Fine tuning Holley 94 2x2

AnthonyG

AnthonyG

Well-known member
As I was going for a cooler look and the holley burning to rich, I changed from a Edelbrock 500cfm 4 brl. to a 2x2 Holley 94 set-up. I noticed after running it for a while the plugs were still getting dark. Full description for analysis purpose, 2x2 Holley 94's on 4" tunnel ram spacer on my 8BA with Merc. crnk, 3/4 isky, oversize Chev hardened vlvs. The 94's are set up with direct linkage and have .051 jets. After making sure butterflys are shut I used a tach to adjust the mixture screws attaining what I think is the highest RPM at idle then resetting the idle adjustment screw to approx 800 rpm. Changed plugs from Atolite 216's to Autolite 437's with the longer tip.

Here's the questions:
Should I readjust mix screws with vac. gauge ( better / worse than with tach )?
Is the .051 jet size about the right size for my engine? ( consensus?)
If I do need to go smaller on jets I've read don't jump more than one size?
While I can see the jets I'm thinking it's safer ( not to lose the jets down into the intake ) to remove and replace them on the bench?
If jets are changed ( smaller ) should I readjust the mix screws?
 
What distributor and coil are you using? What is your timing set at? I setup my 2x2 on a stock 59 l and played with everything from jets to power valves. My setup runs great but correct ignition setup is paramount! I'm in toms river and can give you a hand.
 
To me, setting the idle mixture screws with a tach or vacuum gage is about the same. A vacuum gage may be a little easier since the needle responds faster than the tach.
#51 main jets are about what Holley 94's came with or close enough for starters.
As far as being too rich, if you're 3/4 Isky cam has significantly lower manifold vacuum, the power valves in the carbs may come in too quick, causing the richness, and not because of the #51 jets.
For example, if you're manifold vacuum at idle is 15" Hg, you should use a 7.5 power valve (opens at 7.5" Hg). So the power valve should be approx. half of the idle vacuum.
As far as changing jets (if you do) I would say it's safe to go two sizes at one time if you think the plugs are dark enough to justify it. If just slightly dark, then one size at a time.
I would base a lot of it on how the car performs, and how the plugs look.

The jets can be changed with the carbs on the engine without a lot of danger about dropping down the intake, but maybe easier on the bench if you're back can't take the leaning over.
And you're last question, yes, if you change main jets, you should double check the idle mixture adjustment.
 
34s4ever, Thx for the offer but only in Lavallette in the spring and summer. Live in the Poconos fall and winter. It's where my 3 car garage is. New Mallory 3 bolt electronic no vac adv., timing approx 5 to 8 adv. Actually has been running great but only for a hundred or so miles. Went with the new plug, Autolite 437's with longer tips to get further past the Offy heads. Will see if that lightens up the plug color after another couple of hundred. Then if still dark go per Scicala and check the manifold vac. which I think is ok then change to .050 jets and hope I don't have to mes with the PV's. But if the vac. is low they will be my last try if none of the rest works.
Thx scicala for the good info as well.
 
I have tried all kinds of combinations but here is what I have done with a similar set up. 51 jets but I moved the power valve in the front carb to 3.5 and rear to 1.5. I know this will cause some arguments but when you run a vacuum gauge and watch what is happening under normal driving and acceleration up hills I was running most of the time with the power valve open thus running rich. at 5/8 to 3/4 throttle the 3.5 pv comes in and at full throttle the 1.5. I tried same pv in both carbs just ran too rich.
 
I'd try 49 jets and 4.5 power valves, take a good long done the pike, find a place to pull over and remove the plugs. I'll bet they will a good color. Walt
 
On the ignition...put a timing light on the thing and be sure timing starts to move right off idle and moves a considerable amount by circa 2,000 RPMS. I'm not even talking numbers yet, just confirm that the thing actually moves in the low RPM spectrum!
Do NOT assume that Mallory put in a useful advance curve...they seem to prefer random, but with a bias toward very slow curve unsuitable for a flathead, and the resulting retardation can mimic richness at the sparkplug.
 
Thx Walt and 38 Ford Guy, Good tips, if the new long tip plugs don't do it I'll consider them in the mix.
 
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