02426 inconsistant idle

Hi guys, I have a basically standard 426 which ever since I went up one main jet size I have never been able to get it to idle sweetly. When warm it can just be sitting there running and suddenly the idle speed will rise for no reason, sometimes it drops back by itself and sometimes I have to give the throttle a blip to bring it back down. I also find it easier to start if I give the idle screw one full turn (up). Has anyone else come across this before? im stumped, I've cleaned the carb out many times.

Have you checked for air leaks?

All I would add is give the carb a very good cleaning (cleaner and air through all holes). Then fiddle with the jetting/adjustments. If it has been a while then don't forget to check the valve clearances. When things get tight unstable or no idle can be one of the first signs.

Thanks, the valve clearances are nearing the limit but still within so I thought it wouldn't be that. Is there a way to check for air leaks or do I just have to go over every part and make sure it's sealed nice and tight?

You can check for air leaks by spraying carb cleaner on the joints at the carb and boots. The idle will shoot up if you hit a leak when it sucks the cleaner in. You should be able to feel or hear exhaust leaks. Hope this helps.


Make sure the slide plate is installed correctly, hole goes down. I had the same issue once.

I've found the air leak and she's running sweet now, thanks for the help.:mad:

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