Vapor lock--a foolproof if a bit radical solution...

[Michael Oritt]

So much attention seems to be devoted to issues of vapor lock/heat soaking, I thought I would post an absolutely foolproof--if a bit radical-- solution to this pervasive problem I cam up with several years back.

The car in question is NOT my 1954 100 Le Mans but rather my first race car--a 1622 MGA-powered Elva Courier equipped with two HS6 SU's. On hot days it was often impossible to get the car to restart once the engine got hot--which often happens when, for example, there were delays on the starting grid and it became necessary to shut down due to threatened overheating OR during restarts after an all-in black flag etc. In such situations when the engine was "heat soaked" no amount of cranking would work until the engine cooled down and on a few occasions I actually missed getting off the grid--quite frustrating to sit there watching the race proceed without me.

The solution I came up with was to provide a simple, positive way of getting relatively cool air into the combustion chamber: The intake manifold had a balance tube in which there was a threaded. plugged port. I inserted a brass 90 degree ell into the port and ran a fuel-proof hose (1/2" ID) back through the firewall to a brass two-way ball valve with a lever handle which I mounted through the dashboard near the steering wheel so that the handle was easily accessed simply by reaching under the dash.

When it came time to start/restart a hot engine I would crack the valve open with one hand and push the start button with the other. Invariably, despite high ambient or engine temps the car would fire off immediately and I would close the valve immediately as it almost seemed like the car had received a straight injection of starting ether! My ultimate intention was to replace the manual valve with a spring-loaded version that would immediately close when released but I sold the car before doing this.

I'll admit this might be an extreme solution but if one lives in a very hot high temp/humidity climate and/or is continually plagued by what we call vapor lock or heat soaking (luckily not a problem from which my 100 suffers) it is worth exploring.

 

[Rob Glasgow]

Michael, I can see where that would work on a “fail to start” vapor lock but my issue has always been with stumbling on restart after the engine is good and hot and the ambient temp is high. Takes a mile or so to smooth it out. Any suggestions for that?

 

[Michael Oritt]

Rob--

The arrangement served as a "reverse choke" for starting purposes only and cracking open the valve provided a source of cool air, diluting the overly-rich mixture to the point where ignition could take place. Once that happened I was literally "off to the races" using WOT and I never had any problems with the mixture once the engine fired off.

From your description it sounds like after ignition your car's mixture is temporarily overly rich and if it takes a while for your engine to smooth out then perhaps leaving the air valve partially open after start-up, and closing it as things stabilize might do the trick. Assuming there is an available port on your intake manifold it really wouldn't take very much to rig up a temporary setup with a hose to the cockpit and a valve you could adjust to see if the setup provides relief.

I hope it works for you and if so the naming/renaming of your first-born in my honor will be sufficient.

 

[Rob Glasgow]

Michael, yes it sounds like a easy experiment. As far as the naming, would you prefer ‘Reverse Choke’ or Ball Valve’. I see some issues with either.

 

[GregW]

I think it would depend on the first born being a boy or girl.

 

[steveg]

Rob,
A friend has fixed vapor locking on his BN6 with a combination of insulating the bridge pipe between the carbs and use of Joe Curto's "coozies" around the float bowls.

 

[Rob Glasgow]

Thanks Steve, I‘ve added those modifications recently and now waiting for some hotter temperatures to see if they help. I used some DEI insulation.

 

[Michael Oritt]

Rob--

I understand your concern with the term "reverse choke" and will amend to the somewhat wordier "supplementary cool air inlet system" instead.
As to "ball valve" I see no problem with it and suggest perhaps you should broaden your horizons....

You did very nice work in cladding the lines and bowls and I hope it works for you. I guess I should count myself fortunate for not having this problem on my 100.

 

[Keoke]

That is what he said Greg:

BOy--OR--ITT Gril