I'm no "guru", but lots of years of humpty bug stuff makes me pretty damn familiar with Webers. Whats up? What's it doing?
Popping and spitting on start. Not bad around town, just pops every once in a while. On the freeway it's pops an spits avery so often at high RPM, more so at lower RPMs - like when it's in overdrive. We seem to get them to run decent one day then they're out the next.
Ya, the one thing with Webers, when they're tuned "razors edge", I found them to be very susceptible to atmospheric pressure changes. Back with my most insane "streetable" bug, I had two complete sets of jets that I would change for the day after looking at my wall mount weather station. Since your situation seems to be across the board lean, I think I would start by raising the float heights just a smidge... See if that does the trick. I'm ***uming you have them synced and all that, right? If that doesn't solve the deal, the next step is 1 size larger on the idles and mains as far as jetting. Getting this set up just a shade rich will really go along ways to making better drive ability without too much messing around. I do have a good book that I have used for years with this stuff that I could probably send some scans of if you need them...
I forgot to ask one thing, and take no insult please - This is happening with all three and not just one, right? And, you're double sure you have no intake leaks, right?
What he said and do not go over 3 1/2 psi on the fuel pressure. Pops at the carbs is lean, pops out the exhaust is fat. Set the floats at weber factory specs
Ralph & Steven from Calaveras work at Pierce right? Should give one of them a call, they might be able to help. -Juan
Good point on the fuel pressure Riceman! I've been looking for a spec for float height on this deal too, but I'm not finding anything concrete. I do have a recomended jetting table in my book for 4200cc six cyl, which would translate into about 262 cubic inches if your interested in seeing how close you are. Webers are awesome when you get them dialed in,but what freaks the average tuner out, is that there is several different ways to do each step that will result in absolutely minuscule differences. Trying to keep it as simple as possible to do the fine tune is usually the best bet.
Emulsion tubes with holes higher on the tubes between the air corrector and main jet effects the mixture strength. F-16 is lean for street use, F-9 is richer for a mild hopped up motor and a F-11 is more for a full blast race motor. I would suggest you use 10-32 allen head bolts and nyloc nuts in the linkage arms at the pivot rod.
I'm no guru I'm just learning by reading what the guru's say, but what about the air rushing past the carbs and reversing the intake flow like a chimney draws the air up and out? or sort of like the principle of an old spray gun? how does turbulence effect them, I've seen cars run ****py because the carbs come to some kind of scoop but were not sealed from the turbulence under the hood, this doesn't seem to be the case here, though. Comments?
Ya Riceman, I was just looking at the same thing! It would depend on what's in there right now though. I'm looking in my book and the 4.2 litre recommendation in that set up calls for F2. I'm wondering if that's what Pierce set up as a baseline. KIRK, when you have a chance, undo the ****erfly nut on top of the carb, and take a medium straight blade screw driver, and pop a main jet and holder out. If memory serves correct, it should be the larger of the two groupings under there. You'll have a main jet, an emulsion tube, and a holder, inside there is an air correction jet, but lets not worry about that right now. Get some numbers if you can for the main and emulsion. Might as well pop the idle too. It sounds like a big deal but it's super simple, and we would have a baseline to work from. I think rice man might be right, the simplest way to do this might be with a more aggressive emulsion tube. Remember what i said about many ways for incremental changes? Welcome to Webers!
As I said '46 SuperDeluxe, I'm no guru! Truth be told it's been a good ten years since I have really spent allot of time around Webers - and most of my time is with IDFs and IDAs. I do see that he has some velocity stacks on his inlets, and that will usually shield the venturis from having the mixture ****ed back out.
Kirk, I've tuned several ( street) cars on Webers. One was a stock engined 4inline that would outrun and out accelerate a stocker, while giving much better mileage. So I must have gotten it pretty close. I never changed jets, or messed with it once I had it dialed in. I just drove it daily ( and beat the **** out of it...) All by feel, moving back and forth between jetsizes, untill I found the right ones. ( if I would have had a Inovate Wideband, that would have taken a lot iof the guesswork out of it ) Paying somebody to do it on a Dyno would have been quicker, but you can do it yourself... I can look up the ISBN numbers of my Weber books for you if you are interested in going that route.
How are they scynt is the ? Dissconnect all linkage and start at idle. sometimes if one carb comes on before the other it will cough like to let the others catch up. You see what I mean. Good luck
It is called "Fuel Stand Off " at the inlet of the air horn. It has been found on dyno test that 180 radius lip air horns work better at drawning in air , since air flow follows the surface area it has contact with. 30% better than stock Weber air horns and decreases fuel stand off. Webers do not like air flow going across the tops of the air horns. Also too big of a venturi size at low rpm will not have enough volecity too **** in the fuel mixture if too fat making fuel stand off worst. A cool looking air filter to break up the cross flowing air across the air horns will help.
I'm with the side airflow theory mentioned earlier. Gave up trying to dial my 3 Dellortos in, converted them to throttle bodies!
I can't say that I know one but I knew one. He died in '03. Good luck buddy, there will be someone there.
I think that a balance tube between the carburetors could be a worthwhile addition, it usually will improve low end performance considerably.
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