Got the 460 4bbl started in our '76 F250. She has been sitting all wet winter long here on the Pacific northwest coast.
After running about 30 to 45 seconds I let up on the gas and she died with strange sort of dieseling sounds and clouds of white smoke from the carb throat. Is this water vapour?
Got her started again and after running about 2 minutes, the engine tried to quit. I pumped the gas pedal and the engine "caught" again. After another 30 seconds, same stalling effect which I could correct by pumping the throttle. This happened over and over again.

Any suggestions? Are the floats sticking? Should I sacrifice a goat to the Carb Goddess?

Thank you in advance!

PS. I have a NAPA manual choke conversion on the Motormaster carb (D2VE:8620:LA)

 

The white smoke out of the carburetor is from the engine turning backwards when it dieseled. I imagine it made a "hissing" sound?

The stalling problem could be related to idle speed, or the choke being open, depending if you're starting it hot or cold. Very rarely does dieseling happen to an engine before it's warmed up, but if the throttle is stuck open far enough, I guess it's possible.

 

One question....did you put in anything like Sta-bil into the tank before letting it sit all winter? If not, you're probably running fairly bad gasoline, and considering the location, you have more than your share of water passing through the lines due to condensation. White smoke is usually steam....as it is one of the major telltale signs of a bad headgasket when it comes out the tailpipe. As such, coming out the carb body tells me that it could be coming from the fuel lines and hitting a hot intake....hence, steam and running problems.

Before messing with adjustments on the carb, I'd put in some premium gas and something to eliminate moisture (like heet, or similar product). It's a cheap possible solution, and at least you'd be able to eliminate your fuel supply from the equation before moving on to carb repair/adjustment (everybody likes twisting those screws prematurely).

Just a thought.

 

Thank you fmc400 & Behemoth:

Don't recall a "hissing sound" - more like running on after a shut down, but with tons of white smoke. Perhaps I was opening the manual choke too fast right after starting... At the moment I'm using a 5 gallon plastic outboard motor gas tank in the bed since both OEM fuel tanks are leaking (lost $40 worth of fuel last year - bugger!). Does it matter if the plastic tank is riding higher than the original gas tank(s)?

She was acting up all last summer - would quit without warning and hard start with some occasional spectacular backfires even when warm. Thought it was an electrical problem and gave up when the bad weather came.

Yes, I used some Seafoam last year with no real improvement. Carb always needed priming after 5-7 days so I began to think it was an internal carb float bowl leak problem even last year.

Will send through some fresh Premium gas with Methyl Hydrate to absorb any water.

Is it easy to open the fuel bowls and check the floats without taking the carb off or do I have to pull the carb?

 

I'm beginning to think you have a couple potential problems here....

The fuel tank location shouldn't really make a huge difference as the old saddle tanks that sat behind the back seat sat higher than the under bed tanks. As long as the fuel can run to the pump on a relatively level plane, I'd think you'd be fine there.

The fuel bleedoff over time could be carb, but it could also be a bad diaphragm on the mechanical fuel pump that allows it to bleed back to the tank.

The steam is still perplexing, though. Another potential thought, although fairly unlikely, maybe there's a crack in a water jacket of the intake manifold that allows enough water in to cause the smoke and make the truck run like crap. I just never hear of intake manifolds cracking, so that doesn't seem very plausible. The way you're describing the trucks running paired with the white steam, could suggest you've got the beginnings of a bad head gasket, and the pressure is forcing its way back up the intake in the form of a backfire, which could explain the steam. The problem with this is that you'd also be seeing the same white steam coming out of the tail pipe, which you haven't said you've seen.

Does the steam smell sort of sickly sweet? If so, that's antifreeze, and it suggests the head gasket or crack somewhere.

I'm not really going after the carburetor, as a carb would have no reason to generate white smoke or steam....white colored smoke almost always suggests steam and antifreeze being burned off (whereas black means fuel, and blue means oil), and carbs just don't have coolant running through them. A bad head gasket would explain crappy running and steam, and a bad fuel pump would explain fuel bleedoff when parked. I'm not ruling out carb problems, but I think there's more to it here than just that.

 

Behemoth: OK, you've presented some good logic for me to chew on...

No sweet antifreeze smell that I recall but will check the smell more carefully next time (the Mrs says I can't smell anything!) and look for tail pipe white smoke.

It's unlikely to be a fuel pump problem as I replaced the pump/filter assembly a year ago. Also, I always disconnect the plastic fuel tank (and hide it) when I leave the truck - the marine disconnect stops any fuel from escaping backwards.

There is a crack/leak in the casting at the front of the engine which has the water pump attached to it but it only shows when the engine gets hot. That only happened twice in the last 4 years!

Then there's the manual choke upgrade/downgrade, depending on one's opinion... I read somewhere that you have to plug a vacuum hole on the 4bbl carb if you change the auto choke to manual. Don't know where the hole is however.

Thanks again for your thoughts - I won't get back to the truck until mid May.

 

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Is it easy to open the fuel bowls and check the floats without taking the carb off or do I have to pull the carb?[/QUOTE]
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I would take off the distributor cap and spray electrical contact cleaner.

If the carb hasn't been rebuilt in awhile, it wouldn't hurt to take the top of the carb off and look at the float. If the float is soldered copper and no fuel inside, the float is good. Maybe the needle is sticky, spray it with carb cleaner. Also you might want to try bending the tang on the float just a tish to put more pressure on the needle. If the float is made out of foam, replace it without even thinking about it.

Hope this helps you

LeRoy

 

Ok here's an update - got to the truck yesterday and only had about 30 minutes to work on it. I disconnected the fuel line to the carb, checked the wire gauze strainer was clear. Then hooked up a hose and small funnel. Filled the empty float bowl with Seafoam and held the tube up above the carb. After 10 minutes the Seafoam level was unchanged.

After a hard start, she ran beautifully - no white smoke, no signs of stalling.

I'll do the distributor cap clean next time and clean the plugs,

Looked at the carb but have no idea how to open the float bowl. Can anyone direct me to a manual on Motorcraft 4300/4350 carb servicing?

Thanks everyone!

 

try pouring some gas into the carb an then starting it an see what that does. If it runs fine then it might be bad gas or fuel pump problem.

 

Kalve: that's the way I've always started her when she's been sitting for a week. This poor truck sits under a canopy all (wet) year and only gets used rarely - usually for a 10 minute drive once every week or two. Really bad conditions.

The fuel pump/filter is almost new but the gas is from last autumn...

I know nothing about the carb except it's a 4bbl and surely needs cleaning. Next is methyl hydrate and more Seafoam plus dist cap clean. Oh yes, an oil change.

Thanks

Mr. hopefully Fixit

 

Hopefully, final update here... Got back to the truck 3 days after the last successful running. She started right up and ran flawlessly. I may be deluding myself (much drier/warmer weather now in mid May) but the problem indeed seems to have been carb float. Added extra Seafoam to premium fuel ($11/bottle!!!).

Probably a good time to sell the truck now.