2 x4 hollys how do you tune these boys?

KobraKarl · #1 (**permalink**) 12-17-2002, 10:11 PM

hi guys... i know a few of you are running 2x4's out there. i am running a 1966 stock set up (out of a thunder bolt i think)fomoco mid rise, they ,or one of them is running so rich im fouling out with fuel , the heads and valves are stock and i have been told any thing resembling a lean mix may burn the valves whats the drill?? any help is sure welcomed .thanks Karl

speed220mph · #2 (**permalink**) 12-18-2002, 05:39 AM

One thing you don't want to do is to continue operating you car with it running rich. It will wash down the cylinders and wear them out real fast.

Holleys are notorius for warping the main body of the carburetor, so your problem may not be tuning. The carburetors may need to be torn down and the metering block mounting face trued. This is done by filing those surfaces--two per carburetor--so the gaskets can provide a good seal to the metering blocks. Before you remove the carburetors, though, check that the float bowl mounting bolts are snug. Don't overtighten them.

Another problem Holleys have is a blown power-valve diaphragms. A good pop back through the carburetor(s) will do this. Replacing the power valve will fix this problem.

Mr.Fixit · #3 (**permalink**) 12-18-2002, 06:27 AM

The most common carburator problem is that they don't get setup correctly in the first place. You don't want to run too rich, but you don/t want too lean either. You ought to take the carbs off, put new gasket sets in them, see what size jets and power valves you have (they may need to be changed) and then start tuning them. If that is more than you want to do, check your float height settings first. If one is too high, you will run rich. If one is way too high, smack the top of the adjustment screw with the handle of a screwdriver, that can fix a stuck needle and seat valve. A blown power valve will do the same. Wrong power valve or wrong jets can too.

mr0077 · #4 (**permalink**) 12-18-2002, 08:26 AM

Karl, Kountzecdobra had a good method you might try...take the carbs off and tune them one at a time on a single-four engine of known quality...you'll probably find the rich one has something busted or outta whack (blown power valve would be my guess). after tuning each one, one at a time, bolt them on the 2X4 manifold and reset the idles and you should be ready to rock.
On the car, back off idle on one and tune the other one (float level, mixture), then reverse the procedure and tune the other carb. Finally, try to get the idle airflow (or throttle opening) the same on both for final idle setting.
Good luck!

KobraKarl · #5 (**permalink**) 12-19-2002, 09:05 AM

thanks guys, i guess its time to quit dodging a couple of carb rebuilds. on a 2x4 set up should the idle circuit be active on both carbs ?or just the front?

mr0077 · #6 (**permalink**) 12-19-2002, 09:17 AM

Hmmm...Kountzecobra???
I have both of mine operating...very small throttle opening on each one. Seems like someone said the factory setup used only one carb, not sure which.

kountzecobra · #7 (**permalink**) 12-19-2002, 12:07 PM

MR0077 has the right idea of tuning both carbs separately. On the dual 600 Holleys, you may try tuning like he explained and set idle mostly on front carb, then open rear carb about 1/4 turn from closed position. Try leaving about 1/8" slack in the rear carb linkage adjustment and see what happens. There will be a little trial and error in tuning, but this should give a good start. Remember one thing, nothing is more critical than float level settings on a Holley carb! BTW, Ken, what was wrong with your car last Sat?

mr0077 · #8 (**permalink**) 12-21-2002, 10:54 AM

David, I had a stripped nut on the front of the right outer pivot bolt on the rear end...it has a shoulder on it and when it worked toward the rear and slipped out of the upright it had about 1/8" slop in all directions (out, in, up, down), so it was toeing in on acceleration and out on deceleration, meanwhile crabbing down the road in between...kind of a queasy feelin. $5.00 worth of (4) new nuts and both sides are fixed.
I took your advise on the carbs and pulled out the rear choke and assembly, just fine tuning the single (front) choke right now. MUCH better, thanks.

Ibr8k4vetts · #9 (**permalink**) 12-21-2002, 06:47 PM

This helped me http://www.bob2000.com/carb.htm
Mike

KobraKarl · #10 (**permalink**) 12-21-2002, 10:42 PM

wow what a great site, he didn't discuss 2x4 setups but an hour and a half of reading has given me at least a vocabulary and a basic understanding of cicuit function .thanks Mike

Art Burtt · #11 (**permalink**) 12-30-2002, 05:50 PM

When and if you replace power valves make absolutely sure the gasket under it seats properly. If not you'll never get it to run right.

KobraKarl · #12 (**permalink**) 12-30-2002, 09:31 PM

thanks Art,that had the firm ring of personal experiance.I bought my kits today complete w/ power valves. tommorrow i clear bench space,and get a little dirty i will take extra care with the gaskets!
karl

427 S/O · #13 (**permalink**) 01-05-2003, 12:44 PM

KobraKarl! Art is right about the gskets, I turned my carbs up on end and tighten with my fingers first, this way you can make sure the gasket is centered.
Mind if I ask what size jets and PV your using?

KobraKarl · #14 (**permalink**) 01-08-2003, 09:45 AM

hi Pat, jets are 62 .power valve is 8.5 .this is just how i got them and this is my first time through them, i really dont know what is best for my engine. it was flood fouling ,but i suspect a p/v or float needle. any suggestions?

KobraKarl · #15 (**permalink**) 01-20-2003, 10:12 PM

Hi all

just wanted to toss in a BIG THANKS ....it turned out that you were all pretty much on the money with your remote diagnostics

1 loose srews throughout

2 three of four mating faces warped .006 or more

3 a blown p- valve

4 a bunch a non holly parts.

anyway aday and a half later they look "right outa da box"
now ...i got to clean a manifold.................then

/

SCOBRAC · #16 (**permalink**) 01-23-2003, 05:31 PM

Does this mean your manifold isn't for sale? Just joking..

Reminds me of the only day my 1980 MGB didn't start on the first turn of the engine (no joke) It cranked and cranked.. nothing.. I started smelling fuel.. Hmmm.. I opened the hood and there was gas everywhere.

I looked around and ever nut bolt and fastener on the carb was loose.. It was my day off so I went to the parts store got a pair of rebuild kits for the strombergs and a repair manual (see I told you I wasn't kidding).. I got home and tore off the carbs.. What the hey they were loose already.. I have rebuilt carbs before.. besides I got the book to get me through reassebly. I get every spring, ball valve orfice and jet laid out on the driveway, get them all cleaned surfaces prepped and I open the book to start thr reassembly..

The book tells you how to remove them.. ok.. turn the page.. "PLEASE REFER TO YOUR BRITISH LEYLAND DEALER FOR ADDITIONAL SERVICE"

This was 1987.. It took a few hours. But I got them back together..

KobraKarl · #17 (**permalink**) 01-23-2003, 07:01 PM

Scobrac,

that post preceded by a day the dissapointing discovery that a low rise manifold had been mounted on my medium rise heads.it is FOR SALE . cleaned up nice.

I think a lot of us have done " that one" tear it down (hell i can remember that) a couuple hours later it dosnt look so obvious any more