Hey guys, figured Id see if I could pick the brains of the experts, and get some good advice off here before tucking my tail between my legs and throwin a 4 barrel intake and carb on this thing. The set up is SBC 350 mild cam stock heads ect... I have a weiand staggerd 4x4 with 4 holley 94's, straight linkage. Running 2.5 psi fuel pressure. The problem i have is: it'll start and run, but it idles really high, (idle screws are all the way out and butterflys are completly closed) and when you give it any gas it falls on its face meaning it backs off as if it wants to die. I have not had the carbs apart, or messed with the idle screws, I bought this intake set up from a fellow hamber who said it was on a running workin car previously, and that it should be bolt on, but we know how that always turns out. Also I have a speedway carb sync deal, but I havent tried anything yet. I know nothing about tuning or messing with multiple carb set ups and I am completly green to this stuff so any help would be amazing!!! Thanks!! Oh hers a picture for all you picture junkies!!
It REALLY sounds like a BIG air leak. Look for the obvious, gaskets and pipe plugs, but another thing is that most 4X2 setups are quite old, made for a different generation of heads with very small ports. Could you have enough port mismatch to cause a leak directly at the head flange?
yeah, my first inclination from dealing with motorcycles is that its running real lean, I'll have to go through and look for any possible air leaks, it did put new base gaskets under the carbs when I put it all on, it seemed as if the ports were all the same on the intake as the heads and I test fit the intake gaskets to the manifold and it matched up
have a look at the carbs to see that all/any of the vacuum pipes are blocked. other thing you could try is blank off two of the carbs and see how it runs
They ALWAYS say it came off a running car but they never say how shitty! The 4 barrel replaced all those multi-carb setup for a reason. I have a half a dozen multi setups (which I am going to be selling)and still run a Holley 4 barrel.
I don't think he's gotten to the multi-carb problems yet...I suspect a big air leak totally bypassing the carbs!
hey thanks so far guys, I've finally got a moment to run out the garage and start Messing with this thing again, I'll prolly pull a carb an see whats in it for jet size an powervalve, but I dont think i can assume there all the same. Shit I might as well just pull these carbs and tear into um for rebuilds, or at least to know whats goin on, I'm sure figuring this out would he a lot easier with jet size, powervalve, howmany turns out the idle mixture screws are, and float bowl settings.
It will be worth the time to learn them..and know what you have as you said.......multi carbs are capable of running like a Banshee.............Littleman.......I agree on the potential air leak as well...
Jets and power valves have nothing to do with idle, unless it is REALLY high...and if so, this is a byproduct of the problem: Whyinhell is it idling so high?? Look for a leak. If you can't see anything up top, the ports may well be pulling directly from the valley. Give the thing a big shot of WD 40 down the oil filler hole and see if anything happens...
well.... I've cotton the idle to come down quite a bit by playing with the timing and messing with the air idle screws, I've got them at 1 turn out and it seams to idle ok. I don't have a tach so I'm not sure what rpm. It still falls on its face when I give it gas. I think I'm dealing with lean jetting and or too small of power valves? Not sure yet. Can anyone tell me appropriate jet sizes, idle mix screw turns and power valve size?
Going from idle to "flat on its face" is surprisingly often an overrich condition! If the throttle plates are completely closed, and all idle fuel is going through the lower idle ports (none through the off-idle) port; there is little air velocity in the manifold runners, and a condition called "puddling" occurs. Puddling is the buildup of droplets of gasoline on the sides of the runners in the manifold. When the throttles are opened, the instantaneous air sweeps all of the droplets into the cylinders, creating an instantaneous A/F that is too rich to fire, thus the engine "falls on its face". Try readjusting the idle mixture control screws on each carburetor to maybe 1/2 turn (or possibly less), readjust the throttle positioner screws to a small opening (maybe 0.008~0.012) AND SYNCHRONIZE THE CARBURETORS! As mentioned by Bruce, unless you have a REALLY high idle, neither main jets or power valves (unless the power valve(s) is/are always open) have any bearing on your current issue. Jon.
Thats the best way, tear em down & see what you've got, could be something obvious, maybe not. If you rebuild them you know what you've got, I always set up my engines with Tri- Power cause I like the response and the way they look, but I never put anything together without rebuilding the carbs first. I also never buy anything new so I don't trust what the seller says about how nice the set-up is. They're easy to rebuild and then you're sure. Oldschool66
Are all the accelerator pumps working? It's an easy visual check. If one or more and not working it will fall on it's face.
A good source for leaks on old carbs are worn throttle shafts. Easily overlooked on a nicely restored carb. Give them a wiggle and see if there is play.
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