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MG MGB Technical - Poor Running When Hot - Part Two

I tried to revive this thread from the archives, but it must have been exceedingly dead. I'm posting anew my latest efforts to stop the car from running poorly after a hot start. By that I mean the engine is still hot from a previous run in hot weather (90°F or greater).

Insulating the fuel hose seemed to help, so I thought I'd try insulating the entire fuel line from where it enters the engine compartment all the way to the rear carburetor. I used a cheap closed-cell poly pipe insulation intended for 1/2" water pipes in homes.

I may try to find something better suited, but in the meantime it does make a difference. We've had a week of 90°F-plus weather and the car has behaved much better. It's only blown gas out of the float bowl once or twice and has not run poorly after starting.

I suppose this might have been less of a problem when when the car was manufactured. But these days our "gasoline" contains as much as 10% alcohol, and I wonder if alcohol produces more pressure than gasoline at a given temperature. -G.

Glenn G

Not pretty, but if it works!! There are lots of products on the market, most are reflective as well as insulative, which ought to improve things even more. Is the fitted heat shield in tact? If you have a steel header, wrapping it will cut down on the under bonnet temp and the heat soak to the float chambers.
Allan Reeling

It looks like you are running the stock exhaust manifold, which is much better at keeping heat out of the engine bay than a header. With the heatshield insulation in place, I never had a fuel boiling problem. Now I'm running the Moss supercharger system, which uses a single SU HIF44 carb. Moss makes a special heatshield for the system, but I've never had a need for it, even when running ethanol mixed fuel. It does get pretty hot under my hood, but I've yet to suffer from fuel percolation. RAY
rjm RAY

I agree the insulation looks ugly and I hope to find something prettier that can do the job. I'm not sure why this car, a '67 GT with an 18V engine, is so sensitive to the heat. It has a stock exhaust manifold and heat shield in good condition. Today I got stuck in stop-and-go traffic for a good 15 minutes and the car never blew gas or ran rough, even though the coolant temperature reached 230°. More about that in another thread. -G.
Glenn G

I modified my electric fan to run with the ignition off. (By moving the live feed from the switched fuse to the unswitched fuse)
Now when I pull up and switch off the fan will start up as I'm walking away from the car, and run for a few minutes.

This makes restarting much easier.
Martin Layton

Really shouldn't be needed, it's only responding to heat soak on switch-off, and can cause flat battery and even fires if problems develop. If a UK car doesn't restart normally when the temp gauge is showing maximum heat soak then there is something else wrong.
PaulH Solihull

Glenn- I really think the 10% alcohol is the trigger of my problem. The heat shield is fine, the car is not running any hotter and all of the ignition parts are new. I also have a 58 A and it does not have the hot start problem so that compounds my confusion and frustration !!!
steve ohanessian

This thread was discussed between 01/06/2011 and 04/06/2011

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