MG-Cars.com
MG TD TF 1500 High speed miss BBS discussion at MG-Cars.net
MG-Cars.net
Welcome to our resource for MG Car Information.
Recommendations
Parts
MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.
MG TD TF 1500 - High speed miss
| Hello All, I've got a high speed miss in the engine at about 3500 RPM. Runs just fine at anything below this speed. Have put on new rotor, new dist cap, checked the gap on the points and the plugs but still nave the problem. I have about 1000 miles on the car since my rebuild. I had this problem at about 500 miles and it turned out that the points spring was apparently contacting ground at higher engine speeds. I corrected this and it's been fine ever since. Now it's back and appears to be a different problem because the points are okay. I had the dizzy rebuilt by Jeff at Advanced so I assume that it is okay. Any ideas. I'm thinking that perhaps the valves are not adjusted correctly although I set them recently. I don't know if this will cause the problem but it's about the only thing left to try in my mind. Mark |
| Mark Strang |
| What did you set the plugs at? Workshop Manual calls for something real tight like .020" on the plugs, and you're still running points and not electronic ignition. One of our toys wasn't running too clean and I closed the gap a touch and it did clear it up. |
| Jim Northrup |
| Mark, it may be worth a look at your fuel system. There are a number (3, I believe) of screens that fuel has to go through before reaching the jets. There are the filter screens at the carburetor fuel line banjos. There's the filter in the fuel pump. And there's the filter screen in the fuel tank at the fuel line. You could probably just check the fuel flow out of the pump. Perhaps Dave D. will remind us of the spec for that. Good luck. Bud |
| Bud Krueger |
| Jim, I closed up the plugs to 0.021" and the points to 0.014. Advanced Dist suggested the points gap and the WSM suggested the plug gap. I think that one of these two things probably solved the problem last spring. The current settings are the same as before. Bud, Dave D. did my fuel pump. I don't have any known problems with the screens but I'll check again. Mark |
| Mark Strang |
| Mark - just to make sure that you are not having a fuel delivery problem, remove the fuel line from the carburetors and direct it into a quart jar, marked at the 1 pint level. Turn the ignition on and time how long it takes pump 1 pint - should be 48 seconds (anything below 60 seconds is actually good). Cheers - Dave |
| David DuBois |
| Have you replaced the condensor? I have seen them cause an only-high-speed miss. I don't think this is the problem here, but I once chose not to replace the perfectly fine-looking points on a car that had been sitting for many years, and found that the points spring had lost it's tension. Talk about a high-speed miss! Tom |
| t lange |
| Is it a dead miss (ie rythmic) or random? Did you try pulling the choke? If choking helps, then likely fuel starvation. Make sure the coil wire is not pulled out of the coil or dist. cap. George |
| George Butz |
| You didn't mention if you have the stock air filter setup, or aftermarket.... Some drivers have noted a high-speed miss, after going to "pancake"-style air filters.... Another possibility, is the rotor itself....Using the replacement black rotor, will sometimes allow cross-firing at high speed..Using the red, custom replacement, will cure this. Edward |
| E.B. Wesson |
| Is charging system up to snuff? Check your voltage, for what that's worth. A low battery may have enough cranking power but low voltage translates into poor ignition. I added a voltmeter to watch the running voltage go up and down, like idle vs running, especially with lights on! To monitor charging better, I even changed the guts in the aftermarket ammeter to a very responsive one (Lucas is nice & responsive). Even switched to a new Edsel voltage regulator. |
| Jim Northrup |
| Looks like we are going to have rain from Lee for the next few days. I'm not interested in test driving in those conditions so I'll make what changes I can and test when the rain stops. Mark |
| Mark Strang |
| new plugs new plugs NEW PLUGS Ellis |
| Ellis Carlton |
| Hi Mark: I had a similar problem with my TF after putting in an Advanced Dist. dizzy. I thought it was to blame for a sudden loss of power at speed. After a lot of trials I found that there was no overflow line or vent on one carb. Before the new dizzy the engine never had enough power to use sufficient fuel to cause a problem. An original nut, washer and banjo fitting and voila no more miss. It may be possible for a plugged overflow pipe to cause the same problem for you. Godspeed in Safety Fast Jc P.S. Jeff's rebuild of my dist is the best $s I have spent on the TF!!! |
| John Crawley |
| Timmed for 30 degrees @ 3,000 RPM? Mine had "slipped out" and was doing the same over about 4,000 RPM. No problems on yesterdays run and had it up to 5500 RPM a couple times. |
| David Sheward |
| Lots of rain so no test drive. I do think however, that I may have found the problem. When checking the points again I discovered that they were set at 0.018! Now, depending upon which dizzy you have they should be set at either 0.010-0.012 or 0.014-0.016. Mine is the later version. I set mine at 0.013 and I'll see what happens. Can't be any worse. I know that I closed up the gap and supposedly set the points at 0.014 last spring and the car ran fine. Obviously something went astray. Hopefully the rain will stop soon. Mark |
| Mark Strang |
| Mark, Is your distributor properly grounded? That can cause a miss at speed. warmly, dave |
| Dave Braun |
| Dave, Grounded? What is this that your talking about? Isn't it grounded by virtue of the fact that it is installed in the block and bolted in? Is there an actual wire involved? Mark |
| Mark Strang |
| Yes, Mark, a separate wire. Evidently under certain conditions the distributor loses its ground at higher engine speeds. Since the clamp is very well grounded to the distributor body, but it floats (collared centering bolt) you need a ground wire from the clamp to one of the engine bolts. You're not the first person to have omitted it on installation. Heck, I forgot about it until I was almost done with the car. The wire can be seen both in the installation section of my website and the engine teardown section. Take a look at my website, http://www.dbraun99.com and go to picture 50 of the MGTD15470 » Engine XPAG TD2 15613 » Installation warmly, dave |
| Dave Braun |
| On my tombstone : "SAFETY DONE, Here lies David, he is finally done learning new things about his T Series Auto" |
| David Sheward |
| Dave, I can do that easily enough. It won't hurt. Thanks Mark |
| Mark Strang |
| dave and all, i'm not seeing how this is more of a ground than the locking bolt that goes through the clamp, threaded through the block and locked against the distributor housing. what am i missing? regards, tom |
| tom peterson |
| Tom, Note that Section C.7 of the Workshop Manual says "Disconnect the bonding wire from the cylinder block to the clamp and the the distributor can be lifted straight up." Note that the clamp is to be removed with the distributor. Of course, the factory also wanted safety wire on "earlier models" at the clamp to block bolt, but I skip that. The distributor clamp "dowel" bolt that goes to the block has a collar at the head. The bolt goes through an elongated slot on a bent tab that does not contact the block. The whole clamp assembly floats vertically, depending on the dimensions of the distributor body. Dirt and crud can build up in there, as well as airspace, and prevent grounding at that point. The clamp's only purpose is to prevent rotation of the distributor. The distributor itself has a fairly wide clearance with the bore. The shaft rides on bushings. Oil films on those surfaces and the gear can prevent grounding as well. Any loss of ground will probably be at speed and intermittent. The later TD/TF (engine number 20942) distributor clamp does not require a grounding wire. warmly, dave |
| Dave Braun |
| Well, the rain from Lee finally stopped and I was able to take Maggie out for a high speed run (high speed is a relative thing when talking TD's). I ran her right up to about 62 mph per the GPS with no missing at all. I didn't even have the cowl shake that many folks talk about at about 3500 rpm. I did this a couple of times with the same good results. I can assume that the point gap setting must have been the problem since that was the only thing I changed other than bringing the plug gap to 0.020 from 0.021. I was suprised to see that the tach was reasonably accurate given that it probably has the 5% error that is usually typical with old instruments. The speedo even held somewhat speady without much bouncing. It was a real pleasure to reach those speeds especially with the toe-in corrected. I can see how they were fun to drive at higher speeds. During the past 1000 miles since the rebuild I've been reluctant to go much faster than 50 mph but now I feel much more comfortable at higher speeds. The group that I hang with however, usually goes at 45 to 50 mph. I guess that I'll go with crowd, however, I wonder what a 4.30 rear end would be like! Perhaps I need another TD to tweak a bit. Could be exciting. Thanks for all of your help. Mark |
| Mark Strang |
This thread was discussed between 05/09/2011 and 09/09/2011
MG TD TF 1500 index
This thread is from the archive. The Live MG TD TF 1500 BBS is active now.