Stumbles from idle....again

My 62 OTS runs great…starts easily,except sometimes, even when warm, it will stumble from idle ,say I engage the clutch at 700 rpm and accelerate it may stumble until it gets going a little faster…If I rev to 1500 and release clutch all is well…This issue has been around forever,what is the common opinion??

Have you checked/topped off your dashpot oil. Checked/lubricated your distributor advance weights and springs? Checked your ignition timing from idle up to 3000 rpm ? Still running points and condenser for ignition? Check the dwell angle? How old are your plug wires?

First thing I did was top off the dashpots…seemed to be a bit better…using Pertronic , dizzy is new…timing on on…wires pretty new…


Just solved same issue on a 61. Stumbles can often be caused by a build up of grime in the SU suction chamber and piston - which causes the pistons to fall and rise slowly/inconsistently/erratically. One at a time, undo the 4 screws holding the SU suction chamber - clean the inside with a soft cloth with thinners and remove any grime. Also wipe the edges of the piston. If you turn the piston upside down then the oil will need to be refilled. The pistons are matched to the chambers.

On my car, one of the chambers had more more ‘dirt’ than the others. Stumble completely cured. Hope this helps.


That could also be a spot of water in the fuel: if you don’t drive it much, a pint of alcohol in the tank before driving may help.

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Scotch or Brandy?

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I hate scotch: I’d recommend Everclear. :slight_smile:

Lets guess that it is a mixture issue…how do i determine if its too rich or weak?

Have you gone through the carb tuning process? Use the little pistons while idling for each carb. If you lift and engine speeds up the idle mixture is a little lean. Slows down idle mix is a little rich. Check to make sure the big carb piston moves up and down freely and jets aren’t hanging up. Vacuum tubing to distributer all tight. Vacuum advance diaphragm working and not leaking. I have had good luck with the pertronix ignition conversions. Make sure all the ignition connections are tight. Good luck

If it’s too weak it will improve if you turn it ½ richer and vice versa, or put the choke on. Also, it will improve as it warms up if it’s too lean.

I have a similar issue. Mine is too lean from 500-1000 and then fine, until I tune it so it is way rich at idle (550 in D). Then it has a rhythmical misfire but far more torque instead of stalling and stumbling until it clears out. I‘m trying everything including the suggestions here before I start my own topic.

My idle is perfect…but I do agree there was more power with a more erratic ( rich) setting


Here is a suggestion to try to isolate the problem.

When engine is warm and it does the stumble effect, turn one of the three carb mixture screws clockwise one turn. This will richen the mixture.

Then see if the problem goes away for a few days

If problem goes away, it is related to that carb.

If problem does not go away, turn the mixture screw of that carb back 1 turn, and then move to the next carb and turn its mixture screw clockwise one turn



I would think it’s going lean off idle something to do with carbs
slides worn,
You can listen at the exhaust to help decide which cylinders are stumbling

I also find that when the idle is perfect, might mean your timing is just a bit slow.
I would try advancing a couple degrees to see if that helps. If it pings to much then move it back. Also make sure your vacuum advance is working while you are at it.

All good ideas…thanks;;;;;;;;;;;