Spark plug gurus…

[Steve76063]

Ok gurus…400 mile drive yesterday returning from Mid-America so I thought I’d look at my plugs to check my carbs. 
plugs are 1-4, right to left (I guess bottom to top, the pic rotated when imported).  
I think #1 looks a little rich, and #4 a bit on the lean side.  Checking with gurus to see if I should try and tweak my jets/carbs (dual 40 DCOEs) or if I’m being nit-picky. 
my inclination is to leave everything as is. 
 

I added a video of #1 because part of the insulator looks right/lean while the rest is black. 

Edited May 3 by Steve76063
Added video of #1 plug

[Stevenola]

For #1 rich you could:

 

-check idle mix screw for lean best idle

-check that your accel pump jet isn't dripping into the venturi (there's a tiny washer under the accel pump jet and confirm the cover is tight also)

-check that the main jet isn't dripping into the venturi at low revs

-confirm you have the same jets for #1 as the other 3 barrels

 

That's about it since #2 looks good.  I wouldn't mess with the others.

 

[Preyupy]

Make sure you check that the jets are all the same (make sure someone has not drilled one and not marked it)  Also check the balance between ALL of the throats, it is not uncommon for a throttle shaft to be twisted enough for the 2 throats of the same carburetor to be flowing a different amount of air.  Check the resistance of your spark plug wires, make sure they are all the same.  

[Preyupy]

There is also the possibility that someone has tightened the Idle Mixture Screws tight enough to damage the carburetor body where the screw comes through.  This changes the opening and could allow a lot more fuel through with the "Screw" open the same amount as the other throats.  This is hard to spot without removing the carburetors and inspecting from inside the carb behind the throttle plate.  

[Steve76063]

Good things to check...Thanks guys.

[TobyB]

This was why I ran 4 egts on the race car-

 

plugs don't tell you which circuit's the problem.

 

+1 for everything Byron said, but adding that you should balance the carbs

when they're up 'on the linkage' not at idle.  So you'll need a way to use the linkage to pull the

rpms up to 1500 or so, and hold it there.  THEN check balance.

 

I found that setting 'best idle' by leaning each barrel until it stumbled, then opening

just a bit past where it settled down gave a good, even, slightly rich idle that worked best.

12ish on the wideband.

 

Also, check and recheck float levels- they directly affect all a/f ratios.

 

t

unisyn

[John76]

1 hour ago, TobyB said:

So you'll need a way to use the linkage to pull the

rpms up to 1500 or so, and hold it there. 

This is an easy-to-make tool that I use.

 

 

 

 

[TobyB]

true- and ingenious!

 

t

 

off to buy parts to make one for brake pedals, too.

['76mintgrün'02]

Good one, John. It reminds me of the stick I made when the choke’s fast idle cam was not working. Sliding the plastic-capped-end towards the tunnel raises the rpm. 


So does sitting down on the seat if you haven’t removed it!

 

Your tool inspired me to modify a mini Quick Grip clamp to be used as a throttle control under the hood. 

 

I added a padded end to the linkage a while ago to make it nicer to push on and that also makes a good place for the clamp’s foot to sit. 

 

 

It works so well I added it to my timing kit. 

 

 

Tom

[Dudeland]

Check your check valve going to the brake booster.  If it is leaking it will lean out #4 cyl.

 

Cheers

 

 

 

 

[John76]

On 5/5/2024 at 8:12 PM, '76mintgrün'02 said:

It works so well I added it to my timing kit. 

Nice Tom.

Perfect when you have a tach function on your timing light.

Hopefully EVERY person who visits this forum has a Innova 5578. 😄

 

 

[Dudeland]

On 5/4/2024 at 2:31 PM, TobyB said:

This was why I ran 4 egts on the race car-

 

 

What is your setup for the EGT's?  is it standalone or Canbus?