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MG TD TF 1500 - Having a difficult time getting sorted out.,,Help!

While my '52TD runs o.k., it is not what it should be.
The PO had rebuilt the carbs, but they have always been on the rich side, so I went back and tried to adjust....
I immediately noticed that the jet was below the edge of the bushing in each carb, but the nut was all the way up....To fix this, I took a few thou off the bottom of the nuts, in the lathe...I can now get the jets flush.
I also noticed that the new (ES) needles , were not fully seated in the pistons, and addressed that...(bases flush with piston).
I also centered the jets with a centering button, and adjusted/balanced the air with a Unisyn (old-style).
Checking the timing, using an electronic (EQUUS)light, I found the advance to be almost 19 degrees, at idle! I also found the points at less than .010.
So I addressed those issues....
I am still not happy with what feels like a lack of power....I can see from the light black smoke (at idle), in the exhaust, that the car is still running rich...
The car is not missing upon acceleration, but just feels "weak".
Using a dwell meter, I can't get the dwell above 35 degrees....Should I open the points further (now set to .012)? I have an asymmetric dizzy.
Even though I now have the timing at exactly 5 degrees BTDC, should I advance further?
I know that I should see fuel inside the jet, but can't see any...What, if anything , does this mean.
Finally, I have not checked the float heights..., could this be the source of my apparent lack of power?
Getting really frustrated...
Thanks for help
Edward
E.B. Wesson

Ed-
Go back to your thread on the MGB board and read my latest.
If you cannot see fuel in the jet, the float levels may be very low. This should make it run lean; If it is still rich, there's a good chance that the PO has lowered the float levels in an attempt to compensate for incorrect assembly of the jet "stack", which causes internal leakage resulting in always rich - that's where we started.

FRM
FR Millmore

Try to get a copy of the NEMGTR's The T series Handbook to keep around for things like this. You can just read and absorb at leisure as well. Great and detailed explaination of all of the above, with the theory behind everything. For now, search the archives- this has been covered in great detail many times before. George
George Butz

Ed,
George has a point about rereading some basics, like the Workshop Manual... such as raising the carb piston with the pin... float lever setting... check plug color... remove the mouse nest from the tailpipe... take off the parking brake (note any hot drums, too)... tire pressures... maybe you have a bunch of toe-in...

A little black smoke at idle won't really indicate air/fuel ratio running. I installed an air/fuel ratio meter and while it starts out really rich at idle, it
leans out at speed (for what its worth, I'm waiting on another jet needle, a steel float needle and smaller H1 float as we speak).

Try pulling out the enrichener while driving around and see if it peps up.

When all else fails, strap on a blower!
Jim Northrup

No one mentioned the dwell, but if you hook up the dwell meter incorrectly to a positive ground car, it will read wrong. For positive ground, hook the black lead to the CB terminal on the coil (the one going to the distributor) and the other lead to a good ground. Usually when I see a dwell that only goes to 35 someone has mistakenly hooked to the battery and the coil, or their dwell is 55 degrees and the dwell meter is hooked up wrong. Dwell is how long the points are closed, so to increase the Dwell, you close the gap.

For timing, run the engine at 3500 RPM and time for 32 degrees BTDC (the mark should be 1.05 inches before the TDC pointer, or use a dial back timing light). Then test drive. You can also check the timing at idle to see for a reference. Your idle speed should be less than 800 RPM. If you can't get below 800 your timing and/or your carburetors are misadjusted. The TD's distributor has a lot of early advance, so you will typically not see your static timing figure at idle.

warmly,
dave
Dave Braun

Dave et al....
What I did do today, is set the dizzy to 8 degrees, and the timing to 32 degrees at 3500 rpm....(using the electronic light/meter)...
I set the points to .010...
Since I have no way of knowing yet, if the bushing or shaft is good, other than to wiggle the dizzy, that will have to wait.
Coil is Lucas high performance,(40,000 volt), so I have the plug gap at .025.
As far as attaching the dwell meter correctly, I had the black wire on the dizzy terminal to the coil and the red wire to the ground from the battery (POS).
I am going to use Dave's explanation on his web site, and see if I can get the carbs closer to correct...
Am definitely going to disassemble both carbs this Winter, and make sure that all the new parts were installed correctly....
I do wonder if the ES needles run too rich for this car.
At this point, the car is drivable, and doesn't buck or blow black smoke , except at idle....It just feels as if it is holding back....
Jim
In this car, there is no lifting pin on the carb body....(there is a pin on the float chamber..Is that the one you mean?).
I do have the Uni-Syn kit with lifting tubes/wires,etc., and have observed that both carbs go up and down in sync...Have centered the jets.
Edward
E.B. Wesson

A thought! The pistons may have been swapped around during an overhaul. Suction chambers and pistons were matched to give a controlled leakage of air between the piston and suction chamber. A vacuum drop test will determine if there is a problem.

I've personally not done it but I believe you clean and lightly oil the assembly with WD-40. Invert the assembly with the piston against the top of the chamber and plug the holes in the bottom of piston. Take the time for the chamber to slide down and fall off the piston. I believe times should be:

1 1/4" and smaller carb = 3-5 seconds
1 1/2" and 1 3/4" carb = 5-7 seconds
2" carb = 7-10 seconds

But you'd better check with someone who knows!

If vacuum drop time is too fast, carb will tend to run rich. If drop time is too slow carb will tend to run lean. If it runs too fast you can't do much about it.

AJ
A R Jones

Ed,
That pin on the float is the "tickler" that will prime gas if the pump is running. Used them frequently on my limey bikes many moons ago.

The Workshop Manual describes raising the slides with a screw driver if there's no lifting pin. This will only diagnose idle mixture, though.

Have you looked at your plug color? After cruising for a while, switch ignition off, slip it in nuetral and pull some plugs to get some good feedback.

It could be running lean at speed. It won't cost anything to try pulling out the enrichener to see if it picks up power. This sorta reminds me off a guy exclaiming his Triumph Bonneville didn't really have as much power as others bragged about. I walked out to the street and opened his choke... when he took off, he almost wheelied over backwards! I think he headed home to change his drawers.

I just got a KL needle for our single 1 1/2" SU on the Magnacharger. Can't wait to experiment with adjustments, but using an air/fuel ratio meter is almost cheating.
Jim Northrup

AJ/Jim
Did the drop test, and all seems fine...I have not driven the car since adjusting the float levels....
Too late, I realized that Dave called for 7/16, and the WSM called for 3/8....Since I was using WSM for reference, I made them 3/8...(Hopefully this will be o.k.)....UniSyn also calls for 7/16....
Gets really confusing when you get conflicting info.
I'm going to drive it , but will readjust the plugs to .022, to see if that makes any difference.
Thanks for all the input.
I will keep working at it.
Edward
E.B. Wesson

Ed-
What is the achievable measurement of the jet below the bridge?

The difference in spec float levels should not matter, it isn't that critical, but the 7/16 is not a bad idea if rich running is the problem.

On a TD, it is extremely easy to remove the jet stack whilst the carbs are on the engine. Only need to remove the air fliters, the choke levers, and unscrew the big nut on the bottom, and the entire stack falls out in your hand. That's the same nut you had to loosen to center the jets. (If you did not have to loosen it to center the jets, there's your problem) (or you did summat erroneouslish)

FRM
FR Millmore

Remember these cars do run a bit rich at low RPM and at idle, but you really shouldn't see much smoke. If the float/jet fuel level is correct, the jets/needles correct and in the right place, the only other place fuel can leak in is through the top jet bearing cork seal. It is easy to not remove a squished old one, install another one over the top of it, and you have an internal leak. What about Jim's query about plug color? They tend to be a little black at idle, but if you drive it hard, then shut it down and pull plugs the insulator should not be black (whitish/or tan). Do the plugs from 1/2 look like the 3/4 plugs? That will tell you a lot. Lastly, many SU problems turn out to be ignition! George
George Butz

Hi Ed - I have been following your posts and want to encourage you to join the Southeastern MGT Register - we are based in Atlanta and we have a GOF in Athens, GA this October 14-16th.

We would love to help you with your car and have you as a member of our Club.

Best Regards,

Jeff
Jeff Delk

If I turn the jet-adjusting nuts down , even half a turn, the carbs start running rich, so I have to keep the nuts all the way up....
I tried the suggestion , made earlier, to pull out the choke slightly , while running, and the car began backfiring....
I did drive the car today , with the following things done:
Timing: 8 degrees BTDC
Points: .010 (assymetric cam)
Plugs: .022
Float level: 3/8"
Jets: centered with ES needles (these have less than 1000 miles on them).
Needles: reset so base is flush with bottom of piston.
Jet adjusting nuts: all the way up
Oil in dashpots...
Carbs synchonized, using Uni-syn, and wire rods to check.
What I found was the overall acceleration has improved. The car does not hesitate, or buck, but the idle is irratic, once warmed up...A couple times , it felt like it was going to die, (at idle), unless I gave it gas...
Before I drive it next, and after checking the plugs, I'm going to run the adjusters down about 3 flats, and see if things improve...If not, I will re-set the floats to 7/16, and see if there is any improvement.
I think I'm also going to perform a vacuum leak test with propane, and see if there is a leak somewhere, which would explain the irratic idle.
Thanks again for your input...Please keep it coming. I'm determined to make this car run as well as my other MG's did.
Edward
E.B. Wesson

Edward,

You're clearly looking at all the right things and the advice on this thread is sound and wide ranging. My guess would be that you're leaking fuel through the jet bearing 'cork' seals as mentioned by George Butz. You need a repair kit and to carefully fit the new seals and accompanying brass washers, checking the flatness of the large washer at the top! I once had similar symptoms caused by a slightly buckled top washer, hard to spot!

Then forget the use of 3/8" or 7/16" round bars to detrmine float level except as a starting point. With the top chambers off, you can see the fuel level compared to the top of the jet, and and adjust the float chamber prongs, to get a level just below the jet - see Archives for exact specs. Don't be surprised if the prongs of each float chamber are spaced differently! If you want, the level can also be slightly altered by rotating the float chamber by slackening the large brass nut; otherwise keep this tight!

There is no way that the adj. nut should be at the top of it's adjustment - fuel is leaking somewhere - don't assume recent 'new' jets/ needles are to size - quality control is not what it was! I assume choke is not holding jet down - we've all missed the obvious! I find the Colortune very useful in gauging mixture - once set up correctly the SU should stay in tune for years. Hope the above is of some help.

Good luck,

John
J C Mitchell

This thread was discussed between 21/08/2011 and 23/08/2011

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