Vapor Lock anyone?

[thorsen]

Last year, before the restoration, my 1972 250C stranded my wife once and me once. I didn't think it was vapor lock because I could see fuel coming out the accelerator pumps when I moved the throttle.

As part of the restoration, I replaced all the suspect parts - new Petronix ignition and coil, replaced the Zenith's with Webers, rebuild the exhaust manifold/heat-risers, and generally tidied things up.

Tonight while I was trying to charge the AC system, the engine stopped running after about 15 minutes. The bowl vent on the Webers let you see the fuel level, and sure enough they were dry.

The previous owner bypassed the mechanical fuel pump and installed an electric pump of dubious origin. I am replacing it with a higher-quality one and I suspect that will solve my problem. I am having the windshields installed this weekend, so I should be able to drive it Saturday.

[t walgamuth]

Modern fuel is much more volatile than fuel of years gone by. On older carburated cars its a good idea to keep your mechanical pump and add an electric booster in the rear near the tank.

After they sit for a while just turn on the pump (I used to wire them to the ignition....thats not recommended but I never had any trouble from it) and wait til it stops glugging and your bowl is full. Now just give it a couple of pumps and crank it over and it should start.

With a booster pump in the rear you should be good to go.

Tom W

[thorsen]

It was a weak fuel pump. The replacement kept the engine running for the ~30 minutes it took me to charge the AC.

[todds]

My Webers boil pretty badly too, not while running at all but after a hot start of any kind. Sometimes it can be a bear to restart because it'll flood the engine having vaporized all the gas and the choke then being on. I think these carbs are just more susceptible to it. You can floor them though and unload the choke/etc and they'll start. It tends to hurt your gas mileage a bit too! I've been setting my choke as lean as possible to avoid it, and sometimes I'll just turn the key without starting and let the chokes heat up to turn them off as well.

One thing I thought might work is making a pair of relatively thin steel block-off plates for the heat risers, then some sleeves on each stud (or maybe just a few washers) therefore leaving an air gap between the exhaust and intake.

Standard going-to-work 80% city 20% hwy traffic gave me a lousy 15mpg with the associated flooding/etc, is about 215 miles to a tank of reg'lar. This past weekend driving to NY on the hwy, going 60-65mph, the little six revving it's head off returned an astonishing 19mpg! I thought it was a mistake but I got the same mileage driving back too, my range was up to 275 miles on the same tank of wicked expensive 87 octane. I think the combination of steady-state driving and no hot restarts allowed the Webers to really shine mileage-wise. My little timing fuel adjuster on the side of the distributor is maxed out to full advance, I'm sure if I turned the distributor a little and went with premium gas I could do marginally better, but I'm afraid of the prices! I always thought it was about the same city/hwy for this car with it's painfully short diff but I guess "Boston highway driving" and "highway driving" are two different things.

One thing that helps with the Webers and heat is to make sure the fuel line is routed on the FAR side of the carbs away from the valve cover and far enough up away from the hot manifolds/etc. They can be set up either way, one side is just plugged off from the factory. I also heard that simply making a giant shroud of sheet aluminum up around the sides of the carbs will work wonders (but it'd be painfully ugly and kludgy looking)

[thorsen]

I like the idea of the air space between the manifolds - that would probably help a lot. I have a spare set of M130 manifolds sitting on a shelf - maybe I will experiment with those.

I just dread the thought of pulling the manifolds again, although by now I am quite skilled in it.