TR2/3/3A timing DM2P4 dist, TR3A - vacuum?

[NutmegCT]

Good morning all.

I'm going to check the timing today. I've had a fast, varying warm idle since I got the car; can't get it lower than 1200rpm and it varies from 1200 to 1800 all on its own. Checked for vacuum leaks, throttle shaft play, etc.

Figured I should start with the basics - timing. Engine has slight ping on hard acceleration under load, but other than the idle issue, seems fine. Seems lots of folks here have "fast idle" problems.

There's a vacuum advance on the DM2P4 dist (standard, no electronics). Should that vacuum line be disconnected and both sides plugged when initially working on timing?

Thanks.
Tom

 

[martx-5]

TR3 timing is supposed to be set statically...without the engine running.

The procedure as I do it...Make sure your points are set to spec first.

1. On the side of the distributor is a knurled nut that is used to advance and retard the timeing. You will see an A and an R with an arrow. There are also graduations there. One of the graduations is longer then the rest. That's the midpoint...set the timing adjuster there.
2. Bring the engine up to the timing mark on the pulley by turning the engine clockwise as looking from the front. If you go by it, don't back off. Go around again, as you don't want to introduce timing chain slop into this. Now the engine is at TDC.
3.Loosen the clamp on the dizzy.
4. Hook up a test light or voltmeter to the point side of the coil, and turn on the ignition.
5. If the test light is on, turn the dizzy CCW until the light goes out, and then turn it back (CW) until it just goes on.
If the test light is out, turn the dizzy CW until it just goes on.
6.Tighten the dizzy clamp.
7.Turn the knurled nut in the advance direction 2 graduations. Each gaduation is two degrees.

Timing is now set for 4 deg BTDC. You can use the knurled nut to make any running adjustments now, and always know where your timing is set.

I read through what I wrote three times and it seems to be right. It's alot different just doing something then writing about how to do it. I'm pretty sure I got the procedure correct. I hope the CW-CCW thing is correct. Normally, I just check which way the rotor turns and decide then.

 

[dklawson]

That was great Art. CCW till the test lamp goes off, then CW until it just turns on.

Regarding the 1200 minimum RPM, when you're making carb adjustments, make sure the fast idle adjustments are completely backed off (and/or linkage is disconnected between the carbs and free). The fast idle cam can be holding the throttle open just a bit making it impossible to lower the RPM even with the idle screws backed completely out.

 

[Geo Hahn]

Same procedure I use (except I use a buzzer instead of a lamp) and no matter how many times I do it I always have to think about which way is which.

Could the varying idle be due to a badly worn distributor bushing? You might take ahold of the roter and see if you can feel some play in the dizzy shaft. I think excessive play there will cause variance in the points gap which in turn introduces variance in the timing, etc.

 

[NutmegCT]

Help! I've followed Art's procedure (thank you - best outline I've ever read).

Verified points are at .015 when fully open. Moved the vernier to the longest line (midpoint) on the graduated scale. Used crankhandle to bring timing hole to just under the timing pointer. Loosened dist clamp. Hooked up test light to ground and low side of coil.

Ignition on - voila! Light is on. But the dist will only turn a small amount CCW; can't turn the light off unless I turn the dist CW. It's like the dist is almost fully CCW and won't go any further to "turn off the light".

I know I'm on cylinder 1 - used a compression gauge to see the pressure go up. Dist rotor contact is positioned at the 5pm (wire #1) point.

Could the dist be 180 degrees off? Is there something obvious I've overlooked (again ...)?

There is a small bit of play in the rotor shaft, but turning it fully back or forth doesn't affect the light going on or off.

Tom

 

[NutmegCT]

embarrassed beyond belief -

When I cleaned off the vacuum unit area, I just noticed I've got a 25D, not a DM2P4.

Any difference in the timing procedure?

T.

 

[Geo Hahn]

...Dist rotor contact is positioned at the 5pm (wire #1) point.

Could the dist be 180 degrees off?

I think so. The rotor should be pointing at #1 plug when #1 is at TDC (about 11:00, not 5:00)

 

[Geo Hahn]

... Dist rotor contact is positioned at the 5pm (wire #1) point...

Of course someone could have the wires in the wrong position... #1 should emerge from the upper left opening (below the 'L' in Lucas).

Possibly soneone got everything 180 degrees off and 'fixed' it by installing the wires 180 degrees off too. That works but makes the ignition system look like a bowl of spaghetti.

 

[TR3driver]

Tom,
Procedure is the same for 25D and DM2P4.
There is a huge range of adjustment once you loosen the pinch clamp, so perhaps you do need to work back CW. The nominal position should look something like this.

Normally, the dizzy can only be installed one way; but once the pedestal has been removed, the gear can be engaged wrong with the cam. But, if the car was running before with the dizzy body turned anywhere close to the position shown, I doubt that is the problem.

Given the serious damage that continuous knock can do (even if you can't hear it over the other noises); I like to run mine retarded enough that I can just barely make it ping by deliberately lugging in 4th gear with the engine hot.

While you're at it, check out the centrifugal advance. With the timing light connected, you should be able to see the mark move smoothly as you slowly rev the engine up, and let it back down. If it jumps around, there is a problem inside the dizzy. IMO you should also check the vacuum advance, but you'll need an external source of vacuum
https://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92474

 

[piman]

Hello Tom,

when using the strobe to time, always disconnect the vacuum line. Personally, I never bother with plugging the line, it makes no odds to doing the timing.

Alec

 

[martx-5]

Nutmeg... When to loosened the distributor, did you loosen the two bolts, or the pinch bolt. If you just loosened the two bolts on the pedastle, there isn't much movement in turning the dizzy. You need to loosen the pinch bolt.

BTW, when you line up the timing mark on the pulley, it will be at TDC on EITHER #1 cyl or #4 cyl. It doesn't make any difference for this procedure.

 

[NutmegCT]

Progress.

I started from scratch. Discovered that if I twist the rotor (there's play in the rotor), I can get the "light test" to work. Twisting and holding the rotor I could rotate the dist to bring about the "light on" or "light off" situation. In an earlier post I said the rotor pointed to 5pm. My mistake; was pointing to 11am.

Followed Art's good advice again, finished up. But wondered about that last statement:

7.Turn the knurled nut in the advance direction 2 graduations. Each gaduation is two degrees.

As the vernier was already set at the middle (the longest graduation line), turning the knob toward advance only revealed one more graduation line (not two). Seemed like there were 3 lines to the left of the middle line, but only one line to the right. Probably not a big deal. So I kept turning to where the second advance line (4BTDC) "should" be. Note that before I even started this project, the vernier was adjusted fully retarded - the knob wouldn't turn any more in the Retard direction.

Now, for the first time ever, the idle is actually around 800rpm. Actually at first after setting the timing, it was below 500, ignition light on, very rough and lumpy, so I bumped it up with the throttle adjust screw just to where the ignition light went off, around 800rpm.

Took it for a test drive. Absolutely no ping on hard acceleration up a hill with hot engine. Very smooth acceleration and decel. However, when I got home and cut the ignition, there was a one or two second "run on".

Started up again immediately, and found it difficult to start without pumping gas and pulling choke out to first notch (activate fast idle cam). Then even tho' warm, the engine would drop down below 500rpm when I pushed in the choke knob. Note I had just screwed down the throttle screw to raise idle to 800, but it had dropped down again even tho' the screw was still "in".

After another short test, I realized the warm idle is still changing speed. Maybe the play in the rotor shaft?

So the issue now, I'd think, is the run-on and continuing uneven idle.

The big progress for me is that the idle is now actually adjustable below 1500rpm.

By the way, yes - I was loosening the pinch bolt (slot head bolt with a square nut on the end).

Note that Moss, TRF, VB are "out" of dist bushings for this Lucas 25D, number 40897A, so I guess I'll have to live with that sloppy rotor shaft.

But making progress nevertheless.

Tom

 

[dklawson]

They all beat me to it. Make sure it's the pinch bolt that you've loosened.

Geo Hahn, regarding your first post above, I've seen bad timing scatter on my Mini that through iterative tweaking of the timing and mixture adjustments went almost completely away. Before doing those adjustments my engine's idle RPM drifted up and down a lot. Based on that (and without explanation) I'd say that when both the timing and mixture are off you can see wide idle RPM fluctuations.

 

[NutmegCT]

And just to make this really interesting -

If I turn the throttle adjustment screw (throttles connected) to raise the idle - if I leave the raised idle at 1000, it slowly drops down to 500, 400, then really lumpy, then dies. If I leave the raised idle at 1500, it oscillates between 1200 and 1800 or so, but never drops so low to kill the engine.

Interesting - very interesting. Should there be any play in that rotor? Some sources here say that some freedom to manually turn the rotor is no problem; others say it shouldn't have any play at all.

Tom

 

[dklawson]

You must be able to turn the rotor (twisting). The rotor sits on the shaft with the 4-lobe cam that opens the points. Under the breaker plate it is connected via springs and bob weights to the spindle shaft that goes into the block. If you can't twist the rotor back and forth a little bit, your centrifugal advance is seized up. On the other hand, you don't want radial play that would indicate wear in the spindle bushings. You should not be able to push the rotor to the side and get a lot of motion.

 

[NutmegCT]

Doug - thanks for that clarification. I indeed can twist the rotor, but there's no "side to side" play in the shaft. Looks like the bushing is ok.

Still puzzling that when the idle is set somewhere above 1000rpm, it stays with only minor +/- variance. When it's set down below 1000 (i.e. turning the throttle adjusting screw in, to see 1000 on the electronic tach), the idle then continues to drop slowly 'til the engine dies.

Weird.

Tom

 

[TR3driver]

When it's set down below 1000 (i.e. turning the throttle adjusting screw in, to see 1000 on the electronic tach), the idle then continues to drop slowly 'til the engine dies.

Have you checked that both carburetor venturi pistons land with a distinct 'click' when you raise and release them ? Your problem could be caused by an incorrectly centered jet causing the needle to bind slightly only at the lowest extreme of movement.

I like to check with the mixture nut turned in an extra turn or two; just to be sure the needle doesn't rub the jet at all when the mixture is set correctly.

Also, if the engine gets 'lumpy' and starts to load up, you might have a float valve that leaks just a little bit. When the engine takes less fuel than leaks through, the level starts to rise and makes the carb go rich.

 

[NutmegCT]

Randall - the pistons make a satisfying "clunk" when lifted and released. Don't think it's a binding situation.

The car has had a "varying idle" since I got it back in February. Before setting the timing, I'd back out the idle screw all the way but still have idle at around 1500. I could watch the idle slowly change from 1500 to 1200 to 2000 while I was just standing there. Only since yesterday when I set the timing has the idle been below 1000. That's when I noticed the idle would continue to drop and finally kill the engine.

Does this sound like a leaking float valve? I've never had the floats off and opened.

Thanks.
Tom

 

[Harry_Ward]

Tom,

The symptom you describe could be a lot of different things.

Grab hold of the throttle shaft running across the fire wall which connects to the gas pedal and check for worn throttle shaft bearings. Shaft will move up and down if they are worn and excessive play may cause erratic idle speed.

Check for carb linkage binding or excessively worn linkage connections.

Make sure the gas tank and float bowls are venting properly.

Check for rich fuel mixture. Spark plug electrode will look black if rich. Turn mixture adjusting nut in clockwise one flat of the nut until spark plugs are tan in color.

Check for lean fuel mixture - plug electrode will be white or burnt looking. turn mixture adjusting nut out or counterclockwise one flat at a time until plug electrode tan.

Don Elliot suggested in an earlier post to remove the bolt at the top of the float chamber, remove the lid, inspect float chamber for any specks of junk which may be blocking fuel flow. At this time you could also check the floats for any leakage. Also make sure the float needle moves freely in it's guide and is not overly worn or sticking.

Check float level with the shank of a 7/16 drill. hold cover upside down and place shank of drill across center of float cover lid. If the forked float lever does not come into contact with the drill shank, bend the lever at the start of the forked section to make slight drag contact between shank and fork. Make sure both sides of the fork are level with each other or float will not float properly.

Check fuel flow from fuel pump for erratic flow. Remember the stock TR3 fuel pump kind of just spurts with no great flow. If flow incorrect check and clean screen in glass sediment bowl attached to fuel pump and replace any external fuel line filters installed.

If the carb throttle shafts are not worn and leaking air then Lastly the butterfly valves may be worn if they reused the old ones.

Oh yeah and check for loose nyloc mounting nuts on carbs to intake. Actually was riding in an MG once when one of the carbs was flapping around on the intake. Although with the car just idling we couldn't see it until I grabbed a hold and started shaking things. Tightened it up and off we went.

Check for loose fuel line fitting sucking in air on intake side of fuel pump.

 

[TR3driver]

The varying idle doesn't sound like a leaking float valve. I was thinking more of the slowly dying below a certain rpm.

I'm a little confused, since yesterday you posted that it didn't vary much above 1000 rpm, but today it does. Is that right ?

What does the timing mark do while the idle rpm is varying ?

What work was done on the car before the high, varying idle developed ?