Dieseling MG

[daver80]

66B- Due to carbon buildup I'm sure, my old B diesels every time I shut her off. Is there any way- without any extensive measures or disassembly, to clear this up. Is the old addage "just run it hard and blow it out" really a solution? Thanks! Dave

 

[Keoke]

Hi Dave, I am gonna tell you how to stop that easy but wait a bit. If it's carbon build up you may have a bit more tuning to do; Idle speed too high , Engine Temp to High, Sparking Plugs too Cold, Plug gap not right, Etc. However, in lieu of correcting the problem all you need to do is to slowly let out on the clutch, left foot on the brake as you shut the ignition off. On the other hand, some of those MG folks may have a better solution---Keoke-- :laugh:

 

[daver80]

Keoke- Yes, I've been doing that clutch trick for a while now, I should check those other things- easy enough. Dave

 

[PAUL161]

Old trick with a model A Ford, which were noted for doing that, was to run the engine at half throttle and spray a mist of cool water in the carburetor. It breaks loose the carbon build up and blows it out the exhaust. I don't think I'd recommend doing this though on a modern OHV engine. But it did work!

 

[DrEntropy]

I'd be for keoke's list, and some 93 octane FRESH gas.

If it continues to diesel after that, the water injection. :shocked:

 

[Keoke]

Hey Doc! are you aware that lightly spraying brake fluid in the carbs will remove the carbon build up?--Keoke

 

[DrEntropy]

Yeah, but th' HUM it makes outta th' tailpipe is "off-putting" :wink:

 

[Keoke]

Oh Yeah You are right!, I forgot you gotta be way back on the back 40 to do that.---Keoke- :laugh:

 

[MGZT260]

Install a "hidden" fuel pump switch to kill two birds at once. Now you will have a cheap anti-theft device, and you can shut off fuel supply to carbs prior to shutting off ignition. Higher octane fuel can be a temporary help, as can letting car idle for a full minute before shutting off. Riding lawn mowers have solenoids in carbs to prevent this as do some late model cars - but none I know of adaptable to a B.

 

[billspohn]

Ignore it or fix it. There was a reason the British would pull the head for decoking regularly.

 

[Graham]

Be carefull!!.
If its "running on" it's most likely the rubbish fuel we are being given nowerdays, but it may also be detonating while its running and that can melt you pistons and generaly wreck the engine. If its making a "rattling" noise under open throttle under load (pinking), like going up hill in top gear check it out quick. Pinking (pre ignition ) is bad enough, but detonation is the spontanious explosion of the mixture in the cylinder and sounds just like pre ignition but can be a lot more devastating. Timing too far advanced, mechanical advance springs not working correctly, too hotter plugs or like you say carbon buildup are likely culprits but also too leaner mixture making the combustion chamber too hot can also cause your trouble (also look for vacume leaks around the manifold).
Hope I didn't scare you too much but your symptoms can be quite serious.
Graham

 

[glemon]

Mess around with the easier suggestions on the list, if they don't help resign yourself to killing it with the clutch. Generally speaking anything that will get it to run cooler or idle lower should help.

Most of the british cars I have owned, which include Spridgets, Bs, Big Healey and TRs have had a tendency to run on to some extent. The Spridgets were the best, the Big Healey and B the worst.

The worst was a B I had in college, it wouldn't just diesel a little then die, it would actually keep going, in a bucking, nasty rough sort of way, but still keep going for quite some time after the ignition or spark was cut off.

 

[DrEntropy]

I bet it would actually run BACKWARDS on shutoff!