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MG TD TF 1500 - Have you ever had one of those days

I learned a little more about my TD today. Also how to kick myself in the pants.
I had decided to tackle the problem of the engine over running when you turn off the ignition (Dieseling). It was pretty bad and the engine would not stop - Put it in gear and let the clutch out to force it to stop. Not to satisfactory.
Took the carbs off and got some Teflon seals and O-Rings from Tom Bryant (Thanks Tom - work fine) Complete carb kit and new overflow pipes from LBCC - set up the carbs as per Dave Brauns excellent right up (Thanks Dave - so impressed I left a donation :) ) and the rascal started right up. Tweaked the balance with my air gauge and set the tick over. I will play with the best jet position later - as something else puzzled me.
I noticed my Tachometer did not work? VThats a first in 40 years - So started to remove the under dash cover and removed the steering wheel. Having done that noted that when I had my gauges refurbished in 1990 down in Tonbridge Wells the trip zero knob did not extend enough down through the dashboard but came up flush with the bottom. That rang a bell from the Things to do List and resolved to do it now. I also looked at moving the indicator (winker) switch up behind the dash as per LaVerne's. Which would mean moving the heater switch as well (same panel) - In the process of doing this noted the winkers no longer worked either?????
This was becoming involved - I still had not worked out why the Rev counter was Inop.
To clarify the Rev counter - back in the days of first rebuild 1970. I had had another TD for 13 years and the Rev counter was always an issue. The small bit of Bowden cable between the slug that goes in the Generator shaft and the gearbox would break. I decided to find an electronic Tack and fix the problem for good. - The gearbox could still be there but the dynamo wouldn't drive it. Found a Datsun Tack (positive earth) that just fit the hole - if you cut off the raised part on the back of the original rev counter. - Some epoxy and it was done. Screws in the face of the Jaeger face plate matched perfectly - could not believe my luck. Looked perfectly normal and problem solved - until today.
First of all - had to put back my Indicator control panel - seems there is insufficient room behind my center panel with the winker indicator light mounted. I gave up on that idea for now & will probably have to fabricate a new panel.
I checked the wiring behind the panel and could see nothing wrong!! Took a while and I dont remember the cockpit being this small down there. Had trouble getting me down the leg tunnel :)
I remade the 3 connections on the pneumatic indicator switch anyway.
Time to get out the WSM - turn to page N 23.
The power for the rev counter comes from the A4 terminal on the fuse block - Check the fuse - Der - should have done that already. Yes, fuse blown - Oh good - looks like it is solved - NOT, new fuse blew right off. Got a short somewhere? There are only 4 green wires on the two linked terminals A4. So disconnect all and ohm out individually to ground. Sure as eggs are eggs, one was shorted to ground. OK put the 3 good ones back on the terminals and see what working?
Rev counter worked (Thanks God - did not want to mess with that) Winkers working now also.. Low petrol light not on - too much fuel in the tank. OKK Wipers Dont work - no power. SO now I know which wire has the short. Strange - I have not worked on the wipers for years, how could that have shorted out??
At this point light dawned on Marble Head.

Mort - do you remember when you kindly sent me a windscreen screw, as one of mine had fallen out? Well it was on the driver side (RHD) that is also where the wires go up to the wiper motor K..
Yep - the screw was shorting out the two cables in the windscreen. I did shorten the screw but obviously not enough. Blows the fuse every time and I was blaming it on the winterK

I have seen the enemy and the enemy is ME .......

Everything now back as it should be. Lesson learned - always check all your systems when you add or change anything on the brute.

Sad to say after all this - the over running is still with me. Still have to sort out the optimum position of the jets by adjusting both jet nuts together - up or down . Also the jets still do not return to the no choke position when the choke is pushed in. I can push them up manually about a 1/16 to the home spot?
I am going to have a glass of wine now - possibly several K. and tackle this later.

The Dieseling worries me - as it is either too much fuel or something igniting the minimal amount of fuel from tick over - with ignition off.
Could it be carbon built up in the head?? If you have any other thoughts - it would be appreciated?

On a positive note - I did manage to fix the trip knob by adding a flexible spring to extend it - which allows the thing to bend whilst fitting the speedo into the tight dashboard hole.
Something tells me this is going to be a busy first year of retirement ..... Oh Well.

Rod.
R. D. Jones

Hi Rod,
We've all had days (or weeks) like that.
The running on has nothing to do with mixture, it's probably carbon buildup as you suggest.
I had the same problem with my TD back 50 yrs ago. I was told to expect it, by a very competent race mechanic, when I installed higher compression pistons & took a skim off the head surface. It wasn't carbon buildup there, but was a hot spot somewhere in the combustion chamber, even tho' I'd broken any sharp edges.
I always had to just let the engine idle a few seconds before shutting it down, and pressed the accelerator to the floor to get some cold air thru just as I turned the key. That solved it almost always, for as long as I owned the car (many yrs).
I hope it does it for you, you didn't mention trying that.
Al
54 TF "Emma"
A W Parker

Rod

This is my experience with dieseling, it is not directly MG related however it comes from a very close cousin. In the 60s I owned a 3a Austin Healey Sprite which I had replaced the SU carbies with a 45 DCOE weber, port and polished the head, fitted extractors and installed a quarter race cam. This car would always diesel unless I added an octane boosting agent to the super fuel that was available in those days.

Many dollars were thrown at this car with it under going Dyno tuning on many occasions to appropriately jet the Weber. Rightly or wrongly I was advised by a well known racing mechanic that the fact that the car dieseled was a good indication that the motor was in first class mechanical and tuning condition.

Take this comment on its merit I am sure it will raise a few eye brows.

Graeme
G Evans

Rod,
well, you fixed a few things that could be fixed,,, but the "running on", well,,,,sorry to say,, that's always going to be there,, Putting it in gear,,, turning off the ignition,,,,, and then easing off the clutch whilst applying the brake is a much easier way to solve the problem,,,,

SPW
STEVE WINCZE

Rod, make sure the initial timing is set at 5-8 BTDC.
then lower the idle speed to 500 RPM, no more than 600-650. & use high octane gas.
Len Fanelli

Most likely carbon build up. Mixture or carb condition has no bearing on this whatsoever. Set the carbs up properly and go with it. The hot spot(s) just ignites the fuel just as compression heat does in a diesel. Consider using a bottle of Techron or one of the Lucas products, they are suppose to remove carbon really well. Remember, all fuel injected cars immediately cut fuel flow when the key is off. Even Briggs and Strattons with carbs have a solenoid on the carb to kill fuel at shut off. The SU's just keep supplying gas/air as long as there is vacuum as they are suppose to do. This was pretty common back in the day, so put it in gear and let the clutch out and enjoy. Gerge
George Butz

Rod,

Glad you liked my write up on carburetors. And thanks for the donation to the site! Some people have found that replacing the stranded choke cable with a solid cable helps return the jets. Not all jets stick that last little bit, and I've been wondering if the cause is found in the final bit of adjustment while centering the jets. The jet housing has two jet bearings, and you would think that would resolve any movement issues, but some jets seem to hang just a tad, and the springs aren't strong enough to return them all the way.

One good way to decoke a cylinder head is to buy the SeaFoam Deep Creep, it is SeaFoam in sprayable form. With the engine idling over, spray some into each carburetor until the engine dies. It will smoke some. Then let it sit for an hour or so, or whatever the instructions say, and start it up again. The neighbors will think you are fogging the neighborhood, but it does knock the carbon out. Set the carburetors to the instructions in my piece, and see if that doesn't take care of things.

Otherwise, you did attend to the ignition side of things first, right? You want to be about 8 degrees BTDC, or 32 degrees all in at 3500 RPM... if your distributor won't do that, send it to Jeff Schlemmer at Advanced Distributors. He'll fix it up properly.

Warmly,
dave
Dave Braun

I forgot about the SeaFoam, that is the best stuff. Dave may be right about weak springs too. I think there were some new ones around that were not right, seems people said to order from Joe Curto? Make sure you remove the linkages and that each jet lever returns smartly on its own. Then attach the back one to the linkage first and adjust accordingly. Then attach the link to the front, and carefully adjust the connecting rod length. The choke knob may be out just a fraction from the chrome housing at rest so you are actually pushing the linkage forward the last bit of movement. This can take some effort to get this just right. George

George Butz

Thanks Gents,
I really appreciate the suggestions.

I may look for some springs locally to see if a stronger(only a tad) will do the job. If not, I will get some piano wire from the local model shop and try that. It don't take much to push the jets back up and it will resolve the "To rich" running issue that was confirmed after having the oil analyses.

Dave B,
what do you think is the better depth for the petrol in the jet bearings?
I set it to 0.170" give or take a thou :) and I had to move the floats up quite a bit to achieve that. Certainly not what the book says for bar size now.
I have set the jet heights to give the slight rise in RPM's when lifting the dashpot a tad and that puts the Jet nut around mid travel. Tick over is regular and smooth. She runs really well.

As a check to the state inside the chambers - I removed the speak plugs. That was telling - They were bisque brown on the center electrode and the spark arm? But a little sooty around the bottom of the plug. There was however some buildup of what looks like calcium on these bits. It removed easily with a scalpel and a good wire brush. It may well be that this was glowing when the compression cycle hit and was igniting any residual fuel. The overrunning has not occurred since I cleaned them but I have not taken the beast for a good run yet - That's tomorrow. As long as the rain holds off.
It may be just a red hearing but it overran yesterday - even after a short run. Today it did not - so far - fingers crossed.
The Sea Foam suggestion may well help remove any other deposits in the head and I will definitely give it a try.

Thank you sirs - Its nice to have all those brains on your side.


R. D. Jones

That is a nasty looking plug, crudy, and it appears worn (the center electrode looks rounded on the edge). Change them! If the rest of the combustion chamber looks like that, it is indeed carbon build-up. George
George Butz

I forgot to add the cleaned Pic :)

Have to say the plugs have only done 9000 miles since 1996 - Bad MG driver... :)

Probably time for a new set but I hate to chuck anything that works OK.

What is the equivalent here in the USA for plugs?

Rod


R. D. Jones

Rod, 1st check the thread depth of the threads in the head to confirm if you have a 1/2" or 3/4" reach cylinder head.
It sounds like you are almost as frugal as I am!
Buy a new set of spark plugs!
After 9,000 miles the plugs should not have that much build up of deposits.
You may want to consider an engine rebuild in the future.
Len Fanelli

Totally correct Len,
But I think I have been running rich since I got here and have now addressed that issue. With luck when we look at putting in the Roller cam later this year. I will certainly ask Erik to have a look at the head as well. I don't lack any power (what there is of it :) )
So I am hoping some of this may have been on the plugs form before. I can't honestly remember when I last took them out .... Hey - If its working don't fool with it - right?
Well this has been the week to fool with it some. I'm sure there are more thing coming up. :)
R. D. Jones

This thread was discussed between 12/07/2013 and 13/07/2013

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