Carburrettors - faults and faultfinding

From VW T25(T3)-Tech
Jump to navigationJump to search

Dud: I have a 2l Aircooled with what seems like a carburrettor problem.

There is a little machined hole (which could possibly have had something fall out?) behind the bypass idle cut off valve on the left carb which has just started making a very loud air sucking noise (audible in the cab with the window shut). When I put my finger over it at tickover it raises the rev's slightly.

I have just disconected the bypass idle cut-off valve by pulling out the power lead on the left of it. This has drastically reduced the sucking noise. From what I understand the point of this valve is really to stop the engine running or causing backfire once the ignition has been turned off, a problem on the Aircooled's due to hot spots. Is this correct? I am also keen to know if in temporarily disconnecting it there will not be any major issues other than those mentioned above, or other damage as a result of me disconnecting it?

Secondly, does anybody have any idea why it has suddenly started making this sound? Could the valve be faulty? Could something have fallen off that was covering the hole making the noise (I did find a paper hole punch shape and sized bit of metal nearby in the engine bay)?


You should have a little steel disk fitted to that hole, there are actually two of those, they are machining holes that are blanked, similar to core plugs. It is quite common for these to fall out, you will need to block this up with a similar flat disk, if you dont want to take the carb off then use some 5 minute epoxy and glue the disk into place, other than that when you remove the carb you will see a second small disk, these are staked to place, just copy that one and make sure they are sealed otherwise this will cause a very weak mixture and risk of overheating.

Base settings for the 32-34PDSIT carb on 2.0L CU engines:

Base settings for the 32-34PDSIT Carb:- 3 .5 turns out from home on the air and mixture screws as a base setting and you will not be far out. The all important throttle base gap of 0.1mm then balanced to a throughput of 8.5 cu/in measured at tickover on a carb balancer. Thanks to Steve8090 for this information!