Lumpy Idle When Hot

[DavidThorn]

The subject car is a late BJ8 with electronic ignition. It runs fine and pulls well, but when hot the tick-over becomes lumpy. Its ticking over at about 800 RPM. I have changed the coil, and checking the plugs after a run they seem to be a nice greyish colour; not too light or dark.

When cold, the tick over is fine. It's not misfiring when hot, just lumpy and uneven.

I think carburation, but I have reset it to the guidelines given in the pictorial guide elsewhere on this site, but it made no difference.

Any suggestions?

 

[bdcvg]

Sounds like fuel starting to boil in carbs or feed line.

 

[Bob_Spidell]

My BJ8's--and my BN2's, for that matter--tickover gets a few RPM slower and lumpier on hot days. I've always attributed it to hotter, less dense air causing them to run rich and 'load up.' S.U carbs are supposedly somewhat 'altitude compensating,' but when I'm going to run above 6,000 feet altitude for long I'll lean the carbs and bump the idle a litte.