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MG Midget and Sprite Technical - Running rough

Too hot to get at it yet but something 'went' and I lost power and its very rough. (not like a blocked jet) This was after a few miles and then 1/2 a mile after a stop for fuel.

Small puff of smoke when it happened. Had to run a few miles back and no excessive smoke during that, oil OK, temp OK, no oil leak, engine sounds 'different', (like something is sort of rotating loose?), coolant level OK. Car starts and sounds OK when ticking over.

Plan to take off rocker cover and look, look at plugs. Sounds and feels a bit significant though. Will take off sump to look if no progress through the aforementioned.

So any further immediate thoughts for diagnosis would be helpful.

Don't have my own compression tester by the way and can't get one till tomorrow at best.
Dave Squire (1500)

Compression tester should show up if it's a head gasket problem. That would be my guess.
Dominic Excell

Yes Dom, I have been awaiting the failure after my first diy replacement ever a few weeks ago. I'm not totally sure but it doesn't look like its gone yet.

I drove 7 miles back, no HGF symptoms other than rough.

Just looked at plugs, all OK.

Nothing wrong under rocker cover. No creaminess, no odd oil flow trails, no condensation, nothing broke.

So: I did stop for fuel and the tank was the emptiest I have ever had and the car was laid up for nearly ten years to Christmas so probably stirred up the dregs. And I have had carbs block before but nothing like this for effect on engine roughness. So I will check carbs next. They need a good clean up anyway on the outside. I have an in line filter that I will now fit - doh - too late probably.

Now never done this before so I need to dig out the book / look in the archive. If I end up in the archive see you all in about a month then! :-)
Dave Squire (1500)

Dave,
it might just be as simple as Sod's Law - have filter but not fitted

car you get some fuel pumped to open carb pipes to see what the flow is, best done with the help of a glamerous

if ok then look at fuel in fuel bowls, float, (seat and) needles

if ok look at and clean out carbs, check all gaskets in and out

check it's not on the ignition side

you could do the old screwdriver (handle end) to ear on the engine to locate origin of noise

guess what a recent JT vid was on
Nigel Atkins

Im guessing the exhauste came loose, broken bolt, lost nut and broken donut

2nd guess is a vacume leak....what color was the smoke

Cracked manifold spacer, loose intake manifold, loose carb...butterflys, loose hardware

If nothing obvious...stick a vac gauge on the intake manifold and google how to read a vac gauge...that will tell you a lot

Prop

Prop and the Blackhole Midget

I am thinking you are right Nigel. I am getting fuel out of pipes, have flushed them out between the float chambers but of course I don't know if I am getting actual fuel into both carbs properly cos they have to be back together with the top on to pull fuel.

Now I have sat and cooled it a bit, and gone over what happened, and started and revved it from cold, it makes me thing it is fuel related especially as I have had crap in the system / carbs before that has just blown out. (and twice I think it was after refuelling as well).
Anyways cleaned vacuum chambers and checked jets moving OK. No reason to think vacuum not working. I've never took jets apart or more than cover off float chambers so float chambers next and see if crap in bottom of those.
Then as usual I will be trying to find 'the how to' this time for the jets if it still is not fixed.

Still not put that filter in - mutter - mutter.
Dave Squire (1500)

which vacuum are you thinking of?

you know there are vids to help with this stuff and recent ones adding more info too

one of the more recent vids will make you smile :)
Nigel Atkins

Thanks Nigel, I widened my u-tube search and came across a bloke from a Mini / Moggie parts supplier who had posted a good 'take the SU HS apart' video and explained how to clean from scratch when in bits.

The carbs are off and the float chambers have crap in. I know they were clean when I started the car for the first time at Christmas cos I cleaned them out. (In line filter going in now). The rear most float chamber has the greater crap of course. This is cleaned out now and I have ensured all the linkages have been cleaned and are working correctly together with each carbs individual controls.

Thinking of taking the jet out but aware that there are other bits like seals in the float chamber end. Is it likely I will need new seals? Or is there a good chance that it will come apart OK, and go back together OK today, without the seals being renewed?
Dave Squire (1500)

Sounds like you may well have stirred up the gunk in the tank and ingested same... Note that you can do an easy fuel line flush by taking the hose loose from the inlet side of the pump and inserting the tube from a can of compressed gas... think, computer duster. Give it a good shot and any crap in the line will be blown out pretty effectively. I did this with my car a few years ago... tank out... and shot fuel a good six feet behind the car. Sounds like you're on track with the carb cleaning, so best of luck.

-:G:-
Gryf Ketcherside

This thread was discussed between 01/06/2013 and 02/06/2013

MG Midget and Sprite Technical index

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