carb fire

[johng]

all you mechanical whizzes out there

my 5.7 chevy has a rochester 4brl carb, this has had an internal fire at some point in the past. The float is half melted, and the metal cylinders/framework that surround jets in the primary throttles are melted away.. :Sad:

The engine has single point LPG... upstream of the carb..

any ideas as to what causes backfiring appreciated (I can only think plug leads arcing, dist. cap same)

thanks
John

 

[Geo]

any ideas as to what causes backfiring appreciated (I can only think plug leads arcing, dist. cap same)

Are you sure the engine is or has back fired, ie poping and banging when running, or are you asuming it has, hence the fire in the carb
A back fire in the true sense of the word is when fuel and a source of ignition appear together at the wrong time inside the engine, your referance to cap and leads would cause a misfire, the unburnt fuel could then result in a backfire, incorrect ignition timing is the most common cause of backfireing along with carbon build up on high milage engines,also poorly seated or damaged valves or valve timing errors the list goes on im afraid try to give a more presice description of your symtoms aprat from just a melted carb, wich may have been caused by over fueling and or dirty oily air filter and burnt after the engine was switched off
Geo

 

[johng]

Geo thanks..

erm.. there are no other symtoms to speak of really.. I just want an idea of what may have caused it, any connection to LPG, and what to do next.. a large tank of fuel and LPG at the back of van is a bit scary

I did a compression test last week, and all 8 were equal and good...

the van was running well enough before I decided to strip the carb, but I have no point of reference with a chevy engine really there has never been a backfire or noticeable misfiring in the short time I have driven the vehicle..

can I ask how overfueling or a bad AF could cause a fire?

Damage appears to include ,float, filler block, power piston assm, melting of alloy of main body and air horn...

timing is controlled by a vacumn advance but I have not had the chance to check this much.

The LPG point was made because, when i have looked at LPG fitting before, the question of plastic manifold and sequential systems (and backfiring) keeps raising it's head.. so what is the link between LPG and backfiring if any.. ?

I brought a carb repair kit, but it will be wasted on this carb, there is too much damage for it ever to be efficient. so now a second hand rebuildable carb seems the cheapest way out of this money pit I am in.. anyone got one ? (boats use them too it seems)

John

 

[johng]

some pics..

 

[Geo]

Hi John carb engines are know to "Spit" every once in a while and a carb thats not set up properly can soak air filter and when engine spits it sets light to the excess fuel, same aplies to a dirty air filter that is virtualy oil soaked, it is highly unlikely this fire ocured whilst running, due to the inrush of air a sustained fire long enough to cause the damage you described is remote, as the fire would be dragged into a cylinder away from the carb The most likely scenario is a small backfire as you switched of and walked away the fire was allowed to continue unoticed till it ran out of combustable material, hence the amount of damage
as you have been running on LPG the plugs will appear very clean anyway,so there will be no clues there
I would be looking at checking ignition timing
Geo

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[Lindy-C]

JC would know but he's still in the States

 

[johng]

Thanks Geo

I have only done 70 miles on 3 different journeys (Mainly petrol).. so I wonder how long the carb has been in this state.. how much power I may lost with it like this, how it ever ran !

J

 

[johng]

JC would know but he's still in the States

thanks LC
can he smuggle a carb into his suitcase

 

[Lindy-C]

Probably could have done John, but I have no means of contacting him as I have no idea where he'll be.
Could put one in the next shipment though - if you can't find a Rochester, surely a Holley would work? I know thats what he did with one of our old busses years ago.....from memory the Holley was a better unit

 

[johng]

hmm

I have this nice rebuild kit now, and finally got my head around how the roch works today ..

grrr bloody RV

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[Lindy-C]

You could always flog it and buy a tent!

 

[American Dream]

These engines WILL backfire in the carb if given too much Gas at startup, although it sounds like yours ie an extreme case.

Has the unit got an air filter fitted?

I have a 440 charger block 7.2 v8 and it doed the same on startup.

These engines need a lot of fuel in the system when starting, especially from cold.

If it spits at startup just keep the accelerator down and any potential fire blowback gets sucked into the engine.

 

[johng]

AD.. hmm

It starts with some difficulty..and needs to be warm before I can drive it really.. One reason I decided to strip the carb was that I noticed the primary choke flap had been forced permanently open with some flat string.. this was (one reason) why it took a fair while to start and needed gas... quite why it was forced open and not temp/vac controlled I have not found out yet

IT has an LPG mixer (sprint australia) in place of what I imagine was a stock air filter housing.. and because this the air filter is bigger circumference and not as tall, and is 'open'

pic follows

Has anyone got an old rochester lying about ? for a boat even...

John

 

[American Dream]

AD.. hmm

It starts with some difficulty..and needs to be warm before I can drive it really.. One reason I decided to strip the carb was that I noticed the primary choke flap had been forced permanently open with some flat string.. this was (one reason) why it took a fair while to start and needed gas... quite why it was forced open and not temp/vac controlled I have not found out yet

IT has an LPG mixer (sprint australia) in place of what I imagine was a stock air filter housing.. and because this the air filter is bigger circumference and not as tall, and is 'open'

pic follows

Has anyone got an old rochester lying about ? for a boat even...

John

My Primary choke had been removed!!!

I invested in another Carb to use as a donor and replaced the missing items.

Why people have to pr.t about with vehicles I don't know.

There is a rumour This results in better fuel economy but IMHO if the engine is a Pig to start, what's the point.oh:

PS Mine's driveable from cold and idles well even when cold now.

Tweaked the idle mixture screws and she now runs well.

 

[johng]

yikes..

I dont suppose you still have the old carcass, for a crate of ale ?

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[American Dream]

yikes..

I dont suppose you still have the old carcass, for a crate of ale ?

I do but it is 99% complete and I am keeping it as a spare as getting rare to find.

Trawl ebay.That's where I found mine.:thumb:

It would be too big for yours. 625 CFM Carb.

 

[johng]

ok there was a chap in Gloucester selling one, BIN £50 ? some water damage though, should be cleanable..

these second hand units are only $20 on ebay .com

 

[American Dream]

ok there was a chap in Gloucester selling one, BIN £50 ? some water damage though, should be cleanable..

these second hand units are only $20 on ebay .com

Yep.Just bear in mind the carriage charges and import duty on top of that IF the sender is prepared to ship to the UK.

There are Rebuilt carb suppliers over there but mind you you use.

 

[johng]

ahem..

colourful language

 

[pappajohn]

ahem..

colourful language

eeerhem!! sorry, but is this guy for real ?.oh:
if i knew it was on fire i wouldnt be waiting to see if 'it'll go out on its own'.
i'd be stood on the bumper p***ing on it if thats what it took.

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[American Dream]

This Guys a right P......oh:

Running the carb without an air filter and standing there looking at it alight!!!!

A setup.:Angry:

Language is a bit choice too.

 

[johng]

I think it's genuine

a contender for the darwins nearly ....

John


ps have located a carb in Florida, cheap.. so think I will be ok may even drive my RV one day

 

[American Dream]

I think it's genuine

a contender for the darwins nearly ....

John


ps have located a carb in Florida, cheap.. so think I will be ok may even drive my RV one day

Excellent.Have you any pics please? I'd be interested in seeing them.

 

[johng]

of my new carcass?


just an old lump sitting in some Florida lock up

I had a thought.. when I last ran the Van back from MOT I noticed a rad leak, it got pretty hot... what about flashpoints and heat of carb under that insulated center console ?

the more I think about the more I can't believe it could have ran like it was, suggesting it happend on my last journey..

J

 

[American Dream]

of my new carcass?


just an old lump sitting in some Florida lock up

I had a thought.. when I last ran the Van back from MOT I noticed a rad leak, it got pretty hot... what about flashpoints and heat of carb under that insulated center console ?

the more I think about the more I can't believe it could have ran like it was, suggesting it happend on my last journey..

J

The gas system has a vaporiser attached to the vehicle's cooling system.
You say the RV overheated?Yes it would have raised the operating temperatures under the cowling but by how much?

You have a pretty powerful Rad Cooling fan on there and there is a fair amount of coolish air being passed back over that area.

Surely you would have noticed if the carb was giving trouble?

The Carb In the Pics Looks Reasonable.Is it the same carb as yours?

Pics of RV would be nice to see.:thumb:

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[johng]

Sorry AD I realise what pics after I re-read your post..! dooh..

carb, well I hope its right, the seller isn't communicating much.. I know I need 800 CFM hot air choke, I assume that is simply affected by venturi size.. mine are 1 3/8" and 2 1/2" respectively... he wont tell me his sizes.. yet.


Learning fast..!

LPG vapouriser, I may have some questions to follow concerning that.. the LPGA fitter (before I got RV) took the Heater matrix out of the loop and just left it so.. should be a case of re-routing pipework from .block.top of heater.out from bottom heater.into vapouriser.out into rad. I hope...

Fan.. I am thinking to replace with a double electric after reading a good tuning book.. an extra 10 horses would be nice

I did not detect bad running really any time I drove it.. (about 6 journeys of varying lengths in a year)

pics of the old wallet-gobler, see hear

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