No air bypass screw on early Weber 40's

[Sharktrainer]

I have mounted a dual sidedraft setup and found that there is no air bypass adjustment. Not sure how old they are but have brass floats. One side sucking 7 the other only 3 via my syncrometer. Don't know what to do at this point. 

[Simeon]

How do your butterfly plates look when closed?  Throttle shaft can end up twisted to give different openings. You can try bending back to cure (or do the right thing and rebuild with a new shaft / butterflies). 

[Sharktrainer]

They checked out well when I freshened the carbs up. Same gap per the pair. Didn't inspect though to see if the plates were tweaked. 

[Simeon]

Did you check the plates next to each other to take into account the knife edge on them or any aftermarket filing or even holes?

 

Silly question but I assume you have the same size choke in each side?

[TobyB]

All of the above, plus sight down through the progression holes and see where the plates are.

That's one of the 2 big things that matter to these carbs at idle.

 

The shafts are surprisingly easy to bend, and bad throttle linkage can do it in a couple of pumps.

2 crescent wrenches will fix it, and then fix your linkage.

 

Very few older DCOEs have the bypass- it showed up as an 'emission' carb

(because if it has more screws, it's more emissionable?) about 20 years ago.

 

But.

 

Do a careful valve adjustment first, make sure your plugs and wires are good, and recheck the timing.

And a compression test too, because it'll measure the relative pumping of both pots.

Just because the quality of the flame in the pot can make a HUGE difference in how well the cylinder flows at idle.

 

hth

 

t

Edited June 26, 2017 by TobyB

[Sharktrainer]

Sorry, just finished with linkage finite adjustment which took me almost to the edge of madness, heh.

 

They looked fine, just a little surface rust by the screws that hold them to shaft.

 

I swapped out the points mechanical advance distributor for one from Ireland that does away with the points. Regapped plugs to .035". 

 

Compression good all across.

 

Valve adjustment 6 weeks ago.

 

Idle screw where it belongs now before anyone spots it. Guy I bought the carbs from had them on a Nap Z engine which is on opposite side of engine.

 

 

 

Edited June 26, 2017 by Sharktrainer

[2002Scoob]

You're rocking Old Italian DCOE's. There definitely is no air bypass on these, I've got a set of these old girls that are 40's of the same style. Takes some fiddling and a bit of black magic to get them running properly, but as long as they're in good shape and well tuned they're great carbs. 

Edited June 26, 2017 by 2002Scoob

[Sharktrainer]

Any idea of good baseline for jets, emulsion and air correctors? Running stock cam on e12 head and headers to 2.5 free flow exhaust. I live in Hawaii (Maui) at sea level and temperatures are always the same 80° + - 10°

 

I have;

 

55f2

 

115 main jet

 

F15 emulsion

 

200 air corrector

 

I bought from the local VW shop 170 air correctors and 125 main jets but haven't installed.

 

 

Edited June 26, 2017 by Sharktrainer

[2002Scoob]

What size chokes do you have?  

 

Here's a link to my recent experience getting Italian DCOE's up and running. 

 

My current jetting is 115 mains with 210 air correctors, paired with 32 chokes. No clue my elevation, but I'm also running a 292 cam.

 

However, with the 50 F9 idle jets I have I think they're a tad too lean for my setup.

 

I had a mechanic last month take a quick swipe at tuning it just to get me cruising nicely and he didn't touch the idle progression circuit, only the main/air correctors and was able to make it pretty darn well. But this weekend I started having some lean coughing on the tail of the progression circuit (likely things settling from heat-cycle or mixture screws) that I haven't been able to tune back out again, and noticed he had to put the mixture screws pretty far out to achieve a decent AFR to transition into the main circuit (3+ turns out on long-taper mixture screws where it should be 1.5 or less).

 

Good luck! There's lots of super knowledgeable people on here that helped me get as far as I could. 

 

 

 

 

[TobyB]

115 is a little on the small side- see how that goes and depending on your CHOKE size, you can try

the 125's to see if they're too big.  Then get 120s...

 

Quote

had them on a Nap Z engine

 

Set your float level.  I'll betcha it's not right.

 

and look at the throttle plates through the ports I've circled, below.

If the throttle shaft's bent, it'll be obvious as you move it slightly

and compare one side to the other...

 

t

 

[AlanM]

On 6/26/2017 at 0:56 PM, Sharktrainer said:

I have mounted a dual sidedraft setup and found that there is no air bypass adjustment. Not sure how old they are but have brass floats. One side sucking 7 the other only 3 via my syncrometer. Don't know what to do at this point. 

Do you mean that one carb has more flow on one throat than the other, or do you mean than one sucks at 3 and one carb sucks at 7 on both its throats.  If the latter is the case you will only have to adjust the mechanism that connects onto the arms to even up the flow at idle.  I would go with the 125 mains and 200 airs at this stage with the 32mm chokes, and maybe a 50 F8 rather than an idle with such a large corrector hole.

From smallest(richest) to largest idle corrector hole is as listed.

F6, F12, F9, F8, F11, F13, F2, F4, F5, F7, F1, F3

[Sharktrainer]

Sorry for the delayed response and appreciate all your suggestions. Was working off island.

 

On my way to work here in about a half an hour but did tinker with early this morning, upgrading to 125 mains as suggested and when I went to install the mains into carb #2, I realized I had forgotten to tighten down all the jets under the round cover down. One idle jet was near falling out....duh, heh.

 

Runs way better now, but still not right.

 

To clarify my syncrometer readings, I now have on first carb, 5 and 5, rear carb 3 and 3. I will after work look at the throttle plate orientation through the screws with rubber o-rings.

 

The VW shop here on Maui selection of jets and etc is hit and miss, with mostly all the ones I want out of stock. No 120 mains and have on hand a set of 4 of 175 air correctors. 

 

Will see how the 200 corrector F15 and 125 main goes on the way to work.

 

Also, have 34 chokes.

 

Hope to get these right or I'll have to put back on the 38/38 for the time being.

 

 

 

Edited June 28, 2017 by Sharktrainer

[Simeon]

If you have 5-5 on one and 3-3 on the other then you just need to balance the front and rear carbs.  Figure out how your linkage works for adjustment and wind the 3-3 out to 5-5. 

[Sharktrainer]

Slave cylinder shat the bed when I jumped in the car after work this evening so been dealing with that. Waiting for friend to come by to bleed it out. Thankfully I anticipated this to happen and ordered months ago.

 

Will try adjusting rear via linkage tonight if time allows.

 

Edited June 29, 2017 by Sharktrainer
Photo

[2002Scoob]

2 hours ago, Simeon said:

If you have 5-5 on one and 3-3 on the other then you just need to balance the front and rear carbs.  Figure out how your linkage works for adjustment and wind the 3-3 out to 5-5. 

 

Correct me if I'm wrong, but you should want to bring the high carb down to meet the low carb on your sync'ing, no?