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MG Midget and Sprite Technical - MK3 1275 engine dies when stopping at crossing

Lately my engine (MK3 1275 RWA 1971) dies when I have to stop for a crossing, when I engage the clutch to select a lower gear the engine stops. When starting it runs direct and fine. Any ideas?
Niek Lammerts

what RPM is the tickover set to?
David Smith

idle is at +- 1000 RPM.
Niek Lammerts

Im going to suggest thrust washers/bearings

But on a 1275, this is really rare and almost unheard of... if it was a 1500 then defiantly

To test... find a hot looking babe in a dental floss bikini and have her start the engine in N. And have her slowly press the clutch peddle in and out while you watch the crankshaft pully ... if it stays soild, great, if it moves back and forth... congrats, you get to remove the sump pan and replace the thrust bearings

But like I said... if so, your 1 of 7 people in the last 20 years to have to do this with the 1275

Maybe another possiablity might be a worn/parished rubber boot that holds the clutch fork ... but id think that would be easy to have heard long before now.


Maybe the brakes are dragging.... eeehhhhhh, doulbtful


Personally I dont think its a vacume leak...I know that will be suggested, but you would have alot of other issues ...

Hmmmm

And there is no other issues? Acceleration, shifting, missing/misfire, pinking, over heating, erratic idleing, surging, ect ect ?
1000 + rpm, is a good idle
Prop and the Blackhole Midget

Possibly badly worn carbon release bearing?
Bernie Higginson

It has nothing to do with washers/bearings etc. I believe it is a fuel problem, but need some ideas where to start
Niek Lammerts

Did you test the crank shaft pully for lateral movement to elminate the thrust washer bearings as suggested above ?

Why do you think its fuel related ?

I was thainking a sticking choke... but with idle at 1000 rpm, id think thats enough to over ride a rich carb

Bernie has a real possiablity diagnoses of the carbon release bearing seperating/going bad, alot of those are going bad more so now then ever before

Prop
Prop and the Blackhole Midget

Longshot could it be heat - do you have the heatshield still fitted between the carbs and exhaust manfold?
It could be bearing related. The revs on my 1971 1275 MkIII drastically reduced when the clutch pedal was depressed - the clutch thrust release bearing failed shortly sfterwards. You can tell if it's going to fail if there's a grumbling noise when the pedal is depressed...
Jeremy Tickle

I had a recent thread where my 1275 would die at traffic lights just as you were about to move off. On my drive with the engine idling I could cause the engine to die instantly with the merest application of my foot to the accelerator. It amounted to taking up the slack in the cable and moving the butterfly by a tiny amount. Blipping the throttle didn't cause the problem.

In the end it was the inlet/exhaust manifold gasket leaking at the inlet of the rear carb. I replaced and or cleaned most things but it only ceased when I replaced the manifold gasket. When I got the carbs and inlet off it was obvious what the fault was but it puzzled me for a couple of weeks until the eureka moment.

Rob
Rob aka MG Moneypit

Niek.

Should you follow Props advice and find yourself a hot babe in a dental floss Bikini then whilst your problem may not have been cured you outlook will have improved !

From your description I take it the engine is off choke and warmed up. . .assuming this is the case I would start by increasing the idle speed to see if the engine will die at increased idle revs.

There after I would be checking mixture and ignition timing.

Are you running points or do you have an electronic set up ?

have you taken the float bowls off and checked them for a sticky mechanism ?

Can you check the rev counter is working properly, could it be that it is showing 1000 rpm but actually your idling to low when warmed up and under load the engine just finds it all too much ?

saying that im not sure how you would check a rev counter against its reading, wiser folk than me will know I expect.

do report back as it is an interesting topic

peter
P Bentley

one good way to chech a tacho is to use a decent timing light that shows RPM, Snap-on for instance.
David Smith

Niek,
I have the same problem. But only when engine is really hot. It is not regular problem, does occure only time to time, so far I was not able to figure out why. I noticed that idle RPM goes down when engine is hot and I believe it has to be something connected to heat/fuel vaporisation. I am on standard SUs and points. I am able to prevent the problem by increasing RPM by throttle pedal when I use the clutch. Not really final solution, but it works.

Do you have this problem with cold engine?
S.
Stepan Marek

I think it is most likely an air leak in the inlet manifold, between carbs and engine.

When you take your foot off the throttle to slow to a halt, the butterflies on the carbs snap shut,cutting off the air supply, but the engine is still spinning and sucking so it creates a lower pressure in the manifold. If there is an air leak at the manifold it will pull in air, further weakening the mixture which is already weakened as the needle has dropped to close off the jet. Dropping to a lower gear as you slow down will exacerbate the problem as the engine revs increase in the lower gear, accentuating the manifold
depression. Try heel and toeing as you go down the gears.

Richening the mixture will compensate and may stop it from stalling, but the proper cure is to find and fix the manifold leak. Potential sources are the gaskets, the butterfly spindles or maybe you have a brake servo connection and that is leaking?
Guy W

I will start to check if there is an air leak, this seems to me the most explainable course of the problem, also it happens mostly when the motor is on temp. When it is cold there is no problem (mostly choke is still on)
As the weather is not that great, it may take some time to do a run.
Niek Lammerts

To follow on guys comment Dont forget to look at the carb black spacer blocks for cracks...I have an extra free t shirt if needed

Prop
Prop and the Blackhole Midget

I'm with Bernie here - exactly he same symptoms cured by new clutch assembly/release bearing - after that, launch control was never better!
M J Chapman

I suppose it depends on how you interpret the statement:
<<when I engage the clutch to select a lower gear the engine stops>>

The clutch is of course "engaged" when your foot is lifted OFF the pedal, so it wouldn't be the thrust bearing. I took it literally, that as Neik lifts his foot off the pedal and the engine revs increase in the lower gear, and the engine then dies. I was maybe misinterpreting the intended description.
Guy W

I just remembered I still had a photo of the worn release bearing which I managed to take with my mobile phone through the aperture in the bell housing. you can see there is no carbon visible at all!


M J Chapman

Any update by the OP on this?

Rob
Rob aka MG Moneypit

Im guessing he found the problem and left us hanging

I dont recall seeing his name before
Prop and the Blackhole Midget

This thread was discussed between 20/09/2015 and 08/10/2015

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