Opinion on this Spark plug reading.

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Woodie

Take-off EH!
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I have been reading up on how to tune by reading the plugs lately, Its seems as though this is a learning process that takes some time and understanding to be able to be accurate. I have read quite a few posts by YR as well as RRR and the other experienced posters on this form... These plugs are Autolite #65 in a 71 340. Hydraulic Roller shaft. Air-Gap with QFT 650 DP carburetor with stock jets and squirters. MP distributor curved to 34 total 15* initial and all in by 3000rpm. No vacuum advance. Any opinions on this would be appreciated.

Woodie

Screenshot_20190827-200455_Gallery.jpg
 
Are the deposits toward the electrode on the insulator shiny? A close up pic with the plug vertical and the ground strap opening toward the camera would be beneficial for the expert plug readers. Also, what fuel are you running and is it an ethanol blend?
 
I have been reading up on how to tune by reading the plugs lately, Its seems as though this is a learning process that takes some time and understanding to be able to be accurate. I have read quite a few posts by YR as well as RRR and the other experienced posters on this form... These plugs are Autolite #65 in a 71 340. Hydraulic Roller shaft. Air-Gap with QFT 650 DP carburetor with stock jets and squirters. MP distributor curved to 34 total 15* initial and all in by 3000rpm. No vacuum advance. Any opinions on this would be appreciated.

Woodie

View attachment 1715385595
How many miles on that plug?
What fuel are you burning?
Street or strip?
Those black deposits on the insulator would indicate a rich condition on the top end.
Looks like your a little shy on timing - more advance
This may help, it's pretty good plug info
Reading spark plugs
 
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How many miles on that plug?
What fuel are you burning?
Street or strip?
Those black deposits on the insulator would indicate a rich condition on the top end.
Looks like your a little shy on timing - more advance
This my help, it's pretty good plug info
Reading spark plugs
Plugs have less than 25 miles on them. Fuel is 10% ethanol rated at 91 Octane. Street motor, but I rev it to 5800 all day long.

I am thinking on a fresh set of plugs this week and do a good pass and kill the engine and pull a plug for a more accurate reading. I was, and I am curious what others thoughts are by posting the pic above. I am going to read the link you posted. Thank you
 
IMO the only way to get a true plug reading is to put in a fresh set of plugs , do a blast , pull over and pull one or more plugs , then read . To me , looks rich up on the porcelain and lean down by the gap. Look for a tan or dark tan . Better rich than lean in any event .
 
IMO the only way to get a true plug reading is to put in a fresh set of plugs , do a blast , pull over and pull one or more plugs , then read . To me , looks rich up on the porcelain and lean down by the gap. Look for a tan or dark tan . Better rich than lean in any event .



That's only if you are tuning for WOT. The OP isn't there yet.
 
I have been reading up on how to tune by reading the plugs lately, Its seems as though this is a learning process that takes some time and understanding to be able to be accurate. I have read quite a few posts by YR as well as RRR and the other experienced posters on this form... These plugs are Autolite #65 in a 71 340. Hydraulic Roller shaft. Air-Gap with QFT 650 DP carburetor with stock jets and squirters. MP distributor curved to 34 total 15* initial and all in by 3000rpm. No vacuum advance. Any opinions on this would be appreciated.

Woodie

View attachment 1715385595



You need more initial and a bit less total. Your idle circuit is pretty damn close. Your cruise and WOT is pig rich.

That means you need to pull some main jet out of it, and tune WOT with the power valve channel restricters.
 
You need more initial and a bit less total. Your idle circuit is pretty damn close. Your cruise and WOT is pig rich.

That means you need to pull some main jet out of it, and tune WOT with the power valve channel restricters.
Appreciate your input YR. Thank you. I can feel there's more in this combo. It's been a bit of effort to get it this far, I would like to take it all the way. This combo is great for the street.
 
Yr said it , wot or secondary is fat af.
The timing is high side range of great. Further down it goes the more timing is in play and that's not great. Stay at the bend or a hair below like you are.
 
Yr said it , wot or secondary is fat af.
The timing is high side range of great. Further down it goes the more timing is in play and that's not great. Stay at the bend or a hair below like you are.
Agree on the timing ,a hair too much ------------
 
Power Valve is 6.5Hg
Main jet #70
Secondary jet #76


The power valve is probably opening too late. The jet doesn't look outrageous but I'm not familiar with the emulsion/bleed package of that carb.

Also, if you pull the power valve out is there replaceable jets behind it?
 
The power valve is probably opening too late. The jet doesn't look outrageous but I'm not familiar with the emulsion/bleed package of that carb.

Also, if you pull the power valve out is there replaceable jets behind it?
I will put a vacuum gauge on it tonight and see what I have. I pull the PV and check to to see as well. I appreciate your input.

Woodie.
 
Thanks... as I was unaware of that. My understanding is 1/2 the value is the PV value. 13hg equates to 6.5 and so forth...


There is a thread over on another part of this forum that 12many started. I think it's in the carb forum, but it may be in the performance forum. I'm horrible with the search function but I know 12many started it.

In that thread there is some detailed information on why the 1/2 idle vacuum is wrong. Rather than type it out again, you can just go read that thread. 12many posted really good info in there. I hope he's not done yet. I think the summer heat was getting to him. So hopefully when the fall really hits he's back at it to do the picking the fly poop out of the pepper tune up!



Edit: it's in the Fuel and Air Systems forum. I bumped it up so it should be at the top or near the top of that forum.
 
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Thanks... as I was unaware of that. My understanding is 1/2 the value is the PV value. 13hg equates to 6.5 and so forth...
Holley's attempt at a nice one-size-fits-all sizing method. (I'm sure it works for some people) Driving with a vacuum gauge hooked to manifold vacuum is the best way to size the PV. You'll see what the vacuum does, when, and then you can pick a size that enriches right when you need it to. Man those plugs sure are black as you move down the porcelain, especially for 25 miles...
 
Holley's attempt at a nice one-size-fits-all sizing method. (I'm sure it works for some people) Driving with a vacuum gauge hooked to manifold vacuum is the best way to size the PV. You'll see what the vacuum does, when, and then you can pick a size that enriches right when you need it to. Man those plugs sure are black as you move down the porcelain, especially for 25 miles...
Thanks for the additional info. Yes, they are fat further down... with stock QFT 650. I'll get a good tune in this with all the help on this thread. Thanks again.
 
Made some progress this afternoon. Like YR and others have stated.. Hooked the vacuum gauge up to the manifold and checked it at cruising speed. Had close to 12hg. Went and purchased a 10.5pv and installed it after dinner. WoW it's much crisper than before and pulls hard. Tip in is crispy. Going to pick up some new plugs tomorrow and do a pull and see where I am at. Also like indicated before, going to bump up the initial 2* and see were it falls on the ground strap. Then hopefully start trying to lean out the top.

Woodie
 
Just wanted to post an update my progress. Bumped up the timing 3* to 18* and re-jetted the front and rear. Went from a #70 down to a #68 on the front and a #76 down to a #73. Installed fresh plugs and verified float levels as the same when started. Vacuum was down and the plugs white after 2 good pulls. My thoughts were that it was way to lean and was down on power. Went back and re-jetted. Bumped th front up to #69 and the rear up to #75. Verified float levels once again and went back out for a few good pulls. Here are the results. The last pic is a comparison between the same plugs in #8 cylinder. What are your thoughts? Can hear the difference in the exhaust note, it sounds much crisper.

Screenshot_20190831-161708_Gallery.jpg


Screenshot_20190831-161646_Gallery.jpg


20190831_162416.jpg
 
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