The V8 Owners Forum -

Posted: **Fri Sep 04, 2009 9:08 pm**

Hi guys my name is Dave Holmes, people call me Holmsey.
I run a modified Ford 302 V8 in a 1955 F100 pick-up.
I have had it on the road just over a year and had no real problems.
This weekend when I went away on a 650mile jaunt, I ran out of LPG and when I switched to Petrol, the brass floats in my new 650 edelbrock carb collapsed. Has anyone any ideas why and if there is a cure?

This should be a photo of them.

Posted: **Fri Sep 04, 2009 9:27 pm**

That's bad!

Sorry that I don't know what the cause is but I'd be interested to find out

Posted: **Fri Sep 04, 2009 9:35 pm**

The theory I have had so far is that the carb was hot and the cold petrol entering the float bowls cooled the floats so quickly they collapsed.. Just wondered if anyone else had had the same problem and if they found a cure. Cheers for a reply

Posted: **Fri Sep 04, 2009 11:15 pm**

Never seen that before!! And I can't think of a single reason why that could occur. I'd be surprised if a temp difference could do that. Is there any way that LPG could get into the float bowls?

Chris.

Posted: **Sat Sep 05, 2009 5:50 pm**

Don't Know Chris, I will have a proper look at the carb this coming week. that is why I signed up on here hoping someone could give me the answers. Cheers for reply

Posted: **Sat Sep 05, 2009 6:17 pm**

Holmsey wrote:The theory I have had so far is that the carb was hot and the cold petrol entering the float bowls cooled the floats so quickly they collapsed.. Just wondered if anyone else had had the same problem and if they found a cure. Cheers for a reply

Thinking about what your theory I'm not too sure that it holds true. If the carb was hot then the pressure inside the floats would increase, when the cold petrol was then introduced it would cool the floats so the pressure inside them would just return back to whatever it was when they were first soldered up. They would have to get very cold before enough vacuum was created in order for then to crush like they have.

Not that any of this helps you solve the problem! sorry!

Does LPG have a very high latent heat of evapouration? the reason that I ask is that if the LPG in the bowls somehow evapourated before the petrol supply was switched on then maybe that froze the floats. Its a bit of a lame theory but there you go!

Posted: **Sun Sep 06, 2009 6:48 pm**

I wonder if a backfire would do that?

Chris.

Posted: **Mon Sep 07, 2009 2:34 pm**

Very interesting, they had to have been subject to a good deal of vacuum, there is no other way they would have collapsed.

When they were manufactured they must have been pretty hot as they were soldered shut, meaning very low air pressure inside them, even lower when cooled down to ambient temperature. When surrounded by freezing cold fuel from carb icing from running on lpg, the pressure inside will have dropped to a tiny amount, put together with a few psi fuel pressure has to be the only way. I'd also say the only other reason this is not seen more often is because not many people run lpg with 4bbl webers (appologies if that is incorrect).

Maybe I'm wrong, but as far as I can see it's the only physically possible solution!

Try warming one up with a hot air gun (carefully) to see how much it takes for it to pop out again.

TC

Posted: **Mon Sep 07, 2009 3:40 pm**

Cant imagine this would be caused by contaction, that has to be gas pressure doing that, your not running a blower or turbo? wrong fuel pump, injection V carb pump,
The next question is the LPG switching over correctly and/or plumbed in correctly,
Summit sell Phenollic floats for Eldelbrock carbs, http://www.summitracing.com/search/?key ... loat&dds=1

not the soloution, but may be an answer

Posted: **Mon Sep 07, 2009 7:45 pm**

Hi guys thanks for your input, no I am not running a turbo or anything like that. The only thing I have changed is to much higher performance Cam shaft and inlet manifold.
There was no backfire, runs pretty sweet on LPG.

Posted: **Tue Sep 08, 2009 8:07 am**

I'm glad my SU's have floats made of thick plastic!

I would have to agree that the pressure inside the floats would have been minimal from when they were constructed. The sudden cooling effect of Petrol entering the carb would probably have cooled them v v quickly and caused them to crumple. I am sure that the evaporative cooling from Petrol would be waaaaay higher than dunking in Water!

My only problem is that the floats rub on the bottom of the bowl when running on gas and will therefore get a puncture at some point.

Posted: **Wed Sep 09, 2009 6:31 pm**

I'm guessing that after a long journey on LPG - with no petrol 'cooling' the
carb - the carb will be fairly hot. Now if you substitute 'hot engine' for 'Carburetor fire', this makes sense:

6) Why Floats collapse after a Carburetor Fire:
If you have a carburetor backfire, and the carburetor is burning inside the venturis, the main-body gets hot quickly. This heat transfers to the air in the carburetor heating it and the also to the parts around the air. The brass floats have air inside of them when they were made. The air in the float gets hot, expands, and trying to get out of the float. Many times there are very small places where the air can escape but fuel cannot get into the floats. As soon as the engine is restarted, the cold fuel enters the bowl, the float is still hot. The float cools rapidly vs the lost air inside the float. Because the air pressure outside is now higher vs the inside of the float the float collapses (just like it would under boost). Now you have a big problem. The black Nitrophyl floats do not suffer this problem therefore as we know are a better component to use in a boosted carburetor. At least now you can explain to your buddy why his float looks like Chit when he was not running any boost through the carb, LOL!

Written by an ex-Holley employee, taken from this page:
http://buick455dragracing.blogspot.com/ ... facts.html

Posted: **Wed Sep 09, 2009 9:01 pm**

Well there ya go... Cheers IanT...

Now all I have to do is stop it happening again ;o) At least I know the cause.

I have fitted a phenolic (not sure of spelling) read plastic spacer between the carb and the manifold, that is supposed to keep the heat from the carb.

I am now waiting on some new floats, guy in Uk I have ordered them from (and paid) says 5week.... I have a meeting I wanted to go to in a week.. so gotta source some more and try and get my money back ... Cheers for all your help mucho appreciated.

Posted: **Thu Sep 10, 2009 12:18 pm**

Steve Lang can be quite quick if he has a shipment coming over.

Posted: **Sun Dec 20, 2009 9:59 pm**

Hi Ya,

I've got a LDV Convoy with a RV8 in it, running on a Edelbrock 1404 and LPG. I've just had the same problem with my floats. I've had the odd misfire over the last couple of weeks and then i couldn't get it started but it just kept flooding. I don't however recall running it in petrol after a run on LPG.

Did you manage to resolve the problem with Nitrophyl floats?

Cheers Richard

The V8 Owners Forum -

Collapsed floats

Collapsed floats

Re: Collapsed floats