Plug reading

[Aron Gleason]

Yesterday I took the car out for a cruise, it was running really good. No more stumble when I stab the throttle, but the tip of the plug is white and the rest is black. Just wondering why its like that?

 

[Geoff 2]

What heat range?

 

[Bird 426]

Timing witness on the ground strap is about right. Should have 2 or 3 threads of color for the correct heat range. Idle circuit looks to be clean. Rich at wide open throttle?

 

[RJRENTON]

What heat range?

The plugs were a NGK -5 heat range.......plugs were very similar in appearance to those in my Stihl lawn and leaf blower, and spot on identical to my LawnBoy running 93 octane and synthetic oil at 50:1 ratio at a steady 4000 RPM @ ~ 12.75 A/F. Cuts grass all day long and never misses a beat, starts with one pull.......
BOB RENTON

 

[RemCharger]

Looks like 5670-6. Could drop to the stock 5 and see.
I'm most impressed Bob has an A/F ratio sensor on his lawnmower, and it's a 2 stroke.

 

[gtxrt]

if it is 5670-6 that is too cold. what is your timing set at ? It looks like you could bump it up a little. if you have the right plug and the right timing you need to lean it out. they are way too rich.

 

[Aron Gleason]

What heat range?

Ngk 6

 

[Aron Gleason]

if it is 5670-6 that is too cold. what is your timing set at ? It looks like you could bump it up a little. if you have the right plug and the right timing you need to lean it out. they are way too rich.

Wow. You're spot on with the plugs being a 5670-6. Timing is 19 initial 38 total. And yes it needs to be leaned out, when I was breaking in the new cam and lifters my headers were glowing red so I thought I needed to go bigger jets in the primary. But it was all in the timing.

 

[Geoff 2]

NGK 4 or 5.....or you could drive Renton's leaf blower around & leave your car in the garage.....

 

[RJRENTON]

NGK 4 or 5.....or you could drive Renton's leaf blower around & leave your car in the garage.....

It was the LawnBoy mower that had the best plug (1) coloration......although the Stihl leaf blower was acceptable as well. The LawnBoy results were best only because of sustained hi RPM operation........NGKs worked well.....I have no results from my B&S powered tools.....I'll just stick with Champion CJ-8Y.......no complaints........points to ponder.....
BOB RENTON

 

[gtxrt]

are you sure 38* total with vacuum hose off. what carb are you running?

 

[Aron Gleason]

are you sure 38* total with vacuum hose off. what carb are you running?

Yes im sure its 38 total with the hose off cause its a mechanical advance distributor.

 

[gtxrt]

Yes im sure its 38 total with the hose off cause its a mechanical advance distributor.

that could be one reason the plugs look like that no vacuum advance. not enough timing at cruising speed.

 

[Aron Gleason]

that could be one reason the plugs look like that no vacuum advance. not enough timing at cruising speed.

I had the FBO 10 degree bushing in the distributor, and i had it at 26 degrees initial and 36 total.

 

[Aron Gleason]

The plug that has some white is plug #1. The other plug is from #5. I do have a single plane intake, but wondering why 2 plugs look so different?

 

[HEMI-ITIS]

Your pig RICH! Lean it out,

 

[RJRENTON]

The plug that has some white is plug #1. The other plug is from #5. I do have a single plane intake, but wondering why 2 plugs look so different?

View attachment 1869765

View attachment 1869766

IMO.....it's a fuel distribution issue, possibly due to slight velocity differences. Are you sure, the carb settings are the same...let to right primary and left to right secondary. This is NOT a vacuum advance issue or vacuum leak under the carb. Something else to consider is uniform coolant circulation.....one head getting more coolant than the other. Do you use a spacer under the carb for heat isolation??? These upset fuel distribution velocity and cylinder filling uniformity. Just a few points to ponder.......
BOB RENTON

 

[Aron Gleason]

IMO.....it's a fuel distribution issue, possibly due to slight velocity differences. Are you sure, the carb settings are the same...let to right primary and left yo right secondary. This is NOT a vacuum advance issue or vacuum leak under the carb. Something else to consider is uniform coolant circulation.....one head getting more coolant than the other. Do you use a spacer under the carb for heat isolation??? These upset fuel distribution velocity and cylinder filling uniformity. Just a few points to ponder.......
BOB RENTON

Yes the mixture screws are the same left to right, front to rear. And I have a 1/2 spacer.

 

[Aron Gleason]

Your pig RICH! Lean it out,

The thing is, I leaned the primary side 4 jet sizes down

 

[max426]

This may help. What single plane manifold?
Jim