Erratic idle (1850) - SOLVED

[Toledo Man]

Since Tuesday's West Yorkshire meeting, I've noticed that the car has an erratic idle. I took the opportunity to get it on video and I've uploaded it to YouTube If anybody has any ideas of what it could be please let me know. The carbs have been balanced and I'm getting a spark at all 4 plugs although they could do with replacing along with the HT leads.

[matt of the vivas]

Check for an air leak - make sure the gaskets at the inlet manifold to head and inlet manifold to carbs are not leaking. Block off the brake servo and advance / retard pipes and try it - both have diaphrams in that can fail and allow an air leak. If that checks out then look at the carbs again - have you got waxstat jets?
Why did you balance the carbs? Was it doing it before you balanced them?

[Mahesh]

I've had exactly the same problem whenever I do the mixture on the carbs.

Starts off like yours Dave and some adjusting later stops.
If this happened for no reason check your jets and the
connection to the float chamber. (clean the chambers out as well)

[Toledo Man]

At the meeting, I was adjusting the idle screws so I thought I might've got the carbs out of balance. I'll fit a new set of spark plugs first. They need replacing anyway.

[Jon Tilson]

Air leak somewhere. You can even hear the hiss....

Jonners

[GTS290N]

Fit the club alloy mounts.

[Galileo]

In my experience, hunting like that is usually an air leak as said or too rich a mixture. Try spraying around spindle with WD40/carb cleaner.

[Toledo Man]

I've fitted new spark plugs and I've topped up the dashpots too and it hasn't made any difference. I will be fitting solid carb mounts in the future so in the meantime I'll seal the rubber carb mounts with some sealant.

[Mahesh]

Mine only does exactly that when I change the mixture,
are you sure a lump of greasy splodge has not got caught
between the jet and jet bearing kit nut when you pulled the choke out.

Another I noticed when rebuilding is the is a small dimple on the jet, if yours has broken off it would throw the mix out to the other.

Sorry, just remembered your on Strombergs, seems a shame to delete after typing.

[markas]

Can certainly recommend the club alloy mounts. had them fitted over the winter & the kickdown cable adjusted, which apparently also strongly influences tickover behaviour. Car now idles at a rock steady 650 rpm.
Hope you get it sorted.
Mark

[Toledo Man]

Mark, I'll be getting solid carb mounts. Until then I'll use some sealant as a short term fix. I'll take another look at my kickdown cable as well.
Mahesh, I'm on SU carbs so you haven't totally wasted your time.

[Mahesh]

Instead of sealant, use gaffer tape if it's only for checking and not a permanent fix.

[Toledo Man]

The sealant will be used in place of the gaskets to eliminate the possibility of any air leaks there. I think the cracks on the rubber mounts are just on the outside. I'll find out when I take them off.

[Karlos]

With the engine running, you could spray the carb mounts with any light penetrating oil. If the idle speed changes you will then know you have leaking mounts due to poor mating or decrepit rubber on the mounts. No need to dismantle.

Have you checked your breather pipes too? Last set I hd lasted about 10 months and then went hard and split apart. I now use some non-standard tubing.

If the carb butterflies and/or idle speeds are unbalanced that will not necessarily cause an irratic idle.

Good luck with the investigation.

[xvivalve]

He was good, but I still prefer Palin, Chapman and Cleese.