Hot Rod Forum banner
1 - 20 of 21 Posts

·
wind & fire = guides to power
Joined
·
1,529 Posts
looks lean to me.
also the area in the background was more than the area in the foreground, so the camera focused on the background
 

·
Registered
Joined
·
336 Posts
The gray tinge looks like you are running aviation Gas.

Regardlesss it is either lean or the plug is too hot. I am thinking that the plug is too hot because it looks like little white dots of melted porecelan on the plug.

Ric
 

·
wind & fire = guides to power
Joined
·
1,529 Posts
What is the temp crossover to AC plugs? it looks like it could be a 46, too hot for a performance app. What motor is this? if it is a 350 try AC 44's and work on the accelerator cam and squirters to fix the off idle stumble. Also make sure there is no (very very little) slack in the accel. pump linkage.
 

·
wind & fire = guides to power
Joined
·
1,529 Posts
Yes, a too hot plug will cause pinging at higer rpm or extended loads.

Try some AC44's and

check the accelerator pump linkage for slack to cure off idle stumble.

Is your fuel system up to par?

If you can install the 44's and bring one of those plugs after a run we can help you further.
 

·
Registered
Joined
·
61 Posts
Discussion Starter · #12 ·
Ok i put in the AC44s like you said, seems like the pinging at high RPM has gone away, seemed to be idleing a little smoother as well. I pulled a plug from #1 and they were white! almost like when i had put them in. Ya so i know its lean. I drove around for 10 mins or so getting on really hard, sitting at stop lights, crusing at 55. I didnt have any of the lean signs though, backfire through the carb stubbling when i got on it.. So what would be the best way to fix this get some bigger jets for the carb? change the power valve? thanks... if you want a pic i can post it later but its lean.
 

·
wind & fire = guides to power
Joined
·
1,529 Posts
I take it you have checked the float levels? if so, yes, try the jets. Since you said it did not have any signs of being lean I would only change the secondary jets if it is a double pumper. If it is a vac sec try setting the rear floats a little higher than normal instead(you can use the clear sight plugs for this if you want).
This will allow you to drive slightly lean for fuel economy and give the correct fuel ratio at WOT.
To check the plugs at WOT accelerate full throttle until about 4000 rpm and(without lifting off the throttle) kill the engine and pull the plugs.
 

·
Registered
Joined
·
297 Posts
72Nova383,


Since you stated you were running lean due to the white plugs, like others have stated, check your float level. You should see the level of gas in the bowls just at the bottom of the clear sight plugs.

Then set your idle circuits with a vacuum guage. What is your vacuum rating in gear (if it is an automatic) or in neutral if it is a stick?

Your jets should be on from the factory.

HERE is a link to the document for your carb to adjust it properly.
 

·
Premium Member
Joined
·
6,623 Posts
Definite detonation, little silver balls under the side electrode give it away...otherwise the mixture looks Ok.

Try a little less curve depending on if it's doing it on top or down low in the rpm range. I would try limiting the mechanical advance a little before lowering the initial timing first...more initial is always beneficial if it's not detonating off idle through 2000 rpm.

Forget the split fires, buy champion cheapos for testing,,,,the nickel plating turning blue on the side electrode half way down means your mixture is good.

Straw color would be lean...

This is for a single full throttle pull mind you, normal driving will ruin the test coloring so do your plug chops and read the plugs in the field at 70F, 1000mb atmospheric pressure and 30% humidity.

Haha, let me know where you have weather like that...I have always wanted to test under perfect weather conditions.:D
 

·
Premium Member
Joined
·
3,519 Posts
definately detonation... looks like its been going on for a while, have you not been hearing spark knock?

I would say its time for a leakdown/compression test and get this crap solved before you bust a ring land or something. If it were mine I would pull all the plugs and see what the rest look like, see if you can track this problem down to a couple of slugs, or if its happening to all of them.

I might even pull the heads to make sure the slugs on it. In fact, if it were my mill, I definately would.

K
 

·
The Smell of Nitro in the morn
Joined
·
2,411 Posts
72Nova383 said:
No, i use Moble 91 octane and sometimes use a little octane booster. ya it is redish...and a little whitish inside. If it is lean can that cause the stumble from idle?
The cheap octane booster can give the deposits on the plug.
If you do re-jet the carb do the primary's up 2 sizes not the secondaries, as you use the primary ones to dirve on most of the time.
For plug reading
http://members.uia.net/pkelley2/sparkplugreading.html
For the carb, here's Hollys site with free downloadable manual and trouble shooters guide, how to set squirters.
http://www.holley.com/HiOctn/TechServ/TechInfo/FMCTech.html
The way the threads on the plugs look like they were not torqued tight enough, get a better brand of plugs.
 

·
Registered
Joined
·
61 Posts
Discussion Starter · #19 ·
heres a pic of the AC44's

Hi thanks all for the feedback. Im going to check some stuff today, float levels ect..Ya there was some pinging going on but just at WOT when i got on it and after it switched to 2nd gear. you could just hear a little. Ive tried doing a few things, adjust timing, retarding it till it went away, but i just could never get it to go away so i tried changing the spings in the distributor so the advance wouldnt come on so early, i put stiffer springs in. that helped. So now i tried changing the plugs to the AC44's a colder plug than the splitfires i have in there. When i was pulling out all the Splitfires they all looked the same. This pic was when i was just driving around for about 10 mins getting on it, sitting at stop lights, ect
 

Attachments

·
Premium Member
Joined
·
6,623 Posts
You need to limit the total centrifugal advance not put in stiffer springs...kinda defeats the purpose of ramping up the centrifugal to boost torque in that rpm range.

BTW Forget tuning with plug heat range...you do that after you get the mixture and timing right.
 
1 - 20 of 21 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top