Contact breaker backplate seized and some general ignition system questions

[Ade B]

Evening from the UK. Bike is an October 1977 100RS on the original points ignition.

I'm trying to dial out some hesitancy between 2000 - 2500 rpm and also some suspected pinging/pinking at 2750rpm under load. The pinging passes quickly and the bike pulls strongly from 2900rpm to 7000+.

I've refurbished the Bing carbs, with new jets, needles, diaphragms and o-rings according to spec and set the idle and mixture. I've had one attempt at balancing the throttles but couldn't get them as close as I'd like according to my recently acquired carbtune pro.

So I've started a more rigorous (for very non-engineering me) round 2.

Have checked resistance in the coils with the battery disconnected. (LH primary gives 1.5, RH primary 1.6, LH secondary 6.51k, RH secondary 6.72) the coils look like they could be original.. These numbers don't appear to align with anything I can find online - any thoughts? (The resistance of the multi meter is showing 0.1 ohms..)

I've new plugs fitted (Bosch WR5DC) which on inspection after the last 150mile run look ok.

So...

My next target is to check the timing again. I've a strobe lamp arriving later today and am in I'm in the process of installing new contact breakers, having pulled the existing (Norris) breakers off.



On attempting to move the static timing, the backplate appears to be seized in position.. Is it as simple as at squirt with wd40 and then free it up with some gentle persuasion. I'm loathe to apply force without understanding that this should work? Is it simply a case of gently working away at the plate to free it up?

Thanks in advance

Ade

[Ade B]

Appear to have answered by own question - hopefully no damage done.



Looks like the felt pad could do with replacing..



I've cleaned this up.

Should there be any sort of lubricant behind the backplate? Appreciate once set it shouldn't move. I'm going to try to get a replacement seal for the enclosure as well as it looks like the current one is past its best.

Would be grateful for feedback, this is all a bit of learning curve

Ade

[gspd]

You sound like you're headed in the right direction in the points plate department.
Should there be any sort of lubricant behind the backplate?
A cleanup and a squirt of WD-40 should do. It only seized up because the (crapped out) seal around it let water in.

WR5DC are resistor plugs. They shouldn't be used with stock (resistor) wires.

[Ade B]

Thanks GSPD, appreciate the reply, I had clocked yesterday in my online research that the plugs were resistor plugs.

Another thing on the order list... NGK BP7ES appear to be compatible.

Interesting note on the parts vendor site which suggests that the WR5DC were OE on the R100RS hence the purchase..

I'll put the Denso W22EP - U back in for the current round of fettling, they appear to be non resistor plugs and an equivalent to the NGK BP7ES..

[barryh]

Have checked resistance in the coils with the battery disconnected. (LH primary gives 1.5, RH primary 1.6, LH secondary 6.51k, RH secondary 6.72) the coils look like they could be original.. These numbers don't appear to align with anything I can find online - any thoughts? (The resistance of the multi meter is showing 0.1 ohms..)

Thanks in advance

Ade

Those resistance figures are OK. The original Bosch coils were nearer 1.2 ohms than 1.5 ohms but resistance values that low are notoriously difficult to measure accurately as you already acknowledge by mentioning the 0.1 ohms.

[Ade B]

Thanks Barry

The multi meter was actually showing 0.4 ohms - my brain struggles to retain information for more than seconds

In other news, having rewatched another youTube video, with the benefit of using the various bumps and nicks in the back plate and points plate I managed to relatively easily set the points gap and faffed around with the timing.

A couple of observations:

• Firstly following first setting the static timing, the advanced timing (F mark) was absolutely miles off even with the back plate rotated for maximum retard. After backing everything off, moving the backing plate to maximum advance, resetting the points gap slightly narrower than the baggy 0.4mm I was using to try to achieve some more clockwise rotation, with the back plate then rotated fully clockwise to get the max retardation I get an accurate static timing setting but the F mark appears at around 2750 rpm and the advance weights still have a little further distance to go, reaching full extension at around 3000 rpm as I believe they should

Does this suggest wear elsewhere in the system (75k miles on the clock) or am I missing something?

• 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..

Irritatingly I appear to have stripped the thread to the gearbox breather bolt despite what I thought was babying it.. It just about holds the earth strap lug, which I cut into a 'C' to allegedly prevent too much bolt undoing.. I fear nipping it up further and may look at loctiting it in place and just disconnecting from the battery terminal in future..

I'm going to take it for a run and see how it goes as priority #1 is to deal with pinging, fingers crossed. I think I'll hold off round 2 of throttle balancing until I get the new plugs.

My wrenching skills need to step up somewhat before I attempt the larger list of projects I have

[Ade B]

And back from short ride out.

Its behaving like it did before I increased the points gap and changed the plugs. ie. rough and no power although it will idle and run through the rev range.

And it is still making a noise I can only describe as marbles in a tray rattling as it passes through 2700 rpm under load... is this pinging?

Will revisit once new plugs arrive... two days of intermittent faffing and it is worse than when I started

[gspd]

• Firstly following first setting the static timing, the advanced timing (F mark) was absolutely miles off even with the back plate rotated for maximum retard. After backing everything off, moving the backing plate to maximum advance, resetting the points gap slightly narrower than the baggy 0.4mm I was using to try to achieve some more clockwise rotation, with the back plate then rotated fully clockwise to get the max retardation I get an accurate static timing setting but the F mark appears at around 2750 rpm and the advance weights still have a little further distance to go, reaching full extension at around 3000 rpm as I believe they should

Does this suggest wear elsewhere in the system (75k miles on the clock) or am I missing something?

When everything is new and the points are properly adjusted, the plate should be more or less in the center of its rotational range.
You probably need a timing chain and sprockets if you are near the extremes of the plate's travel.
Replacing the springs on the advance mechanism won't hurt (if not already done).

As far as the noise in concerned, I won't even venture an opinion without a test ride.
"under load" is too subjective a term.
Under load at 2750 rpm is definitely not a great idea, especially in the higher gears.
Keep the revs up. See if that helps.

For now, get a slightly longer bolt and secure your ground cable to the transmission case bolt right beside the one that's stripped.
Next time the trans is out, helicoil the stripped thread.

[Ade B]

Thanks GSPD, springs already replaced. I think I'm bumping up against the limits of an old and tired bike, it was very shiny in the advert (and still is)

By under load I just mean bigger throttle openings accelerating hard through the gears as opposed to gradually pulling higher rpm. I've yet to fully pin the throttle to the stop or hit the red line out of respect for its age, and brakes..

Back at work next week and out on my unpowered bike with a friend for tomorrow's bank holiday so will pick things up next weekend after the new plugs arrive and we've picked the kids up from grandparents. I've been looking up electronic ignition but feel like if there are underlying issues with the oily bits, they're not going to go away on their own..

Just need to try to stop it snowballing too rapidly...

Cheers

Ade

[Ade B]

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