump issue. Perhaps way too lean, or the pump has too little pressure.

I use a rather cheap fuel pressure gauge from Harbor freight that literally only takes five minutes to hook up. I haven’t had a moment to address my issue, but my fuel pressure is 70% higher than my Triumph Manual suggests.

You say it only happens when hot. But you say not during slow city driving. Okay, you may need to rule out your coil, and make sure it’s not failing when hot. I’ve chased that issue endlessly, and most people tell you there’s no way to test a coil other than to swap in a new one. You might try that.

Frankly, I don’t think your problem is points or timing, though all of the wires to your distributor and coil should be carefully checked, especially that wire leading from the ignition to the positive side of the coil, and the other leading from the coil to the distributor as others have mentioned.

You could put a multimeter on the positive side of the coil where the ignition wire connects and verify that you have somewhere near full battery voltage. Then you should wiggle the wire and see if your voltage changes. If it does, that wire is bad and I can tell you from experience that will cause your car to sputter and shut down regardless of whether you’re in city traffic. Of course, when you’re doing this testing, the ignition must be switched on. That wire is a serious, yet often hidden, source of a lot of stalling and sputtering issues.

My next thought is that I don’t think you can totally rule out vapor lock inside your fuel lines. You seem focused on the heat issue, and that leads to fuel/vapor issues. I would visually inspect the fuel lines to make sure they are not in direct contract contact with an excessively hot heat source, and I would check that fuel pump as well as your carburetor floats. I am not familiar with ZS carburetors, so there’s not much I can add there, but incorrect float adjustments could cause your problem as well.

I hope some of this helps.

 

[PDIGIO_6x3]

All good points. I will investigate. I will point out though that I've swapped to the Pertronix ignition about 2 months ago. Hasn't been a problem, but up to now, I don't know if it's contributing to this new phenomenon. Would someone normally pair the Pertronix ignition with the flame thrower coil? I didn't do that, but I hear about it and wonder if that can help, since you bring up the coil I suspected from the beginning.

 

[KVH]

All good points. I will investigate. I will point out though that I've swapped to the Pertronix ignition about 2 months ago. Hasn't been a problem, but up to now, I don't know if it's contributing to this new phenomenon. Would someone normally pair the Pertronix ignition with the flame thrower coil? I didn't do that, but I hear about it and wonder if that can help, since you bring up the coil I suspected from I’m suspicious of Pertronix. I also hear they don’t always pair right with coils. Others love them; but when my car won’t run I’m inclined to return to stock.

I’m suspicious of Pertronix and wonder how they pair up with the average coil. When my car won’t run, I’m inclined to return to “stock.”

Check those wires and see if your multimeter jumps around. If it does, you may be surprised.

Let’s assume the wires and current are good, your coil is good, your battery and cable connections are good, and your Pertronix is working. Given you say this problem is highway relevant and not a congested inner city issue, I would suspect fuel.

Have you pulled your spark plugs and inspected them? I wonder if your plugs are lean and powder white? Maybe not. Just a thought.

Also, how new is your fuel pump? Based on my experience, I would say the newer it is, the more likely it is defective in some way.

 

[PDIGIO_6x3]

My fuel pump is also new. I got it about 2 months ago as well from Rimmer. The Moss one I got about 3 years ago had some weird adhesive on the diaphragm that worked its way up to the float needles. That caused a flooding disaster until I put in a secondary fuel filter. Well, all that's resolved with the new pump. There could be something to the lean fuel mix. I've inspected my plugs several times. They look normal to slightly lean. No question. However, it isn't severe. I do have the Goodparts tri carb setup. So, maybe I need just a bit more pressure? Could it be that the mechanical pump just isn't keeping up? Not sure, it doesn't seem to be an issue until it's been running for a while.

 

[KVH]

Yes those carbs could be the issue. Why not ask Richard what the recommended pressure is for a three carb setup, and then check with a pressure tester. Hot fuel and incorrect pressure can cause issues including rich running if the floats are defeated.

 

[PDIGIO_6x3]

Ok, it was definitely electrical. Be sure when plugging in the blade connector of the coil to the ignition wires, you don’t miss actually connecting, but just sliding the plastic insulator over it. I pulled the spark plugs one by one. I noticed a strange pattern of deposits. For the most part, they looked normal except two. Now if they were both on the same carb, I’d lean toward a bad adjustment. One was carbon black, and a bit wet, the other on another carb was dark as well. I started pulling cap wires off to check for loose or low resistance. All checked good. I believe the + lead was the cause and most likely arcing under the loose connection to the coil once everything under there got good and hot. Added a small amount of dielectric grease to all leads, drove around for a while, no more misses or sputtering.

 

[KVH]

That’s great. Sounds like you have it resolved. If that spade connector was loose to the extent of materially interfering with spark and coil function, I still think that a multi tester would’ve showed voltage variation while testing that connection.

It might be worth it to double check.

The thing about a loose wire at that coil post is that it could cause the car to sputter and stall at almost any speed. I’m always a little leery about believing that an electrical issue will show up only when the engine is hot – – but it’s possible.

Good luck m; stay safe. Have fun.

 

[PDIGIO_6x3]

The only problem with testing this particular instance was that I had to pull the wire off the coil anyway. It practically slipped off with almost no effort. That made me look to see why it was so loose a connection. Well it was only loose because it was never positioned onto the blade. I will wring out the wiring again tomorrow to be sure I have good continuity. I did check the charge to the battery while under there, 14.6V.

 

[PAUL161]

I don't think someone would want to do it but, when we were racing years ago we were using a nitro mix in the fuel and we had to cool it with a can filled with ice and a coil of copper tubing to run the fuel mix through, it was dangerious stuff if it over heated!

 

[PDIGIO_6x3]

Cool stuff Paul. Not sure I'm at that point yet. LOL