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MG Midget and Sprite Technical - solved backfire thru carbs but still have issue

I have the MG midget running now but when I set the timing the eng runs at about 2000 rpms, I have tried tuning the carbs down but cannot seem to get it to idle properly (is about 1000 correct). Also the car overheats. Does not seem to be a blown head gasket. I am hoping it my old radiator. I remove some of the 50/50 mix I had in it and added distilled water but it still over heats. I am ordering a new radiator!
As far as the timing goes on my midget I have the pully notch marked but I cannot see the timing tab because the car was wrecked in the front at some point before I got it and the cross frame is bent in a way that keeps me from seeing the timing tab. I have it timed with the mark I made pointing directly down (6 oclock exactly). Anyone have any idea about where it should be? Also do I need the vacume advance disconnected when timing it, it does not seem to make a difference when I disconnect it.

Thanks in advance

Ken
Frustrated again in Atlant but things are looking up!!
Ken Bargeron

Hi Ken

Static timing with the notch facing downwards when the spark occurs is fairly close. The vac should be connected, but is irrelevant as there's no vacuum with the engine not running (assuming you time static, i.e. engine off).

If you can't get the idle down to 800 rpm, the cause may be:

- you need to adust both throttle-stop screws until further unwinding has no effect on the throttle shaft (have a go when the engine's not running and you can see the effect thagt screwing them in has on the rotational position of the shaft)

- check for each side that the cam on the choke shaft is not holding the throttles open (this controls the fast idle when the choke is pulled on; there should be clearance when choke off between the cam and the adjusting screw)

- putting the vac pipe on/off the engine should cause the revs the drop (on) and rise (off, as air leaks into manifold). If this is not the case, then there's a fault in the pipe or vac bellows.

- check the vacuum pipe is good, and also the diaphram in the dissy is OK; best way to do this is suck on the pipe from the carb end. There should be no flow of air when you suck - just movement of the diaphram/vac advance unit which you may be able to here. The vacuum should remain if you pop your tongue over the end of the pipe, and release when you remove your tongue. If the pressure isn't maintained as described, then pipe or vac bellows are leaking air (causing engine revs to rise).

- If above OK, then you may have a leak in the manifold, either in the gasket to the head, or between the carbs/spacers, or a missing/leaky vac take-off or similar on the carb or manifold. Eg. there's a vac take-off on the manifold or ported vac pipe on the bdy of the (layer) SU carbs that must be connected

- if above OK, are the butterflies correctly aligned - do they make a light-tight (or near) seal when the throttles are closed?

A
Anthony

This thread was discussed between 09/06/2008 and 10/06/2008

MG Midget and Sprite Technical index

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