How do I balance tow chokes on the same Weber?

[bill308]

Ken,

I've always found that balance is most important at idle and just off idle. After about 2000 rpm and maybe lower, it should not be a concern because the actual flow imbalance is very small relative to the air flow at higher rpms. Having stated this, when I do my balancing, I first balance just off idle by actuating the throttle linkage and holding it at about 1200 rpm. Once this is balanced, I relax the throttle cable and use the stops to do the final balance. This assures me that just off idle, all carbs are in synch, which makes a big difference in driveability, espically when starting from a standing stop. All cylinders are doing their part under these conditions so high reving is not necessary. Maximum available torque is immediately available.

I can't think of any circumstances where I would would want to work directly on the progression holes. One of the progression holes on my DCOE-18's was located improperly. It was the first one to be uncovered, so it affected off throttle tip in. Rather than try to relocate it, I carefully champhered the throttle plate locally, only afecting this one hole, so that it was uncovered at the same time as its cousins. This cured an off idle miss and completely solved the problem, with no adverse side affects. Incedently, one can get a very good view of the progression hole to throttle plate interaction by removing the progression hole cover plug and directly viewing the throttle plate throught the progression holes with the engine not running.

Bill

[bill308]

Sean,

I understand the simplicity of using a hose to judge balance on a multi carb setup. I used this same technique with my old TR3's and early on with my elan. I have to tell you that this is not a very good gage of flow unless you have particularly sensitive and calibrated ears. I've used 4-methods over many years and in order of effectiveness, hose, Unisynch, BK syncrometer (SK synchrometer is better, a smaller version of the BK), and multibank manometer. By far the best tool is the multibank manometer, as shown earlier in this thread. If you don't have vacuum taps fitted to measure manifold vacuum, then the next best tool is the synchrometer. The major advantage of the multibank manometer system is that it can measure all cylinders simultaneously and measure them off idle, as well as at idle. It is also very sensitive. Balance the column heights and you are good to go. Some later carbs, like my DHLA E's, have vacuum taps fitted. Alternatively, you can drill your intake manifold to accept hose barbs. The manometer method takes all the guess work out of balancing and accounts for vacuum leakage due past O-rings and throttle shaft leakage.

Bill

[bill308]

Sean,

I understand the simplicity of using a hose to judge balance on a multi carb setup. I used this same technique with my old TR3's and early on with my elan. I have to tell you that this is not a very good gage of flow unless you have particularly sensitive and calibrated ears. I've used 4-methods over many years and in order of effectiveness, hose, Unisynch, BK syncrometer (SK synchrometer is better, a smaller version of the BK), and multibank manometer. By far the best tool is the multibank manometer, as shown earlier in this thread. If you don't have vacuum taps fitted to measure manifold vacuum, then the next best tool is the synchrometer. The major advantage of the multibank manometer system is that it can measure all cylinders simultaneously and measure them off idle, as well as at idle. It is also very sensitive. Balance the column heights and you are good to go. Some later carbs, like my DHLA E's, have vacuum taps fitted. Alternatively, you can drill your intake manifold to accept hose barbs. The manometer method takes all the guess work out of balancing and accounts for vacuum leakage due past O-rings and throttle shaft leakage.

Bill

[Bruce Crowthorne]

I had to take the carbs off at the weekend to replace the fuel hose, so I had a look at the two out of balance chokes.
Turns out that you can see the difference between the chokes by looking at how the throttle disk uncovers the first progression hole.
On mine the No3 choke was about 0.5 mm (measured by eyeball!!) "ahead" of the No4 choke.

Since the difference was observable by eye I ruled out the drilling holes in the butterfly.

So I held one choke by hand and applied some pliers (yes I know a bit crude) and gave a gentle twist. After a few tries I got them visually the same.

When back on the car I hooked the Carbtune back up and all four chokes are within 1cm of mercury (I assume that is what the scale is on a carb tune) no 1 & 4 run slightly higher vacuum but I think they are close enough.

Thanks for everyone's contributions
Bruce