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MG TD TF 1500 - Down on Power
|Hopefully someone can lead me in the right direction with this one. My 1950 TD is down on power and today I was unable to get up a hill that I went up last summer. The car slowed drastically and was missing like crazy. The car following me said that there was black smoke from the exhaust. The thing is that it ran fine on the highway and the temperature only went up a few degrees. |
Once we got back home I pulled all of the plugs and they were very sooty with a black dry soot. I checked the compression and it was 135 in all 4 cylinders. The timing was set statically at TDC. The carbs haven't been changed but the rear carb is wound right up, the front one is close so it shouldn't be running rich. I resurfaced the carbs a couple years ago as there was a leak, could this require more work?
|Brian - The black smoke and sooty plugs would indicate that you are running very rich. carburetor tunning is in order. Cheers - Dave|
|Either the needles in the pistons are mis-installed too high in the pistons, requiring the jet to be screwed up too high and still run rich... or your floats are set too high allowing the fuel to be too high in the bridge allowing too much fuel to be drawn into the carburetor for a given mass flow of air.|
Check your points too. Too little gap can cause problems under load.
|I would go for the carbs, check the mixture which is too rich, check the needles and in case change them with EW, which allow a leaner mixture - as I have done.|
Good luck, Denis
|Denis L Baggi|
|Brian, remove the floats, & shake them, they may have fuel inside.|
|Anything change with your choke cable?|
|gblawson - TD#27667|
|Interesting, it appears that you all agree that it must be carburation. The only changes made recently were to install float bowl caps that do not have the hole in the top. At that time I went back to regular needle and seat ( took the gros jets out) and set the float forks as per various postings in the archive. I will go back and recheck that work.|
Dave Braun, you have mentioned the setting of the needles. As the seat doesn't sit absolutely flush with the top of the bridge inspite of all efforts, the needles, if installed so that the shoulder is flush with the bottom of the piston, will never close off the fuel flow completely or for that matter allow for really lean running. I have experimented in the past with locking the needles in various locations but the only way it wants to run is with the needles flush with the bottom of the piston. This makes for rich running.
Guess I will have to spend some more time in the garage and as always I am open to suggestions.
|Change the distributor rotor before touching the carbs. You said you changed the float bowl lids to the non-vented ones. Make sure 1) your overflow tubes are not plugged (remove and blow through them) and 2)the fiber washer with the cut-outs is between the float bowl lid and the overflow tube base (only one washer). If that is all OK, try running without the air cleaner, as the tops frequently get pushed in, causing super-rich running. If your car has always run fine in the past, forget about changing the jets. Also, make sure the damper tops have the vent hole. George|
|One common problem that fits your symptoms is the jets not returning all the way up, even with the choke cable pushed in. They seem to get a buildup of crud up around the shaft where it enter the bottom of the carb. I periodically clean mine by pulling the choke out, lowering the jets. I then wrap a strip of cloth with some carb cleaner sprayed on it around the jet body and clean it. I squirt a little light oil on the jet body before returning to the up position.|
|D C Congleton|
|D C Joe Curto has the correct return springs that work.|
|Thanks for all of the advise. As indicated above I have pretty good compression on all 4 cylinders and they are all the same at 135 so ruled out valves and rings. I have rechecked the carbs and everything appears to be set according to the manual but did find a couple items. The front carb piston was sticking so that would be part of the problem but an even bigger one is the rear carb. I mentioned earlier that I had closed the jet adjusting nut all the way so my rich running I assume was actually coming from the front carb with the sticking piston. That said I have been unable to get the rear carb to suck any air! With the car running at idle (?) I put my hand over the front carb and the car died....doing the same thing to the rear carb does absolutely nothing. When reving the engine the piston will come up a little but again nothing meaningful.|
Obviously this is why the car was not running well and had no power but does anyone have any thoughts on what the next step is???
Once again, thanks in advance.
Its entirely possible your throttle shafts are worn and you're sucking air through the shaft ways.
Under these circumstances the butterflys are always partly open allowing the mixture to be excessive.
A simple check is to disconnect the throttle connection and try to wiggle the shafts.
You also want to make sure that in reconnecting your throttle shafts, that each butterfly is correctly positioned and that they are synchronous in their opening and closing.
|Gordon A. Clark|
|Thanks Gord, I did check the throttle shafts and they don't have any noticable movement and they don't appear to be leaking around the flanges. I will check the butterflies tomorrow.|
|Vacuum leak between intake manifold and head or carb?|
|I take the liberty of repeating to change needles to EW. Also George is pointing to a critical point, vacuum leak intake, which could come from not well tightened manifold bolts, or from other sources, including the opening at the bottom of the intake manifold, which must absolutely have a screw.|
|Denis L Baggi|
|Brian - Two things, First, I would reiterate what George said about the overflow banjo washers, make sure that the scalloped washer is between the lid and the banjo fitting. If that is not in that position, the float bowl will not vent to the atmosphere and will cause problems. Second, You say that there is no air being drawn into the rear carb. Recheck that the linkage to the throttle shaft on the rear carb is tight and doing it's job. Cheers - Dave|
|i am starting to get confused. aren't leaking shafts normally associated with inability to set proper low idle? did i read your initial post correctly that the car was running fine before you worked on the float bowls? if so, why do you now think it is now a jet/needle problem? if you cover the air inlet and the engine does not miss a beat, as you know, it is getting air from somewhere or it wouldn't run. the "t-type restoration handbook" has a very thorough article on synchronizing and setting up the carbs. i am with david and george here, if before you worked on the float bowls everything was fine...i would suspect the problem lies in that area. float level or float needle not seating to shut off fuel into the bowl, bad or incorrectly located washers. i am curious as to why you switched from the grosse jets. if you have now adjusted other things since the float bowl work you may have created other issues. it might be time to start from scratch on the carb set-up. proper washers in the proper location on the float bowl, grosse jets or a good needle and seat, a float that doesn't leak, proper float level, center the jets, sychronize and adjust the carbs per a manual you can have out in the shop to read as you work. best of luck. let us know what you find. regards, tom|
|I am just about to head out to the TD but just to confirm, the washers are both located correctly under the overflow banjos, the floats are not leaking, the float level was set using the info found in the archives, the float needles and seats are brand new with steel tipped needles, the overflow pipes are clear and the plungers both have a vent that appears to work.|
The car ran well previously but did lack power and I had run the jet on the back carb fully up but still it ran rich. The needles and jets were new "standard" ones. The rear carb may not have been working properly for a while though as I have the original intake on it and this doesn't allow you to actually see what each carb is doing. I have taken it off until I can get things operational. I have had a problem in the past with a leak where the carb attaches to the intake but this was supposedly fixed and I have also had a problem with the shafts not working together. I sourced new parts for shaft so they should be working together but I will advise what else I find other than the front piston that was sticking.
Sure appreciate all the responses!!
|To check for vacuum leak, let it idle, spray carb cleaner on the gasket junctions. There should be no change in idle speed. If it speeds up there is a leak. Turn fuel pump on until clicking stops, remove the float bowl lids and check fuel level. Or you can remove the suction chambers and pistons, pull the jet down (choke it), and look at the fuel level in the jet bridge hole. I can't remember the exact level, but it should be near the top, but not flowing over. Make sure you don't have a fouled sparkplug, bad wire, etc. I have spent too much time fiddling with the carbs when it was ignition (and vice-versa). A TD will run super-rich with a TD MkII needle in the 1-1/4 carb- I found that out too.George|
I had almost the same problem with my 1950TD
no power running rough sotted plugs.
It showed up to be the head of the distributer beeing loose on the shaft and
wobling. fixed that and the car hasbeen runnig fine in 6 years since.
Goode luck. I am shure you in the end will solv the problem.
|t g sorensen|
|Update....the front carb had a sticking piston, this was easily fixed, rear carb needing adjusting badly but also does have a leak around the throttle shaft. I now have them set so that both carbs are sucking the same amount of air but they are still running rich, even with both adjusting nuts almost closed. It looks like new needles and seats are definately in order. Haven't road tested it yet as I now have clouds of blue smoke coming from the exhaust. Why this would appear now I have no idea but I do know that the valve guides are very poor and upon taking the valve cover off there is an awful large amount of oil being pumped around the rockers. As compression is good I don't think a ring has gone so I guess the head will come off and be sent out for repair.|
Your problem won't be completely resolved 'till you o/haul your throttle shafts.
|Gordon A. Clark|
|I agree that the carbs will need an overhaul and this will be done this Winter along with replacing the valve guides and valves.|
I did get out to the garage today and after reading about the oil pressure relief valve opening at 75 pounds I thought I better check the relief valve as I was seeing over 100 pounds pressure until the car warmed up and after seeing the amount of oil in the rocker area began to think that something wasn't right. Pulled the relief spring out and found that someone had installed a spacer. Reinstalled the spring and the pressure is still high (about 75 pounds) when cold and there was less oil smoke so a new stock size spring will join the list of parts.
This thread was discussed between 19/08/2007 and 22/08/2007
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