Contact breaker backplate seized and some general ignition system questions

[Ade B]

I've used the bike over the last few weekends trying to keep it above 3000rpm on the road, and aside from a crappy idle when cold which settles down when warm, I noticed the 2700ish pinging noise seems very pronounced when cold and blipping the throttle through the revs, and it appears to be coming from the lower front cover area which suggests either:

A resonance related timing chain rattle - as mentioned above, a worn chain would tally with the maxed out retarded back plate setting. It did quieten down as the engine warmed up.

Or

The advance weights are catching on something as they move outwards, which seems unlikely as if this was the case the noise wouldn't disappear at 2800 rpm! To rule this out, once it cools down again, I could pull the front cover and see if it makes the same noise...

Or

Its pinging and just resonates at the engine case to the front..

Not managed to see the specialist chap yet due to reasons beyond my control.. hopefully get an update this week.

[Ade B]

Timing chain was very worn and loose and has now been replaced, I've not yet needed to adjust anything as the bike is running sweetly following an extensive engine refurb, so hopefully all fixed.

[Rob Frankham]

Plugs and a few other bits and bobs arrived today. Put them in after work and fired it up.

Started instantly and ran well. Pulls well through the rev range (at sensibleish suburban 2nd gear speeds to not upset the neighbourhood).

Checked timing with the strobe, idle is good and F mark is bang on at 3000ish.

Dropped the tickover speed when I got back. The choke cables need some tinkerage as they don't fully close the aux carbs, pushing them down with a screwdriver lowers tickover slightly and presumably further leans the mixture.

The weird pinging noise is still discernible at 2700ish rpm under acceleration in 2nd gear for a split second. It could also be a fairing resonance, hard to tell.

Will attempt to balance the throttles again at the weekend.

I've found a localish airhead specialist who I'm going to visit following a long phone call, will hopefully augment my ham-fisted attempts to get the thing running sweetly.

Pleased

Ade

Previous post...

Secondly, the Amazon special timing strobe would only work off the RHS plug lead and it didnt matter which way I clipped on to the LHS (there appears to be a polarity to the plug lead clip and it needs to go on the correct way), no flashing, even after swapping the leads over from the coils. The plug leads both measure the same resistance give or take which suggests there may be an issue with the LHS coil? Cranking the engine with the plug out and earthed produced a spark to the LHS..

This is interesting and possibly relevant. The strobe should work on either lead. The polarity of the two sparks is the same on airheads. Some wasted spark systems use a setup and coil where the spark goes down one plug lead, through the engine mass and back up the other lead... the coil used only has one secondary and has a lead connected to either end. The system used on the airhead, whether it has one twin or two single output coils, is not like this. their are two secondaries (one each on twin coils or two on the twin output coil) and this means that both sparks fire in the same direction.

Why is this relevant... if your strobe only fires with an impulse in one direction (ie. it's polarity sensitive... which I doubt), then it should either fire on both leads or neither. If it's not polarity sensitive then it should fire on both. The implication is that one lead (or coil output... or plug) is not producing sufficient impulse to trigger the strobe which may be an indication of a poor spark, even if there is a visible one.

Rob

[Ade B]

Thanks Rob

The bike is running very well at the moment post a comprehensive engine and drivetrain refurb by a specialist, but I suspect there are a few electrical anomalies lurking. On the list! There is water in the instrument binnacle and replacing a blown fuse for the tail light and instrument lights has upset the voltmeter below 3000 rpm. A bunch of varying electrical connectors are incoming.

[Rob Frankham]

Just to pick up on what you're saying... again... I can't be sure quite what you mean by 'upset the voltmeter below 3000rpm' but...

The norm for the voltmeter is that it reads around 12 -12.5 volts with the engine off (no lights). Drops sharply as the bike is started then recovers rising to around 14 volts at 3000 rpm. If the revs drop below this, the voltmeter reading will drop gradually (and, if the bike is left to idle for too long it will eventually drop to a point where the engine will stop). If your voltmeter is displaying behaviour that varies greatly from that, then it's probably not the meter but the charge circuit having issues.

The only way replacing a bulb should have any effect on the voltage reading is by putting an extra load on the charge circuit which should be minimal for a 5 Watt filament (might be worth checking the bulb you have in there and that it's wired right).

Rob

[Ade B]

The voltmeter reads a constant 14ish V when above 3000rpm. Below that it veers all over the place, particularly if I hit a bump. It's intermittent which makes me suspect the wiring connection or water in the instrument housing.

I replaced a fuse not the bulb. To access the headlight bucket I partially dismantled the S fairing and put some strain on the cables so I suspect that didn't help.

I now think I can access the bucket without moving the fairing as I now know I can get to the screw at the base with it in situ.. I'll have a poke about, check bulb ratings and connections at the weekend.

edit: had a quick look just now and a small bulb holder and blown bulb appeared from behind the fairing dash.. prodding this appears to affect the stability of the voltmeter reading so I may have discovered a possible culprit.

Its a bulb format I've never seen, assume equivalent spares are still available...

[Rob Frankham]

Is it the illumination bulb for the voltmeter? in which case, it should be BA7 12v 2W bulb. Visibly smaller than the more ususual BA9 bulbs (e.g. the airhead sidelight bulb and the base has elongated protrusions rather than pins. Readily available from auto electrical shops or on line (e.g. https://www.vehiclewiringproducts.co.uk ... panel-bulb). Might even get one at Halfords if you're lucky.

You can also get a LED versions (e.g.https://www.ebay.co.uk/itm/355739154477?) but they may be too bright... Also make sure the light part isn't wider than the base or it probably won't fit into the voltmeter...

Oh BTW, I meant 'replacing the fuse' rather than 'replacing the bulb'. Stupid error...

Rob

[Ade B]

Yep, motorworks also has them.

Thanks