Ignition timing? Something else?

Mick Rae

Active Member
Ran out of day light today, so just having a ponder.................forgive the long post, just feel its best to give all detail. Especially as its something small I have done wrong most likely!

I decided today to check ignition etc - always felt the car was a wee bit sluggish, starts and runs well, but just, well, sluggish a bit. Although I suspected timing, I decided to start by checking everything else. I put the disclaimer in here right now that I am not expert in these matters!

First I checked the dwell - it was 40, so then I checked the points gap, sure enough it was a bit on the big side - set with feeler gauge to 15 thou. Started up, checked the dwell, it was 55 - figured close enough (I am right in thinking 57-60 is the region - starting to doubt myself now!). I checked the ignition timing (strobe) The 8 degrees mark was a bit over (like a good cm) to the right of the pointer (overly retarded right?). So using the A-R adjuster on the distributer I put things to the 8 degree mark lined up with the pointer - vac advance disconnected and plugged, engine idle at 650 rpm (rpm measured on meter, but corresponded well with dashboard rev counter).

Went for a drive................car feels more sprightly, so that's good. But has a weird miss - grand in first gear, then if accelerated hard in second or third, an intermittent miss (like a bit of a stumble really, no backfire, just a sharp stumble/miss), once up to 4th, fine - well, nothing noticeable, cars running lovely......but maybe, just maybe, the miss was there once or twice, hard to say at steady speed). Overrun no problem, but then if overrun in third gear for example, applying throttle causes a couple of 'hics' then fine.
So I went home. I checked the points again - all good. I changed the rotor for a new one - didn't help. Put the old rotor back and changed the distributor cap. Made no difference. Checked the timing again - yup, 8 degree lined up with pointer, as I had set it. I cleaned the coil contacts, the distributor to coil contact. Went for a run. Was same, intermittent miss, well, maybe a little better, but still there.
So now I'm sitting here thinking.
1. what am I missing? (no pun intended)
2. Could closing the points gap cause such a thing to happen, seems doubtful as its now correct and was incorrect before?
3. Could altering the ignition timing be the issue? I remember my old MG needed to be retarded a bit with unleaded (premium) from book figures, but that would pink, not miss, and there is no pinking at all from the Rover............I ran out of daylight as was going to retard back to where I found it, but didn't fancy being at the roadside in the dark, so packed up and decided better to look a fool but get good advice than go round in circles. FWIW, engine has 41K on it. As a wild card, the front end has been raised, and it wasn't driven since, did consider maybe some muck in tank has been moved by sitting at that angle and what I am seeing is dirt in the fuel system, but no, cant be it - has to be something I have done today as regards the above. I will appreciate all your advices, remember, my enthusiasm is not matched by my experience sadly :)
 
Yes changing the dwell by 1° will change timing by 2°. Timing sounds about right, assuming the advance works ok and resets when revs drop (I’ve had that in the past). I would also pull a lead and check the spark and make sure it’s nice and fat.

I would also check plug gaps, they seem to be overlooked a lot these days and can have a big impact on running.
 
Thanks sdibbers!
So if I understand you right then, me initially changing the dwell would have been what retarded the timing - essentially then, I haven't done anything totally daft, as I reset timing to 8 degrees. Have looked at the 'advance in action' with strobe, it seems to be fine, increase revs, it advances (painted 8 degree mark goes to left/anticlockwise), and then returns smartly at idle. I was just convinced it had to be something I had touched today that was causing the issue. As it happens, I have a new set of plugs on my shelf - I just didn't want to change anything else until I found my error. But next chance I get I will pop in the new set, check for a good spark, correctly gapped, and see if that does anything, hope so - but if not, is retarding the timing by a couple of degrees worth a go, or is that just pointless and nothing to do with anything I am suffering from you reckon?

In a slightly perverse way, I like this sort of faffing around, as its opportunity to try to learn a bit from y'all. I've never dealt with points before (other old cars had Lumenitions) and my first thought was to go electronic, but I kinda like points in terms of their simplicity, cheap to change, original-ness, so want to get familiar with it all, and having to fault find is a good place to begin (even if I am the fault!)
 
So if I understand you right then, me initially changing the dwell would have been what retarded the timing - essentially then, I
Yep, you’ve got it.

I think you’re right to assume that something changed that caused the misfire during the work carried out. It could also just be a coincidence (I’ve had that happen in the past and it makes for a huge red herring).

Let us know on the spark, I’d say the timing change shouldn’t cause a misfire under load as you’re seeing. 8° is about right and shouldn’t cause a problem.
 
thanks - I learned something, means today was a good day - away a day now, but hopefully back for round 2 at the weekend some point.
 
Me again - follow up. My appointment got cancelled last minute, so had time to play again, excellent!
On sdibbers advice, I looked at the sparkplugs. All a lovely colour, all perfect gapped. Still, I have a new set, so what the hell, may as well rule the plugs out, so put them in.......... Running perfect, 30 mile round trip, no stumbling, indeed, running really nice! So I am left wondering now: Is it even remotely possible that altering the points gap etc yesterday could have somehow placed additional load on plugs/a plug that was just about coping until I changed something? Do spark plugs 'work harder' under load, and hence if failing would show up then? Or did Rover build in a self-repair function that happens overnight and the old plugs are fine? I worry that this return to normal service is temporary without knowing that there is an explanation for all of this :) New coil and leads on order to rule every last thing out (and no bad thing, the whole ignition system is looking decidedly second hand, but at same time I like 'if it aint broke'......................
 
Glad to hear it’s running well again. Couple of thoughts for you:

How well connected were all the HT leads? If they are in place but not pushed home that could’ve been an issue.

Another thing is if the old plugs had internal resistors (for radio suppression) the resistor could have been failing. I’ve had Champion plugs fail out of the box because of this and use NGKs now for that reason.

You asked if the plugs work harder under load. They sort of do. When the throttle is opened you have more air and fuel in the cylinder and that makes it harder for a spark to jump across the gap. Hence why misfires tend to show under load.
 
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Interesting. Old plugs were Champion, new are NGK. Thanks again sdibbers, for your advice, and the explanation/education, really appreciated.
And Cobraboy, yup, from MG ownership I know all about the quality of new ignition parts, pretty shocking sometimes. Red rotors from the doc is about the only ones that I can trust!
I'm sticking with points, for the meantime, thanks both, much appreciated
 
Old plugs were Champion, new are NGK.
Unfortunately, Champion have rather nose dived in quality in the last few years. It had got to the point that would measure their internal resistance before fitting them. Typically I’d find one in four were way out of spec out of the box.
 
Last few years? I think Champions have been substandard for decades, if they have gotten worse it doesn't surprise me. Long time NGK fan personally, though I like Bosch plugs too.

Yours
Vern
 
Last few years? I think Champions have been substandard for decades, if they have gotten worse it doesn't surprise me. Long time NGK fan personally, though I like Bosch plugs too.

Yours
Vern
I was thinking the last decade, but I think you’re right. The last set I tried was four years ago and that’s when I saw the 25% reject rate. Ones over here in the states seem to be made in S America.
 
Last few years? I think Champions have been substandard for decades, if they have gotten worse it doesn't surprise me. Long time NGK fan personally, though I like Bosch plugs too.

Yours
Vern

The last set of Champion plugs that I bought was missing a tip on one of the electrodes. I prefer to run NGKs

I was told years ago that the only thing a champion plug is good for is a lawn mower.

Then I took up flying and found that the most common plug in light airplanes is Champion! As part of the preflight checks you run the motor up to load at 1800 or 2000 RPM. Then do a 'mag check' where you switch to one mag and then to the other while the plugs working harder. This checks the magnetos and the plugs for miss fire under load.
 
Crikey! Slightly more important that your engine runs well, more than my head scratching for the fear of needing a tow truck at some point! How long flying does it take to stop obsessing over engine note, takes me long enough with a car :)?
 
The last set of Champion plugs that I bought was missing a tip on one of the electrodes. I prefer to run NGKs

I was told years ago that the only thing a champion plug is good for is a lawn mower.

Then I took up flying and found that the most common plug in light airplanes is Champion! As part of the preflight checks you run the motor up to load at 1800 or 2000 RPM. Then do a 'mag check' where you switch to one mag and then to the other while the plugs working harder. This checks the magnetos and the plugs for miss fire under load.
Funny you should say that. My friend had the tip fall off a NGK plug in his 500 Abarth last week, damaging the bore pretty badly.
 
Crikey! Slightly more important that your engine runs well, more than my head scratching for the fear of needing a tow truck at some point! How long flying does it take to stop obsessing over engine note, takes me long enough with a car :)?
you learn after a while about the characters of the airplane motors. You learn to advance the throttle slowly when you line and start down the runway. otherwise you might get a bit of hesitation which is scary for the passengers.
At the club where I fly there are two planes with identical motors, lycoming o-360s. In the Cessna 172 the motor would always start up very easily. In the piper cherokee it would be difficult to start. But once running both planes would fly well.

You learn about mixture adjustment. You have to lean at altitude. At high altitude airports they lean during taxi to avoid fouling plugs.

Make sure you know where the towbar is before you hit the starter. If the prop hits the towbar, then you need to do a sudden stoppage overhaul, and replace the prop. Cost will be around $20k. I always put the towbar in the brackets for carrying it in the airplane.
 
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Of course - hadn't thought about mixture vs altitude in context of planes. Fascinating, would love to be a passenger some day in a small plane. 20K. That's an expensive bit of oversight!
 
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