Re: IML: '68 Rough Running

[David Whitney <hazegreen66@xxxxxxxxx>]

What's your vacuum reading at idle?  If it goes up and down (I suspect it does) you almost certainly have a vacuum leak.  I recommend the spray test around the gasket areas -- air horn, carb to manifold and maybe manifold to heads.

 

When you rebuilt the carb, which spring did you use to control the metering rods?  If your power step is trying to kick in at idle, that could also cause surging.  Another symptom of this problem would be running rich at idle because you're not in the economy step.

 

The different color springs have different strengths so they step up the rods at different vacuum levels.  If you are using a way strong spring and your idle vacuum is low, you could be wavering back and forth between steps.  WARNING to people who don't do this often -- those little screws on the metering rod caps love to fall inside the carb, which may result in much cursing and disassembly.  Use rags/duct tape/something to securely cover the primary and secondary bores when removing the metering rod caps.

 

Last but not least, make sure the throttle cable is fully returned and peer down the primary throats.  If your transfer slot looks like a tall rectangle, your throttle plates are not fully closed and you are actually idling off the primary circuit and not the idle circuit.  Another symptom of this is you can't adjust the mixture using the screws on the front of the carb.  This also causes rich running at idle.

 

Can't help with the needle question.  I look forward to seeing the answer.

 

Happy motoring,

David

'91 K-Imperial driver
'66 Crown Coupe project
'66 LeBaron dual air and every option known to man

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