Ehtanol Fuel Boiling in Bowls

[Keith_M]

Keith--

We are all guilty of using the terms "fuel percolation" and "vapor lock" indiscriminately but they describe different problems. The solution that EV proposes might help with vapor lock that occurs in the fuel lines, and maybe that is more of a problem in Scotland than fuel percolation which is what we Healey owners in The Colonies suffer from due to the intake manifold's close proximity to the exhaust manifold, not to mention high temps under the hood.

Lest we start feeling sorry for ourselves this problem is common to a lot of older cars with carbs--for an interesting PM article go to:

https://books.google.com/books?id=0...NAhWEOSYKHQD9BrUQ6AEIKzAC#v=onepage&q&f=false

This is a really good article that clears up my misconception about boiling of fuel in the carb bowls. I assumed that boiling prevented fuel from reaching the jets, but it turns out that boiling actually allows more fuel to reach the jets and therefore floods (rather than starves) the engine. I now understand why your tube to the intake manifold works!

 

[BOBBYR]

Hi Guys, You really have an interesting problem here . Has anyone put a inferred thermometer on the float bowls as this fuel is boiling ? I'm not doubting you . I have never run into this problem myself
BobbyR

 

[Keith_M]

I've never checked the temperature of the bowls, but it happens to me a lot on hot days. It only happens if I drive on the highway for a while and then stop and turn off the engine. If I restart within 10-20 min, the engine will miss for a while until air moving through the engine compartment cools things down. It used to happen to me if drove hard and then stopped at a stoplight for too long (with the engine running), but adding a Texas-Cooler-type fan and an electric fan has pretty much taken care of that problem.

 

[Michael Oritt]

All--

This past weekend I raced the Elva Courier, to which I have fitted the air valve, at the PVGP. After about three laps of hard racing we were black flagged in due to an on-course accident and lined up for a restart. My indicated engine temperature was about 230 degrees when I shut down and the temp didn't cool much during the five minutes or so we waited for the restart. When given the green flag I simply opened the valve and pushed the start button--the engine started instantaneously, I closed the valve and was off like a prom dress.

Again I am not saying that this fix is for everyone but it simply points the way that the problem is too much fuel and not enough air--not the other way around.

 

[BOBBYR]

Hi Mike, that's a pretty interesting fix you've created. I believe you when you say introducing a blast of fresh air gives you an instant start . Are you saying that your device clears vapor lock in the intake manifold ?
BobbyR

 

[Michael Oritt]

Hi Mike, that's a pretty interesting fix you've created. I believe you when you say introducing a blast of fresh air gives you an instant start . Are you saying that your device clears vapor lock in the intake manifold ?
BobbyR

Bobby--

Though the terms "vapor lock" and "fuel percolation" seem to be used interchangeably they really describe opposite conditions, the first being an absence of fuel in the mixture and the second being an overly rich condition brought on by too much fuel being introduced to the combustion chamber. Nevertheless the result is the same--difficulty in starting the engine.

So yes, I am saying that the "breath of fresh air" allows me to start the engine instantly whereas before I installed the mod I often sat on the grid cranking a hot engine until, eventually, it would fire off. This might not be a big problem in normal conditions but in racing it is important to have the engine running when the green flag comes out, sometimes made difficult by delayed starts, restarts, etc.

 

[Elva150]

Got one more comment to add....might be different cause/effect than yours..but along the same lines...

This was a real issue on starting our HP Bugeye (and other H/HS carbs) race cars, back in the day: Got hot, stopped, wouldn't restart; without lifting the dash pots or waiting forever. You'd be stranded out of course (think: Ponca City on July 4th) if spun/stalled...couldn't restart...race over... was a real bummer.

Quick fix was to lift the dash pots. Of course, that took a 2nd set of hands, with hood opened. No good, 'cept in the pits with a "crew". A better fix was to use a choke cable from dash, to rear carb; use it to lift/push up the carb's piston (cable, replaced the lift pin on body....cable pushed rather than pulled...). Buddy with GP Spit. did this with good results.

What was later discovered (my "real" mechanic buddy): We'd run about 30 deg. total advance, lumpy cams had lots of overlap, not much vac at cranking. Most of Lucas distributors have a 13-15 deg cam (30 at crank) for dynamic adv..... so, the static advance was practically nil. Wouldn't fire off the "lean" mixture, as it was too retarded. We modified the distributors to limit the centrifigual adv. to 11-13 deg... either by brazing on an extension to the cam, or putting a sleeve (brass tubing from hobby shop) on the posts to engage cam stop earlier. This clear up all the hot restarting issues. Discovered this in early 70's and still using on most of my vintage/race BMC/Triumph cars, today.

I'd say that Mike's valve is doing the same as lifting the SU pistons, gets a bit more air/mixture going in to light off...

As to heat soaking and boiling with ethanol, don't know. Try to stay away from it, running "pure" gasoline as much as possible. Do know that early 260Z's had the recirc. line and added insulation on fuel lines. Needed it to work. Underhood heat can be issue. So the Big Healey issue here, might take a different solution than working on the distributor as I reported.

Just another experience to pass along.

Bob L.