Heavy Black Smut on Plugs

N

nstegall

Member
I have a 1986 V8 Buick with a new remanufactured four barrel carb. It ran great for about month and then the plugs had heavy black smut on them. It continue to do the sam about every two or three hundred miles with new plugs. I have not done anything to the carb. I only get around 8 to 9 miles per gallon. Everyone here has different opions, but none seems to fit. Looking for suggestion on what to do to resolve this issue.

Many thanks,
Neil
 
Remove the carb, and take it to a reputable carb man. You may need to ship it to find a real pro, carbs are getting rare. If the carb gets repaired correctly, your new plugs should clean up after a few miles.
 
I agree with don rebuilt ,that doesn't mean anything these days you get new parts that are defective as stated take it to a reputable builder something is wrong with the carb I bet it wouldn't pass emissions test may have been rebuilt with parts that are not compatible with the fuels of today, just my 2 cents worth
 
You said the carb doesn't need to be looked at because it was just rebuilt. Name something else that's more likely to cause the problem besides a carb issue ?
I would start with the carb regardless of who rebuilt it. Stuff does happen. My first guess would be a soggy float.

Sal
 
There's probably lots of black soot on the inside ends of the tailpipes too.
I agree with Don, Frank and Sal. Something is wrong with the carb, no matter how new it is.
The bad mileage and all that black soot is from way too much fuel going thru the carb & engine.
You didn't mention the car using oil or blue-ish smoke out of the exhaust so it's not likely to be oil.
(and the plugs would be wet from the oil)

If the place you got the carb will do an exchange you might be out less dollars, but you could end up with another like the bad one you've got. Hopefully it's not an example of their normal quality of work.
frank long island said:
.... may have been rebuilt with parts that are not compatible with the fuels of today...
Click to expand...
Any internal part not compatible with ethanol could be ruined. Starting with the: float valve(s), floats, diaphragms... etc. etc.

.
 
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On many of the forums guys are quick to blame the Carb and then the real culprit turns out to be excessive fuel pressure caused by fuel pumps that are off shore produced and are producing pressures well over specs. This is something many do not bother to check,find out what your specs should be and then run a test this video may help show you what is involved. https://www.youtube.com/watch?v=maPgobDE_1E
 
JeffB2 said:
On many of the forums guys are quick to blame the Carb and then the real culprit turns out to be excessive fuel pressure caused by fuel pumps that are off shore produced and are producing pressures well over specs. .....
Click to expand...
True enough. nstegall didn't say anything about changing the fuel pump, so the assumption is he has the same one as when it was working fine, and before that. Since the carb was most recently changed before the problem happened, it may(?) be more likely the culprit.
And yes, double checking the fuel pressure while you're under the hood already is a good thing, even before doing something with the carb, to help narrow down where the problem really is.
The car may have a defective or missing fuel filter and there's crud stuck in the carb float valve...
.
 
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Also, assuming your Buick has an original type carburetor, it's not uncommon for Quadrajet floats to absorb fuel and cause a higher fuel level.

Sal
 
Sal, I have rebuilt hundred's of Q-jet carbs. the #1 cause on most of them was the stupid neopreme ( or what ever it was made of ) float. there are brass floats available for them ,but they can be finicky, but not bad. I used them when I could get them. I personally like the Q-jet carb. I think it is easy to work on, just has lots of parts. I think that is why they get a bad rap from most people. there used to be many parts available over the counter of the GM dealers to really make these thing work . you just need an assortment of metering rods and springs, etc. just like most carbs. ran one on my '75 K-20 P/u for 29 years. had to rebush the throttle shafts once and several rebuilds over the years. I also think the key to any carb. is clean filtered fuel. just my .02.----- JIm
 
Jim, I agree with what your saying. I've done 100's of Quadrajets also, along with all domestic carbs. Totally agree on the floats. I also use the brass floats to replace the soggy ones. I believe the material they are made of is called nitrophyl. Kind of like a thin hard shell over a styrofoam sponge.
I also think Q-Jets perform very well. The reason people use Holley's is because of the hot rod reputation, and they are more attractive visually.

Sal
 
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