SPLITRAY

OK, So I have drained all the fuel from carb and tank, replaced fuel with 91 octane fuel and replaced the plugs. Ran good for awhile, but after idling for 20 minute or so it starts popping out the exhaust again???

So, is it time to start re-jetting/re-rodding the carbs idle circuit to decrease the fuel? The plugs begin to foul as they did before but I shut it down before the plugs became so fouled that it popped at every revolution. We are talking about a 800 CFM AVS series Edelbrock sitting atop a RPM air gap manifold.

Am I on the right track here?

Mr D.

Do you have a spare Carb to throw on it?

SPLITRAY

No, got rid of all that stuff (Actually two carbs) when I moved to AZ from WA state.

tbarb

How old is the coil and spark plug wires. Can you see raw fuel going into the carburetor venturi. Do the emulsion screws kill the engine when turning them in. How much idle vacuum and is the vacuum steady. How long did the car sit for you to believe the fuel needed to be drained.

Need more information before anyone can guess at your problem.

SPLITRAY

While I bought this built engine in 2010 it has about 1/2 mile on it. Everything on the engine is essentially new. The only reason I drained the fuel was that it was "regular" fuel that I just purchased with my truck stricky for the purpose of adjusting the carb and setting timing etc. until I could get it to a gas station.

The mixture screws do work, and the vacuum is steady at 14-15. Well, it's as steady as you can get with a 488/510 lift camshaft and 450 HP 383 stroker. The cam, heads, manifold and carb are Edelbrock matched components. Ignition is what I believe to be a "Proform HEI system. That is the setup the engine was built with. The engine starts immediately and runs strong. Great acceleration too.

The only issue is after idling for 20 minutes or so it begins to foul then misfire and pop out the exhaust.

tbarb

Where is the timing set, consider 18-20* initial timing. Are the emulsion screws adjusted when the motor has warmed to hot. That's very important. What idle RPM speed keeps it happy and how far out are the emulsion screws.

FWIW, You want to make sure the primary throttle blades are set with only .010-.020 transfer slot and give the engine any additional air from PCV or secondary throttle blades. If those slots are exposed to much the screws will not have effect.

SPLITRAY

I have to recheck all that now as I don't remember, however one of the issues was when I was setting all that stuff it would start to foul just waiting for the engine to warm up to adjust the carb.

It likes 850 RPM, and as I recall the screws were out 3/4 turn or 1-3/4 turn out...Can't remember. Have to start all over now that I'm settled here.

Frankie the Fink

If your plugs are fouling in the time it takes the car to reach operating temperature I would be looking at severe oil fouling vs fuel fouling. Have you confirmed which one it is?

SPLITRAY

Plugs smell like fuel and are wet, when it starts popping bad the exhaust is black as in hydrocarbons, and there is no sign of blue smoke or oil usage. Oil is also clean.

tbarb

Check the heat range of the plugs.

At idle can you kill the motor turning the emulsion screws in to their seat or does the engine still run. No issues with choke, right? Can you see any fuel coming from the venturi's when the engine is idling. What kind of fuel pump and could the fuel pressure be high overcoming the needle and seat. Approx 6psi is good.

When you get a chance post a picture of a fouled plug from the engine for everyone to look at.

warrenmj

Make sure your exhaust manifold bolts are tight and the also the bolts where the manifolds connect to the exhaust pipes. If there isn't a good seal and air is being sucked in, you can get the condition you describe.

I had the same issue a number of years ago and someone recommended checking the exhaust connections. I had loose bolts at the manifold/pipe connection. As soon as I tightened them up, the problem disappeared.

DansYellow66

I agree with the above - exhaust leaks lead to exhaust popping. But sounds like you do have a running rich problem. Edelbrock carbs have a reputation for running rich but since your description seems to indicate this is all developing at idle, it should be able to be tuned out with the idle mixture screws. The primary and transition circuits shouldn't even be in play at 850 rpm. I think I would pull the carb off and do a complete check of all adjustments and especially the float settings - they may be too high. And as noted above - make sure the choke is opening all the way.

SPLITRAY

Funny you should mention that. When i fisrt set up and ran the engine it quit on me and I wasn't getting fuel. Took the top of the carb off to find that the needle was jammed into the seat. Feul pressure was too high. Put a regulator on it and run fuel at 5 psi.

Fixed that problem but the fouling issue still exists. Used copper gaskets at the head to ex manifold. Retorked three times. Heated engine, let cool overnite, retorq, heat engine again, let cool and retorq, etc.

I used to get black soot from the gasket area but not anymore since the retorq procedure.

SPLITRAY

No fuel visible in the top of the carb at all, in fact the T plates remain dry. The primary T plates look like there is no gap at idle, as do the secondary T plates.

Electric choke is not hooked up yet as I am try to decide the best key on/off place to wire it in.

I can kill the engine by screwing the mixture screws all the way in.

Holley fuel pump with Holley pressure regulator set at 5 PSI. The original brand new "Proform" pump failed and pumped fuel into the block. and the Holley pump jammed the needle into the seat so I had to put the regulator in.

SPLITRAY

I've tuned with these screws until I was too nervous that it was running way too lean.

Choke is not hooked up.

I have had the carb apart when the needle jammed into the seat because of high pressure. All settings were at the Edelbrock's spec sheet.

VinceP

double check that the plug wires are on the correct plug

Mossy66

You say it's a 800CFM carb on a 383CI engine. I don't know if that might be too big a carb. Heck, the 427s back then used a 780cfm. Maybe your carb, while fine at high rpm, might be just too fat at idle for your engine. A 427 pulls more air at idle than a 383.

Of course, there are a s-load of 383s out there. Are they all using a 800cfm carb too?


Gerry

ETA: Where in AZ are you?

SPLITRAY

These components are all supposed to be engineered matched parts.

I'm in AJ.

Mossy66

Apache Junction?

I guess I would wonder who engineered and matched the parts. That being said, they may very well be. Perhaps they were engineered and matched for high rpm performance, and not so much for idleing for 20 min.

Perhaps others with 383s will chime in with what carb works for them. Otherwise, I have friends with Corvettes near Cave Creek. I could send out a couple of carbs to let you try, if they are willing, if it comes to that.


Gerry

SPLITRAY

It's Edelbrock's engineering.

I didnt want to move all the car stuff I accumulated and even sold two carbs.