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.Click to view attachment Click to view attachment

Sadly I have found quite a bit of water in modern fuel, along with rapid evaporation due to high alcohol content.
I’m about to remove/replace/fix my third car this year regarding the entire fuel system.

I would suggest that it’s possible those floats/bowls may have had something other that fuel in there during the long storage.

I’m now going backwards with carbs.
Put a shutoff on the main fuel line.
Idle the car when parked.
Turn off fuel
Let car die when carbs are empty.
Use fuel pump to fill them up each time ( turn key and wait for tone to change)

PMO is now owned by Empi,,sorry for your loss..

Do you think this is from modern fuels? The car did sit for at least two years with empty bowls. Then I put about 800 miles on the car with mostly modern gas, two fill ups were normal old school gas.

Matt

So glad you found the root cause, Matt, and that the fire didn’t do more damage. Glad it made it through the Gathering!
Onward!

If the carbs were rebuilt years ago, yeah its possible the floats were made with plastic that was not ethanol tolerant. I have no idea what they are made of now. I know I just rebuilt a set of carbs for my bus and I'll be watching the floats.

Zach

So what I’m finding is the fuel at the gas station has water in it because of the ethanol.

I’m never going back to the local station, but I suspect it’s everywhere.

It would be hard to say if the cracks in the floats cased the fire or the fire cased the floats to crack...would need more details on the previous state of the carbs/ floats? Perhaps Dry seats too, from sitting for 2 years?

Hi Matt, Sorry to hear about your fire. PMO Induction would like to help get your carbs back in top condition. Please message me at robm@empius.com

also for reference PMO gaskets, diaphragms and seals
are E85 compatible.

Rob, thats a great offer. Thanks for stepping up to the plate. I have your PMO's for the last five years and love them. Mark

Thanks Rob. I will be reaching out.

Matt

Zoinks!

At least you did find the smoking gun.

It may not be the floats fault, more what someone stored the car with. Bad gas, wrong gas?

Either way, seems like a straight forward fix.

I had a line on a CIS 911 crack many years ago. Sprayed fuel everywhere while driving. First stop sign, could smell it. Pulled over shut down. No fire = damn lucky.

Stewart's Premium alcohol free

@Rob @EMPI

Now that is a very nice offer.

I think the gentleman who owned this car before me knew how to take care of it.Click to view attachment

sorry your car was damaged by a fire. Engine fires are scary for sure.

It's my understanding, and your photos would confirm, PMO carbs use IDF floats. I have two sets of IDF carbs from the late 80s which have been in on and off use since bought. I have never replaced a cracked float in an IDF. I've never been particularly careful about where I buy my fuel or prepare my cars for winter, though they only sit for a few months tops. CT has been 10% ethanol for as long as I can remember. A little fuel stabilizer in the fall. Some dry gas once or twice a year and it's never been an issue for me.

I think it's highly probable the fire cracked the floats and not the other way around. I'm not going to go and toast one of my IDF floats to prove it. I am an engineer that works on autoclavable devices made of plastic. I believe the plastic IDF floats are made of is a thermoset plastic. that means it wont melt when subjected to heat, it'll just degrade. I feel it's completely expected that a plastic float would crack from the heat from an engine fire.

I am not an engineer. I am a craftsman, god given. You might be right, then again The fire did not affect the other carb. Look closely to other carb photo, you can see cracks staring. I could see the fire making cracks bigger but not both sides. Fire was put out within 90 seconds. The plastic did not show any signs of melting, only of a dry rot. But I am willing to learn. I crave knowledge.

Matt

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.

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

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.

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.

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.

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 :-)

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

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.

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

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

Click to view attachment

Click to view attachment

I will try.
Matt

My floats float.
Matt

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

Click to view attachment
Ready to try again.

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.

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)

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.

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.

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

I have found it's better to be lucky than good

One float dry the other soaked in gasoline two hours. The one that soaked in gasoline weighs more than the dry one.Click to view attachment Click to view attachment

But does it still float?

Yes it still floats but it started at 12 grams too before being soaked in gas. The other float stayed 12 grams soaked or dry. Maybe that is within tolerance but you would think both would either increase in weight or stay their dry weight?

Interesting stuff.

While it's curious that one of your floats gains 3g when soaked in fuel and the other does not I think there is very small likelihood this caused a fire. It still floats. The fuel level may be slightly higher in the bowl with the heavier float, but if it still floats and the float mechanism, needle, seat, etc are working properly it's still going to shut off the fuel supply.

Additionally, part weight is used to optimize the mold filling process. 3g is a very small difference. I'll bet if you weighed 30 new in bag floats you would see 3g variation.

Now I also think you would be crazy to put those old floats back in service. I mean two of them were in a fire. you have the whole carb apart anyway. I would go through them.

That said I think something else is the cause of your fire. I would carefully go through the carbs paying attention to all plugs, seals and gaskets. Then I would methodically set them up paying special attention to things like fuel pressure and float level.

Paul Abbot's Performance Oriented website, Weber Carburetors by Pat Braden and the Haynes Weber Carburetor manual are all good sources for general rebuild instructions (yes I know PMOs are not specifically in there, but lots of stuff is the same) and setup methods.

That is my plan this weekend. Still waiting on parts from Empi.

Matt

@mate914 Scary situation, glad you put out the fire. Have you checked the fuel lines for cracks/leaks? What was actually burning during the fire when you were putting it out?

Also it is unclear in your test did the float still float in gas after sitting for 2 hours?

The carburetor was on fire inside the manifold and carb itself. Then the filter lit on fire.
Matt

PMO tech update
Floats need to be under 12 grams . The float I had that started fire is 15 grams.
Still pointing finger at float. Matt .Click to view attachment

Certainly looks that way,honestly had no idea the were molded foam,assumed they would be hollow as the old style metal floats were on many older carbs ,my DCNV 36's were brass on my 1.8 engine .
Anyway the outcome would be the same if the float valves couldn't hold a seal,no mention of fuel pressure ? could be a key point.