Carb'd cars and vapor lock

[supersportsp]

Greetings folks,

 

I have a carb'd (Weber 45 DCOEs) Zetec in my Caterham. The last two summers I have been experiencing issues which I now think appear to be vapor lock. Car gets hot driving around town/in traffic, starts to run rough, then dies. Let it cool down (hood off is faster) and car restarts and runs fine.

 

Bruce from Beachman and I have been through all of the electrical issues and replaced and or revised a number of components that could be impacted by heat. But, the more I read, the more I think it is actually a fueling issue and likely vapor lock.

 

Question is this. Has anyone else with carb'd cars had issue with this? I have seen some info that the gas formulations the last few years, particularly on the West coast are contributing into making carb'd cars more prone to this.

 

If you did experience this, how did you solve it? Seek out optimal gas formulations? Modify the fueling system (ie move the fuel pump) to help limit or alleviate the issue?

[coffee break]

This is either "outside the box" or just off-the-wall.

Add a fuel return line to the system. Install a pressure regulator next in line to the carbs and a T before the regulator. With an electric fuel delivering more pressure than the regulator allows you would be getting cooler fuel from the tank.

[DeanG]

I shielded the fuel line from the transmission tunnel forward. I don't know if the problem is resolved as I haven't driven in extensive heat since the fix.

[NVP66S]

Take 1: I had an old car with twin sidedraft Solex carbs (kinda like Webers) and it did the same thing. That car had a manual prime lever on the side of the mechanical fuel pump, and a few jabs at that lever always got it running again. I fixed it by making a longer rod that drove the fuel pump off the camshaft.

 

Take 2: A friend of mine made an off-field landing with his Continental engined airplane. This happened soon after takeoff, and that was after a half-hour in August waiting and idling for takeoff clearance. We decided that he had bubbles in the fuel line, as that installation had both mechanical and electric fuel pumps, and good pressure. He looked at the fuel pressure gauge before takeoff and it was good. Here, even though there were 2 pumps in series, there was still very little flow to the idling engine, and bubbles (vapor lock) formed; not enough cool fuel coming from the tank to overpower the heat added from the hot engine.

 

Modern fuel injected cars have solved this problem by putting the pump inside the tank (below it is OK too) and by flowing a continuous loop. So try the advice above: Insulate the line to reduce heat pickup, and if that doesn't work, add a return line to circulate cool fuel.

Dan

[yellowss7]

When I autoxed in the Summer, While sitting in grid waiting, if I sat too long, my car would start to require more and more throttle to keep the car from stalling, then if I didn't get to the line quickly, no amount of revs would keep it running. It would cut out and require the bonnet and air filter to be removed and cool off for a a few minutes it would be fine. It felt to me like the heat soak from the hot tarmac would cause an air compensation issue with the fueling. I never had a problem any other time on the street or track, just sitting idling for long periods in really hot weather. I think a bonnet cut out for the air filter would have solved the issue. And my car is on Fuel Injected TB's. Tom

[rx7locost]

These symptoms are common with MGA's and modern fuels. The fuel in the bowl actually boils causing a lean mixture. One way to confirm a lean condition is happening is to enrich (apply choke, if present). If the engine smoothes out, then this is the cause. A few have found a solution by installing a boat bilge pump and directing outside air directly onto the fuel bowls on the carbs thru the use of air tubes. This works for SU carbs. Might work on Webers?