Balancing Webers

[Mad Mart]

I'm trying to balance my 45 DCOEs on my Sprint. The problem I'm having is getting the two cylinders on the same carb balanced. I know one of the compensation screws on each carb must be fully closed. The other is used to bring the two cylinders in balance by bringing the higher down to the lower. But I can't get the higher one to come down to the other no matter how far I unscrew the comp. screw. I can get it close but not spot on. Same for both carbs. Any ideas?

[Dolly-Nut]

I closed them all off and then balanced the 2 carbs by setting the average between both throats equally - this gave the best overall result.
Consider that it may be an air leak causing the imbalance, or the servo could be affecting one of the throats. The spindles can also bend/wear over time and what makes that worse is when the linkage is connected at one end of the spindle, ideally the linkage (and return spring) should be actuating between both carbs and not on one end of the shaft, causing it to twist slightly once the throttle is opened.

[Mad Mart]

So you only balanced the two carbs then Dan? My linkage is connected in the middle, can't say I've ever seen them connected at one end. You could be right on the spindle wear but I did do a spray test and no leaks were apparent. Looking at the photo the readings are from left to right as you would be looking at the carbs.

[Dolly-Nut]

Yes, that's the same as what I do, just balance the carbs by the average of both readings. I found if I attempted to balance every throat by use of the bleed screws the idle would become annoyingly high because it would be letting too much air in. To counteract this I leaned off the idle mix but that just caused idle and light throttle misfires.
My readings at best were similar to yours. I've had several cars with DCOEs now and I've never had all throats perfectly balanced. I think the problem is that the difference in butterfly openings can only be set between the two carbs and not each throat like with bike carbs. Bike carbs are the way to go and I'll be trying it soon by connecting some ZX6-R carbs to a Weber manifod. The only issue is going to be getting them at the correct 30~deg angle without having to cut the bonnet about.

By the linkage being connected in the middle I mean the throttle cable assembly opening the butterflies from the centre of the carbs, I couldn't remember how yours was setup.

[soe8m]

dcoe_a1.gif (11.13 KiB) Viewed 3472 times

The butterflies you cannot adjust within one carb but with the air bypass you can have all cilinders the same. Normally you have them one turn open and check. Try to have one carb first and then the other. It's a bit turning on all screws the same time. When they are all equal you can adjust the idle rev at the linkage but most of the time one or two you have to reset again a bit after adjusting the linkage. Also adjusting the idle mixture does have influence so that must be ok too. You must adjust the mixture screws in the way each cilinder does idle at the highest revs. That's the most ideal setting. Then turn down the revs by linkage and airbypass.

But the highest idle rev by mixture must be with the mixture screws about 1 or two turns. if this is not the case the idle jets are too big or too small.

Jeroen

[Dolly-Nut]

I'm pretty sure the idle speed screw shouldn't be used. And I've never heard of anyone setting the air screws at 1 turn and going from there, if possible they should be closed imo to keep the idle down otherwise you will struggle to have it below 1500rpm.

[Mad Mart]

The air by-pass screws are there to balance the airflow between the two venturi on that carb. One should remain closed whilst the one on the higher flowing venturi should be opened to match the flow of the other (which doesn't happen on mine). The adjuster screw between the carbs is there to balance the airflow between the two carbs.. The idle speed screw is then used...to set the idle speed...simples.

[1300_2door]

The air by-pass screws are there to balance the airflow between the two venturi on that carb. One should remain closed whilst the one on the higher flowing venturi should be opened to match the flow of the other (which doesn't happen on mine). The adjuster screw between the carbs is there to balance the airflow between the two carbs.. The idle speed screw is then used...to set the idle speed...simples.

Sorry Mart, I may be misinterpreting what you mean, but it sound the wrong way around to me. Surly the bypass should be closed on the higher flowing side, then the lower side is brought up

Gordon

[Dolly-Nut]

I don't think so because effectively what they do is 'bleed' off unwanted/excess vacuum, therefore lowering it.

[1300_2door]

I was assuming Mart was measuring air flow not vacuum, that would explain my confusion.