weber 34 jetting experiment

JOHN G

Well-known member
I figured I best start a new thread on this since we got a little off topic from Patrick's original thread. I have been messing with the jetting on my trips as they have been too rich under WOT. I got out the drill bits and my torch kit last night and soldered shut my outboard carbs main jets. I loosely fit numbered drill bits in them beforehand to set up a baseline. Soldering was easy-clean out the jet opening with some steelwool,flux,apply heat, blah,blah. I figure by my crude calcs. that a #54 drill bit would have me roughly in the 145-150 jet size so that is where I started(done with a hand drill). I found my #1 carb float a little off in the process so I adjusted that. I put the jets in late last night and will fire/test drive this evening. I had 160 jets in the outer carbs previously and they were dumping WAY too much fuel. I'll post results and a complete list of sizing soon.
 
John I have extra main jets that I can mail to you to use for measuring the bit size . I have a 170 , 155 and one I can't read .
- Al
 
On typical tri-power installations the outboard carbs usually have no power valves and no idle mixture controls.

I recall an old timer showing how to modify Stromberg 97's for a flathead and recently I saw an article on converting Rochesters for use on a tri-power setup. Same thing had to be done.

I suspect that if you set up the 34's for progressive operation you should do the same sort of thing.
 
I may be a little, or a lot, paranoid. Still, I feel uneasy about tuning for stoichiometric with the log, I'd rather shoot for slightly rich.. On the other hand, I can see where the duals or trips would give much more even fuel/air mixtures across all cylinders.
 
I agree that I'll never be perfect on the mix, but I was severly rich at WOT. There were plumes of fuel vapor out the pipes and the plugs would get cajunized after a few good runs like that. Big thing is that I have never been able to do much on the freeway because of this. Granted the car was built for around town use, I would still like to be able to shoot down to Summit or something without worry of cylinder wash! Never saw the Weber Direct place-good info on that one. The car has always run very well on the center carb and up through about 2/3 throttle, but thats where it started to fail-I get some surging under WOT that is probably flooding. If I can get the linkage hooked back up real quick, I'm going to fire and drive to work this morning. I'll post results and sizes of this run.
 
Drove to work yesterday-ran pretty good. I can't tell if it has less oomph or if it is in my head. The surging seems to have lessened and I'm not smoking out the pipes. I'm really beginning to think that the surging is ignition related(dizzy). I had a bad vac plug on one of the outboards and that seems to have had more of an effect. My d2 was curved basically by ear and I don't believe it to be right. I'm using manifold vac for the dizzy right now and may try port again and playing with the springs again-I have an aquaintance with a dizzy machine, but haven't been able to get to his place. The reason I say ignition related to the dizzy is that under medium hard accelleration, the engine bogs/stumbles for a sec when the trans shifts to second like the timing drops off. Overall, the car actually runs pretty well-I'm just trying to get it as good as possible. I have checked for vac leaks and haven't found any so tuning seems to be the logical next step.
 
Don't know where the triple post came from, but any how, I seem to be making much headway. Tonight, I pulled the advance off of manifold vac and back to port-Big difference-the surging has pretty much disappeared and the engine is much smoother than before across the range. I was running pretty hot at idle in traffic due to vac advance adding too much advance-that problem seems to have been eliminated. As far as the jets go, this is the current setup... Main idle=65 Center main jet=170 Outer carb main=custom jet size(soldered/drilled)to a #54 drill bit-this is roughly equal to a 145-150 jet size. I have no more smoking under WOT and I am going to add a couple of degrees to the initial timing and see if I can get away with it.
 
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