carb fire help please.

[haycait911]

had a bit of a carb fire today, my first. now I know why I use metal intake horns. is this a normal burn pattern? would like to have an idea what caused it. doesn't seem to be the usual backfire, single throat, burn. any thoughts much appreciated. Don.

[Joe Bob]

Tear em down, likely a float stuck, over flowed and a hiccup.

[haycait911]

Originally Posted by Joe Bob

Tear em down, likely a float stuck, over flowed and a hiccup.

in process. you gotta admit though....... pretty cool burn pattern

[haycait911]

this hole was full of fuel when I took off the carb. which would indicate an float bowl overflow, I think.

[dafischer]

It does get exciting, though, doesn't it? I had all four needle valves freeze in the open position after sitting all winter. It started very quickly, but got very interesting equally quickly.

[haycait911]

to be honest it happened while driving and I didn't notice. that was until the engine suddenly wouldn't go below 4k. plastic from the center horn had melted and flowed onto the butterfly where the fuel cooled it and jammed the butterfly open. drove home at 4k rpm. wasn't bad except at stoplights where I looked and sounded kinda silly. FWIW 4k is a very high idle speed and I don't recommend it. fun times.

I needed to change the venturis anyway so it's all good.

[roblav]

That could have been a LOT worse!

[al lkosmal]

Don,
This is the kind of excitement you don't need. looks like the center stack caught on fire and the heat melted the edges of the adjacent stacks. Very cool burn pattern..........glad it didn't spread.

regards,
Al

[haycait911]

Originally Posted by al lkosmal

Don,
This is the kind of excitement you don't need. looks like the center stack caught on fire and the heat melted the edges of the adjacent stacks. Very cool burn pattern..........glad it didn't spread.

regards,
Al

me too.

well, carbs are back in with correct venturis and METAL air horns. no real harm done. I've got three plastic ones for sale if anyone needs them

[1QuickS]

It wasn't a singular float sticking issue as the burn looks like fire was coming up from emulsion tubes for all three cylinders. Perhaps a single spit back through the intake on one cylinder ignited the fuel vapor and all three emulsion tubes began burning their air/fuel mixture. This might explain the unusual burn with heat directed near the emulsion tube wells and not up the throttle bores like when an engine burns completely up after filling with fuel after a float bowl siphoning event.

Your vent pipes are missing. You could have had a "percolation" issue that the spitback ignited. Once the fire started the fuel will boil in both fuel wells leaving fuel in the unused emulsion tube well filled with fuel.

Spitback can be ignition timing, carb tuning or carb wear. Looks like cylinder #4 is dark inside the bore which would be my guess for the source of the spitback. The darkness is carbon being left after burning inside the throttle bore. Note how clean bores #5 and #6 are in comparison to that of bore #4. (Perhaps the carbon resulted from the fire or was an accumulation of spitting-back...???) Check for throttle shaft clearance and for edge wear of the throttle plate. If the throttle shafts were reinstalled then the installation alignment of the #4 throttle plate could be less than ideal which could result in unwanted idle air passage. You can see also that the melting was greatest at cylinder #4 with the least amount of melting occurring at cylinder #6 which is furthest away from the source...speculation.

Metal air horns will not melt but the fire can still occur. If you buy this then you might think that the melting air horns alerted you to an issue that metal horns would not have divulged...like the canary in a coal mine alerting the miners to poisonous gas.

The plastic horns were not the cause of the fire, just a causality of it.

[haycait911]

thanks Paul. I was kinda hoping you might chime in. I kinda just threw these carbs on without proper set-up just to get the engine running. I'll go back now and set them properly. and install some vent tubes.

much appreciated.

[blucille]

Had a similar situation, I've been working with paul on it too, as he has helped me in the past. I'll post photos later, the bigger question is how to avoid this in the future....and yes, always carry an extinguisher.

[roblav]

You need the vent pipes, and so do I!

Do you carry an extinguisher?

[Ronnie's.930]

What I want to know is what kind of plates are in the Mopar box?

[Steve@Rennsport]

Paul offered some great feedback about some of the causes,...

I would only offer some advice about fire extinguishers. You REALLY don't want to use a dry chemical one if you have a fire due to the huge collateral damage they cause. These things corrode virtually everything they touch and wholesale replacement of any parts the material touch is required.

Its a big & very expensive mess to deal with.

I'd kindly recommend a Halon extinguisher since the additional cost is FAR less than the cleanup from the dry chemical ones.

[haycait911]

Originally Posted by Steve@Rennsport

Paul offered some great feedback about some of the causes,...

I would only offer some advice about fire extinguishers. You REALLY don't want to use a dry chemical one if you have a fire due to the huge collateral damage they cause. These things corrode virtually everything they touch and wholesale replacement of any parts the material touch is required.

Its a big & very expensive mess to deal with.

I'd kindly recommend a Halon extinguisher since the additional cost is FAR less than the cleanup from the dry chemical ones.

sadly Halon is banned in Canada. I think there's a substitute though. Halotron?

[haycait911]

Originally Posted by Ronnie's.930

What I want to know is what kind of plates are in the Mopar box?

ahhh..... finally. someone's hit upon the key to the whole problem

actually it's 'plating'. just stuff that needs to go to the metal plater someday.

[docrodg]

Halotron is the replacement for Halon, and is made by a company in Utah. Being a gaseous oxygen displacement agent it is far better than dry chemical agents for use where sensitive equipment is being protected. In fact, Halotron is commonly used in large server farms to protect those expensive computers and hardware because any equipment not damaged by the fire can be used without repair required. Always have an extinguisher handy and know how to use it.

[gumba]

I had a carb fire a few years back. It was caused by the intake valves sticking open due to poor diligence from the engine builder. I had the carb (46mm Weber) checked out by the local race shop and it seemed fine. Put everything back together and seemed fine. This is where having a dual a/f gauge paid off. Both banks read 12.5:1 at idle. When I started to rev the motor one bank would go lean, 17:1, then back to 12.5:1 at idle. Did this a few times, same thing. I sent them out for repair.