Welcome to our resource for MG Car Information.
MG TD TF 1500 - Cutting out at 4,000 rpm.
|I'm still here making progress but engine is cutting out at exactly 4,000 rpm in the garage and on the road - no difference. It simply won't go any faster even if given full throttle. Engine is unmodified from before restoration and ran fine at that time.|
From the archives:
"If you can produce the symptoms just by reving the engine without driving it, the problem is most likely electrical, as ignition probems are not load related. If the problem only shows when you drive it, i.e. putting it under a load, the cause is fuel related."
That said, I checked all the usual ignition stuff (wires, plugs, new rotor, dizzy cap, points, etc.) All seem fine. I have a new condensor but wsm says you have to "solder" it in! Huh? Gotta be kidding me! True? New one has a hole for a screw. Dizzy was not removed during restoration so timing shouldn't have changed.
I also checked the carbs for usual stuff, made a few adjustments of the flats, but made no difference at all. Fuel is brand new. Car starts easily, etc. Just won't go over 4k.
Any and all suggestions will be greatly appreciate, as always,
|Runs good up to 4k? |
Timming or advance issues maybe?
|Is the accelerator or carb linkage bottomed out or stopping travel at this point?|
|David - I didn't remove the dizzy ever. Timing has always been fine.|
Dallas - all linkages are brand new and working fine, but I'll double check.
|Try a different coil, and make totally sure the coil wire is fully seated in both the coil and center of the dist. cap. Originally, the condensor for the early 40162 distributor was soldered to the base plate, with a wrap-around mount. The later ones use the smaller screw-mount type, which easily replaces the long NLS soldered type.|
|George, I don't got no different coil, sigh. All wiring is seated. Coil has worked fine in past, no changes except I replaced the little copper rings that make the contact with new ones. I'll double check however.|
Fyi, I have a "later" 40162F distributor which according to wsm has the "high lift" cam. I just checked my gap and it's spot on at .015" as required with markers on front of engine at TDC. My condensor appears to be soldered however...more confusion???
|I do have one lingering point of confusion about coil wiring which might apply here, although I doubt it. My car is Neg. earth. PO had coil "-" terminal wired to fuse box (i.e. power) and "+" wired to bolt on dizzy (ground). Since car is neg. earth I would think this is backwards, but it's always run fine. Someone once told me here that it doesn't matter but other way would give "better performance". My question is now is it "safe" to reverse the wires to test this or not?|
|Coil polarity has to do with the beginning and end of the windings, not battery polarity....You can try reversing the coil, but it may not help (won't hurt anything , however)....|
I think you need to look at the mechanical advance mechanism, and make sure all is o.k. there.
Yes, reverse the wires.
Original condensors were soldered, and replacements were supplied either loose to be soldered in, or as assemblies with the base plate.
Common reason for the "rev limiter" action is sticky points, fixed by a drop of light oil on the pivot shaft; there is a tendency for this to get gummy whilst sitting.
Or, you can take the points apart and clean the pivot and lube properly, not forgetting to put a smear of Lubriplate on the cam at the same time. Also, some points have weak springs which causes the same problem: bend the points spring backwards so it applies a bit more pressure when reassembled.
|Ed's post; "I'm still here making progress but engine is cutting out at exactly 4,000 rpm in the garage and on the road - no difference. It simply won't go any faster even if given full throttle."|
I have a question; is the car cutting out = stop running, or just will not producing more than 4000 RPM's?
The few times I have had a problem of will start, run, idle, but just no speed. It has been lack of fuel; several time plugged filter, (twice water, once sand) once Float stuck and would not allow fuel to dump into carb, twice it was a weak fuel pump. In these cases there was enough fuel at low RPM's but not enough for higher.
Sometimes I wish we all lived next door to each other so we could see and learn, at least for me seeing and doing sticks better.
|FR, yes "rev limiter action" is exactly how I would describe this! So I just went to adjust/clean the points and made a good mess of it. I "slackened the two screws" per the WSM but all I can manage to do is move the whole point assembly "off the cam" and I can't seem to set gap. I can only get them totally open or totally closed now! There has got to be a trick to setting these points. HELP! She won't run at all this way. Hope to get advice and try again with a clear head in morning...|
|GD, good question. By "cutting out" I did NOT mean it stopped running. I meant it just won't rev past 4k.|
The engine has to be turned such that the points rubbing block is on a high point of the cam in order to set the points gap. With the screws just putting a drag on the points, the whole points assembly will pivot around the brass post that the moving side of the points pivots on. Move it until the gap is correct, then tighten one screw and recheck gap. If OK, tighten the other screw. The screws should have a spring washer and a flat washer each; if these are missing it is much harder to adjust. Then reset timing, because any fiddling with points changes timing.
|ed, i think this is what you are talking about in regard to coil polarity. if you change earth in a car without changing the coil wires it would affect spark plug performance. it would NOT limit your RPM to 4000 how ever. regards, tom|
|ed, does the engine cut out at 4 grand or just stop revving at 4 grand?|
|ed, is the distributor advance working properly? regards, tom|
Let me phrase the question this way, does it start missing, misfiring, firing erratic, ie. cutting out?
...or is it running smoothly at 4k?
Please set us straight on that.
If it won't go past 4000 just sitting in the garage, then it likely isn't starved for fuel, (but new linkage could be suspicious).
What did you set your plug gaps at?
It won't cost anything to set them to factory specs, which is pretty tight, .020-.022" ...and make sure the points plate is snug.
Whatcha got to lose?
|....no one has mentioned that perhaps the tach is reading low??? (I keep thinking about you in your garage keeping the pedal to the floor and the little engine running flat out)....|
|Need to adjust your rev limiter.|
Seriously, sounds like the linkage is not adjusted correctly and not fully opening the throttle. Disconnect the linkage at the carb and work it by hand and compare the results.
|Point float? Just a possibility. Seen it happen before in race engines using the old point system. On a 4 lobe cam, excess point gap can cause points to float at a particular RPM, especally if they have weak springs. PJ|
|I'm with FRM and Paul. 'floating' points would cause this symptom, let's wait what the results are with properly cleaned, lubricated and adjusted points?|
|Willem vd Veer|
|My money is still on advance mechanism. This is what my TF was doing before I discoved the broken spring in there. The car did sit for a while whilst you were doing all the other work. I would certainly look at that before re-adjusting the carbs.|
|Guys, before I can do anything I must get some setting on the points. FRM, when I do what you say to set the gap when on the high lobe that's fine. But when I rock the car off the high lobe the part of the points that was touching the high lobe just sits there! It does NOT "spring" back down on the lobe like it used to before I screwed it all up yesterday. In other words the points stay open! Then if I loosen both screws and close the points they just stay closed when I rock the car. What am I missing? How do you do this? It can't be this difficult!|
I've watched Twist's video but it applies more to a B. I don't have any "adjustment" slot for a screwdriver like he had. Nor can I easily remove the points like he does.
Hope this is clear?
|HOLD THE PRESSES! I worked on the spring tension and I think that was why it wasn't working in last post FRM. I then was able to reset the points to .014". It now revs up all the way! Sounds like it was indeed "point float". I'm off to a road test. Will report back soon...wish me luck if you read this.|
|I'm back! SUCCESS! Took her up to 5000rpm with zero cuttouts. It's amazing what just a few thousands of an inch makes on those points I guess.|
Thanks to everybody for all the great advice & guidance once again!
|That ain't luck, it's skill!|
For everyone who suggests throttle linkage: Ed described this as happening in the shop and on the road. That is a speed related thing, not a load related thing. The throttle requirements to get 4000rpm are very different under the two conditions, as throttle is load related. You can pretty much get 4000 under no load by just screwing in the idle screws, but even full throttle won't do it if the hill is steep enough.
|Glad to hear your back on the road!|
|Now you know why pertronix is such a good idea. No points to adjust. No rubbing block to wear.|
Glad you found the trouble, points can be a pain in the a**. On the other hand they are out in the open and just looking can tell you if they are working correctly. With a black box (molded like Pertronix) You can not tell if it's working until you replace it.
Just my 0.02 worth.
|ed, did you reset your timing after adjusting the points? regards, tom|
|Tom, I've never touched my timing - ever! It seems to run just fine though.|
This thread was discussed between 03/08/2011 and 05/08/2011
MG TD TF 1500 index
This thread is from the archive. The Live MG TD TF 1500 BBS is active now.