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Too retarded? I'm talking about my bike, not me.

Hi Everyone. Any views on this, please?

Just pulled the WM20 out of the garage after a couple of months unused. Fitted Ian's new battery box. Looks good. Old box (hard rubber) had split in various places. Lost a very small amount of oil (wet sump) when starting.

However, managed to start the bike only when fully advanced.

Nothing's been altered since I last rode it. Except a spark plug. I haven't touched the points in a long, long time. That might be significant.

The last mechanical fault I had was a burnt exhaust valve. Seemed a bit odd because there's just 4,000 miles on this engine, which was fully rebuilt. I have noticed that the bike never was very sensitive to the advance/retard (which I thought was fairly normal for an M20). I have also noticed that the mpg has never been higher than around 40mpg (some people tell me this is too low).

I'm now wondering if I've been living with an overly retarded ignition for a long time leading to a low top end speed (45-50mph), and a burnt exhaust valve.

So, does anyone else have an M20 that starts fairly easily on full advance? Or does it sound like my suspicions are correct? Any views welcome.

email (option): dannydefazio@sumpmagazine.com

Re: Too retarded? I'm talking about my bike, not me.

Danny it's quite simple to check your timing through the 1/4" timing bolt on the head. Use a drinking straw or stout piece of wire and mark it adjacent to the top of the hole when the piston is at TDC. Now put another mark 7/16" further up your gauge.
Pull your handlebar lever to full advance and turn the engine in the forward direction until the top mark on your gauge is at the top of the hole on compression stroke. This will be easy to determine on a running bike as the points will be around the 10 o'clock position. With the gauge at this position the points should just begin to break. I use a 1.5 thou feeler gauge,(some use a fag paper). If your points are well open, then you are too far retarded. Which will cause your bike to run hot and as flat as a witches tit!

Ron

email (option): ronpier@talk21.com

Re: Too retarded? I'm talking about my bike, not me.

The MO1 magneto does give its best spark at full advance so it might simply be that the spark is a bit weak. With a confident swing after compression, it should start OK when advanced...but your other symptoms do suggest that it might be retarded.

Can you get the motor to 'pink' ?

Re: Too retarded? I'm talking about my bike, not me.

Hi Ron, Hi Rik

Ron: I did check the timing with a straw (or something similar). But it was long ago. I might have done a poor job of checking, but I had always thought it was okay. I'll check it again tomorrow. But should you be able to easily start an M20 on full advance? That's my real question (I see that Rik has suggested that you can start it perhaps with a heavy swing through, but it seems to start fairly easily on full advance).

Rik: I can't remember the M20 pinking. My Triumph does occasionally, but the Triumph has a higher compression. Pinking, as far as I can remember is a symptom of an over-advanced ignition (or poor fuel, or both), which I think is what you're getting at. The M20 seems happy generally, but I have had the other issues (poor mpg, low top end, burnt exhaust valve). I can repeat the check that Ron suggested, but I was wondering what other indicators might be present.

I'm tempted to sort it out by trial and error. On my T140, I've never checked the timing except by trial and error, and feel. That's 20 or 30 years of riding them. But the M20 clearly burned an exhaust valve, and I don't want a repeat of that. Or worse. The bike doesn't seem to run that hot, note. But "hot" is, of course, a relative term.

Any other suggestion welcome. Thanks to you both for replying.

email (option): dannydefazio@sumpmagazine.com

Re: Too retarded? I'm talking about my bike, not me.

Danny, I usually find with a correctly timed bike, that the engine will want to kick back on full advance, necessitating the need to retard it for start up. But with poor compression, a good swing will get the engine spinning fast enough to overcome this......Or a weak spark as Rik suggested. Also the points gap can alter the timing somewhat!

Ron

email (option): ronpier@talk21.com

Re: Too retarded? I'm talking about my bike, not me.

It is not unusual for the points gap to gradually close down or open up during use. Both conditions will affect the timing...

So, the first thing to do is check that...Clean the points and reset if required to .012" when fully open...

Then check the ignition timing itself...If you have a solid copper head gasket (which every self respecting M20 owner should have.. ) remove the head to do this...it doesn't take much effort and is a far more accurate method...

Turn the engine over until the piston is at 7/16" before TDC on the compression stroke (with the handlebar adv/rtd lever in the full advance position...)
Then check the points...they should just be breaking...

The short lifespan of your exhaust valve could be down to more than one factor but in combination with your lack of top end performance, the possibility of a retarded ignition setting would be the first thing I would look into...Ian

email (option): ian@wright52.plus.com

Re: Too retarded? I'm talking about my bike, not me.

Thanks Ron and Ian. I'll have to get some bloody spanners out now. I was hoping that you guys could just yell at my bike or something and sort it out.

I get no kick back on starting. And no pinking or hissing, etc. So it's not showing any problems of advanced ignition.

The early death exhaust valve, poor mpg, low top end and starting on full advance are the obvious clues to retardation, so it's back to first principles, and all that.

I gather that no one thinks too much of my suck-it-and-see idea?



email (option): dannydefazio@sumpmagazine.com

Re: Too retarded? I'm talking about my bike, not me.

Come on Danny...I'm an engineer and consequently obsessed with accuracy when doing a job....

'Near enough's not good enough' 'Measure twice, cut once' 'Do it right, do it once' etc. etc... ..

It's always worth going the 'extra mile' to get it right....Ian

email (option): ian@wright52.plus.com

Re: Too retarded? I'm talking about my bike, not me.

Ian, I play guitar. You can tune a guitar perfectly with a tuner, and then play it, and it sometimes sounds bloody awful.

But you can tune it by feel, and although the tuner says it's wrong, it sounds right.

If you ever take up the guitar, throw the tuner away and give me a call. It'll sound a whole lot better...


email (option): dannydefazio@sumpmagazine.com

Re: Too retarded? I'm talking about my bike, not me.

Hi Danny...Maybe...There is an argument that the 7/16" BTDC fully advanced timing figure may no longer be the optimum taking into account changes to modern fuels...

However, I would have to test the power output on a dyno with various different ignition settings to achieve an accurate answer to that question one way or the other...

So, I'm not quite ready to start guessing my ignition settings yet....

Get the tuning wrong on your guitar and you get an odd sound...get it wrong on your M20 and you may have more serious consequences... ...Ian

email (option): ian@wright52.plus.com

Re: Update; Plus a note to Ian

UPDATE: Just checked the points. The gap was closed down to around 9 thou. Reset it to 12 thou (give or take an inch). Checked the timing too as best I could. Seems okay to me. Starts okay, but not on full retard. Needs to be advanced by maybe a quarter to a half, which I think is about right (not Ian Wright's right, but my right. Right?).

email (option): dannydefazio@sumpmagazine.com

Re: Update; Plus a note to Ian

.... ....Ian

email (option): ian@wright52.plus.com

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