Inliners International Forums General Discussion Engines Spark plugs and jets

I've got a couple of runs in with the Camaro since fixing the oil pan gasket leak. Saw what might be a bit of transmission fluid leak, but no evidence of oil pan leaking. Cross your fingers! It's L6-250 with holley 4bbl 390 cfm and Clifford intake manifold.

The main jet before the fix was far too large, plus 1&2 were black as night. New plugs are much better, please have a look, what do you think?

https://youtu.be/WrvwVFbFAiA

What main jet? What power valve?
What's the carburetor "list number"?

Holley 4160 Adjustable Float Carburetors 0-8007
Carburetor, Model 4160, 390 cfm, 4-Barrel, Electric Choke, Single Inlet, Dichromate

Was: Main Jet 54, Power Valve 9.5 - cylinders 1&2 complete carbon

Now: Main Jet 52, Power Valve 8.5 - Cylinder 1 dark brown from video.

When I had the 9.5 in it, the bogging was gone and I could easily spin the tires. Now there's bogging and hard to spin the tires off the line. Of course, the tires squak when going from 1st to 2nd (200R4) at the higher RPMs. I've got reasonably fat tires in the back and the original 3.08:1 differential. My goal is not to spin tires, but it's an indication of how well it runs off the line. Love to try taking it to the drag strip, never done that before.

Lots of discussion on the other thread about timing. Distributor needs to be trimmed, but gotta fix this.

Thanks!
Mark

when you stepped the jetting down why did you change the power valve? with just 2 jet sizes I would have left the power valve where it was at then Rechecked things. Number 1 rule only change one thing at a time. so you know what each thing changes, makes it easy to go back one step. just my2cents

Great advice Larry! I say the same thing at work, just don't follow it myself.

I'll go back to 9.5.

It looks slightly rich still, but I'm planning on a trip over the mountains the 4th. 3500'. Will slightly rich cause a problem? Less oxygen seems like it should be leaner. I don't know.

Will slightly rich cause a problem?
Bad mileage, perhaps fouled plugs.
Less oxygen seems like it should be leaner
Correct
Clifford suggested #48 jets and 8.5 PV for the 235, which uses less air volume.
The WOT fuel volume from jet A vs. jet B is not the ratio of their areas, since the main only supplies the cruising (high vacuum) circuit. WOT fuel is also supplied by the PVCR which in your case is .038".
Remember:
1. Holley jet # is not the ID except by coincidence

2. the PV rating is not the size or area, only the vacuum point when it opens. All PV add the same fuel volume in the same carburetor.

Now when you say Clifford Do you mean CLIFFORD when he was alive? Or Clifford as in who has taken over. A big difference their in my2cents.

That's what I read was offered with the stovebolt kit (not casual conversation), which I would guess had been successful.

I just wrote an Excel (.xls) spreadsheet that compares jet sizes @ high vacuum and WOT by percentage changes, e-mail me for a free copy.

np

??

what is your ??

Sorry, didn't understand "np"

Alright, back to the magic formula. I had my power valve numbers incorrect in the above. Documented the changes here.

Holley Carburetor, Model 4160, 390 cfm, 4-Barrel, Electric Choke, Single Inlet, Dichromate
Started with
• Offenhauser intake, unheated
• Power valve 10.5
• Main jets 54 (.054" diameter)
• 35 accelerator
• Secondary jets 59
• Set timing to 18BTDC initial
• Cylinders 1&2 plugs are really fouled, 3-6 dark brown. Believe the unheated intake had something to do with the inconsistently.
• Great performance off the line

Next change
• Clifford intake, water heated
• Power valve 9.5
• Main jets 52 (.053" diameter)
• Cylinders 1-6 darkish brown but at least consistent
• Bogs down off the line

Final change
• Power valve 10.5
• Main jets 51.2 (.051" diameter)
• Cylinders 1-6 light brown and consistent
• Great performance off the line!

According to my official Holley chart and the Holley web page http://tinyurl.com/y68zdppq
#50 jet is .049" drill
#51 is .050" drill
#52 & #53 are .052" drill
#54 is .053" drill
#55 is .054" drill
Are the sizes you gave the drill sizes by test? Do the jets appear unmolested?

Primary MJ + .038" PVCR + .059" secondary = WOT jet areas (2 each)
.050" .011663 In.2
.051" .011822 In.2
.052" .011984 In.2
.053" .012149 In.2
.054" .012317 In.2

Each successive drill size adds about 1.4% to the total WOT fuel, 14.7 becomes 14.5 etc.

To compare any change divide A by B.

Very cool, thanks for the analysis! At WOT, there is not a much difference due to the PV and secondaries, but cruising should get another gallon or two per mile. I need to think about this.

Thanks!

Nice work Mark. Many others will appreciate your time tuning and documenting your carb. What is your elevation for reference?

Thanks, Tom.

We're at 500', usually drive between 200 and 500' elevations out here.

Wish us luck. July 3rd taking her to Spokane over the mountains, 3500', and 285 miles. Far less than the original trip from Wisconsin to Washington, but still makes me a bit nervous.