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MG TD TF 1500 - Carbs Idle have me stumped

My 54 TF has completed a restoration and total rebuild of engine. When I started, the carbs were fine and we took them off and set aside. They run poorly. Seem to have enough power on hills etc, but they wont idle below 2k. with screw all the way backe off. I just took apart the float and suction mechs and they were clean and looked up to par. The needle was straight etc.
Two questions.My engine guy says it idles rough cause I only have 300 miles on it. I can buy that. But he also says that is the reason it wont idle slower.
Does this make sense?
Here is the main question. I want to drive it for its first showing at the GoF in VT. When I synchronize the carbs, they wont sync until I get the rpms up to 3- 3.5k. When I adjust the mixture nuts, and do the lift the piston test, one carb runs fine at no back off of the nut, in other words completely at the top, and it does not seem to be affected by the lift the piston test or when I increase the number of turns backing the jet off. Now the second carb, it runs about the same thru many turns of the nut and when I lift the piston, it starts to completely die, regardless of how much I have adjusted the nut up or down 0 to 25 flats.
I did lose the two idle adjusting screws and have new ones ordered. Think the springs were too weak to hold in. Also ordering new jet springs as they tend not to close the jet heads. I have checked the butterfly to make sure it is in right, the needles, etc and all looks well. Any ideas on this crazy carb?
K E MURPHY

I had that problem on the 72 B and found out that one butterfly wasn't closing all the way when the other carb was. In other words, the carbs weren't matched up, so one carb was leading the other. Juts a possibility. PJ
Paul S Jennings

Along with what Paul wrote, I would suggest that you look closely at the butterfly disks in the carbs to see if they are closing completely around. I have had problems in the past because one of the disks was not seating properly - loosening the disks and moving them so they close completely around their circumference cured the high idle problem. Cheers - Dave
D W DuBois

Thanks guys. I will look again closer. How do you adjust those, one thing I have never done?
Also had a local guy say that maybe a jet isn't centered, thus bad idling but runs ok and has power at speed. ?
K E MURPHY

Another very possible explanation is air leaking between the carburetor and the intake manifold or the intake manifold and the head. This will cause higher than normal idle that is impossible to adjust out.

As for making sure the butterfly disks close all the way the best way is to remove the carburetors and look. If they're still on the car, separate the carbs by loosening the that zigzag thingy that holds their throttle shafts together and turn the idle screw on each carb all the way out. Remove the piston in each carb and look in...the disk should be closed. If they are then replace the pistons, turn the idle screws down until the car will start, balance each carb, and then retighten the zigzag thingy.
Gene Gillam

My butterflys had been installed backwards by PO. They are beveled. There is a long post a few days ago about this same topic. You might check it for more input.
Ed
efh Haskell

Is the baffle still in place (along with its retaining bolt) in the intake manifold? I have seen some cars with that fallen loose. That makes it impossible to balance the carbs and some very strange symptoms. Check for the bolt at the center bottom of the intake manifold (not the air manifold),
Lew Palmer

I know you had an earlier post on this same topic - have you taken some time to read through the instructions in the shop manual - those instructions provide a clear, logical framework for looking in to your problems.

I would back up, slow down, and make a careful check of all the adjustments. The fact that you have a fresh engine would not cause the problems you mention - so I would have to disagree with your mechanic.

I would do the following:

1. Do a compression test on your fresh engine - make sure you have even compression - on a new engine you should have even compression.

2, Confirm that you have spark to each of the four plugs. Confirm that your plugs are firing - you may need to replace or clean them based on your descriptions.

3. Double check your valve clearances - what spec clearance does the new camshaft call for?

4. You should be able to balance the intake on the two carbs at a speed much lower than 3.5K rpm. Once you find some throttle adjustment screws.

5. Reset your float levels - have you confirmed those settings>
6. With the domes over the pistons, check again for centered jets - remove the piston dampers and check for a solid drop of the pistons to the bridge - do your pistons move freely with the covers on and the dampers removed? slightly oil the outer surface of the hollow piston rod and make sure the cover to piston movement is smooth for each carb.

7. Adjust your jet nuts all the way up, then back them down 12 flats as a starting point. Or adjust the jet to .070 below the bridge as a starting point.

You may have a vacuum leak as mentioned you can identify this with starting fluid - sprayed around the intake manifold gaskets and around the intake ends.

Make sure your high speed idle adjustment screw - on the front carb is not in contact with the lever/base causing a false idle for the front carb.

I would also continue on this thread rather than starting yet another on the same topic.

Take a deep breath and approach things in a deliberate manner - hopping around will only cause more problems for you - good luck.
DLD

Thanks DLD for your comments, I have copied them down and now will look for the harder cures. I have it idling at 2k and at speed it runs fine, so I will drive it to GoF.

I did read the T handbook the NEMGTR put together. I have not done compression or check plugs. If I have a plug issue could it affect only one carb?
Have not rechecked valve clearance. Have not checked vacuum leak. WHAT WILL THE STARTING FLUID DO IT THERE IS/IS NOT A LEAK?

My adjustment screws did not help much. I know about the choke screw and it works ok. The floats and levels are perfect. The Suction chamber cylinder drops and clunks just as they should. Have oiled the shaft etc. I think I have adjusted the nuts at 6 flats but will look at 12.

Thanks for your help and I will not post a new thread.
K E MURPHY

Hi Mr. Murphy,

To answer your questions,

Plug problems can impact things and would cause a carb to seem unresponsive - cylinders 1 and 2 are served by front carb - cylinders 3 and 4 by the rear carb.

On the starting fluid - if engine speed increases when you spray an area - you have an intake leak at the location sprayed. No change when sprayed means no leak in the area - check the joints at intake to head and carbs to intake. - Also check throttle shaft points on carb bodies.

What did you find when you checked the discs in the intakes? look carefully at alignment and movement - as well as orientation - no beveled surfaces should be seen from the outside looking in - open the throttle and check for smooth movement and closing. You loosen screws and move disc while closing to adjust - screws have split ends which need closing to loosen the screw. Ends are opened again once adjusted and tight

Hope you can locate issue before your trip

Good luck
DLD

K E.
Hope you get it sorted out before the GOF,,, FWIW, we are heading out on Wednesday morning,, going up Rt 7 from New Cannan CT

SPW
SPW Wincze

K.E. -

Regarding the number of flats - 6 per jet is correct - my mention of 12 for the set was misleading.

Good luck - let us know what your problem was once you find it.
DLD

Thanks guys. I did the manifold starting fluid check and it did run a tiny bit faster. Tightened the four nuts holding the two carbs on about 1 /12 to 2 flats each but didn't seem to help. I checked again and the butterfly discs are completely closing. Now here is something that is important but not sure how: one carb is starved for air and wants to suck my hand in and needs the unisyn almost completely open to run. The other carb could care less, can almost completely cover it with hand or unisyn. Idles at 2,000 or more, but runs at speed ok.
K E MURPHY

Ken,

You need to tighten the manifold hold-downs. The reason that carb could care less about the uni-syn is it's getting air flow in from some place other than the front of the carb.
Gene Gillam

Ok - finally an answer on the difference in the suction. I will check it out. Could this be cause for fast idle too?
K E MURPHY

This thread was discussed between 04/06/2014 and 06/06/2014

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