General TR Fuel Boiling in the Bowls

I can’t quite remember the thread on this earlier. But, I had trouble starting my car the other day and noticed that gas was boiling through the fuel line into the float bowls. The car only sat for 30 minutes.

My recollection is that the difficulty starting is related to the fuel boiling into the float bowls while the car seats after having been driven.

The solution, as I recall, is to wait a half hour so for the flooding to dissipate. Is that correct?

Is there some other fix?

You can try to stop the excess heat by installing a heat shield between the carbs and the exhaust manifold. Or treat the exhaust manifold to reduce the heat coming off of it. But most cars do not do this so there might be some other problem such as poor timing.

charleyf said:

But most cars do not do this so there might be some other problem such as poor timing.

Click to expand...

FWIW, few years back I went on a caravan with the local club up Angeles Crest Highway. We stopped on the way up for a biology break. About 20 minutes and on our way. Every single Triumph in our group had trouble getting started, and blew black smoke when they did.

Might have something to do with was they sell for petrol in CA, but its clearly a common problem.

Adding one of Joe A.s heat shields helped a lot, but did not eliminate the problem on my TR3. Since I already have an electric fan, my next step will be to rig the fan so it continues to run for a few minutes, to blow some cool air past the float bowls. More insulation on the heat shield, or ceramic on the manifold would probably ly help too.

Its certainly good to check that there isn't something causing high EGT. But driving even moderately hard is going to heat the manifold to somewhere around 800F, and the carbs are right above it. With the car stopped, and no fan, guess where that heat goes.

One fairly subtle cause of high EGT is wear in the carburetor jets.

I do have a heat shield but it seems to do little. I'll try wrapping the manifold and also putting some kind of heat shield around my fuel line from the pump. I noticed that stretch of steel was really hot. Right as it exits the pump. Another problem may be that I've snugged the fuel line away from the fan with a ziploc tie around the upper radiator hose, and it's possibly touching that hose.

I didn't have any luck with just the heat shield preventing fuel percolation...but by adding a couple layers of Heat Insulation on the top of and on the bottom of the heat shield floor, percolation became a thing of the past...you might try it.
https://www.summitracing.com/parts/hsp-721202
There are 3 layers, an adhesive, a woven mat of insulation and a reflective top layer.

Modern fuels boil more easily than ones of the 1960s and create vapor bubbles in the fuel lines and fuel filter, if you have one. I'm amazed that fuel gets past them at all. I did a lot of experimenting with this when I had my Bugeye Sprite; I found that arranging the fuel lines so they sloped upward everywhere allowed bubbles to vent through the carbs, preventing them from forming in the lines.

Beyond that, anything that keeps the carbs cool should help. I don't like the idea of doing anything to insulate the exhaust manifold, like wrapping it; the heat doesn't go away, it just heats up something else. I think that the ideas of increasing the heat-shield insulation or increasing air flow over the carbs are much better. Also, you can just open the hood if you have to stop awhile on a hot day.

Also, make sure your metal fuel line isn't touching the head or block without some insulation. There's supposed to be a rubber bushing in the clip that holds the fuel line to the thermostat housing where it goes around the front of the head. If that's missing, it's a good place for heat to transfer straight to your fuel line from the head.

I have similar issues when over 90deg and the car sits for over 20 min. I remember someone posting a link to I beleve Joe Curtos carb cozzies for the fuel bowls.They are fitted foil faced heat shield with velcro.
Anybody try those?
Tom