Balancing 34-PDSIT Carbs on 1982 Aircooled CU 2.0L Engine

[OgsT25]

Hi all, looking for help diagnosing an issue in two parts. I stripped down and rebuilt CU 2.0L air cooled engine over the winter - put it back into the van recently. 
  Part 1: Following rAtwell’s guide to balancing/syncing the carbs. Using a motorcycle-style mercury manometer connected to the vacuum stubs on the carbs. It was clear that the left carb was pulling a lot harder than the right carb. The values were about 40cm mercury head for the left carb, and wasn’t registering above 10cm above the right carb. I think this means the carbs are really unbalanced/unsynced but the engine idles just fine.
 Part 2: Decided to check the compression on the cylinders to see if the carb pulling difference was stemming from the cylinders. Testing the compression on the cylinders I’ve got the following values - a confirmation that these are A-Ok would be great. Note the difference of 15psi across the lowest/highest compression. 
 Cylinder 1: 115psi
 Cylinder 2: 125psi
 Cylinder 3: 128psi
 Cylinder 4: 130psi
 Any help towards a diagnosis would be very helpful - I would like to avoid removing the engine again but will if I have to haha! 
  
  
  
  
  

[sarran1955]

Hello new member,

Those compressions are ok, but not great. I would get your compression tester calibrated or checked.
The compression will go up as the engine 'runs in', probably 10 psi after 200 miles.

I note you mention vacuum spigots on both carbs...
Do you have a CU or the earlier CJ engine..

Here are 2 short videos with a CJ engine:







This video may also help, especially if you read some of the useful comments that explain better than I did..



and then maybe:





Air-Cooled Bliss...

Cordialement,


 

[OgsT25]

Hi Sarran, thanks for the warm welcome - we’ve been watching your videos for years and really helped when setting up the timing on the bus.
To answer your question, it is definitely the CU engine - not the older CJ.

Is it correct that both carbs should be ‘pulling’ the same amount of air at idle? When at higher revs the carbs pull similar pressures but the left is definitely doing all the work at the lower idle speeds.

Thanks again for your help.

 

[sarran1955]

Hello,
Thanks for watching the videos...I hope you are subscribed..

I feel with the standard Solex twin set up that the left hand (master) carb dominates the rh (slave) carb when the regime is changing..
acceleration or deceleration.

Once the engine is steady under load the vacuums settle down and the airflow should be the same on both carbs. There is a text posted (shade tree mechanics??) that includes an air volume test at high rpm. The important thing is that the carbs are progressive with no air leaks and that the mixture is not lean at high rpm under load (risk of cylinder head overheating).

Air-Cooled Bliss..

Cordialement,

[BOXY]

Did you check the air flow with the balance bar disconnected? I've been messing with my van recently and found the ball socket on the right hand end had gone AWOL and the ball was loose on the carb bracket. With the bar connected I was getting 6kg/h on the right and 7kg/h on the left at idle. As I increased the revs the difference got bigger because the right throttle wasn't opening as much as the left due to the floppy linkage.
Hopefully someone will correct me if I'm wrong but with the bar disconnected you can adjust the air flow on the throttle stop screws on each carb. Once this is set at idle, (and your linkage is not floppy) the air-flow should match at higher revs as well once the linkage is connected. If it's not you can adjust the connection rod to bring the throttles into sync. (adjust down to the lowest carb reading to make sure you don't weaken the mixture.)