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MG Midget and Sprite Technical - really high idle

hi all,

finally fitted the engine to my midget and managed tio get it to run yesterday :) but it's 'idling' at about 3000rpm.

theres no accell. cable fitted at the moment and as far as I can tell, the linkage on the carbs is free to move and the springs are pulling the throttle 'closed' as they should.

choke is also disconnected.

the engine is 'unknown' that I got from ebay a while ago, it's apparently from a Morris Marina (according to the serial number) so I had to swap over a few bits to make it fit.


fueling: I have fitted a 'facet' pump and a 'filter king' regulator.


any thoughts ?
phil near bristol

oh, the carbs I'm using are from the original engine in the midget, just bolted onto the 'new' engine.
phil near bristol

Presume you have already backed off the throttle adjusting screw and the jet adjusting screws on the carbs?

Any air leaks around the manifold?? Time to rebuild carbs?

Stuart K

Also see this thread - another source for air leak:

http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&mode=thread&access=&subject=97&source=T&thread=2009060317003713933
Stuart K

Remove air filters and visually check that the throttle butterflies are **completely** closed (even a small crack open will increase idle). If they're not - check operation of linkages (stop screws should all be OK if the carbs were running OK on previous engine).
Next, it could be an air leak at carb / spacer, spacer / manifold (but not if you "transplanted" the carbs undisturbed, complete with manifold from the previous engine) - or inlet manifold / head gasket. Spray with WD40 to see if you get a temporary change in idle level - if you do, there's the problem.
Otherwise you need to start looking at the jets - are they moving smoothly as they would when the choke operated?
Steve Clark

cool, this is the kind of info I'm after :D
the carbs were last used about 26 years ago, so could probably benefit from some 'tuning' I've not touched any of the throttle stops etc as my dad assured me the engine ran fine when he parked it up :D

I'll check for air leaks, I optimistically reused the gaskets on the manifold, and I have separated the carbs as I needed to remove the grub screw arrangement that holds the throttle cable to the linkage as it had rusted solid.
phil near bristol

... are all the vac pipes on the carbs/inlet manifold?

A
Anthony Cutler

yeah, all vac pipes present and secured.
phil near bristol

Is the fast idle cam holding the throttle open?
S E Bryan

<<the carbs were last used about 26 years ago>>

There's the clue I think Phil.

They'll be all gummed up with old petrol residue. Really need to be stripped down and cleaned up.
Or stripped up and cleaned down, depending on your mood.
Steve Clark

ahh just do the bare nececity's
i always love a little bit of shoestring enginering!
Onno Könemann

Check that you have clearance between the heatshield and throttle cable's connection bellcrank, don't want that holding the throttles open.
Check for throttle shaft leakage by spraying something where the shafts go into and exit from the carb.

http://homepage.mac.com/jvandyke/shaftleaks.m4v

I had to refit my throttle disks two days ago as a little gap equals high idle. I probably have some throttle shaft leak too yet.
J Van Dyke

This thread was discussed on 15/06/2009

MG Midget and Sprite Technical index

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