Bike idles progressively higher in Neutral

[Blurredman]

Hi guys,

I've had this issue for a long time now but I still can't get it to stop doing it! It's pretty annoying!


The bike idles well and strongly settling at a constant 1,300rpm on the dot and that's great for me, but I like to select Neutral for the long traffic lights. And this has been fine for the first 6 months, but in the past few months the following issue is happening more readily.

But I cannot because when I do the idle increases 200rpm fairly immediately and then will slowly rise up to 1700 where it will then get carried away with itself and seem quite uncontrollable.


If I put the bike back in gear (to stop seeming unprofessional to the other car drivers), it goes back down to 1300 and will sit there happily.

There isn't any real clutch drag to say of. The bike doesn't move without the brakes off, but obviously disengaging it and not being in gear reduces the load on the engine and that combined with a slightly high(?) idle may be what is making it run away with itself..


Could be a tiny air leak somewhere?? Everything is nicely tight and other than that the carburettor is great. I'm really happy with this model revision (30n3) - It's my favourite! I am tempted to turn in the air bypass screw by half a turn and just see what happens.

[Blurredman]

Hi guys, so i've been experimenting with what I said above and here are the results.


Now when I got the bike and the carburettor cleaned out I purposely had the needle on a notch higher to make it run richer, and as time has passed and the various fuel channels in the carburettor has cleared through over time (It used to be a real chore to ride this bike) it is now a very flexible machine!

Anyway. I put the needle in the middle position, and it hasn't really changed an awful lot in the machine riding to be honest, it's not as torquey (obviously) but it is more crisp and less engine judder. The spark plug is now a nicer shade of brown than the black that it used to have.

Part of this experiment was to also find out why the bike 'stumbles' when I am at traffic lights. Now, even though the idle is about the same, the voltage being produced is actually higher, sometimes by up to a whole volt! Interesting huh?

But I have today finally realised (duh!) that this stutter that occurs is only when I have my indicators running.And I'm not really sure but I don't think I remember it occuring with the right hand side indicators, which makes me think the connections may not be the best and could prove a high electrical load for the engine.

I have had this once on my Honda CX500 where I once broke the indicator dropping it, and the connection was poor (the bulb was also broken), and even though it seemed a strange reason why- it was the cause for why the bike would not rev above a certain RPM. I concluded that the electrical load obviously effected the whole electrical system, and this also is what I remember when thinking about my MZ problem.

Nevertheless, with this needle adjustment, I'm looking forward to the smoother idle, an idle that does not creep up, and a crisper ride, and not to mention the higher (although neglegibly so!) fuel economy

[Blurredman]

Just an update.

Increased the idle to 3.75 turns from in to accomodate the needle being in the correct position now. So the idle should be a bit lower now. I also checked the spark plug which was a nice brown colour after this extended use after changing the needle position, instead of black.


Also.. something strange.. The indicator problem (bike stumbling at idle when indicators are running) has occured when the indicators were not running.. Therefore I could have bigger problems than simply a bad bulb connection for indicators. To put it simply.. The bike mis-fires but only at idle. When I am in neutral instead of first (with the clutch in), the idle is naturally about 200rpm higher and the mis-fire does not occur. The Voltage of the bike can be anywere between 11.5 and 12v when in gear and 13-13.5v in neutral which all seems fine and correct. I do not ride with my lights on.


I have had the electronic ignition on the bike for I believe 1.5-2k miles now and I don't believe I should doubt the ignition. I will however go progressively slower in my diagnoses. After checking/cleaning indicator connections, I will swap the spark plug with another.

[Blurredman]

Okay guys..

Interesting how no one has responded. However..


The problem is solved.. The other day, the problem was noticably progressively worse to the point I couldn't use indicators at all, and for the first time in months I found myself having to use the headlamp. The bike ran fine at a speed but it would misfire and eventually stall at idle. And once, it stalled outright and wouldn't easily re-start.

Saturday I went for to renew it's MOT, and it stalled out completely again! The first thing, and only thing I could really do at that point was to change the spark plug for one I had spare- which was one thing I was going to do anyway to diagnose the problem.

This has completely fixed the issue. The bike now idles at 1300, with headlamp on indicators running too! I am very pleased this has been resolved.

[MotoMZ]

Glad you solved it.

[DAVID THOMPSON]

old BMW bikes i have had always seemed to have a carb problem

till i tried using a 12volt battery and coil in place of the magneto using the points from the mag

it ran great
so its owner put a 6v coil and battery on it in place of the mag
several years later he did the powerdyno system ////problem solved

http://www.powerdynamo.biz/eng/systems/ ... erview.php

dave

the old mag was good in its day but is a real pain to make work correct when it very old