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MG Midget and Sprite Technical - Cursed/haunted 1500 won't lean off/run properly

Morning all.

Got a mate with a 1500 midget that appears to be haunted or cursed.

It ran a few weekends ago after a lot of messing about. It's been stood for 2 years or so before that.

To get it running, the following was gone through:

New fuel pump, fresh (less than a week old) fuel from an extra pot

carbs taken to bits and cleaned, massive leak from overflow fixed, dash pot off, jet height set, needle is the sprung type (HS4 carbs)

Float chambers cleaned out, all pipes and holes blown through with a straw, fresh fuel run through the floats and carb base using electric fuel pump.

mixture set roughly using "undo 8 flats" or whatever the haynes says, 20 50 in dashpots. Vac advance blocked.

new electronic distributor in, non-ballasted conversion and correct coil (the advance weights were all over the place in the old dissy, +/- 10 degrees timing scatter...

Timed up with a timing gun to the correct setting (which I can't remember right now)

it ran like this, and idles beautifully, but a bit chuggy on acceleration and chucks black smoke out when revved in neutral.

Plugs out - too rich. OK, set up mixture using lift pins and I run out of adjustment on the jet adjuster... Hmm. Running it as lean as it will go and we've still got black smoke (no filters on at this point)

still, it works (ish) until this weekend, where it now refuses to start - I suspect fouled plugs (I'm not there, it's in Shrewsbury)

Any ideas? Guess the carbs are worn out, it idles beautifully (well it was) but chugs and jumps when accelerating at anything above touching the throttle. Now it apparently won't start, as the ghostly curse manifests itself again.

any further suggestions appreciated :)
Rob Armstrong

If you hadn't been so thorough on everything else, I would have said I was a sticking choke cable or the mechanism not closing properly. Or possibly a sticking dashpot piston.
Guy W

Hi Guy

choke was sticky, I un-sticked it, but will ask if it's re-stuck... I know the accelerator cable linkage is a massive bag of hate, busy going through the archives reading solutions for the 1500..
Rob Armstrong

on my 1500 one of the jets had a tendancy to stick down when the choke was off, took it to bits and cleaned and reassembled and been ok since .
mark 1500 on the road Preston Lancs

hi rob, had the same problems lately with my midget albeit a 1098 mkii. done all what you have done suspecting the carbs. on stripping them down noticed it had 2 different jets in, 1 from a 1500. i had no adjustment left so i bought 2 new jets which now gave me loads of movement both ways. but still not run right. i remember the old saying "90% of fuel problems are electrical" so done all the changes in the distributor. i set points at 15 thou like it says no good, opened points up to 20 thou plus and seems to be running nice again. can't be sure till this rain stops. i would change the jets for a new pair as they do wear as only brass, that could cure the adjustment problem,and id still look on the electric side off things if the jets don't cure it. what filters do you run and are the carb needles standard ones.

hope this helps bob.
bob taylor

With the jets right up, it would likely not run well at all...if all was right in other places. Wrong jets? Float height wrong? Sticking choke, sticking jets?

Sooty plugs is basically incomplete combustion, usually from too much fuel to burn all the way in the amount of air you got into the cylinder, but it can be due to other stuff: Compression good? All valve clearances ok? I know it's not easy to measure, but a poor HT voltage will cause this too. Spark plug heat range correct? Blocked air cleaners would do this too, but the fact you set the carbs up in the 1st place suggests this is wrong with the filters off anyway as they wouldn't be there when doing your balancing etc.

What make is the new dissy? I've had mixed results with certain ebay jobs from time to time resulting in poor running etc.

As others have suggested, when adjusting the mixture make sure the jets under the carbs keep in contact with the jet adjusting nut.
For example, if you screw the nut to move it upwards, make sure the jet follows it by pressing it upwards after each adjustment.

Also after starting using the choke, make sure the jets go back to the "up" position when the choke is no longer needed. Otherwise a very rich mixture will result.

If the jets are sticking they will need to be replaced or worked on to stop them sticking.
JB Anderson

cheers guys. looks like the bottom end of carbs needs a good going over.

The dissy is a simonBBC one - I've fitted his stuff on 2 or 3 other cards with great success, so 'should' be OK. It certainly made it run better!

Valve clearances are OK but never did a compression check.
Rob Armstrong

Re. "Won't lean off properly". Check the condition of the float chamber valves, specifically their tips and the the recess that the tips sit in. Good quality viton tipped valves should be used as standard.
Andy Hock

full carb rebuild kit has been ordered and kitchen table commandeered for this coming weekend. They're waxstat carbs on a '79 car, so possibly that's stopped working as well.

Thanks for all advice, and all in the same direction too! I'll let you all know how it goes...
Rob Armstrong

This thread was discussed between 29/03/2015 and 30/03/2015

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