92GTA

I have a 57-61 2x4 245HP carb setup on my 1956's original 265ci engine right now. A 2626S front, and a 2627S rear. No choke, .030" over, hot cam, not sure of any other specs (has about 3K miles on a rebuild from 1965). It's also a 3-spd manual. I have a brand new set of AC-43 spark plugs @ .035" gap, mechanical advance dizzy with the base timing set at round 9* I think (it's at the timing mark 1 in from the edge, cleaned my timing marks but still almost impossible to read). My elevation is ~600ft and dry central CA desert.

I'm going through just trying to get some base settings as they should be. I want to get the idle mixture screws on both carbs set to base spec. How many turns out from all the way in is spec for these carbs and what would you recommend considering my setup? Then I'll go back and check my timing, set my idle, and try to call it good.

I've read that I might need a vacuum gauge to correctly set these idle mixture screws. I don't yet own one (which do you guys recommend and where do I attach it?) but I'm just trying to get everything at as close to a good starting point as I can. I have NEVER tuned a carb, however I understand the basics I think and I am VERY well versed at modern custom tuning of FI. I know that's not even the same ballpark but it's better than nothing and it's all I have at this point lol.

Thanks!

Alex

plaidside

First of all never try to adjust a carburetor until the ignition and timing are checked and set. I think AC-43 plugs are too cold for normal street driving. I run Autolite 85's, R44s equivalent, in my 2x4 and FI cars.
If you are going to invest in a tool the first should be an advance timing light so you can see what your total timing is. With a "hot" cam you should have between 12-14 degrees initial timing and between 36-38 total.
Do a search on timing and get Lars and JohnZ timing articles.
Some others will jump in but this is the way I did my car and it has run flawless for 8 years.
Back out the idle speed screws on both carbs and turn each one clockwise one turn after it hits the linkage. Now gently turn in the idle mixture screws until they bottom and turn out 1 ½ turns each.
If you don’t have a vacuum gauge you can use an accurate tachometer on low scale and do one screw at a time. Start the engine and see what the idle speed is and adjust to the desired RPM turning each idle speed screw evenly. Now turn one idle mixture screw in slowly until the RPM drops slightly then back out 1/8 at a time until the max RPM is obtained and turn in 1/8. Now do the other three making sure that all the screws are backed out the same amount of turns.
If the idle speed has changed readjust and repeat the above procedure.
Joe

bdhulderman

Good advice from the last guy. I purchased a air/fuel meter and put it in my exhaust to see what the mixture was after building the engine in my garage. I was able to check my mixture at idle through full-throttle to get the idle screws set a little more lean at about 13:1 and my primaries and secondary jets at about 12.5:1. It runs great all through the rpm range.

http://www.innovatemotorsports.com/

Good Luck.

Brandt

plaidside

If you use their tail pipe probe you will get a leaner mixture reading at low RPM's then it really is due to low exhaust flow and O2 dilution.
It becomes more accurate at higher RPM's.
Joe

Frankie the Fink

First off as PLAIDside noted...lose the plugs...I didn't even know you could buy '43s anymore. Run an Autolite 86 (the original spec'ed plug for these cars was an ACR46S)...lots of folks think its the '45 but I have the Service Bulletin. I run an NGK equivalent of a '46. These old carbs run rich and you have to have a hot enough plug to burn off the crud after city driving.

Any quality vacuum gauge will work on your car and you need to get to non-ported vacuum...there should be a fitting somewhere on the carbs at the base. If nothing else work backwards from where your windshield washer vacuum line would attach to the carb and use that fitting. If not Paragon sells an adapter you can use: https://www.paragoncorvette.com/p-35...m-fitting.aspx

Next the "highest vacuum at idle" mixture screw setting is OK but then if you really want to avoid 'loading up' at idle you need to turn the screws in clockwise (lean) 1/16 to 1/3 turn (2-3 'flats' on the idle screws). The idle will 'roughen up' slightly but settle down after driving. I have a large manual covering your carbs that I can email you but its too big to upload here. Provide an email address and I'll get it to you...

You can dial these cars in just fine without an O2 setup....the carbs were used on everything from Buicks to Packards before O2 gauges were invented...I think it might just confuse the issue for you....maybe useful later on for optimization. Get your timing marks cleaned up and put a piece of blue painter's tape just under the balancer mark and the right timing mark on the engine and it shows up great under a timing light..

92GTA

I just bought 2 new sets from CC. It's the only one they offered, I guess I'll return the other set and buy the suggested ones...

Thanks! Great replies and advise in this thread, thank you!

Alex

bdhulderman

That's why you do what I did and drill a hole in your headers and put in a fitting for the oxygen sensor.

92GTA

Ok, I'm shopping for the spark plugs right now. Should I get a set of the Autolite 86s for the 2x4 setup then a set of the Autolite 85s for when I put my 1x4 setup back on in the next couple of months?

Also, what is the AC Delco equivilent of the Autolite 86 and 85? I only buy AC Delco or NGK, just personal preference. Would it be the AC 46TS? There are allot of different AC 46 plug versions on eBay and I'm not sure which to buy...

Thanks!

Alex

Frankie the Fink

Autolite 86s replace both ACR45 and ACR46 so you will be fine with those plugs....make your life easy and use the one type of plug...

92GTA

Ok, I'll just bought this set for starters:
http://cgi.ebay.com/ebaymotors/ws/eB...m=270665574973

BTW, I found an online link for that carb manual, thanks!

Thanks!

Alex

92GTA

I recieved the Autolite 86s and set my idle mixture screws and idle RPM screws as recommened. Turns out my mixture screws were dead on already but my idle RPM screws were WAY out of sync. Also I didn't realize the timing marks were 2 degrees each instead of one so now I have it set to 12 degrees of base timing for real now.

She runs MUCH better now, thank you guys!

Alex

amtronic1

No one here standing up for Champions? Well, I'll be over here, in a spot by myself.....

Frankie the Fink

No problem....if your idle SPEED screws are cranked in too far you wind up running off your tranfers slots in the carb throat and not off the idle circuit. The result is that your idle MIXTURE screws have no effect when you try to adjust them....a common (and very frustrating) mistake. The next most common mistake is to adjust the idle to the maximum vacuum with smooth idle. Its important after you reach this condition that you turn the screw in clockwise 1 to 3 'flats' to lean out the idle to avoid loading up the carbs at idle. (This roughens the idle but it will settle down shortly).

There was an engineer on here months ago IIRC that had done a comparison of all the major plug vendors and concluded that Autolite makes the best plug going. Can't speak to the validity of the testing but I distinctly remember the post.