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Old 04-07-2009, 07:39 PM
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Reading Spark Plugs

I have a question about reading plugs......I know how to do it, that's not my question.....

This has been bugging me for years, but I have a 355 with Dart heads and a Holley 4412 500 CFM carb on it, with straight headers (its on a dirt track stock car). When I take the plugs out, the first two on each side (cylinder 1, 2, 3, and 4) the plugs are black as can be, like it's running real rich, but the back two on each side (cylinders 5, 6, 7, and 8), are clean as can be, not running rich or lean, but just perfect. The Carb has .080 jets in it, and runs on 110 racing gas and a 6.5 power valve (if all that helps any). What would make the front set of cylinder's look different than the back four cylinders?

I have just been told that I run to big of a fuel pump on the car, I have a Holley 170 gph pump and I hear that all I need is about 110 gph. I don't think that would have anything to do with it, but I don't really know either. Before you ask, I do not have a regulator nor a pressure gauge so I don't know what it's pumping, but I don't have any problems setting the float so I assume the needle and seat is able to hold it back......?????

Any suggestions? Thoughts?

Thanks guys!

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Old 04-07-2009, 08:04 PM
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I have seen where fuel was leaking into specific runners in the manifold
causing those cylinders to foul plugs. Sometimes it's difficult to detect because
the problen happens after a WOT blast; plenty of fuel is flowing then when the
throttle is closed the needle and seat does not close quickly enough causing
the leakage and ultimately the fouled plugs.
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Old 04-07-2009, 08:30 PM
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if the plugs are really clean then its probably gonna be from fuel wash if its smoking when running and that rich

hows the exhaust pipes ?

really sooty black ?


plug tips should be dry and light tan or gray mix

if proper heat range and fuel mixture etc


good luck
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Old 04-08-2009, 01:31 AM
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What intake manifold? What happens if you replace the 2BBl carb with a 650-750 holley 4bbl carb?

The #80 main jets seem big for that carb.
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Old 04-08-2009, 04:34 AM
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carb

Need to know what manifold is on the car?? Is the carb in the standard location or is it turned 90 deg on the intake??


Running that pump with no regulator is a big problem. Don't those pumps put out 14PSI?? Regulators are cheep and very easy to install. That is where i would start first.

Are you 100% positive that it's fuel on the plugs and not oil???


Keith
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Old 04-08-2009, 06:48 AM
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Thanks guys, the intake we run is a Holley/Weiand 7547, with a single plane intake, it's for a 4 barrell.......We cannot go to a bigger carb, our rules regulate a 2 barrell 500 CFM carb. I wouldn't say I'm 100% sure its gas on the the plugs, but I'd be 95% sure, I'm not a motorhead, I just can race.... The headers at the collectors seem to look normal, not real "sooty", but at each individual tube, the back 4 will have a white color to them and the front 4 will be black......kind of like the plugs......The carb is in the standard location.....It's not smoking when running, always seems to run fine to me.....

I looked up the fuel pump online at my local Speedshop.....
http://www.scpraceparts.com/circle_t...-chevy-sb.html
It doesn't say that I need a regulator, and that the shutoff pressure is regulated at 8 psi? The 110 gph one says 6.5 to 8 psi......does that help with the pump issue?

Last edited by timhollerbach96; 04-08-2009 at 07:12 AM.
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Old 04-08-2009, 07:32 AM
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IMO, a regulator should be used to limit the pressure to around 5 psi.

You may think the pressure is fine sitting still at an idle while you set the float.

But out on the track bouncing around, etc., the extra pressure will lift the needle sooner than you want it to- causing rich mixture temporarily.

Or, could be rich most of the time you're racing, then returns to a normal level while you idle back to the pits.

Have you considered trying an adjustable carb adapter that allows fore and aft movement?

These can help w/fuel distribution problems when you run a 2 bbl. on the 4 bbl. intake for rules requirements.

If allowed, a "turtle" on the floor of the plenum might help, too. (If allowed).

There are air cleaner base plates that help flow w/the 4412, Brenzinski (sp) has them, as well as adapters, but cost like hell.

Last edited by cobalt327; 04-08-2009 at 07:37 AM.
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Old 04-08-2009, 08:48 AM
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Cobalt, by adjustable carb adapter, you mean one that allows your to slide the carb forwards or backwards? If so, I have one, I have it slide towards the back of the motor, I've been told that is where you get the most power, true or not, I don't know, but it's where it's been.......

Thanks!
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Old 04-08-2009, 08:57 AM
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Quote:
you mean one that allows your to slide the carb forwards or backwards?
Yes.

I wouldn't hesitate to experiment with the position of it, just to see what- if anything- it does to the fuel distribution problem that it would seem you're having.

That said, if everybody in the pits has theirs as far back as it'll go, that's a pretty good indication that you would be OK w/it there, too, unless everybody is copying each other and EVERYBODY'S wrong!

I do believe getting a handle on your fuel pressure is the place to start.
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