Hi All

Apologies for my first post being a cry for help! But....

I have a 3.8L MK2, which starts and idles fine, runs beautifully but once warmed up then idles at anything up to 1500rpm. Previously when it did this, a hard rev of the engine would get it settle down but recently this has stopped working. Any suggestions as to where I should looking for the problem?

Many thanks

Steve

 

No need to apologize, the forum is here to help. (maybe post up an intro with a few pics over in the New Member section).

I'm no expert, but I would be looking at the carburettors. IIRC you have SU carbs, these require regular and positive maintenance.

First off check for any worn or sticky throttle linkages. If you have a manual choke, check it is not sticking.

As you perform your weekly engine oil check, you should also check the dashpots (the black star shaped large plastic screw on top of each carb), remove and top up to the required level with engine oil, avoid over filling.

You might have sticky pistons inside the carbs, this can cause high idle as you described. (the pistons need to be able to rise and fall to their full extent).

Remove the air cleaners and with a finger check that they slide up and down easily. (easy enough to remove pistons, by removing the dash pot.)

You could have worn needles (you would replace when doing a carb overhaul).

The floats could be sticky, requiring cleaning. (be careful the are very brittle and fragile when old).

(doesn't sound applicable, but if a float is perforated, the engine can race away in an uncontrolled manner)

For more information about SU carburettors and their maintenance,here is a link. It shows fairly detailed explanations with diagrams.

And as you are in the UK, then the manufacturer sucarb.co.uk website is not a bad place for service parts.

Of course it could be totally unrelated, hopefully our tech minded guru's can give better advice.

 

Other candidate is a leak into the inlet manifold, the obvious one is a leaky reservac tank or valve.

It's an old car, so the post about wear in the carbs is very valid. You can get rebuild kits fairly easily.

 

Hi Chaps

Many thanks for the (very comprehensive) pointers, I shall break out the tools, handbooks and get cracking. I'll also post the results next week.

Kind regards

Steve

 

Moved to new thread

 

A full strip down of the all three carbs showed one butterfly (throttle) was rather dirty and sticky. This seems to have taken care of the problem (fingers crossed).
Many thanks for the help chaps.

 

have you synced the carbs?