1994 GM 7.4 Edelbrock Carbs, Gen V

[tonyiiiafl]

Looking for what you all use for spark plugs. I have right now NGK BR6FS in there. AC has the M$43T listed.

I am not a Champion person

[tonyiiiafl]

I changed the plugs yesterday on Starboard engine. 1.5 hours outboard side, 20 minutes inboard side. plugs came out gapped at .030, spec is .035, probably part of the issue I had a hard time to WOT. evident no dielectric was used as evidenced by the boots being stuck good onto the plugs. Took off teh cap, only 2 screws holding in on, and no gasket. SO, replaced cap with new Quicksilver unit, rotor and new Mercruiser wires. Started it up, skipping! So, after checking my work (did 1 wire at a time!) I pulled 1 wire off teh cap at a time (shocking experience!) when I got to #3, no spark from cap. BAD CAP! Replaced cap with one I had for port engine, fired right off, no cranking! Also, the bilge monster was hungry, so in addition to the various tools it has eaten, it also got yours truly as I slid down into the black hole. Port engine was going to be in teh spring, but when I saw that gap on the plugs of .030, I am going to do it this week.

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[KyleR]

Ouch! Hope you weren't hurt too bad!

[tonyiiiafl]

More my pride. The Admiral had to help me out of the dark hole. Was not pleasant, but that engine runs tops!

[km1125]

Good luck on the healing!! That hurts just looking at the pic!

A smaller gap would have been a bigger issue at light loads. At heavy loads you have a lot of fuel/air in the cylinder and higher pressures which makes it easier to ignite, so long as the spark can make the jump. Making the jump with a slightly smaller gap even makes it easier, which is very important at high loads and speed because the dense fuel/air charge can actually block the spark from jumping.

At lighter loads, you need more energy from the spark to ignite the gas, because it's not heated as much from compression. You also have less fuel and oxygen molecules floating around (and they have a bunch of nitrogen in between them) so having enough of them right between or close to the electrodes can be an issue and that gets worse as the gap gets smaller.

The smaller gap will still have a spark, but there's not enough fuel and oxygen molecules in that smaller gap to ignite, and you have a "miss". Won't happen ALL the time, but the percentage will increase exponentially with the smaller the gap gets.

Ideally you'd like a HUGE gap at low loads and low speeds and a TINY gap at high loads and high speeds. The manufacturer compromises to get the best of both worlds, and that's the spec you're shooting for.

[bud37]

Source of the post plugs came out gapped at .030, spec is .035

Good job on the leg...Geeez....ouch.

Hmmmm...... Interesting as plug gaps generally widen over time, I wonder what they went in at...025-.028 maybe.

Anyway, one down one to go..... .....engine that is not leg...

Edit.......after thinking I checked the NGK gap spec for that plug and it is actually .031" according to their website.

[Viper]

I feel your pain buddy, been there many times. The scar will give you bragging rights though

[tonyiiiafl]

I saw the gap from NGK but my mercruiser engine spec had.35. It idles very smooth now. One could put a glass of water on the spark arrestir and not ripple.

And I am in the middle of recarpeting too.

[km1125]

http://www.youtube.com/watch?v=BtDXmajxXic

[tonyiiiafl]