Need Jetting Info for Holley 1920

[Nailhead]

The engine and carb in my truck came from Arkansas, and now it's at about 5200' in Colorado, so I'm thinking the carb might need a rejet.

Anyone have any info on the jet(s) I would need for this altitude?

Thanks for any help.

[Don Cavey]

The engine and carb in my truck came from Arkansas, and now it's at about 5200' in Colorado, so I'm thinking the carb might need a rejet.

Anyone have any info on the jet(s) I would need for this altitude?

Thanks for any help.

I'm in MD right now, my truck is in FL. I am heading back home tomorrow. I can check the notes that I have in my service manual. I wrote down the jet number when I rebuilt the carburetor. BTW, the carburetor that came with my truck had a different number and I suspect it really was not from an M715; rather from a MoPar Slant-Six since they used essentially the same carburetor.

Also, I am at about sea level in Florida. I have no hesitation what so ever etc.


I can check on Wednesday if that will help?

[Nailhead]

I'm in MD right now, my truck is in FL. I am heading back home tomorrow. I can check the notes that I have in my service manual. I wrote down the jet number when I rebuilt the carburetor. BTW, the carburetor that came with my truck had a different number and I suspect it really was not from an M715; rather from a MoPar Slant-Six since they used essentially the same carburetor.

Also, I am at about sea level in Florida. I have no hesitation what so ever etc.


I can check on Wednesday if that will help?

Sure, Don-- I'd appreciate any info you might have.

I pulled what I assumed to be the main jet out of my spare carb & it said ".672" on it. I remember numbers more like "130" or "65" from my Weber days.

[Don Cavey]

I have not forgotten you. I am looking at the books that I have at hand and don't see my notes right away. But I am sure I have more copies of these manuals so I am still looking. I will keep you posted and sorry for the delay.

I distinctively remember writing the jet number next to the illustration in the TM...

[Nailhead]

No worries, Don-- I replaced the passenger-side transfer case bushings yesterday, so my 715 tinkering impulses are satisfied for now.

[Barrman]

I think you might be surprised at how well it runs with the stock set up at altitude. Binford had his totally stock truck at the FE in Buena Vista back in 2008. 7,990 is the official elevation of the airport. We were camped looking down on the runway, so we were above 8,000.

His truck started every time, idled good and even out pulled my 396 Big Block above 11,000 when we drove to the passes.

I also think the -10 or maybe -20 mentions what to do for extreme elevation. I don't recall it mentioning a jet change though.

[Don Cavey]

A little background so you know where this is all coming from.

When I got my truck, there was no carburetor on the intake manifold. The previous owner handed me a carburetor for the truck. I rebuilt that carburetor but the truck always stumbled when accelerating and it hesitated and surged. One clue that leads me to believe that this carburetor was off of a Chrysler six-cylinder engine was the loop over the top of the throat. Chrysler used an air cleaner that was secured with a wing nut in the center of it. The military carburetor body has what appears to be the same casting with the provision for the loop also. But as you know, it has a surrounding collar that clamps it to the air horn.

I acquired another carburetor that was for sure off of the military 230 Tornado engine. I rebuilt that one and it has been absolutely perfect. No hesitation, no surging just does exactly what it should.

Today, I took apart another military carburetor and the jet has #70 stamped on it. I also took apart my carburetor that I think is a civilian 1920 Holley and that is stamped #692. I did a crude measurement of the opening of those jets and came up with this: The military #70 jet appears to be .070" measured with a new #50 drill bit. The #692 jet measures about .065", kinda between a #51 and #52 drill bit. Being smaller, that could certainly account for my problem with surging and hesitating.

Since you are at around 5,000 feet, I suspect you may need a jet smaller than the #70. If our engines are anything like the small airplane that I fly, you need to lean as you increase altitude, especially to 5,000 feet!

These jets appear to be just standard Holley jets. You could possible get some of them from a speed shop that sells Holley parts.

And as for the plastic "Pump Operating Lever", it comes in the military carburetor rebuild kit. The ones that I had gotten were from 1978 production and all parts were still in excellent condition.

I hope this helps! Please keep us informed when you can.

[Don Cavey]

I see that "Chief 9-Flats" was posting at the same time a was typing. And, I don't disagree what what was said. At higher altitude, you will have a richer mixture since the air is less dense; less oxygen. That should not cause any problems other than more fuel used, possibly a little less power. But it should not hesitate. Lean conditions cause stumbling.

[Don Cavey]

I did a check of O'Reilly Auto Parts and found this listing for jets:

http://www.oreillyauto.com/site/c/se...Redirect=N1599

[Nailhead]

Thanks everyone for the help, especially Mr. Cavey for finding a source for jets!

Now, my plan is this: take the truck to a shop & have the tailpipe sniffed to establish a baseline & see if a rejet is even necessary. Then see which jet is in the carb I'm running, & order jets in two different smaller sizes, install, and have the tailpipe sniffed again.

Why not? I'm curious.