251 stalling after a few miles

[Blurredman]

Hi guys,

Got a curious issue with my '90 251.

I think it's been slowly developing for a year or two, but it's got to the point where the bike is basically unusable and untrustable.

The problem is that after a few miles riding, the bike doesn't seem to want to stay running at idle. I set the idle RPM at roughly 1,300. And this is good when the bike is 'cold'. The bike idles nicely with load such as indicators and lights initially. But as I say after a few miles unless I keep the RPM above 2k rpm, the bike wants to stall. It seems electrical as when it 'misses' (or attempts to stall) the charge light does light up briefly. If I rev the bike I can recover the attempted 'stall', and thus so long as I keep the rpm >2k at lights or stop signs I can keep the bike running. Whilst above 2k (ie riding the bike on normal roads) it seems happy enough.

I have ruled out the aftermarket electronic ignition by way of a friend's own electronic ignition, and equally I have then ruled that out by putting points on the bike. I had tried 2x used coils, and then a coil which I knew was okay, so in total three coils. I have swapped over the regulator and the rectifier from another bike that I know works. But after each change the result is the same.
I must also say that I have used a different rotor, and stator, and a few different sets of brushes/brush holders. Spark plugs too.

Thoughts on what to look at next? I think it's likely due to a charge/load problem (high battery draw), that seems to only be an issue when the bike is warm and at an RPM where the bike doesn't charge... So I suppose I should look at the generator wiring foremost- but is it also likely to be an earth problem? (or would that simply be a shot in the dark?). So as mentioned, the problem occurs with/without lights and with/without indicators. Any help pleeeeease

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[JawasandMZs]

Matt, I had this exact thing happen on my vfr750 about twenty years ago. It was simply the reg/rec getting too hot and relocation to the wind blast by cable-tying it the passenger footrest bracket immediately solved the problem.

You'd know better than me but could you junk the primitive OE separate reg and rec and install a used Japanese combined one?
Is the battery holding charge? Does any of the electrical components or wires feel hot after riding?
I'm assuming you've eliminated the HT lead.
Good luck.

[Blurredman]

Thanks guys for the suggestions but I think I can say I've safely ruled them out one way or the other.


One thing I have tried tonight though, through thankful help of a thread on this forum that I can't seem to find anymore, was to measure for any amp draw by putting the multimeter between the positive of the battery and the positive terminal on the fuse box and found about 50mA when the ignition was off.

Is this consequential?


I did a lot of investigation trying to remove/disconnect componants to see what was causing this draw but couldn't identify a specific area of concern.
But I did carry on, and clean contacts I had missed, including the main earth under the seat again, and also the contacts and wires associated with the coil.

The result was better, but I soon realised that if I pushed the bike in gear (and therefore turn the engine over) I found the ignition/charge light was varying between off, dim and on. I changed the rotor and it gave no difference, I then changed the brushes (after also changing the bike to the original stator) and with the different brushes then got an even better result. The bike idles for a while and the idle is more consistent and the charge light barely comes on at all. But on some occasions it still simply stops dead. Of course, I am doing all this testing simply in my garage on the stand.

Currently have my EI installed back on the bike (had tested the unit by putting points on to remove this possible fault location with no difference).



I still might swap the carburettor from my ETZ250, but I feel this is electrical- as for the most part what work I am doing seems to be getting better results each time. Now before this, after starting the bike the charge light would stay on and I would need to rev the bike to extinguish it, but now starting the bike I can see the light extinguish at about 800rpm which is much better.



But I keep thinking about this 50mA draw. I put the same battery on my etz250 and there is 0.01mA draw there. I have ruled out the fuse box, and the battery itself is fully charged after a few days charging.


I wonder where this draw is coming from and whether it is indeed a cause to my problems or not.

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[Blurredman]

I have found the pertinent thread I was after..


viewtopic.php?f=5&t=10777


Anyway, I did some more cleaning of contacts and double checking things- and then decided to try the ETZ250 again, but I realised I had the earth fuse out. Stupid me. I put one in and what do we get? 110mA draw.

Okay, so this doesn't seem to be the reason for my issues- as that bike was pretty grand electrically, at least the last time I used it.

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[Blurredman]

I also wonder how Les is doing..


You had zero draw at all? Interesting. Now draw with ignition off on a vehicle that doesn't have extra components installed such as clocks, alarms etc is something to look for- but I found it interesting that on the bike that I have no electrical problems, it draws double that with ignition off over the bike that does have electrical problems. Anyway, 50 or 110mA, it shouldn't negatively effect the way the bike runs when it is actually started.


I think, although should be a sorted item. I think it could be a red herring. Or could be a requirement for the persuit of cleaning connections. For what it's worth, I didn't actually answer your question- the voltage display on the 251 is powered by the 15 terminal (+) of the ignition coil so only turns on with ignition. That has also been disconnected without a change of draw.


It's interesting you note the 2.5µF capacitor that was later removed. I always assumed actually that it was in 1986 that the capacitor was removed, but maybe not. My brother's '85 ETZ250 has the capacitor, and my '87 ETZ250 does not. The difference is that the capacitor is required for the rectifier. Later bikes have 200v diodes apparently, and the earlier bikes have 100v diodes. The later 200v rectifier negates the requirement of the capacitor. There is some confusion there as it appears bikes of the '86-'88 period may or may not have the capacitor/100v rectifier. I suppose they may have been up until definitely 1988 been 'using up' old components at the factory.

Neither my ETZ250 nor my ETZ251 (the bike in question on this topic) have such a capacitor. I can confirm that both these bikes definitely have 200v rectifiers.

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[Blurredman]

It seems quite possibly that I've fixed this problem.

I changed the HT lead and cap from a spare that is currently not being used. This is the only item I have not changed, and immediately it seemed there was a difference.

I was able to get the bike idling at 1200-1300rpm for quite some time (perhaps about 10 minutes), and the charge light didn't come on at all even briefly in the test phase.


Later on tonight I did actually go for a ride and it was successful. There is a second thing to bear in mind though is that the battery I was using tonight is poorly. I knew this, and of course with it being dark and the lights being on the issue of wanting to stall did come up when the indicators were put on. I have another battery which is in better condition to try all this out tomorrow and hopefully fully put this issue to bed. So I think that this is a tertiary issue and not the cause of my problems for me to make this thread. Although at 12.58v after left in the garage with all lights off, the battery reduced to 12.38v within 10 minutes, and I have seen down to 12.15v in the past a day resting after using the bench charger. I will measure the poorly battery tomorrow @ 7pm, and that will be 24hours rest, and we shall see what the voltage is there.

I did some high RPM riding too (5k plus) without the bucking/misfire effect I had a couple of times of late, and all seemed well there too.

Another thing I noticed was that the charge light did not seem to kick in and stay on FULL after starting the bike. So what with that, and the charge light not even illuminating slightly at idle (unless it was sustained) for the 10 mile test, it seems that these were connected.

What I find interesting is the fact that the HT lead that was on the bike I installed not more than 2.5 years ago, and although the outer sheath was slightly compressed in places because of the way it was positioned and the vibration rubbing the lead against parts of the frame, it didn't on the face of it look like a worn, broken or kinked lead. This of course also leads me to the cap itself, which I installed only 2.5 years ago as well.


What would be a most definite resolution to my findings would be to put the HT lead/Cap onto a different bike, and see what happens there- but unfortunately I don't have another working vehicle I could easily test on, except my Trophy. My brother actually needs a new spark plug cap, so I am tempted to give him mine and see whether he has the same issues, unless that is I get my engine rebuild on the ETZ250 done first. I do actually intend to buy a length of new HT lead to implement on the Trophy so might try it on that bike before I put on the new HT lead.


Anyway, long story short- the only electrical item (or pair of, rather) I didn't replace seems like the cause of the issues- but still, I suppose it was good to get stuck into the bike's connections and clean and smarten things up in there. It wasn't until late in the day when I made the connection between the (rare admittedly) high RPM mis-fire and the idle misfire. My first thought was the electronic ignition but that seems like it is still holding up extremely well.

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[Blurredman]

I can confirm here that with a better bettery, the bike doesn't falter at all, even with full electrical load. But not just the fact that it can now idle (for as long as I want), but it doesn't mis-fire at high RPM, and what is more a cold engine 2-4k rpm pinking sensation has definitely disapeared too! Oddly enough the engine does feel like it has less low end torque though which is interesting, but that could just be me. Or indeed maybe not.


I measured the ht lead/cap with a multimeter and found no continuity. The cap is okay it seems so looks like a connection loss with the HT lead itself. Cutting the ends of the HT leads a bit to get fresh connection worked but ultimately, I actually installed 8mm lead instead of 7mm anyway so it was always a bit tougher to install. It was also carbon core (I only bought it for the colour). I'll replace with 7mm copper core.

Charging didn't effect ignition and nor did it seems ignition drain, they we avenues that were explored as possible reasons. Electricity does strange things when it isn't controlled properly. Like the HT lead- It's possible there were 2 breakages in the lead (at the HT coil fit and at the spark pluc cap fit). So it jumped between connections twice before even getting to the spark plug.


Anyway- it all seems fixed and I am very happy.

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[Blurredman]

Just a final update:

I can confirm now, that I have done some local miles and on Sunday did 110 miles for the local MZ club meet up, that this problem seems completely resolved.

Everything original to the bike when these problems started have been re-implemented namely the electronic ignition, stator, generator, coil, rectifier, regulator, spark plug. The only two things I need to do now, and in order to give the parts I borrowed back to my other bike or put back on the shelf, is to replace the HT lead with a standard copper core, and put back on the stator housing the original set of brushes(and holder). Then other than the HT lead the bike will be just as it was before.


I still have some small issues to sort out with the bike in general, but the problem of the stalling at idle, and the misfiring at high RPM has been solved.

[Chris W]

Congratulations BM on solving the issue. One related comment re carbon HT leads. The instructions for the Vape electronic ignition strongly state not to use carbon HT leads with their ignition - implication being it adds too much resistance (so weaker spark I guess).