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 09:29PM by sweet66monza.

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.

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
63 greenbriar
65intercooled 180 4sp,autocrosser
62 Rampy

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

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

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

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

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

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

Roger R
Madison Wi
63 greenbriar
65intercooled 180 4sp,autocrosser
62 Rampy

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

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"

I am just starting to tune my 140. All carbs were done by Carbmeister - I don't know the jets off the top of my head. Will know shortly. Secondaries are the '68-9 variety. Not sure what 'not machined for cups' means, but I put them in there. Can certainly take them out if wrong.

Car hasn't been driven yet, just shop tuning.

Starts beautifully cold. Just like my Rampside. Goes to ~1200RPM fast idle.

Hot start is another story. Initially I would give it pump of the throttle and it would 'try' to start . . . . but wouldn't. Could only get it to start by WOT primaries and obviously I could see/smell too much gas when it finally cleared out.

Then I tried just barely touching the throttle and it cranked hot a few times, but then it didn't.

Pulled one plug and it is black - no surprise.

My question is - having the idle circuit in the secondaries, I figured maybe I needed smaller primary jets or less turns on the mixture screws.

I will look at the shop manual here shortly. Just feel like it has too much fuel at idle. I haven't experienced this hot start issue before, but I haven't had a 140 yet either.

gerg
Monroe, LA

Current cars and other fun stuff -> [gregblakeney.smugmug.com]



Edited 1 time(s). Last edit at 03/09/2023 01:27PM by gerg.

Got the RS opened up.

So far 52 main, 50 secondary.

I do have a discharge cluster over the Venturi of each secondary also.

gerg
Monroe, LA

Current cars and other fun stuff -> [gregblakeney.smugmug.com]

gerg Wrote:
-------------------------------------------------------
> Got the RS opened up.
>
> So far 52 main, 50 secondary.
>
> I do have a discharge cluster over the Venturi of each secondary also.

First caveat - not familiar with 68 - 69 secondaries. Only early 65 secondaries.

Do they have an idle mixture screw like the primaries?

Do they have an accelerator pump discharge hole? Early 65's had a single hole. If no hole; no cups are needed.

Jets are ok - to start.

At idle, the engine / carbs run off the idle circuit - not the jet. Adjust "richness" with idle mixture screws.

Do not know what a discharge cluster is?

Early 65 secondaries (and others?) have a single tube...

Ran 51 primary / 52 secondary on early 65 carbs, but it was decades (1980's) ago - different gas.

HTH

Makes sense on idle mixture - not being jet.

What about off idle? Like fast idle - the jet plays more there?

I was surprised to find 1 turn on LH carb and almost 1.25 turns on RH carb.

I can remember now trying to adjust the richness out of the idle a few months back after I broke the engine in.

Shop manual says 49 / 46 for PG 140.

Figured I’d try 50 / 47 (bump for ethanol)

Richness / black plugs makes no sense if problem is idle related with my screws adjusted in from the standard 1.5 start.

Really just starting to tune this thing.

Engine is .060” over
Stock NOS 9889 cam with correct 4° offset crank gear for PG.
18° timing.

gerg
Monroe, LA

Current cars and other fun stuff -> [gregblakeney.smugmug.com]



Edited 2 time(s). Last edit at 03/09/2023 02:57PM by gerg.

gerg Wrote:
-------------------------------------------------------
> Makes sense on idle mixture - not being jet.
>
> What about off idle? Like fast idle - the jet plays more there?
>

Not sure - decades ago I had a piece of scale block the idle tube on one primary (110 / PG engine). Feeble memory - Engine ran ***** below 30 - 35 mph and ran fine above that speed (I was on a freeway at the time.).


>
> I can remember now trying to adjust the richness out of the idle a few months back after I broke the engine in.
>
> Shop manual says 49 / 46 for PG 140.
>
> Figured I’d try 50 / 47 (bump for ethanol)
>

Too lean, I think. I believe most people run 52 in primary nowadays. The secondary can be as rich as you want - my use of 52 caused significant mileage drop is you used the secondaries a lot (around 12 mpg in the city IIRC).

Of course, richer jets may cause an issue with emission testing if required.

> Richness / black plugs makes no sense if problem is idle related with my screws adjusted in from the standard 1.5 start.
>

Though I cannot really recall personally having an issue, I was always concerned about the idle mixture screw - being bent or passage damaged by overzealous tightening.

This thread caught my eye again. As I clicked I wondered what original was and thought 50 Primary and 48 Secondary.Then as I read down I see 49 Primary and 46 Secondary.
I doubt if we can run on 49s and 46s anymore but running fat and rich isn't necessarily a good idea either. Too rich makes less power. We tend to err on the side of rich as "better safe than sorry" but I wonder if it really is safer. Carbon is a bad thing.
I don't want to offend anyone and can't argue with an O2 sensor but 55 Primary seems obscene except in a racecar at wide open throttle most of the time. With the O2 sensor can you see the high speed enrichment come into play?
What about differences in jetting based on distributor curve? 140 Manual seems to be "all in" at 3000 RPMs rather than 4000. Is that as much about the bigger valves as it is about the extra carburetor? Is "sooner the better unless it pings" the spark advance theory?
I'm not trying to pick a fight, I just like learning about what other folks are doing and why. Not much of a consensus here for a new guy coming across this thread but I suppose it's often like that.

Jim Brandberg
Isanti, MN
CorvairRepair.com

Jim a wide band afr sensor and gauge gives you real time air , fuel readings , you can see what ever the carbs are doing , idle , exceleration part throttle cruize wide open . I have had a wide band in my qjet turbo car for years and a portable one for checking random cars with issues .

Roger R
Madison Wi
63 greenbriar
65intercooled 180 4sp,autocrosser
62 Rampy

All great feedback, and I just remembered I have a portable wide band AFR . . . I’ll grab it from the shop. The PO had a bung installed in the RH exhaust pipe in anticipation of EFI I think.

I couldn’t get past the ‘68-9 having a contribution to the idle richness - and I had only looked in the ‘66 shop manual. But the ‘68 also shows 49 main, 46 secondary.

I am going to try 51 mains and 48 secondaries. +2 / +2 from stock. I don’t need a ton of secondary fuel (unless the inrush of air is misaligned with the fuel match - I’ll address if so). Previous-previous owner had the secondary linkage completely removed and in glove box. His wife said he couldn’t stay out of them and wanted better mileage

gerg
Monroe, LA

Current cars and other fun stuff -> [gregblakeney.smugmug.com]



Edited 1 time(s). Last edit at 03/10/2023 09:16AM by gerg.

In my experience, 52s are the best all around in a 140. Factory jets on the secondaries.