3.2 carb engine fire running again, It lives again. Options

[mate914]

Letting sit over night. Two hours after floating in gas, floats sank and absorbed gas.
Matt

The floats are cracked but still float. I was concerned as to what caused the engine fire. I was hoping to find something simple, I did not. Car sat for about two years before I acquired it. I will put pictures of both.

[mate914]

This matches what I saw. Both the fire starting and burning. Have you had experience with carb fires?.

Matt

as OP stated the unaffected side is showing evidence of cracks starting in those floats..no fire on that side because they didn't get waterlogged with fuel and overcome the float valves which is what has happened on the other side,raw fuel getting down the throats results in a decent backfire.
After that event all throats would be on fire as even with pump power off residual fuel pressure continued to flood the fuel bowls and overspill fuel into the throats .
IMO the main backfire would have been when other cylinders fired and blew out flaming raw fuel out the air filter resulting in the burn damage to the filter and surrounding area.
No way that I can believe the floats as heat damage they were just buggered,besides the fire was never in the float bowls anyway.
Nice to see PMS stepping up ,cheers.

[rgalla9146]

I'm not an engineer.
I do have to wonder though, the cracked floats no longer float ?

[nditiz1]

As another member stated these floats are weber IDF floats. Richard from PMO used them in his PMOs. Also, it should be noted that cracks exist in them even when new AND the floats are not plastic at all really. They are foam and solid. So even if you have cracks they will still float. It is believable that the floats can side load upon rising and not fully seat the float needle to stop the flow of fuel. I had this happen on my PMOs before, but it only happened when they had been completely drained. It also made the AFR go completely rich at idle. While driving the bowls are constantly refilling so the side load should have corrected itself. Lastly, if this was the case the fuel usually flows into the throat and not dribble out the top or sides. The gasket is in place to force the fuel to go out the auxiliary venturi.

[blabla914]

it may be the cracked floats that caused the fire. If the fire was really that short maybe that's not enough heat to have done the cracking. If I were you I'd really be looking carefully at other possible causes before declaring victory. there are a bunch of things that just don't square with some other experiences I've had, thought I don't profess to have done and seen everything.

I also have a 6 cylinder 914. I'm running Weber IDT carbs with the brass floats. I cracked one by over pressuring the float bowl blowing some crap out of the idle passages. A sunk float makes the car run pretty bad. It idled surprisingly ok, but getting it off the line took a fair amount of slipping the clutch. did you notice that kind of behavior before the fire? It took me a bit to figure out what was going on, so I drove the car a fair bit like that before I figured it out without a fire. perhaps I got luckly. Going forward those built in sight glasses can help keep an eye out for high float levels.

Back to the plastics, like I said above that plastic is not going to melt. You may see chunks of it missing as it will burn. I've worked with several old school materials engineers that would ID materials by getting their lighter out and burning a piece. Not a popular move in the office, but it allows you to differentiate between thermoset (burns/degrades) and thermoplastic (melts).

one last thing, we deal with materials getting discontinued by manufacturers all the time. I have a feeling the material qualification process for new float materials is likely a bit less difficult compared to medical devices. I would buy my new floats from a reputable supplier.....ie not amazon.

[blabla914]

As another member stated these floats are weber IDF floats. Richard from PMO used them in his PMOs. Also, it should be noted that cracks exist in them even when new AND the floats are not plastic at all really. They are foam and solid.

thanks for this! you know it was a way long time ago, but I think a friend of mine cut one or broke one. I had totally forgotten they aren't hollow.

Now I'm going to have to see if any of mine are cracked and then see if they float just out of curiosity. it does totally make sense they would float even if cracked as it would be the density of the material making them float vs a brass float that relies on air trapped inside.

[nditiz1]

I'm banking on something failed either a brass gasket, or accelerator pump gasket. Were the carbs rebuilt when you acquired the engine? I have a feeling fuel was dribbling out onto the hot engine and caused the fire.

PS - I love PMOs so if you want to get rid of a flamed set, I'm here to help :-)

[VaccaRabite]

There are a couple failure modes for IDF style carbs that could lead to a fire.

1) weeping freeze plugs. I've had to fix these myself. Drilling out the plugs, threading the bores, and putting in NPT plugs with fuel safe sealant. PMOs may not have this issue, but IDF certainly do.

2) a stuck float. Cracked or not, if the float stuck open, once the bowl is filled the gas has to go somewhere. When it happened to me it came out the top of the carb.

3) Any low mounted failed gaskets (accel pump comes to mind) would allow gas to drip on to the engine.

Zach

[blabla914]

Thought of something on the way to work. Here's what I'd do. you have cracked floats. I'd get a coffee can full of gas and put the cracked floats in it, I would use one of the ones out of the carb that had the fire, and I'd see if it floats. If you wanna be super thorough, let it sit over night.

If the cracked float floats, that's not the problem. you need to keep looking for the cause.

[nditiz1]

They float. Cracks in the float doesn't matter.

I submerged this cut one multiple times. The inner foam does not absorb outside liquid.

[mate914]

Thought of something on the way to work. Here's what I'd do. you have cracked floats. I'd get a coffee can full of gas and put the cracked floats in it, I would use one of the ones out of the carb that had the fire, and I'd see if it floats. If you wanna be super thorough, let it sit over night.

If the cracked float floats, that's not the problem. you need to keep looking for the cause.

I will try.
Matt

[mate914]

They float. Cracks in the float doesn't matter.

I submerged this cut one multiple times. The inner foam does not absorb outside liquid.

My floats float.
Matt

[nditiz1]

Since you have the carbs on a bench I would fill them and see where they leak. Even better if you have a small carb pump you can check them as though they were in the car.

[mate914]

Since you have the carbs on a bench I would fill them and see where they leak. Even better if you have a small carb pump you can check them as though they were in the car.

I will do that. New floats from PMB incoming on Thursday. I have PMO rebuild kits from parts klassic. The carbs were set up for this engine by CMS in 2011. The car sat from 2020-2023 not running. I will play it safe putting this mountain lion back into service.
Matt (IMG:style_emoticons/default/flag.gif)

[mate914]

Ready to try again.

[JmuRiz]

(IMG:style_emoticons/default/clap56.gif) good luck, hope it works out.

This whole thing reminds me of when I caught a leaky fuel line on the 356 before driving it…still think my dad was watching out for me to see a leak in a dark engine bay.

[nditiz1]

Good to hear it.

For future reference- peirce manifolds is a great source for weber parts which are PMO parts. I bought my weber/PMO floats from them. The only thing that is PMO specific is the Venturis, secondary vents and the idle air screw (no other carb has this)

[TomE]

They float. Cracks in the float doesn't matter.

I submerged this cut one multiple times. The inner foam does not absorb outside liquid.

It is hard to tell from the picture but it looks like your floats are fairly level in the gas? It also looks like there is enough gas to submerge them if the weren't floating? Matt's floats are no where near level in the gas, they have a definite list. They are in a can right now only thing we could find in a hurry. I am going to find a clear glass to put them in and check them. Also can anyone say if the floats they have seen have any writing on them? Manufacture or any other symbols or numbers? These floats have nothing on them to say where they came from.

[nditiz1]

I'm not sure I'm following, but these ones that I pulled out of my PMOs had no markings. The ones I got from peirce which are weber had the W on the tops of 2 of them. I think the other 2 were blank, but came in weber packaging.

[Rob@EMPI]

Letting sit over night. Two hours after floating in gas, floats sank and absorbed gas.
Matt

The floats are cracked but still float. I was concerned as to what caused the engine fire. I was hoping to find something simple, I did not. Car sat for about two years before I acquired it. I will put pictures of both.

Hi Matt Rob at EMPI /PMO here-we would like to help you get back on the road please message me at robm@empius.com

[mate914]

Letting sit over night. Two hours after floating in gas, floats sank and absorbed gas.
Matt

The floats are cracked but still float. I was concerned as to what caused the engine fire. I was hoping to find something simple, I did not. Car sat for about two years before I acquired it. I will put pictures of both.

Hi Matt Rob at EMPI /PMO here-we would like to help you get back on the road please message me at robm@empius.com

Rob,
I did on the 21st.
Matt