[135SoHc]

1979 B200 5.2 with its matching original carter BBD. This has been a problem for awhile now and I am almost out of ideas. At idle the venturi's are discharging fuel like nothing else, its dribbling out and flooding the throttle plate enough that the engine runs rough and fuel economy has been reduced by a noticeable amount.


The carburetor has been gone through multiple times and everything is adjusted to spec. The vacuum step up piston/metering rods are working as best they can. The assembly draws down when the engine runs and if you lift it up manually it starts to go richer like it should. The two main jets have been replaced with new ones of the same stock size (.086") and as of right now the float is actually set lower than the stock setting because the fuel bowl was overfilling and soaking out through the gasket. It still exhibits the same problem but nowhere nearly as bad.

The only thing left to replace would be the float as it does have the original float which externally appears to be in good functional condition. The next step for this thing is the trash can.

 

[ImperialCrown]

Too Rich. Definitely sounds like float. At this age a float should be considered part of a carburetor rebuild.
That or a piece of debris is trapped in the float needle and seat. The fuel filter should catch the trash unless the inside of the fuel line is flaking rust into the fuel stream or the fuel pump is coming apart inside.
If this originally had a 3-port fuel filter that returned a portion of fuel back to the tank and it is replaced with a 2-port fuel filter, the fuel pressure will be way too high.
Plastic floats become porous and absorb fuel after a few years.
Brass floats can get a hole and take in fuel. If the sunk brass float sits and dries, you won't hear a tell-tale splashing inside when you shake it next to your ear. If they rest on the bottom of a dry aluminum float bowl for a spell they can have a hole corrode into the bottom of them.
A heavy float will do exactly as you describe.

 

[dana44]

I agree, the black phenolic floats can't be touched with bare fingers, the oils in your hands can cause them to absorb fuel, even though they appear OK, it is definitely sinking some. Try the float first, second would be too much fuel pressure, which, if it wasn't too much before, should only be a second option.

 

[135SoHc]

This van only has the regular two port in-out inline type filter under the floor board near the charcoal cannister. I have replaced it a few times already along with the needle/seat assembly since they are included in the kits. This one has the brass tank type float, dad swears its the original one. I would have thought by 79 it had the black plastic version.

Something I did observe though. When I had the air-horn portion of the carb removed to check the fuel level and cranked the motor over (spark disabled) the spurt of fuel into the carb from the feed line seemed rather violent. Granted it would normally never be seen since its all down inside the body and under the air-horn but I was surprised to see it that strong. I was expecting more of a steady trickle. Fuel pump was replaced in 2004, just a stock airtex unit from the parts store.

 

[dana44]

They do pump kind of violent, so at this point I would venture the float itself is failing. I also would think the float would have been phenolic, they started doing that around the early 70s.

 

[Bob Lincoln]

I didn't know you shouldn't touch them with skin oils. My 1966 Belvedere had a phenolic float, I rebuilt it a few times, luckily the float was dead-on even at 17 years old.

 

[dana44]

I have had a couple of them failed this way over the years, one was mine before I was told about it. It's pretty simple, just don't touch the black float with your fingers.

 

[Bob Lincoln]

It wasn't black, it was brown. Maybe not the same material after all?

 

[dana44]

I always knew them as black. If it is brownish, it may be soaked with contaminants. Float it in fuel to see if it does indeed sink. Brass and phenolic black are the only floats I know of, but that doesn't mean other materials have been tried.

 

[Bob Lincoln]

Two 1920 Holleys had the same type float. It was sort of a dense styrofoam-type material (not styrofoam, of course, as that would dissolve). Sort of a brown with a faint gray hue. I don't believe they were contaminated, as the carbs were very clean inside, no residue at all. But always good practice to handle parts carefully.

I just looked at a photo at NAPA online of a black phenolic. That was definitely not the OEM material in 1966 or 1972 on the Holley 1920, at least.

The video on this page shows what it looked like. http://www.carburetor-blog.com/?page_id=233

 

[dana44]

Yeah, don't see that type very often, but yeah, memory refreshment is a good thing, thanks.

 

[ImperialCrown]

I think that the Carter BBD was brass float until the end. They were used in Dodge Trucks into the mid-1980's, while the passenger cars started the switch to the similar-looking, but more modern Holley 2280's in the mid-1970's.
The plastic float doesn't actually have to sink, it can take on fuel and just be heavy to richen up the mixture. Fuel economy and to a lesser extent, driveability may suffer.

 

[dana44]

True. If less than about ten percent is above the fuel, it is not working correctly.

 

[Bob Lincoln]

I've never found specs, but the way to diagnose this is to weigh the float. Above a certain weight, it is to be replaced.

 

[135SoHc]

Some major developments since the last time I posted. I did order and replace the float, even set lower than it should have been it was still pissing gas at idle. No more for me.

The 'fix' >>http://www.amazon.com/Edelbrock-1801-Thunder-Series-Carburetor/dp/B000VDLQB8 Picked up a second hand 4bbl intake manifold from ebay. The rest of the supporting parts are on their way as well. The end of an era and the beginning of a new one for the B van starts next month

 

[Bob Lincoln]

I wonder if the needle is missing from the carb, or installed backwards on the seat.

Did you measure the fuel pressure? For carbs, should be about 7 psi.

 

[bguy]

I hope your new setup solves the issue. Did you ever explore the possibility that the return line to the tank is restricted?

 

[135SoHc]

I wonder if the needle is missing from the carb, or installed backwards on the seat.

Did you measure the fuel pressure? For carbs, should be about 7 psi.

The needle is there. On the 'test stand' (old intake manifold) with just gravity forcing the fuel down it functioned like it was supposed to. pressure was 5.5 steady.

I hope your new setup solves the issue. Did you ever explore the possibility that the return line to the tank is restricted?

If it had a return. This van doesnt have the 3 port fuel filter. Its got a supply and vent line to/from the tank.


Just for fun I borrowed the holley 2280 from my parts wagon (85 B250) and it ran perfectly. I seriously did absolutely nothing other than install it as-removed from another 318 with even more miles on it.

 

[Bob Lincoln]

I think he means, the fuel pump may have a return line, and if it's clogged, fuel pressure could be too high. That would force the needle open and flood the carb bowl.

 

[bguy]

2280 is a good carb. I can almost remember the settings.
As for the BBD, could one of the power valves not be seating?