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Carbon fouled plugs

G

garner67

Active Member
Good news... I finally took my car for a spin around the block. It sure feels good to be back in the driver's seat!!!

Bad news... the engine runs like crap.

Looking for some of your collective wisdom to sort out the issues.

Back story... new 351w engine (only ~2000 miles). It ran great last year (before I pulled the engine out and stored in my garage while it was undergoing paint & body work). Engine sat for about a year without being ran. I thought I had drained all the gas before storage, but I may have not done the job correctly.

Today... the engine starts without any problems at all. It idles great and revs ok, but under any load (i.e. my test drive today) it runs like crap... sputtering & hesitation, but no back fires.

After getting it back home... I checked the timing and it is dead on what it was when it ran and drove well before storing it. Also, the fuel pressure gauge reads the same it did before going into storage (5 psi). Next, I pulled a plug, and it was completely covered in dry black carbon soot; so I pulled all the plugs, and they all looked exactly the same. I had a set of new plugs laying around, so I installed the new plugs; started it again; let it run for about 1 minute; pulled a plug.... the new plug was completely covered in dry black soot.

Here's a pic of what my plugs looked like (not actually my plug, but they all looked like this)

spcarbon.jpg


Where should I start trouble shooting?

- Carburetor issues/mix is too rich?... malfunctioning choke maybe, vacuum leak

- ignition spark too weak?... How do I check the strength of the spark?... Just put a voltage meter on the +/- side of the coil while it's running? Also, how would I go about checking the voltage output?

- Dizzy?... Maybe the cap is cracked?

- Any other ideas?


thanks, y'all.
 
I would replace the plugs and run the engine. Wait and see if they carbon up like that again. With it sitting for so long, it could be it just needs to be run. Fresh gas, fresh plugs and drive it. Then read the plugs. If it runs bad right off with new plugs, then come back here.
 
From what I read, he put new plugs in and the same thing happened. I would chime in but I stumbled on another problem today with mine so that's where my mind is. Sorry.
 
Mike, you mentioned the engine sat for a year. Mine sat for 6 years and I found that my carb was clogged and needed to be cleaned at the very least. I found clogged air bleeds, jets and harded diaphrams. Hope this helps somewhat.
 
My mistake on that. Doing to many things at once.

Sounds like a problem with the carb flooding. Is there black exhaust smoke? You could gap the plugs a bit wider to see if that helps. That causes your coil to build a bit hotter spark I have been told. Vac. or timing would probably cause backfires.

I would rebuild the carb as that is not a big job. Don't just start changing things that are set correct like timing and such. Take it one step at a time. If all that changed was the engine sat for a time, then fuel is the only thing that would really make a difference.

Get a small wire brush to clean the plugs with so you don't have to buy new all the time.
 
If it sat for a year, did you:

add Stabil or drain carb?
 
If it was running fine before it sat for a year, the only thing that could cause these symptons is fuel related.

It likely didn't develop a vacuum leak or become out of time just from sitting in storage.


As suggested, I'd focus energy on rebuilding the carb. If there was fuel left in the carb during storage, it likely varnished and is gumming up an orafice causing the rich looking condition on the plugs.
 
"silverblueBP" said:
If it sat for a year, did you:

add Stabil or drain carb?
Click to expand...

After running the engine with the fuel line disconnected until it died, I completely removed the fuel tank and fuel line before sending the car to the painter. Could the carb still have had some fuel in it, even though I ran it till it died?

Sounds like this is the first thing to start investigating. I'll take all of your advice and only change one thing at a time.

thanks.
 
"cmayna" said:
Mike is the carb pretty new? I mean as new as the engine? What carb are you running?
Click to expand...

Yep, it's a new carb installed by the engine builder. The carb is an Edelbrock 1813 Thunder series 800cfm with an electric choke.
 
Well, my problem may not be with the carburetor. I talked to the repair supervisor at Recarbco about picking up a rebuild kit, and he said to just bring in the carb for a quick test. I brought the carb in this morning when they opened, and I got a call at lunch to come get it.

They tested it on their flow bench and even put it on their test engine. They said the idle mixture was rich, but there wasn't anything that warranted a rebuild. It ran so well, they didn't even charge me for the tests! If/when I need carb work done in the future, Recarbco will get my business... http://www.recarbco.com/

I'll drop the carb back on the car tonight and fire it up, but if it's not the carb making the engine fall flat, what should I look at next?

Maybe look for a weak spark? How do I test for spark strength?
 
Not knowing the details of your 351W build, but 800 cfm sounds awfully large to me.
 
I was thinking that as well, but he said it ran fine prior to pulling it out of the car. My 347 has a 670 CFM Holley
 
Running fine does not mean the carb is right for the engine. I agree, it sounds like to much carb.
 
"Midlife" said:
Not knowing the details of your 351W build, but 800 cfm sounds awfully large to me.
Click to expand...

I didn't choose that sized carb; the engine builder did. I thought the carb was a bit large, but when I upgraded my engine build with VicJr heads (intake 205 / exhaust 160), Magnum roller rockers and a RPM air gap intake, the builder said it needed more carb. If you're interested, here's my cam info: Comp Cams # 35-426-8 236/240 duration @.050 .555/.576 lift

As stated earlier, it was running well before the engine was pulled for paint. Even if it was running rich, the engine did not stumble and hesitate under a load like it did on Sunday's test drive. Also, when I first installed the engine, I checked the plugs a few times during the first 1000+/- miles, and the plugs looked perfect, no black carbon, plugs were clean with a touch of tan color. However, I can tell you the carb sure isn't good on gas (only 14-16 mpg), but maybe I have a heavy foot. I definitely didn't build this car for commuting.

How do I go about checking for a weak spark?
 
"silverblueBP" said:
What about the wires? Mice do some munch'n somewhere??
Click to expand...

I doubt it, but I'll give them a good once over, just to be sure.

A friend here at work suggested I inspect the dist cap to make sure it's in tact. If it has a crack, it might be wack. This is a long shot, but it could have been knocked when I was moving it (bought a house last year & had to move the engine).

Thanks for all the feedback y'all.
 
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