'had my son's 142 running and tried to set fuel/air mixture. Valves are set right, timing is right, points set, linkages adjusted,etc. When I tried to adjust for a leaner mixture than the rough setting of 2 1/2 turns downward, I got an increase in speed even when the jet seats were all the way to the top. There was never a reduction in speed. If you can explain to me what the problem is I'd appreciate it a lot.

Thanks in advance,

Jim Hampton

Have you peeked in the throats of the carbs to confirm that A)the jet tubes are now sticking up higher than the bottom of the throat as they should if they are turned all the way up? (choke staying partially on) and B) that the pistons in there are for sure coming all the way down? (mis-alignment of needle centering, dirty vaccum chambers, weak or missing springs)

I've got the carbs on my Jag leaned all the way too, and it still runs a bit rich... I'm attributing that to wrong needles, which could be your problem as well.

-Matt
--
-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC

Make sure the carb butterflies are synched and almost, if not all the way closed, when you are adjusting idle speed. Make sure the accelerator/choke linkage is not keeping them cracked open.

When Shayne and I were "tuning" my mixture, we ran into the same problem(almost), but only on the rear carb, the front carb would adjust correctly. When we'd richen the mixture until it SHOULD bog down a lil bit, that point never came when adjusting the rear carb, BECAUSE we had a vacuum leak on that carb... Dunno if this'll help you, but you could look into it nonetheless?
--
Kyle - '68 Volvo 142 w/71 b20b and m40...

1) Needles incorrectly seated in the pistons. The bottom lip of the diameter that goes in the piston should be flush with the bottom of the piston.

2) Wrong needles.

3) Jets worn from contact with the needles due to incorrect centering.

4) ???

Definitely check for vacuum leaks.

Float level too high or float needle valves failing to seat properly will also cause rich running and failure to respond to jet setting.

Later, Al