Timing Descrepencies

When I was getting my Commando set up for first start I set the ignition timing at 31 degs as per the Boyer instructions using the static setup by aligning the dot in the window at 31 deg.
Today I thought I would check it with the strobe just to see how close it was and if it needed adjusting. I wasn't too worried because it had been running fine and starts easily, but when I checked it with the strobe I was getting 39 degs at 2500 when according to the NOC of N.S.W. I should be getting a reading of 20 deg.
http://www.nocnsw.org.au/igntntmng.html
Something is obviously not right here but I'm not sure what it is. Anyone with any idea?
The Boyer is not new, it came with the bike.

Mark F said:

When I was getting my Commando set up for first start I set the ignition timing at 31 degs as per the Boyer instructions using the static setup by aligning the dot in the window at 31 deg.
Today I thought I would check it with the strobe just to see how close it was and if it needed adjusting. I wasn't too worried because it had been running fine and starts easily,

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The static setup (dot in window) position can easily be 10 - 15 degrees off and is only intended to get the timing close enough so the engine can be started, that's why it is important to do a final check (@ 5000 RPM) with a strobe.

Mark F said:

but when I checked it with the strobe I was getting 39 degs at 2500 when according to the NOC of N.S.W. I should be getting a reading of 20 deg.
http://www.nocnsw.org.au/igntntmng.html

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The advance curve can vary from one Boyer ignition to another, therefore it's unwise to rely on the RPM/advance data from another Boyer box.

http://atlanticgreen.com/boyerevolved.htm


[Edit] If you have a degree disc, then it's also good idea to also check the accuracy of the original timing marks - as they can be out by a few degrees.

It sounds like I had better get the timing disk out and check the marks. It seems hard to believe it could be so far out and still start o.k.
I am a bit wary about reving it to 5000 on a fresh rebore to check the timing, that was why I used the lower figure.

Sounds like if it's running correctly with full power and not burning your exhaust pipes or rattling on increasing revs, that your alternator mark might be off as others have stated can be the case.

If someones fitted a Triumph unit , it would be ' going the wong way ' ,pulling back as rpms rise .Wether thru ignorance or
inaneity .You could set the carbs fully open and have the throttle set up to close them to match . :lol: :shock: :?

Mark F said:

I am a bit wary about reving it to 5000 on a fresh rebore to check the timing, that was why I used the lower figure.

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For what it's worth, the above-statement always worried me too. Can't imagine revving to 5000 RPM in the garage for who knows how long to set Boyer timing. One of the reasons I went with the Pazon Surefire...static timing was practically dead on and final timing with strobe took mere minutes whilst revving to 3000 RPM only. Just MHO.

Matt Spencer said:

If someones fitted a Triumph unit , it would be ' going the wong way ' ,pulling back as rpms rise .

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No, it wouldn't, the difference between setting up Triumph or BSA/Norton Boyer ignition is the magnet/paint dot is set to the clockwise backplate rotation window for a Triumph.

cmessenk said:

Can't imagine revving to 5000 RPM in the garage for who knows how long to set Boyer timing.

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Two or three seconds is enough.

All you need to do is blip the throttle briefly and have an assistance watch the timing market with a strobe light

to see if it reads approx 31 or so, as 5000rpm is fully advanced with the boyer

That should cause no ill effect to your new bore as it won't get prolonged hot enough

L.A.B. said:

Matt Spencer said:

Two or three seconds is enough.

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Yes, I agree LAB...if everything was perfect on that check. But then you stop, rotate the plate, start the bike and up to 5000 again....strobe...and most likely stop / start again....up the RPMs again before you're satisfied....or just plain lucky.

cmessenk said:

L.A.B. said:

Matt Spencer said:

Two or three seconds is enough.

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Yes, I agree LAB...if everything was perfect on that check. But then you stop, rotate the plate, start the bike and up to 5000 again....strobe...and most likely stop / start again....up the RPMs again before you're satisfied....or just plain lucky.

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There's no need to stop the engine.

1.Rev up to 5000 RPM and check that the moving timing mark reaches but does not exceed 31 degrees.
2. If that is not the case, re-adjust the backplate in the appropriate direction and recheck.
3. Repeat the above procedure until it is correct.

The whole procedure should not take more than a couple of minutes even when working alone, with the engine only revved briefly to 5000 RPM for a few seconds each time a check is made.

[Edit]If a thick rubber mat is placed under the main stand then the bike will not start jumping around at high RPM.

What a bunch of pussywilows.
My Down and dirty best way is just creep up on timing till hints of or back fires then creep back retard till it just don't, then light it and see where it lands and index wheel to see what the mark actually means degree wise.

There is no better time than initial start up to rev to over 5000 for some instants just to see where the Boyer adv stops at which should level off at 4900-5100 rpm.
It you engine can't take in in stride while fast sealing the rings then its better to break in in shop early on that later down the road. There is lot of heat soak mass in a Commando engine and then only really heating when must throttle given under load so don't feel guilty to let the oil films vaporize off. A fan is needed for a dyno power run but not just setting and checking timing over some minutes. Do put thick pad under center stand of course. On second though I've yet to see a video of the Commando center stand dance, hm, could you be the first? Of course each instance of this accumulates toward center stand bend or fracture.

If you can't get Boyer to time back down and still start easy then suspect bad juju in time chain or cam lobes or both. Always check bat volts before bad Boyer thoughts.

pussywilows?????????

Dog

Ok pussies to worry about merely 5000 rpm unloaded, seeze, toughen up and get er done. There's heat sink aplenty and more than sufficient oil wedge separation at 5000 where the real danger lurk idling on barely nothing. If you look at Boyer curve you can pick an rpm you are comfy with and see if lands close but to know for sure Zrrrooommmmm, Zrrroooooom, then just to make sure through the blurr and noise Zrrrrroooommmmmmm again.

ludwig said:

It is perfectly ok to time it at 3000 rpm and set it at 28-30 deg , depending on compression ratio .

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But, at 3000 RPM, a Boyer ignition would still be several degrees away from fully advanced (9-10 degrees away according to the Dynodave graph and 8 degrees according to the NSW figures).
http://atlanticgreen.com/boyerexposed.htm

(Distributor degrees/RPM x2)


http://www.nocnsw.org.au/igntntmng.html

Engine Revolutions Boyer Advance
1,000 6.3 degrees (6)*
1,500 11.4 degrees (11 or 12)
1,800 14.7 degrees (15)
2,000 16.3 degrees (16)
2,500 19.6 degrees (20)
3,000 22.8 degrees (23)
3,500 26.1 degrees (26)
4,000 27.7 degrees (28)
4,200 29.4 degrees (29 or 30)
4,500 30.0 degrees (30)
5,000 31.0 degrees (31)

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ludwig said:

The reason we need igniton advance is that combustion speed , in a given engine , is fairly constant (yes , I know there are variables ..) , and we want max combustion pressure to fall just after TDC .
So with increasing engine speed , combustion must start earlier .

It is only logical that with increasing rpm , ignition timing advances even more .

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As I understand it with increased revs there is nothing to be gained by continuing to increase the amount of ignition advance past a certain limit.

ludwig said:

So I see no reason why not to set the ignition , Boyer or other , at 28°/3000 rpm .
The problem with analog Boyers is not that they continiue advancing beyond 3000 , or even beyond 5000 rpm , but that the advance curve is too flat .
If you set them at 31°/5000 , they will show 25°/3000 ( not enough) and 10-15 at 600 rpm ( too much) .
Ideally , at starting rpm , ignition advance should be zero , or even ATDC , while with a boyer it can be anything between 8 and 15 deg . BTDC.
I bench tested several analog Boyers myself ( 1 mk1 and 3 mk3 ) and did not find the same discrepancies as DD . They all had pretty much the same curve .

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So, if one was to set a Boyer to "28°at 3000 RPM" then it will be correct (according to you) at that RPM figure but will be over-advanced beyond that figure and (again according to you ) will be over-avanced below that figure.

I think I would still prefer to set it according to the Boyer instructions.

ludwig said:

L.A.B. said:

So, if one was to set a Boyer to "28°at 3000 RPM" then it...will be over-advanced beyond that figure..

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No

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According to what test results?

ludwig said:

L.A.B. said:

..I think I would still prefer to set it according to the Boyer instructions.

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fair enough .
personally , I would toss it in the bin ..

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Boyers are fine...as long as you set then up correctly.

ludwig said:

L.A.B. said:

..As I understand it with increased revs there is nothing to be gained by continuing to increase the amount of ignition advance past a certain limit..

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According to what test results ?

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I thought you wouldn't have an answer.

http://www.eng-tips.com/viewthread.cfm?qid=193560

Interesting comments on the advance curves - but I have one factor that is more related to actual sensation of ignition performance with different grades of fuel. (OK I know there is bunch of scientific and anecodatal opinion on this) - but with low RON fuel, it burns faster and the feedback on my Mk2 850 (Mikuni VM34 + Boyer) is a rougher engine performance, as if it needs a more retarded setting. Switch to premium 98 RON and its a different sensation, because the fuel burn is slower and I guess it suits the 31 degree advance curve. A mate with a 750 Combat notices this efffect much more, and sure the hi-comp makes this worse on low RON.
Remember that back in the 60's we had real petrol and the engine designers used those combustion factors.

Mick

Yep the lower octane you can get away with the more efficient the burn and power delivery. PowerArc told me their 3 ajustable spark per stroke allowed hi CR Harley to make more power on cheap regular than best hi test around but couldn't even run w/o detonation on the other ignition systems on best hi test. Amazing if truth and put my money down to find out someday.

hobot said:

Yep the lower octane you can get away with the more efficient the burn and power delivery. PowerArc told me their 3 ajustable spark per stroke allowed hi CR Harley to make more power on cheap regular than best hi test around but couldn't even run w/o detonation on the other ignition systems on best hi test. Amazing if truth and put my money down to find out someday.

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For what it's worth, back when we had leaded premium, I used to have a Honda CB550K with Pops Yoshimura 590 kit, Megacycle cam, S&W springs, carbs from a 750, Martek electronic ignition, and it WOULD NOT RUN WORTH A DARN on any spark plug except ND W24ES "U" groove plugs. Those plugs made it run PERFECTLY; it could pretty much keep up with my '79 KZ1000 up to about 100 MPH, then the KZ started drawing away. In the twisties, I'd catch back up and be right with it.

So, spark plugs can, and often do, make a difference in engine performance; ALL ELSE BEING EQUAL.