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140 carburetor jetting suggestion needed
Posted by: sweet66monza ()
Date: September 18, 2022 07:20PM

I am finally going through the carbs again on my monza and found a few things 15 year old me overlooked/messed up 15 years ago. It has always been marginal-decent but never great, and gotten tempremetal the last few years as I begun to drive it less and less, so it is finally time to make it fun to drive again!

What do you folks recommend for jetting on 1966 power valve carburetors and stock secondaries? I live at approx 2200' elevation. Car is a 140 powerglide. Approx 4000 miles on a full rebuild. Always consistently run 91 octane ethanol free 100% of the time. I am more concerned about performance over mileage, being a powerglide car it needs all the help it can get!!! Ha. I did a bunch of searching and reading but nobody asked about this elevation or a pg car that I found.

Thanks as always!

Cody Hurley
North Idaho (Post Falls)
66 Monza convertible 140/PG, loaded with factory options
66 Corsa turbo coupe, 3rd owner fully documented [corvaircenter.com]
66 Canadian monza coupe 110/pg project car (no picture yet)
65 Monza coupe daily driver 110/4
Also 2 Ford f350 IDI diesels, three Jeep FC 170s, 1966 Jeep CJ5A, two 1954 International R-150 pickups, 5 Rokon Trailbreakers, Chrysler Snorunner, and thousands of parts





Edited 1 time(s). Last edit at 09/18/2022 07:29PM by sweet66monza.

Re: 140 carburetor jetting suggestion needed
Posted by: RobertC ()
Date: September 18, 2022 11:28PM

Ran 51 primary / 52 secondary decades ago at CA sea level (before change to 4 primaries). 65 4 speed.

Doubt 2000 feet makes a difference.

Re: 140 carburetor jetting suggestion needed
Posted by: roger65180 ()
Date: September 19, 2022 04:55AM

your elevation is going to play into jetting . does it seam sort of lazy when stepping on it hard ? that is usually a lean condition . I am at close to 1000 ft and 52 jets run good here but I bet it would be quit rich at 2200 ft . i dont run 140's , 2 110's and QJet turbo car

Roger R
Madison Wi
62 ct pg turbo
65intercooled 180 4sp,autocrosser
62 Rampy

Re: 140 carburetor jetting suggestion needed
Posted by: JimBrandberg ()
Date: September 19, 2022 05:02AM

I often go 51 Primary and 49 Secondary to begin.
It seems 50 Primary and 48 Secondary are what's in there a lot of times.
It seems like I've removed Secondary jets as low as 46.
I'm interested to see what others say. The high speed enrichment circuit throws an interesting twist in the mix.
I was just reading Bob Helt's Corvair Secrets and I think he said a Secondary high speed enrichment would never lift due to the air flow being halved through two carburetors. If that's so, I'd have to wonder about the Primary high speed enrichment.

Jim Brandberg
Isanti, MN
CorvairRepair.com



Re: 140 carburetor jetting suggestion needed
Posted by: RexJohnson ()
Date: September 19, 2022 09:06AM

On my '69 I'm running 55's in the primaries. I use the regular stuff out of the pump so that would make a difference. I bought a wide band O2 sensor and with 54's it was in the 15 to 16 range. I was told by a knowledgeable person that E-10 you need a 14:1 mixture. This engine is pretty stock with a 260 cam and the slightest of porting in the exhaust plus the smog system. Since I installed the 55's it has been running better than it has in a long time. I don't recall what size I have in the secondaries. The best way to know is to use a wide band and see what is happening. I have made up adapters for different sized pipes that just slip over the end of the tailpipe. I use a little aluminum foil to help seal the adapter on and then tie it on with a piece of wire so it can't fall off. I have checked 4 or 5 Corvairs with this and they all have been on the lean side of the scale.

RJ tools
Salem,Oregon

Re: 140 carburetor jetting suggestion needed
Posted by: v8vair ()
Date: September 19, 2022 10:07AM

The O2 sensor needs to further upstream, 15:1 would of melted a piston , that readings wrong. On an air cooled engine I would keep it in the mid 13s
One of the best mods you can do is redrill the pivot hole on the arm of the accelerator pump, gives a stronger and longer squirt.

1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1998 Honda Prelude Dirt track car
1967 Crown V8 under construction
Mike Levine
Cumming Georgia
North of Atlanta

Re: 140 carburetor jetting suggestion needed
Posted by: RexJohnson ()
Date: September 19, 2022 10:11AM

My conv does have a hole ahead of the muffler and I have tried it there and on the tailpipe. It didn't make any noticeable difference. As for the accelerator hole I don't have mine hooked up so that would not make much difference.

RJ tools
Salem,Oregon

Re: 140 carburetor jetting suggestion needed
Posted by: sweet66monza ()
Date: September 20, 2022 12:23AM

Thank you for all the suggestions! I ended up having a 46 in one secondary, the other was illegible, and a 49 in one primary with the other primary also chewed up. I was able to scrounge up a pair of 49s for the secondaries and 51s for the primaries from the parts pile, I think I will start there and see how it does since those jets were on hand without waiting a week

Cody Hurley
North Idaho (Post Falls)
66 Monza convertible 140/PG, loaded with factory options
66 Corsa turbo coupe, 3rd owner fully documented [corvaircenter.com]
66 Canadian monza coupe 110/pg project car (no picture yet)
65 Monza coupe daily driver 110/4
Also 2 Ford f350 IDI diesels, three Jeep FC 170s, 1966 Jeep CJ5A, two 1954 International R-150 pickups, 5 Rokon Trailbreakers, Chrysler Snorunner, and thousands of parts


Re: 140 carburetor jetting suggestion needed
Posted by: roger65180 ()
Date: September 20, 2022 05:42AM

good choice . as Rex said a wide band o2 is very helpfull for tuning.

Roger R
Madison Wi
62 ct pg turbo
65intercooled 180 4sp,autocrosser
62 Rampy

Re: 140 carburetor jetting suggestion needed
Posted by: brentc ()
Date: September 20, 2022 08:23AM

51/49 should work quite well Cody.

You may ultimately try a 53 in your primaries one day which is where I'd expect the best all around performance.

AIR smog carbs and non enrichment carbs need to err a little richer, you probably have the enrichment system type with the little rocket shaped needles in them.

1965 140 has 51/48 usually and 1966 has 49/46 usually on Powerglides. The 1966 was too lean in pretty much every case, in my view. With the original 3839889 can and offset crank the 140 Powerglide can really make power from all the gas you can throw at it, they're fine with pretty rich jetting.

You certainly will find it's much improved now I expect. Running slightly rich also makes a surprising improvement in spark ping, you may be able to advance the timing a little which will also improve power and economy a bit.

Brent

Re: 140 carburetor jetting suggestion needed
Posted by: Ratt643 ()
Date: September 22, 2022 09:08PM

Since its a 140, 52-53 on the primary's. This will help it run a tad cooler. Secondaries try 48's to start with.

1964 Monza Coupe
1965 Corsa 140
1967 Monza Coupe

Maryville, TN
U.S. 129 The"Tail Of The Dragon"

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