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Discussion Starter · #1 ·
I'm working on tuning in a new holley 750 hp thats replacing a worn out holley 750 dbl pump. I'm having trouble understanding spark plug reading so ive attached a few pictures of my plugs. Ive read different write ups on the web but i'm still unsure of heat range, jetting, and timing when looking at a plug. Please take a look and give me your feedback.


Here is a picture of a plug from my old carb, nasty! This plug only has 300 miles on it.




Here is the new carb installed and i also bumped the timing by 2 degrees. I left the old plugs in til i get things closer. This is with 50 miles on it.




Here is a new plug one step hotter with 50 street miles on it.




I can take more pictures of dirrerent angles if need be.
 

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Jason,did you know the first and second plug look like they have a cut back ground strap?Like a Nitrous plug.That's why the second one looks good on one side of the plug but not so good on the other.The first is way off.
I like the third plug the best.It's a u-groove,isn't it? Can you see a light brown ring around the porcelin about an 1/8" inside of the plug?That plug looks about perfect otherwise.I'd check them again in another 200 miles,just to be sure they still look the same.From the last picture,it looks like the engine is just a tad fat and that's a good thing.Better to be a tad fat than a tad lean;at least in the case of an engine.:D I noticed you are in Ohio.If you plan on driving your car when the temp.outside drops,you might need to richen it up a tad more.But that plug looks good,to me, for the warmer months.
 

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Discussion Starter · #5 ·
Eric, yes the first two pictures are of autolite racing plugs and the last picture is a ngk racing plug. ( i should of stated that ) I wanted to try a little hotter plug and get away from the cut back ground strap, so i put a ngk in. Looking at the plugs i can not see the timing indicator on the ground strap like FBO talks about on there site. What about the base ring of the plugs? Does it look correct?

By the way, the spark plugs are sitting on my kitchen table for the best light in those pictures. You must have a steady hand grasshopper :D
 

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Jason,I can't see the timing indicacor either.Other than that the plug looks good.One way of telling is the slight tan color on the porcilin.I also see no indicator that there is any oil in the combustion chamber.From what I can tell from just ONE plug,everything looks great.A touch fat,but just a touch.

If you try leaning it at all,I'd only go down 1 or 2 jet sizes.Or you could try a .001 larger high speed air bleed,on the intermost rear corners of the main body,if your carb has removable air bleeds.

P.S.,If you don't know what I'm talking about,then don't mess with it.
 
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