Author Topic: Help a brother out. Spark plug reading... (Read 481 times)

Sluggo · « **on:** February, 12, 2011, 06:43:59 PM »

I spent the day attempting to set my carb up so my eyes don't melt and it does not smell up the house when I start it in the garage.

Plugs started out wet and black, way too rich although the car ran like a spotted ape.

The carb is a summitt racing 750 cfm vacuum seconday. It pulls 28 inches of vacuum idling at 850 rpm. 95 power valve, silver secondary spring, 77 jets in front and 79 in back.

The carb was set up from the factory. No adjustments other than idle and choke until today.

The float levels were a tad high so I adjusted them just a hair lower than the recommended middle of sight glass. Pulled the top of the carb and changed the front jets to 70s and put the 77s from the front in the back.
The exhaust smell is much more tolerable and the performance only seemed to be off a slight bit, gladly traded to lose the stench.

I also turned the idle screws in a 1/4 turn from 1 1/2 turns. Reset the base timing from 10 degrees advance to 8 with total timing at 35. these changes resulted in what you see in the pictures. The car was driven twenty miles and shut off before the plug was pulled.

I'm running Autolite 25 plugs gapped at .035. The way I interpret the plug is I need a colder heat range (24s) and maybe bump the jets down a tad more, maybe 68s in the front and 74s in the rear.

I'd like some opinions. Fire away.

cmayna · « **Reply #1 on:** February, 13, 2011, 06:15:10 AM »

Slug,
Are those the same plugs you mentioned were first black and wet? If so, I assume you cleaned them? With today's gas it takes a lot more than 20 miles to get a spark plug reading. If that plug had say a couple hundred miles on it, I'd say it's running too lean for it is too white.

Fast68back · « **Reply #2 on:** February, 13, 2011, 06:37:32 AM »

Two things come to mind

1. (agree with Craig) White = Lean
2. Dyno tune....lets see what the TBM is layin down......... (Just in case we line 'em up when you trailer it up to Dallas...)

Sluggo · « **Reply #3 on:** February, 13, 2011, 07:11:13 AM »

Those are the same plugs. I did not clean them they cleaned themselves. I'm going to go one heat range colder before I do anymore tuning.

Sent from android powered phone using tapatalk.

silverblueBP · « **Reply #4 on:** February, 13, 2011, 07:43:02 AM »

Best way to tune it is on the dyno. The last rebuild I did I took it to a chassis dyno in Topeka and spent the afternoon making small changes till it was just right. Well worth the couple hundred bucks. Since I'm color blind, reading plugs is just wasting my time!

Mach1Rider · « **Reply #5 on:** February, 13, 2011, 08:13:03 AM »

Just my 2cts, But it looks lean. short of going on a dyno,
I would go with 74 jets in the front and put the 79 in back.
Cense the jets do not come into play at idle, your metering screws could go in more
to lose that eye watering smell. Most baseline settings are 1 1/2 out for intial start up and
then adjusted once warm for smoothest idle.

Sluggo · « **Reply #6 on:** February, 13, 2011, 03:22:33 PM »

Quote from: Mach1Rider on February, 13, 2011, 08:13:03 AM

Just my 2cts, But it looks lean. short of going on a dyno,
I would go with 74 jets in the front and put the 79 in back.
Cense the jets do not come into play at idle, your metering screws could go in more
to lose that eye watering smell. Most baseline settings are 1 1/2 out for intial start up and
then adjusted once warm for smoothest idle.

Been thinking about it and I think you are dead on. I drove it today and it had a lean surge on light accel. I'm ordering 72-76 jets and some new plugs from summitt.

Sluggo · « **Reply #7 on:** February, 18, 2011, 06:50:55 AM »

Update.

Rejetted it to 74s in the front, put the 79s back in the rear and installed a new set of Autolite 24s gapped at .044. (one step colder)

I also removed the flex fan and installed a Hayden 3817 electric fan with controller.

The lean surge is gone and the car runs awesome without the stench at idle.