Carb Fire!

[Hi_Fi_Guy]

Suffered a carb fire. Wil have the car towed to a mechanic for inspection.

[Bill Douglas]

OMG, I'm pleased you didn't lose the whole car. Well managed.

[yelcab1]

I don't have any input, except to say that you got balls if you sped up and put the fire out by sheer air speed. I have always thought that adding air to fire is … bad.

When I suffered a fire with carbed car, I pulled over, open the hood, and got out my extinguisher and put it out. Then drove home and clean that mess up. For a moment, I thought about letting it burn down and collect insurance.

Well done. Good luck.

[Hi_Fi_Guy]

I always carry a fire extinguisher in the car! You can never be too safe.

[proporsche]

good job saving it..are those Zenith carbs? maybe you float valve-got stuck open..Do you have a fuel press regulator in the system?

Ivan

[Hi_Fi_Guy]

Float was my first thought too. We will see what the diagnosis reveals.

[pmax]

Sorry to hear about this. Congrats on saving the car and yourselves !

Wow ... I posted this yesterday in another thread CA - Festival of Speed - Where have all of the Air Cooled Gone? about your RR incident !!

I would worry about what's melted inside those carbs.

[Hi_Fi_Guy]

I agree. The shop plans on disassembling, cleaning, and rebuilding as a precaution.

[proporsche]

Hi Brian..i just finished last week one Zenith for a guy who owned the 911 for 18 years.Never knew why it was running so bad a spitting gas out of the pipes.
His floats were overflowing...due to the missing regulator and he had 911S fuel pump in the system.I got him PMO regulator and he is a happy camper now...
So that is not your problem i suppose,but it should be only 3-4 bars pressure.Also do you have at least one fuel filter?

Ivan

[Hi_Fi_Guy]

@proporsche
- Yes, I have a fuel filter. Less than 1 year old. Will inspect but was clean last time I checked.

[proporsche]

Yes, the PMO has a return line for the fuel.Funny there are next to you at partsclassssiicc in Arizona.Talk to Kurt he is a great help..

Ivan



Classic Parts for Air Cooled Porsche®
928-255-2824

[Hi_Fi_Guy]

Will do!

[juanbenae]

Originally Posted by proporsche

but it should be only 3-4 bars pressure.?

Ivan

I thought a bar was 14.5 PSI??? did you mean 3-4PSI that carbs require as I understand it?

I too am glad you were able to save the car from any further damage. I can't tell in the photos you included what is remnants from the fire, and/or if the other stacks became so filthy looking from sucking in the melting air cleaner and other combustion by products. can you post a picture of the other unaffected bank sans filter for a clearer idea of the state of the carbs??


running carbs I carry a halon extinguisher in the cabin of the car at arms length and a powder unit in the frunk. if a fire continues after the clean halon does not take care of it I will only then use the nasty, messy powder unit. my plan would be should I experience the misfortune of a fire to NOT open the deck lid simply pushing the halon through the grill so it's most effective at displacing the oxygen as is the method of the type of unit.


as pmax always says carbs are not to set and forget. whenever I take mine out I open the deck lid as it warms up looking for things out of the ordinary before proceeding with the drive. fuel leaks, regulator PSI, or anything im not accustomed to seeing. the fuel blends today require extra attention with carbs IMO.

all in all you had the best results possible considering the circumstance.

[proporsche]

juan...yup my bad ,ofcourse psi;-) thanx for the correction

Ivan

[Hi_Fi_Guy]

@juanbenae other bank looks as new. Clean inside and out.

[porsche930dude]

Stack screens act as a spark arrestor if im not mistaken. Might help a bit.

[1QuickS]

Zeniths have ribs on the top cover (below the gasket for the air cleaner) that act as fuel reservoirs. Any backfire during startup can ignite the fumes. Zeniths seem to be more prone to carb fires than Webers due to this "feature".

Fuel will boil in the float bowls after shutdown and this will cause fuel to rise up vent pipes and spill into these reservoirs; just waiting for the right circumstances to catch on fire. A return to tank regulator (PMO devices are not true pressure regulators, they are actually flow control valves that adjust pressure to carbs by adjusting return to tank flow rate) will not help. Regulators are good to assure over-pressure is avoided but once shut down there is no way to bleed float bowls back to tank without a separate float bowl scavenging system, which is not a half bad idea.

Hot ambient temps, hot engines, high altitude and modern fuel formulations are the problems to recognize and overcome. Insulators (possibly a stack of two or three (longer studs needed) is a good place to start).

[icarp]

Most carbs need less than 2lbs of fuel pressure . The make special low pressure pumps for webers and zenith carbs

[Hi_Fi_Guy]

Originally Posted by 1QuickS

Insulators (possibly a stack of two or three (longer studs needed) is a good place to start).

Care to elaborate 1QuickS? I've read many of your posts here and respect your input.

[1QuickS]

A respected Pelican contributor, Grady Clay (deceased) mentioned in one of his posts that he used a stack of three insulators on his track car to help avoid heat transfer to his Webers after shutdown. He lived in Denver or similar high altitude location. That caught my attention since it addressed one issue that I mentioned: hot engine, hot ambient temp, high altitude and modern fuel formulations.

Can't do much about high altitude, hot ambient or fuel formulations but a hot engine conducting heat from the heads to the intake manifolds and ultimately to the carbs may be mitigated with some insulators between heads and intake manifolds. I think a stack of three is probably the limit due to headroom clearance with the OEM air cleaner housing in the engine bay. Throttle linkage rod from transmission to bell crank at cylinder #3 will need some "adjustment" and probably clearance added to sheet metal where the rod passes through.

Today's fuels have a lower vapor pressure than those of yesteryear which allows a lower boiling point.

Webers have a remedy (sort of) developed by Ferrari for the 512BB which used the triple throat Webers our 911s use. PMO popularized the remedy which has merit but also has some drawbacks. The basic idea is to re-direct boiling fuel in the float bowl down the bores of the carbs before it escapes the throttle bodies & subsequently drips onto a hot exhaust system...a really bad day can follow.

I developed an alternate to the Ferrari/PMO "fix" that improves hot restart issues associated with the typical PMO fix.

When test running Webers that I have serviced it is not unusual to have a flaming spit-back through the intake horns. If there were gas fumes in an OEM air cleaner this spitback can ignite the fumes and if there is pooling of gas in the recesses of the Zeniths then you have a fire with a goodly amount of fuel to burn.

I developed an "anti-percolation" remedy for Zeniths when I was still servicing them but that does not remedy the potential pooling of gas in the top of the Zeniths. Possibly drilling drain holes to allow gas to escape would be good with the risk of this gas getting on the exhaust headers...

Taking precautions to allow engine to cool down as much as possible before shutdown and parking in the shade are suggestions to consider. Also, you could install a fuel pump switch to kill the pump a short time before parking to allow a little drain-down time of fuel in the bowls. An extreme approach would be to plumb the drains in each float bowl and scavenge pump gas back to tank after shutdown.