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MG TD TF 1500 - Engine Sputtering...Still

Hello again.

After experiencing what began as sputtering and even stalling once the engine was hot, I slowly began switching out ignition electrical components thinking that they were the problem. I put in different condenser (first new and then a working old one), new coil, new plug wires, new plugs, new red rotor, new points, new distributor cap. I have sent out a spare distributor to Jeff at advance, but don't have it back yet. The problem still persisted and was getting worse. It's really odd as sometimes the car would run strong and then suddenly, usually coming out of idle I would lose all power for a bit then seemingly clear itself and run normally for a bit...and repeat.
Having run out of ideas I decided to tackle the carbs. I've adjusted them the best I could after watching one of John Twist's excellent youtube videos.
I put in new needles and seats and set the float level to 7/16", a recommendation found in the the BBS archives. I then did my best to tune and balance the carbs, following John's instructions. Long story short is now it idles better than it ever did. It still won't rev though...most of the time. Sometimes it catches and seems to rev but more often it seems to sputter, accompanied by a loud hissing from the carbs. There is also quite a bit of smoke from the exhaust when trying to get the revs up. I would say whitish with a tinge of
I recorded and published my first Youtube video of the results. Sorry it is at 90 degrees, but I didn't want to re-shoot. Anyways you will notice that the hissing is so loud at times that the audio recording on my phone cuts out!
Here is a link to the video:

and without the "s"

and John's original Youtube link

without "s"

Does anyone have any idea of what to check next? I've run out of ideas and would really like to be driving!

Thanks everyone


hampster99 at
Tim Mayor

Hi Tim, would/could there be an intermittent air leak in the manifold? It seems like it is getting fuel but not in the right mixture judging by the smoke out the exhaust.
Regards, Don TF 4887
D J Walker

Blue smoke is oil burning, black smoke is too much fuel. Test for manifold and carby flange leaks using the methods contained in the Archive if there are no leaks, do a compression test.
G Evans

First- Check your battery voltage. You just might start out decent, but run out of voltage if your generator system isn't putting out charge. Ignition needs voltage; you don't leave home without it, for very long. All those new parts won't do any good without it, either.

If you have the female terminals in your instrument cluster, you can plug in a voltmeter to keep tabs on it. I wired one up permanently since it is one of the most important aspects to reliable running.

As for your carbs, go through Dave Braun's instructions. HOWEVER... If it runs great at times, the carb settings are very likely fine.

Sounds like you might may be running out of fuel. Have you checked your plugs after crapping out? Are they wet (lost spark) or are they dry (lost fuel)? Are they black? Are they white?

It does sound really bad. Remove the brass damper caps and make sure the carb pistons are totally free and can be freely raised and then dropped with a click when they hit bottom (there should be no drag at all). Start it up, and the pistons should really pop up a lot with throttle. Timing- Put a timing light on and see if the flash is steady. Clean/mark the pointer and the TDC notch in the pulley (some repro pulleys have two notches- pick the correct one). It should be advanced a bit from TDC even at idle. Remove the float chamber lids and make sure both floats are bobbing and not sunken at about the same level. Remove the floats and look for water in the bottom of the bowl. While opening throttle, put your palm over the carb throat a couple times. If there is crud in a jet this will sometimes pull it through. Whitish smoke is generally water, but bluish oil. Too rich is just black. Does pulling the choke make any difference? George
George Butz

At about 1:35 in the first video you rev the engine up and you can see into the mouth of the carburetors. The piston in the rear carb appears to move up as it should but the piston in the front carb doesn't appear to move. Is the linkage tight? Can the pistons move up and down freely?

Also...when was the last time you adjusted the valves?
Gene Gillam

An update:
Added 5 gallons of fresh gas to the tank this morning as the tank was running low. Started it up and of course it revved up fine, but the front carb was taking in very little air as compared to the rear one now. Checked for intake leaks using propane and found none. Whitish smoke still, and some condensation dripping out of tailpipe. I also did the palm over the carb throats thing a couple of times. I checked coolant level in the rad and it seems not to have changed.
See smoke from today

It eventually stopped dripping, and the smoke decreased.
Took off the carb dampers removed the pistons and gave them a good cleaning with carb cleaner. Also cleaned inside the carbs the best I could. Put all back together, adjusted and balanced carbs. Was running pretty good with way less smoke and it would rev up and then starts sputtering just like before! What the heck. Had to stop working to do something else.
Next I will try the propane again once it starts to sputter. Also picked up a compression tester today may learn to use that right away too.
I had the timing light out the other week, and the timing mark seemed to occasionally "jump" and then settle and then jump again. It is set at about 35 degrees advance at 3000 rpm. I may see if a can video it, but not sure if I can capture the strobe.
Adjusted the valves (cold) the year before last.
The mystery continues...Tim
Tim Mayor


You are doing everything right in your diagnostic process. I would not be concerned about the condensation, this is probably a process of your ambient temperature and humidity conditions.

I would pull your distributor, dismantle, clean and check the condition of the mechanical advance springs ensuring they function correctly. This may sound out of left field, I had a brand new Austin Healey Sprite where the lobes on the distributor were not all the same, I would be checking for constant point opening as each lobe operates the points. Any lateral play in the distributor will create the same symptoms and cause the timing to wander.

As many have communicated the SU is a simple carburetor. As posts suggest too much time is spent maligning these components when the issue is ignition problems
G Evans

Tim, a friend's TD had very similar symptoms. To make the story short -- it was a sticky needle valve in the front carburetor. Replaced it and all was well. Bud
Bud Krueger

Verify that your spark plug wires are in the correct order. Something easy. I had the 3 and 4 wires reversed on the TC when I first fired it up and it sounded a lot like what you have. Next I'd do a compression check to eliminate anything internal and then move on to the carbs. But thats just me.
MG LaVerne

So did a little more tonight. Checked the compression. Cylinders 1 to 4 were 140,142,142,145 dry and 150,152,152,153 wet. I also retested once the the engine was hot and after the poor running began. Interesting they each dropped 2-3 pounds to 138,139,140,143.
Also checked firing order. It is 1,3,4,2 counterclockwise.
Will check the valve gap next I guess, and then on to the voltage.
The rebuilding of the spare dizzy should be done soon, according to Jeff, so should have that back in a week or two too.
Bud, do you mean the main needle or the needle in the float bowl? I have already replaced the float bowl one.
It's a pity because it actually runs and drives really well now...until the missing starts once it gets hot.

Tim Mayor

A couple of people suggested that the carb pistons were sticking, but you didn't mention checking them. If you haven't, that's a good place to start.

Also, when you look into the carb throats, do you see any wet fuel? That's an indication that the float valve is not shutting off or the float level is way too high. Sticking float valves are probably the no. 1 problem with SU carbs.

When you tune the carbs, do they respond as they should?

Did you check the plugs? How do they look?

Since the car runs OK when cold, I doubt that you have an adjustment problem. And, if you did, ordinary tuning adjustments would have fixed it. You need to look for something that could fail or stick as it warms up. Ignition capacitors, carb pistons should be the first suspects.

You seem to be trying things scattershot. Instead, it would be better to focus on the things that could cause the problem you're seeing, and go after those.
S Maas

Tim, If your engine has the clamp type of distributor mount, make sure the ground wire is there and the contact is good. Reason I bring this up, is I had a car that would really act up when hot but not demonstrate the problem when cold and in the garage during trouble shooting. It seems the oily distributer housing gets even looser as the engine heats up and it partially looses the ground at the clamp/ hold down bolt. This old ragged ground wire is often thrown away and not replaced during engine rebuilds, further, it is not shown in a lot of the manual pictures. However, without it in place one can really chase their tail in trying to fix various tuning issues. See image of this ground from internet.

Richard Cameron

Thanks Rich. I was not aware that this wire existed. As it's an earth wire it presumably should be black? Anyone with an original TD confirm the existence, length, colour & the type of terminals used originally at either end? Cheers
Peter TD 5801
P Hehir

Yes, Peter, I suspect a lot of them are not there any more. Here's another picture--- I think one of mine is original. It is the old cloth covered wire , very dark brown, 9 inches long, with soldered terminals 8mm and 6mm bolt hole size.

Richard Cameron

Wow Richard, looks like I'll be making myself up a grounding cable as I am missing that. It sure will be sweet if it is the cure. Thanks.
To answer a couple of other questions the carb pistons are moving freely. There was no wet fuel in the carbs, although there was quite bit brownish gunk (20 years worth) stuck to the internal surfaces, especially the carb discs. I was able to get most of it off with carb cleaner. I replaced both float needles and seats with new ones.
The spark plugs were sooty and black and that didn't surprise me after all the idling it's been doing lately. After I went for a run they were still black, not wet, and much less sooty.
The carbs seemed to behave as described by John Twist in his video when I was tuning. It seems though that I made them richer than before in order to stop the engine from "stumbling and falling"
One thing that may help, and in looking at my original video is really hard to see, is that while in the sputter mode both carb pistons are rapidly vibrating up and down. As I looked at the jet area I could see the pulsating spray of fuel that this caused in each carb.
Thanks everyone for all of your advice. It's much appreciated! Tim

Tim Mayor

Tim, the rapidly vibrating pistons could hardly happen with the proper oil in the chambers. What are you using? BTW, it was the float bowl needle that was the problem. Bud
Bud Krueger

Rich if it's cloth covered & brown it's almost certainly original. The original cloth covered wire on T types was dyed black using a tannic acid based dye. Over time this dye turned the black fabric to brown. This odd phenomena had many people convinced that original harnesses were brown, including a highly respected harness maker here in the late sixties, Vic Longdon. This mystery was finally solved by Rhode Island Wiring a couple of years ago. Cheers
Peter TD 5801
P Hehir

Interesting. 10w30 oil in my chambers. Maybe rapidly vibrating is not a good description. More sort of a small amplitude up down movement kind of at the speed of the ticking sounds heard from the tappets.
I was toying with the idea of what would happen if one one of the intake valves was leaking on the compression stroke allowing some exhaust gasses back into the intake manifold (no nothing coming out of the carbs!). That's why I also did a compression test hot after the sputtering had started. I have no idea if this could actually happen, or what the symptoms would actually be...a mechanic I am not!
Tim Mayor

Tim, the one thing you've said that catches my attention is the timing jumping around. That isn't normal, and is usually related to problems in the mechanical advance components of the distributer. As G Evans suggested, I would pull the distributer, remove the points breaker plate and check the advance components for obvious wear, missing or broken parts. Section C.11 of the WSM shows the simple components.
Richard Cameron

This thread was discussed between 04/07/2015 and 08/07/2015

MG TD TF 1500 index

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