KB Laser - second throttle twin barrel

[mike laser]

Hi there

I’ve recently procured a very tidy KB 1.3 4sp GL w/ 155k on ODO. Very well cared for.

It doesn’t skip a beat, however on full throttle the power response is very underwhelming. It just doesn’t feel 40kw + on a 900kg car. It feel under 30kw… not that I have measured but this is what my senses tell me.

Reading the service manual - there’s a second barrel which should open at 46% throttle load, powered by vacuum diaphragm.

Question: how do I test it works? Looking down the barrel and manually pulling full throttle the second barrel doesn’t open. There is a acceleration squirt so I know the plunger works.

Is the vacuum feed from the engine via one of the hoses or does it draw from the carburettor vacuum?

Where is the diaphragm?

The service manuals says to adjust the second throttle “adjust the connecting rod” but it doesn’t show you what the connecting rod looks like?

I am guessing the connecting rod is our or diaphragm or vacuum circuit is leaking… BUT I’m not actually sure. Is the power output actually supposed to feel this low? I know that’s a very subjective question but I remember they were more zippy. It can barely keep up with traffic. Have I forgetting what the performance of these cars actually is?

Any help would be appreciated!

Mike