Strange idle from cold

R

Rovertron

Member
I've had a recurrent problem with starting the car from cold... normally after a week or more in the garage unused (certainly 91p/litre Optimax is not encouraging it's use). It would start and then the idle would slowly die after a minute or so.

I checked the dashpots first and sure enough they were a little empty so I brimmed those with some engine oil.

The idle is fine now, seems to come off the choke quicker and it wasn't dying anymore. However on blipping the throttle it revealed another problem. The engine revs would decline right down below idle, almost to the point of stopping before recovering again.

Now that wasn't there before...

Would anyone have any idea why?

I took it out on a good blast up the M40 that day and nothing presented itself, fuel economy seems fine, power is defintely ok :) I'm wondering if it has anything to do with automatic enrichment and the choke?
 
I find engine oil is too thick for the carburretor dashpots. Try automatic transmission fluid , this lets the piston rise and fall a bit quicker and prevents excessive richening of the mixture.
When I used to drive a 1.3 Maestro (unhappy days) it wouldn't run from cold with engine oil in the carb
Dave
 
Oh dear... well it was 10w/40 GTX. I see you point about TQF it's much thinner. That workshop manual has a lot to answer for :)

I suppose that leads me to the next question... how to I get the stuff out ? :) Unscrew the dashpot and get ready with plenty of rags?
 
Rovertron,
undo the three screws holding the dashpot cover and carefully remove this. There is a spring underneath it.
Lift piston and needle assy. and tip old oil out.
I used to use 3-in-1 oil in my Spitfire for quicker throttle response but have read recently this engine oil is better!
Regards, John
 
I managed to get some dash pot oil from Southern Carbs in Wimbledon, specifically designed for the job.
Unfortunately I can't tell you what it cost as they threw it in for free when they relieved me of £500 for a complete strip down, refurb and set up of my carbs.

Its only a small bottle 125ml but it doesn't give details of thickness.

It must be available elsewhere.
 
Carburettor dashpot Oil is grade 20 I believe.

Most classic specialists can probably supply or know where to get it from. Maybe worth trying places like Demon Tweeks too.

E.g. After a search I found Quiller Triumph have it listed on the net at £1.
Tel: 0208 854 4777.
 
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