dual Weber trouble
 

Ok I need some help,
I have a stock port 12a that ran fine, I got a set of rotary dual webers from a friend of mine, and rebuilt them.
Installed on the car and followed rotary engineerings adjustments to get it to run.
Pat the gas twice and it starts right up, but will die it won't idle on its own. The only way to keep it running is to keep patting the gas which makes it run rich, and back fire.
It's like it can't draw gas out of the carbs by its self.
For a fuel pump I'm running a brand new stock pump because I had just replaced it right before I got the webers, I know it may not flow enough when I drive it, but I would think it should at least idle with it.
Also I noticed gas seeping out of the side of the carbs where the throttle shafts are, which could be from having to pat the gas so much to keep it running. Thanks for the help

Sounds like its flooding. Sticky needle seats?

It can't be flooding because if I don't press the gas nothing will comes out of the carb, nor will it stay running, if I rapidly move the throttle I can keep it running in the 2 to 3k range, but at that point I'm just dumping gas in it. It's like the idle circuit isn't working.
The only thing I can think of is maybe the fuel psi is just too low even though it's a new pump, I still would think it should still idle.

Shouldn't be the pump. I ran a Holley 465 (requires 6 PSI) with a stock original pump and it ran... ok. sputters on mid to top end, but idled and accelerated ok unless you floored it.

Sounds like your idle jets are blocked or the idle circuit is blocked

i think if gas is coming out of the throttle shaft, you'll find its also a huge vacuum leak, which makes you literally correct.

the engine can't draw gas out of the carbs with a leak. literal truth there.

you may also try playing with the idle speed and mixture screws

Ok, I don't have the choke splitter cable, so I moved the choke levers by hand and had my brother start the and it at least started right and held an idle at 2200 rpm, as soon as I let go of the levers it would run by its self for a few seconds then just die out.
I think the gas may have been seeping out around the gasket for the jet I tightened them a little more and think that solved that but I'll check it again tomorrow in the day light.
I still can figure out why it keeps dying out with out the choke, gas is coming out of the Venturas in a mist like it should when you hit the gas.

The gas coming out when you hit the gas is from the accelerator pump. Your idle circuit is not delivering enough fuel. What Idle jets are installed and how many turns off the seats are the idle mixture screws? Have you tried backing them out to see if that helps?

Yeah it has a stream of gas from the squirter via acc pump but also a large mist coming from the Ventura when you hit the gas.
As for jets I don't know what ever rotary engineering put in it, it came off a stock port 12a do I'm guessing it should be close on jetting.
As mixture screw I turned them all the way in then backed out one full turn. I've tried turning them to different settings with no luck.

I think the mist coming from the venturi when you open the throttle is coming from the main circuit.

If changing the mixture screws does not change anything then the idle circuit is not working, you either have a vacuum leak or the idle circuit is clogged , or is leaking so badly that there is no fuel being drawn through it, or maybe the idle jets are waaaay too small, not likely if it actually ran well on the last engine it was on.

Ok I just went and checked the idle jets they are 45 for both carbs, looking at pierce manifolds that's the second to smallest ones so you think they could be just to small?
The set up came off a 7 my friend bought not running that was stock port, so there is no way of knowing how or if they ran well on that car.

Nope, 45s are what came in them for the 12a, so that is not the problem.

My thoughts are most likely to least likely:

1. Vacuum leak- Not enough vacuum signal to pull the fuel through the circuit.
2. Float level could be too low- If its to low the vacuum will not pull the fuel into the circuit
3. Fuel pressure could be too low (fuel not getting past the needle so the level is low).
4. Check the idle speed screws to make sure the throttle plates are not completely closed.
5. Check the idle circuit with compressed air to make sure it is not clogged. (May not be likely that both carbs idle circuit are clogged?)
6. One last hunch, check the gasket for the top of the carb to make sure it does not block the idle passage, I think it might go through the body and the carb top, if the gasket is wrong or shifted it may block. (This one is a long shot)

Thats all I can think of at the moment.

I think I may be on to something now the primary throttle shafts have a tiny bit of up and down play when you crack the throttle open a bit, the rear carb more so than the front one, could this be what's messing up my fuel mixture, why it won't hold a steady idle with out moving the choke levers?
If so do they make larger throttle shafts?

Worn shafts could cause a leak, but I think you should be able to open the mixture screws up enough to compensate and get it to idle without having to pump the gas peddle.

Now that I have thought about it if the shafts were worn alot, maybe the mixture screws could not quite compensate for it , I guess it would depend on how worn the shafts were.

The rear carb when you slightly open it, you can wiggle the opposite end of the throttle shaft maybe a 16th of an inch, I never caught it before because you can't wiggle it when the throttle is closed. The front carb is the same way but doesn't have quite as much play.

Wow, I would say thats a lot!

Your probably right, That would probably account for a substantial leak.

I once saw an oversized primary shaft on ebay, so you may get lucky there, also check with pierce manifolds to see what they may have, btw I have had much better luck calling them than just going by whats on their website.

Well crap! I called Weber with no luck for oversized shafts.
I'll call pierce next,I sent them an email but like you said I may have better luck calling instead.
I guess for now it's back to the ole trusty modded Nikki.

Try putting some thick bearing grease on the shafts to see if it changes the behavior. That will stop the leak for
testing purposes.

I searched on E-bay and found an oversized secondary shaft, but no primary.

BTW the oversize you are looking for will be 8mm.

I am wondering if it would be possible to machine a relief into the body of the carb that would accept an appropriately sized o-ring or seal to seal the shaft to the body of the carb.

I saw someone do that to a nikki that was being turbo prepped on here. Can't find the link now but
it worked well.

Well no luck with pierce manifolds either. Thanks for checking on ebay for me.
Hmm thinking of the o ring idea, if I had a way to cut a tiny grove all the way around the throttle shaft then i could just slide a o ring on the shaft. That may work.
I'll still keep my eye out for an 8mm throttle shaft, thanks for that info.

I found a bushing online, about 1/2 way down the first page, part # MB0710nu:

Metric Series NU Bearings - up to 45mm Bore

This bushing should or may be a press fit over the shaft, then drill the carb body out to 9mm which is the OD of the bushing, should eliminate the free play and fix it.

That having been said, I am still wondering if you may have an additional problem, If the shaft wore or carb body wore down resulting in the free play, it had to be running and idling, even if it may have not been running perfectly. (just thinking out loud).

that is a bummer, the IDA and DCOE's have bearings, and actual seals, made of leather, but anyways.

the SU carbs have a bushing, i wonder if its the right size?MossMotors.com - Restoration Parts And Accessories For British Cars