Carb fire.. why? Options

[H2ohs]

Hi All, took the car out of storage, cleaned, took for a 20 min ride. Was running great. 3 min from home, it started to run really rough. Not sure if it was on fire at this point, but barely made it home. got out and flames were shooting from the grid. Fire extinguisher was close, so put out pretty quickly. Rain tray melted and made a mess. The carb filter totally burned and destroyed. All fuel lines in good shape, no leaks. So what would make the carb catch on fire like this? float? timing? this pic is after trying to clean the fire extinguisher mess off- it still runs fine actually. Ideas?

[GregAmy]

A typical culprit is a leaking fuel line (how old are they) and/or a float bowl valve that was sticking (or the float was sunk), thus dumping fuel overboard out of its vent.

Clean it up and check through it carefully. And of course replace all the fuel lines.

[Superhawk996]

Sorry this happened. At least you caught it before it became a total loss.

Repost from another fire thread about a week ago.

Is it the mid engine design?

First off I want to say I’m terribly sorry you lost your car.

No, fire potential isn’t related to mid engine. There are plenty of other mid engine cars that don’t burn as often as 914s.

In no way is this list meant to be specific to you, the other car in this link, or anyone in particular. Some of the things I’m going to list I’ve done myself in my younger days.

Top of the list. 914s are and have always been owned by cheap SOBs that are stretched thin financially just to own the car. As a result maintenance gets deferred or gets done by a shadetree DIY to a low standard. Sometimes this is due to money, other times due to ignorance and learning the hard way. This was me when I had my first 914 in my 20s.

Other contributors in no particular order:

Not properly routing fuel lines. Fuel line needs to be carefully routed away from exhaust and heat exchangers and needs to be properly secured to keep it where it belongs. You wouldn’t believe how quickly metal edge can saw through a vibrating rubber fuel line that touches it. Think vibrating multi-tool saw. Basically the same motion happening between two vibrating parts. Free plug for Tangerine Racing - great metal lines that properly route fuel line up though the engine shelf. I’ve seen rubber fuel lines routed up through that shelf without proper rubber grommets. Yeah - I did that too when I was young and dumb. (IMG:style_emoticons/default/screwy.gif)

Fuel hoses should never have another hose touching it or crossing it. Lines will wear though one another if left free to rub on each other.

Plastic fuel lines in tunnel - still a ton or cars out there with these

Using fuel hose that isn’t FI rated (noted by others)

Using old fuel hose - storage time matters. Both on the shelf before you bought it as well as time spent sitting in storage on your car. All OEMs moved away from rubber fuel lines eons ago. Rubber doesn’t age well.

Using worm drive hose clamps on fuel lines (I did this as a youngster (IMG:style_emoticons/default/headbang.gif) )

Regulators and fuel pressure gauges in the engine compartment. These just represent more potential leak paths and usually result in convoluted rubber fuel line routings to get to & from them . Do you really want the integrity of your fuel system to depend on a $10 gauge you bought off Amazon?

Plastic fuel filters in the engine compartment. Yes the OEM fuel filter is plastic and is also mounted down near the engine mount / heat exchangers. Not VWs finest engineering. It was the 70s and lots of drugs were the norm (IMG:style_emoticons/default/happy11.gif) Plastic fuel filters mounted down at the bottom of the floor pan & engine compartment edge can get damaged by road debris leaving fuel spraying right back to a hot exhaust. Believe it or not I’ve seen fuel filters hanging below the floor pan.

Leaky fuel injectors due to age. The rubber j-hoses right off the injectors, and general OEM fuel line routing for FI. Again not well conceived vs a modern car. All that rubber hose running a loop to/from the metal OEM FI tubes that connect to injectors. Would never fly in modern FI design, DFMEA analysis, or litigious environment.

3 port fuel pumps. Again OEM location is sub-optimal. The pump inlet outlet are plastic and can crack with age. At this point many have 50 year old rubber seals that can begin to leak at the electrical connector area and the main pump body.

Electrical connectors and wiring. Some of the wiring in 914s is abysmal by modern standards. Not fully fused. Not well routed or secured. Electrical wires crossing fuel lines. And this is all before 50 years of DAPO “fixes”. I’ve seen so much bad wiring on 914s over the years. Again - did some of it myself back in the day.

Not using grommets to protect electrical wires (including 4 ga battery +) at pass throughs.

Leaking CV joints - throwing grease onto hot exhaust and heat exchangers. Yes, really you can start a fire this way.

Rodent debris. Again, not kidding. Rodents love to build nests below the tin. Leaves get sucked in by the fan and build up. If any of this material gets hot enough it can combust.

Finally as previously stated, engine conversions bring all sorts of other potential issues into play (MFI, CIS hoses, even higher fuel pressures, cobbled wiring, etc.)

Bottom line: be very careful about the condition of the fuel system; this includes carbs. Leaking, weeping carbs may be lower fuel pressure but still can leak fuel onto hot exhaust and ignite. Carb backfires can catch Oil saturated K&N filters on fire which can spread to fuel lines.

Be careful out there!!

[Superhawk996]

This looks suspicious - is the red wire the feed from Alternator B+ shorted out to carb manifolds with insulation burned off to bare wire?

I can’t tell for sure from photo?

Fire appears to have burned longest & hottest on this side.

[peteinjp]

How long was the car in storage? I’ve seen fuel lines weep after being in storage only to seal up after running a bit.
Pete

[bandjoey]

The float in mine cracked down the middle dumping raw gas down the throat

[nathanxnathan]

I wouldn't run a fuel filter on that side of the pump. Best not to have it in the engine bay, and definitely not just loose.

Seems like the fire came from the driver side carb. I've never had that happen but I've read late timing and running lean can cause backfires that can make paper filters go up. Seems like you aren't running a regulator, could be a contributing factor, excessive fuel pressure forcing fuel past the needle valves. Heavy float would be something to look for too. Good thing you were able to put it out.

[Olympic 914]

On a friends car, a lead plug in the side of his Weber carb blew out and squirted fuel all over the engine compartment.

also noticed rough running and a strong smell of gas.

He lucked out and it did NOT catch fire.

[rhodyguy]

There are 2 galley plugs on the inside face of each carb. You can see them in the pass side carb picture. They work their way out and then like a open hose they gush. Are both plugs in place on the burned up carb? Happened to me. No fire but I thought it was all over. Found the plug on the tin and tapped it in with a rock, drove home, took the carbs off and had the plugs replaced on both carbs.

[VaccaRabite]

Hi All, took the car out of storage, cleaned, took for a 20 min ride. Was running great. 3 min from home, it started to run really rough. Not sure if it was on fire at this point, but barely made it home. got out and flames were shooting from the grid. Fire extinguisher was close, so put out pretty quickly. Rain tray melted and made a mess. The carb filter totally burned and destroyed. All fuel lines in good shape, no leaks. So what would make the carb catch on fire like this? float? timing? it still runs fine actually. Ideas?

So the car started popping and then caught fire?

And the fire burned up the air cleaner first?

I can almost promise you I know what happened.

Pops through the carb tops (lean condition) are explosions that happen inside the air filters. If there is enough oil on the air cleaner this can catch fire and the cleaner burns. Melting the rain tray. Once it gets started there is lots of flammable stuff in the engine bay to keep it going. The air filter is coated in oil (thats how it filters, the air passes through an oil membrane and traps dirt that would get through the filter). And carbs that are out of tune will spit gas through the tops of the carb - this leads to the popping you hear. A filter fire would produce exactly the damage you are seeing, and would also explain why the car will still run - the fire did not get involved enough to catch all the other rubber and plastic.

You got REALLY lucky!

I was watching a friend of mine's 914 do exactly this just this weekend. Carbs were popping and it was night time. It looked like a rave was happening inside his air cleaner.

Zach

[VaccaRabite]

@H2ohs

Any follow up from this? A fire thread is always a super important thread for our cars. There is always a takeaway for the gen-pop!

Zach

[930cabman]

This looks suspicious - is the red wire the feed from Alternator B+ shorted out to carb manifolds with insulation burned off to bare wire?

I can’t tell for sure from photo?

Fire appears to have burned longest & hottest on this side.

Very possible it's this simple, it does not look good.

Hopefully the OP will chime in to confirm their findings

[JamesM]

How long was the car in storage? I’ve seen fuel lines weep after being in storage only to seal up after running a bit.
Pete

(IMG:style_emoticons/default/agree.gif) Seen this a lot, especially with injector hoses. Though figured it wouldnt be such an issue on carbs with much lower fuel pressures.

[dr914@autoatlanta.com]

as everyone knows, I HATE carbs on a four. Lean backfire also causes a fire, happened this sunday while I was trying to start my 61 roadster after a long hiatus in my dry storage climate controlled basement. The heat from your jaunt let the leaking fuel atomize and a lose spark set it off.

[930cabman]

as everyone knows, I HATE carbs on a four. Lean backfire also causes a fire, happened this sunday while I was trying to start my 61 roadster after a long hiatus in my dry storage climate controlled basement. The heat from your jaunt let the leaking fuel atomize and a lose spark set it off.

Yes, having many examples and not enough time to give them justice can be a problem.

I know this all too well

[H2ohs]

Thanks all for the help. Been away from the car for a bit but will be able to dig in and report back findings in a week or two. The carbs were installed last year with new fuel lines. Will also fix up the recommendations on filter, etc. I think Zach could have nailed it.

[930cabman]

Please keep us updated with your findings, lucky you caught this when you did, could have gotten messy real quick