140 hp carbs.

[Mike M]

Back to pick everyone's brains again... I have 4 carbs that I want to use on my engine, and have 4 rebuild kits coming. Trouble is, they're all primary carbs from 2 different engines. Can I use them on my 140 hp by just modifying 2 of them to be secondaries? I don't want to spend more on 2 more carbs.

[66vairguy]

Back to pick everyone's brains again... I have 4 carbs that I want to use on my engine, and have 4 rebuild kits coming. Trouble is, they're all primary carbs from 2 different engines. Can I use them on my 140 hp by just modifying 2 of them to be secondaries? I don't want to spend more on 2 more carbs.

Oh-oh! This is like asking "What oil should I use" - The four carb system actually changed from year to year and many have opinions without facts.

First --- Yes folks use four primaries, but their are issues. The year of the carburetors you have is important.

Second --- Years ago Steve Goodman let the world know (I forget where I read it) that the 1968 secondaries were modified to have a fixed idle circuit (none in 65 - 67). This was done to fix a idle mis-fire problem that GM found caused the emissions testing to fail. How did Steve find this out? He lives in a "high altitude" area were ALL cars have to pass a smog test (and you thought Calif was tough). Steve discovered the 68-69 140 HP's passed fine, but the 65-67 failed due to a intermittent mis-fire at idle. Steve connected the dots and used a 62-63 (simple primary) base to have an idle mixture below the secondary top. IT WORKED. No mis-fires. BTW Many assume the idle mixture was added to keep the fuel fresh in the secondaries, and it does, but that is NOT it's main purpose. I do recommend using a solid throttle plate since the notched throttle plates (I'm not sure, but I think the 1960 and 61 were solid on primaries) make getting the RPM low enough tricky.

The 64 and newer primary carburetors are more complex and have features you DO NOT want on a secondary carburetor.
The 62-63 carburetor bases bolt up to the secondary tops without issue.

Why did the 66-67 secondaries cause a mis-fire. That's another LONG story. I've got to run. Feel free to ask more questions.

[Mike M]

Thank you much for the response! One of my carbs has a tag on it , and is a 1962 year model. The other 3 look the same externally, except 2 have plastic vacuum cans (choke kick outs) and 2 don't. The only other obvious difference is that one of the holes in the top of the main jet cluster casting base ( next to the screw that holds it down) is larger on 2 of the carbs. I don't care about stock appearance, or whatever linkage was on them originally...it's all going to be custom made to suit my application anyway. I just want to make it functional without extra expense. I've got Bob Helt's carb book ordered to help me with the rebuilds.

[Lane66Monza]

Start with getting the 2 primaries built and operating properly with 2 blanking plates& gaskets where the secondaries should be. Once you have your engine operating properly, get yourself a set of secondaries and rebuild them and install them.

You might want to consider using Roger Parents throttle system for a 140 engine to improve throttle response.

http://www.corvairs.org/Roger%20ParentC ... -02-19.pdf

[66vairguy]

Start with getting the 2 primaries built and operating properly with 2 blanking plates& gaskets where the secondaries should be. Once you have your engine operating properly, get yourself a set of secondaries and rebuild them and install them.

You might want to consider using Roger Parents throttle system for a 140 engine to improve throttle response.

http://www.corvairs.org/Roger%20ParentC ... -02-19.pdf

A good suggesting from Lane. Roger Parents "65 style" linkage is well made and looks great, BUT the number of adjustment points during installation can be overwhelming for some. I had no ssues making it work, but it took some time. Once dialed it it works well and is great looking hardware.

Not to be negative or contrary, but saying you want things "functional without extra expense" is rarely doable on an old car. Old cars are like boats, something that eats up money.

As Lane said --- Some do avoid the complexity and cost by just running a 140HP on two primaries with NO secondaries installed (use block off plates). Some may cringe at this, but better than a car that won't run due to lack of parts or money.

READ Bob Helt's book and figure out what carburetors you have. There was literally some change every year. Chevy installed the PES circuit to cure a lean spot and allow for leaner over all jetting on the 1965 model year carburetors. I consider the 1965 to be the best carburetor for primaries. They tolerate wear and tear and works well. I run stock jet sizes and the engine my engine runs great, no carbon fouling and no "pinging" and the head temperatures are fine. I know Bob Helt suggests larger jets, but on the 65 carburetors it is NOT required.

Good luck with the car

[Mike M]

Got my Bob Helt book today, and found out I have 2 1960 carbs, and 2 1962-3 carbs. Don't know if I can use these on my 140hp or not, or how to modify them to make them work. More studying will be necessary.

[bbodie52]

This video is loaded with useful information about the Rochester carburetor variations...

FROM THE WORKBENCH OF LARRY CLAYPOOL — CORVAIR ROCHESTER CARBURETORS

Best Carburetors for your Corvair: recommended by Larry Claypool...

viewtopic.php?t=17701

[66vairguy]

Got my Bob Helt book today, and found out I have 2 1960 carbs, and 2 1962-3 carbs. Don't know if I can use these on my 140hp or not, or how to modify them to make them work. More studying will be necessary.

It comes down to your budget. You could block off the secondaries and install the 62-3 carburetors for primaries IF they are in decent condition. These carburetors are decades old and I almost always have to replace the worn out throttle shafts (Clark's sells new shafts). Sometimes I get a bad carburetor that simply won't work due to micro cracks, internal passage corrosion, warpage.

Years ago davemoto head convinced me to buy a soda blaster to clean carburetors and it works great. I clean out the soda with a water/Simple Green solution.

What I'd do is find two good 65 carburetors for primaries, take the solid throttle plates out of the 1960 carburetors and install them in the 1962-3 bases to use as secondaries. The I'd find 1965 secondary tops and throttle shaft linkage to put on the 62-63 bases. Of course the carburetors need to be cleaned, floats tested, needle valves replaces, etc. I'd buy the Roger Parent 65 style four carb linkage.

Well all this takes time, experience, and MONEY that you might not have. So you'll have to decide what to do.

[Mike M]

Thank you, Brad, and 66 Vairguy! Great info. I may have to buy more stuff after all is said and done, but still have to try to use what I have first to see if I can make it work. Using the idea of the primaries first with plates on the secondary holes, why not use my 62's for that and get it running well with that setup, and then remove them and put plates on primary holes and install the '60 carbs on secondary holes and get it running well on them, also. Then reinstall the '62s. I could build a linkage that would only open the '60s at higher throttle position, without changing tops or any other modifications. Just tossing ideas out looking for alternates to doing it "the right way" ;-)

[66vairguy]

Thank you, Brad, and 66 Vairguy! Great info. I may have to buy more stuff after all is said and done, but still have to try to use what I have first to see if I can make it work. Using the idea of the primaries first with plates on the secondary holes, why not use my 62's for that and get it running well with that setup, and then remove them and put plates on primary holes and install the '60 carbs on secondary holes and get it running well on them, also. Then reinstall the '62s. I could build a linkage that would only open the '60s at higher throttle position, without changing tops or any other modifications. Just tossing ideas out looking for alternates to doing it "the right way" ;-)

No reason to put plates on primaries to see if secondaries will work. While the engine will run on only secondaries, it won't run well. The primary and secondary carbs positions on the manifold are designed to work with the airflow fluctuations as each intake valve opens and closes. At lower RPM only the primary opens and it's position works well (and why it is not in the center of the manifold) to provide an even mixture to all cylinders. At higher RPM the secondary position works in conjunction with the open primary to provide an even mixture to all cylinders. The engineers knew what they were doing.

[Dennis66]

The engineers knew what they were doing.

I'll second that. One thing I learned a few years back from a Weber performance book. On inline engines, it was best to have the throttle shaft parallel to the crankshaft. On V type engines, the manifolds were designed (usually) to have the throttle shafts perpendicular to the crankshaft. The Corvair is set up as if it were two co-joined 3 cylinder inline engines. Dennis

[Mike M]

Thanks again, guys! So I'll just make it run perfect on the '62 carbs as primaries, and add the '60s as secondaries, trying to make sure they are all balanced correctly... easy peasy :-)

[erco]

Neither 60 or 62 carbs will have the power enrichment circuit, which you probably want on a 140.

[Mike M]

Yes, I kinda figured that if this experimental engine runs fairly well, with no lubrication or overheating problems, then I will probably invest in proper carbs and maybe electronic ignition. It is not going to be a "normal" engine, and will not be installed in a Corvair. If it is successful, I will show the engine and car build on you tube. If it isn't, well I'll just slowly fade away in shame, always believing that it should have worked if only I had...... ;-)

[Frank DuVal]

Neither 60 or 62 carbs will have the power enrichment circuit, which you probably want on a 140.

For the primaries, yes! For the secondaries, no.