I'm considering a '73 1.7 that some idiot put a single carb conversion on. It would be no problem a put on dual carbs instead BUT my last 914 burned when the right air filter caught fire (backfire?). It normally never backfired but this was on a hot restart after being stuck in stopped traffic on a very hot day.

Has anyone heard of this happening with dual Webers using the typical open sided air filters? I know there must be thousands of cars with this set-up. So, am I worrying for no reason.

Nick

Sorry, but (respectfully) what's your question?

You had a 914 with carbs on it that backfired and started a fire, right? You're now asking if a backfire through a carb can start a fire?

Don't you already know the answer? Best wishes with this potential project 914!

Be careful out there everybody.

914’s aren’t anymore prone to fires than any other car of similar vintage.

My first 914 was converted to dual Webers and K&N style filters. Drove that vehicle more than 100,000 miles without even a hint of a fire.

Now if you neglect maintenance, and drive around with a backfiring engine, you’re going to be eventually have a fire. I’ve seen it happen on a v8 engine lighting up a paper air filter. So what? Don’t do that.

The reality is that if you spend any amount of time looking at pictures of engine bays on this site, you can probably spot two or three fire risks in any given car. In general people don’t take the risk of engine fires seriously . . . Until it is too late.

Bad ideas:
Running carbs without the Bakelite insulators to keep heat out of the carbs.

Routing fuel lines close to exhausts & fuel lines rubbing on other things.

Fuel pressure gauges, pressure regulators and excess fittings in the engine compartment.

Failing to inspect and maintain fuel lines regularly; let’s call it a couple times a year.

Failing to keep valves adjusted

If were you, I’d do some self evaluation of what led up to your fire and make sure you’re willing to commit to not making the same mistakes again. We would love to see you in another 914!

Of course I know that a backfire can start a fire. I guess my real question is why are there no better air filter housings that would keep the problem confined to burning up the filter? That is what I started looking for in the begining but no joy.

There are air box systems out there adapted to 914’s with dual carbs.

But I respectfully suggest you are asking the wrong question. Expecting a plastic or metal air box to prevent a fire isn’t going to happen.

As stated previously, I’ve seen a OEM air metal air cleaner and paper filter lead to an engine fire.

Another home made airbox system built from scratch by the late, great Brent Brock.

Click to view attachment

Note: these airbox systems are done to decrease NVH, not to mitigate fire risk.

Short answer: Yes. They can be a fire risk.
Any time you have a paper element or oil coated fabric element right on the carb top there is a chance it will catch if the car burps up through the carbs.

Anything that moves the filter farther from the top of the carb helps mitigate that risk.

Keeping the car in tune mitigates that risk. If you have a constant lean backfire then you are gambling.

But you are vastly more likely to have a fire start from a fuel leak or an oil leak then from a carb filter fire.

There have been millions of cars on the road with dual carbs over the years. Some of them burned due to filter fires - but the number is really small. So yes, it CAN happen. But if you keep your car in any sort of tune, its not likely to. Keep your car in a reasonable tune, and replace your fuel lines every 5-7 years.

Zach

Thanks, everybody, for the advice. I will not install any carb on any car with out a heat insulator. I think that would probably have prevented the fire but it never occurred to me even though I believed hot fuel in the float caused it. I may still try to find a filter box if only to reduce the intake noise.

Nick

Let me throw one other thing your way that probably contributed.

Don’t shut off the engine stuck in traffic on hot day unless you absolutely have to.

Engine fan is constantly pulling in cooler ambient air when running (assuming all engine seals properly in place). That airflow through the carbs is cooling them.

When you shut off the engine you set up a hot soak that can boil fuel in the float bowls. Especially if you didn’t use the thermal insulators to keep head heat from transferring directly into the carbs.

At idle there is very little thermal load on the engine. Better to idle with constant airflow than shut off and heat soak as a generalization.

Look for some Knecht or Knecht style all metal open weave filters. Nothing to burn.

I will be installing a blazecut in mine this spring... that will help easy my mind