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Old 04-20-2022, 09:26 PM
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Default Fouling plugs left and right

Hello, I have a 455 in my 69 firebird. Street ported edelbrocks, headers, flowmasters, torker 2. MSD ignition, and a holley 850 that was prepped buy a pretty well known local guy. My problem is I keep going through plugs, its always been this way through a few different iterations of the engine over the years. I clean the plugs at 150 miles or so. And I change them at maybe 300 miles. The car does not seem to run any different until about that 150-200 mile mark. The strap is clean but the rest of the plug has black carbon all over it. I have tried numerous carb and timing adjustments and nothing seems to work. Now granted the car does get backed out of the garage often, Idle for 5 minutes to warm up. then back in later. Any other ideas I may be missing? It has been 7-8 years now, so 16 or so sets of plugs. I run NGK R5671A-8 plugs. What really baffled me was last year when I put the roller cam in, I took the heads off for new springs... the piston tops were barely charred with no carbon at all on the top of them. A quick wipe with a rag and the slugs were almost brand new again. Do I need a hotter plug...colder plug? TIA!

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Old 04-20-2022, 09:38 PM
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Is your carb running over at all?Getting fuel somewhere.Tom

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Old 04-21-2022, 03:33 AM
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Run a set of 7's, don't just run the car for 5 minutes , lean up your idle mixture.
If you don't have a choke on the car what I do when it's only being pulled in or out of the shop in the winter to make room is to turn the idle up so it heats up easier and has a stronger idle and runs cleaner..

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Old 04-21-2022, 04:04 AM
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Quote:
Originally Posted by 4dblnkldude View Post
holley 850
Idle mixture adjustable at all four corners, or only adjustable on the primaries?

Is there a choke? Does it work properly? I've never seen an aftermarket Holley electric choke that had the pulloff set properly.

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Old 04-21-2022, 07:12 AM
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Are you using an MSD billet distributor w/o vacuum advance?......

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Old 04-21-2022, 07:39 AM
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What are you running for an alternator and I how are you feeding your coil and msd box? We just fixed a car with a Kauffman 455 in it, msd distributor etc, that didn’t have enough voltage going to the msd. We put a bigger alternator on and changed some wiring to insure the voltage was sufficient and no more fouled plugs.

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Old 04-21-2022, 07:47 AM
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What compression ratio? 8's are pretty cold for a primarily street driven engine, unless there are mitigating factors, like high compression.

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Old 04-21-2022, 08:13 AM
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Does a bad power valve cause the rich soot?
Or the needle/seats might be too high or leaking.

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Old 04-21-2022, 01:49 PM
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Yes, I am running a pro billet dizzy with no vacuum advance. The carb has no choke and the idle mixes at all four corners. I am running a standard 37 amp alternator that is a one wire set up. I am feed the msd right to the battery and have a full 12v switch from the ignition. All great answers!!

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Old 04-21-2022, 02:57 PM
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Post number 6 makes a very good point and to build on that if I might I offer this.

It’s not just volts that are very important with a modern ignition box, it’s current also, NO 8 gauge wire and or poorly crimped spade connectors can be tolerated, in fact I go thru the pain of soldering my crimps and then shrink tubing them.

In terms of wires runs of 8 Ft or more and something that pulls 5 or more amps of current it’s time for 16
gauge wire .
If the wire run is more then 12 ft then it’s 14 ga wire that’s needed.

For good grounds in a high current system like this that you do not want any noise in the ground should not go to sheet metal, but to the engine block, or better yet right back to the Battery.

Many a expensive Ignition box has failed due to running hot from trying to deliver high firing rates from not being able to draw enough current.

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Old 04-21-2022, 08:45 PM
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When you start the car to run it for five minutes, what’s your procedure to get it running without a choke? Are you pumping the pedal a couple times? And how often do you take it out for actual drives/hard drives? It may be as simple as the engine is not being run long enough or hard enough to burn off the initial fuel from starting it. Pump shots deliver a lot of fuel and the engine takes a long time to burn it off, probably longer than you’d think. A wideband would help you see how rich it’s running during this initial period.

Given that the plug-fouling issue has been happening for a long time and has been the same through different iterations of the engine and carb/timing changes, I’d suspect the one constant — the five-minute idle sessions. Maybe let it idle longer and/or rev it higher when you need to back the car out of the garage.

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Old 04-21-2022, 09:50 PM
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"Yes, I am running a pro billet dizzy with no vacuum advance."

The missing timing requires a richer mixture from the carburetor. It contributes to more carbon build-up and heavier fuel consumption but not the root cause.

Not have a choke doesn't help either, as butt-tons of fuel is required to get the engine to effectively fire up, but it will not want to stay running with a good A/F ratio from a carburetors that is well tuned. This means that the entire time things are warming up it's not effectively burning the fuel it is getting. This leads to "washing" the cylinders and spark plugs with lots of raw fuel for initial starting, especially in really cool/cold weather..........

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Old 04-21-2022, 10:42 PM
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Man this is a science. I am going to drive the car in alot of traffic and some highway bursts this weekend. I'll report back.

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Old 04-21-2022, 10:42 PM
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I think the missing vacuum advance is not going to ever play well with too cold of a spark plug on the street. A -8 is really cold, with no timing put in cruising at higher vacuum to increase the operating temp of the plug it is going to fowl plugs worse no matter how hot the spark is. With no vacuum advance you probably need a -6 instead of an -8.

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Old 04-21-2022, 11:41 PM
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When I see a street-driven car with no choke, I just automatically assume the carb is pig-rich at idle so that it'll start and run when cold.

I'm rarely disappointed in that assessment; although it does happen now 'n' then.

Add in the lack of vacuum advance, cold heat-range plugs, and lack of fully warming-up the engine, and this is a "perfect storm" for plug fouling. All we're missing is a 160 thermostat (or even worse--no thermostat.)

Perfect storm for fuel-fouled oil, too.

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Old 04-22-2022, 03:05 AM
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Quote:
Originally Posted by Schurkey View Post
When I see a street-driven car with no choke, I just automatically assume the carb is pig-rich at idle so that it'll start and run when cold.

I'm rarely disappointed in that assessment; although it does happen now 'n' then.

Add in the lack of vacuum advance, cold heat-range plugs, and lack of fully warming-up the engine, and this is a "perfect storm" for plug fouling. All we're missing is a 160 thermostat (or even worse--no thermostat.)

Perfect storm for fuel-fouled oil, too.
Everytime I see a "cold start" video with a carb without a choke ..sit there and Idle I just shake my head...it's too rich! It shouldn't just start and idle!

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Old 04-22-2022, 06:31 AM
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"When I see a street-driven car with no choke, I just automatically assume the carb is pig-rich at idle so that it'll start and run when cold."

+2...it would have to be....

With my 4781-2 Holley 850 DP or the Q-jet my engine would NOT start or run well in cool and cold weather without pumping it quite a bit then "feathering" the throttle to keep it running.

Even with a choke If I were to pull the vacuum hose from the vacuum advance with the engine on fast idle the RPM's drop off and the engine stalls when first started.

Didn't see it mentioned anyplace but a cold thermostat hurts thermal efficiency as well and requires more fuel/timing. I like to see these engines operate at least 180 degrees but still see folks running 160 degree stat's in them for some reason?

I also don't understand fouling plugs to a point where they need replaced. At most a good cleaning and you should be able to put them back in service. I use NGK V-power 7's and they last the life of the engine......

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Old 04-22-2022, 07:01 AM
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Excess fuel especially when the motor is cold is a top notch way to shorten the life of your motors rings and cylinder walls and cut into the lubricating ability of your oil!

Also it’s been proven long ago that any motor will experience the least amount of ware when it warms up fast by being driven, not just sitting and idling for 5 minutes or more.
This is not to say you should should warm it up by driving like a mad man, just a nice 30 mph at 1800 rpm is perfect.

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Old 04-22-2022, 12:15 PM
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I agree with Scott, Cliff, and Jay.

That's a really cold plug. I don't even run plugs that cold in really high compression stuff here. I'd drop that 2 heat range numbers to start. Remember NGK works backwards, a lower number is hotter.

I'd also be running a vacuum advance on there. No reason not to, as they really add another level of drivability that you're missing without one.

Whether you have a choke or no choke I find it doesn't make a bunch of difference as long as the engine is tuned properly and the cam and compression play well together, the engine will be happy with an AFR that's not overly rich and cold starts aren't that bad.

The cars I've had here without chokes will idle on their own just fine on a cold start after just keeping it running for 30 seconds or so with my foot, and the AFR's on those cars are just in the mid 13's for idle, not rich at all. They don't even have heat cross overs in them to heat the intake. The nomad is one of them and all that thing gets most of the time is cold starts to just move it around the shop and never gets fully warmed up, and it's had the same set of plugs in it for at least the last 30 years LOL And it's just a stock points ignitions system, nothing fancy at all.

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