Hey guys looking for a little help, I'm running 6 holley 94's , but I only have the center 2 that actually work, the others are blocked off on a 354 hemi. Starts and runs great, but when I accelerate and get to about 2000-2500rpm it sputters like crazy, I got it up to highway speed and began to pop a bit to. I think I've got the timing nailed down, about 30°-32° total advance. Vacuum advance pulls from the manifold. Accelerator pump shoots a nice stream when I'm looking down it. I put a vacuum guage on and that sais everything is right where it needs to be. I was just thinking the fuel pressure is around 1.5psi , but I know there supposed to be low. I wouldn't think the float bowls would drain that fast even if it was low. At any rate, any help would be appreciated. Thanks in advance!
When it sputters, can you make it quit by letting off the throttle a bit, stepping down more? What does it sound like? If its safe to do so, shut it off when its sputtering, get to the side of the road and look down the carbs to see they have fuel. Whats the vacuum gauge do when driving? Whats the temp gauge do, lean will run hot. Will it run down the road at lower rpms then highway speeds? How big are the air filters? Have you tried running without them?
Yes, 1.5 psig fuel pressure is a low I wouldn't go above 2.5 psig, but that is me....and you and I are assuming that you have the same fuel pressure at idle as at full throttle...another check usually backfire out the carb is lean, out the tailpipe is rich you say 'vacuum is right where it should be'..... if it is above 2" at full throttle, you can add a carb good luck
It will stop if I let off the gas and is fine at lower rpm, and even if I shift gears, until I get to 4th obviously then it continues. Go It mostly sounds like sputtering, like a lack of fuel, and it has popped a couple times, haven't tried shutting it off and checking at the side of the road. Good free flowing air filters, basically just screens. I can't see what the vacuum is while driving.
Fuel seems to be flowing nice when I look down and give it some gas, I pulled the plugs and check ohms going through the wires and while they all checked out good, there was one plug that looked like it hadnt been fired compared to the rest, ill change it out and the plug wires tomorrow and give that a go.
Assuming that this is a new setup, not something that has just started ‘spluttering’ after years of running okay (you don’t say) Jet sizes too small for that size cubic inch ? Those are quite small carbs for size of engine if what I’ve read on here is correct. Incorrect power valves size ?
Yes, it's a new set up, What size power valve and jets would you suggest, that will be my next thought if not the ignition. I believe it has #51 jets and 4.5 power valve
those are sizes suitable for twin carb set up on 239 cubic inch flathead. I can’t make any recommendations but I wonder if it is starving for fuel once you get going, (or your advance weights/distributor stuff is not where it should be - I don’t really understand that stuff) I am trying to run 2 x larger Holleys (1&1/16” - not 0.94”) on a 283 chev and it has been running reasonably well. But not there yet. I think @Dreddybear ran 4 on a 390 cubic inch size engine. Here is a copy of his post from years ago : “I have 4 94's on my 390 Cadillac. I'm running straight linkage, 3 on the acc pumps, 51 jets, and 3.5 PV's. It comes on full right off the line. Doesn't like partial throttle too much, but those old race intakes were meant to go balls out.”
Ok, so I put new plug wires on and it did the same thing, (oh well, I felt like they should be changed out anyways) so just to confirm it does have#51 jets in it and it had a 2.5 power valve, I through a 6.5 power valve in (cause I had one ) and it ran just as bad if not worse. I came across something about blocking them off when running 2 carbs on a two log manifold anyone heard of such a thing?
if you block them off, they won’t work I tried blocking off all 3 on straight linkage (283 chev) and it ran out of puff. Power valve on these are based on vacuum readings. If using 2 carbs you halve the power valve to both carbs. So for flatheads, generally 15hg vacuum, uses 6.5 - 7.5 power valve Use 2 carbs cut that in half so 3.5 power valve in each. float levels are important also for these carbs. as is fuel pressure, 1.5 lbs is a little low, most on here run at 2.5 - 3 lbs from what I’ve read, but some do run as low as what you are. I still wonder if those two carbs are just not enough at higher revs. .
I have raised up the fuel pressure to 3lb now as well. My vacuum is 15lb so I suppose a 3.5 should be about right. Of that doesn't work I'll get 2 more carbs going I guess
more info, although some links are gone now….. https://www.jalopyjournal.com/forum/threads/links-to-holley-94-technical-info.286574/ if you click on the red arrow in post 15, it should take you to the post, about running 4 carbs on a 303 olds engine
The Power Valve might work opposite from what you are thinking, at 3.5" they probably aren't opening enough, anytime your vacuum exceeds 3.5" the power valve closes and won't supply any enrichment; if you have a 6.5 PV then they open until the engine sees 6.5" or greater. They also have a bit of a range where they start opening sooner than and reach fully open at the rating. The power valve selection is not calculated from how many carbs you have, 2 carbs do not take 1/2 of the power valve rating a single carb would have. To select the power valve you should have a vacuum gauge where you can see it while driving, size it for when you pull into the passing lane and give it some more power, that'd be your target vacuum. What do your plugs look like? they are the window into the combustion chamber, you'll need to pull all 8 to get an idea of how well balanced the fuel distribution is on the log manifold. I expect your plugs will be quite white and your jetting will go into the low 60's and the PV about 6.5 with a modest cam.
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