Atlas automatic advance

Hi , I was struggling with my freshly rebuilt Atlas which do not start (though she did at the very first attempt, but then after no way!!) ........after long fettling with float height , I had a look to the mag timing , and though I had timed it with a degree wheel at 31°, I had just checked it right now , just with a poke , and it looks way out , could it be possible the AAU had slipped on the taper??????

Not unless you/someone timed it wrong in the first place.
Did you jam the A/R wide open on full advance when you timed it at 31 BTDC :?:

And check it again before fitting the timing cover and removing the nut/whatever you used to jam the A/R open :?:

If theyre not the originally matched items , the taper might be a gnats dick out .

You usually check the mateing with a bit of lapping paste or blue , either way .

Any ridgeing radially could be a bother , youd stone it smooth . So Yes , may notve seated ,
Pays to check the retainer threads clear & free also . Really want to lock the Mag. Sprocket rather than
attempting to strech ( a part of ) the chain . SO , the nut shouldnt bind , should wind on past fitted psition unimpeded .

Also the Rear Face of the Nut , & face of sprocket should be free of burrs & distortion . Lap again if in doubt .

Hi, what amazed me is that it starts ,the first time, then I have to check the carbies to tune them , mainly the float height (they were flooding at the beginning, then the height was too low , then I went between and it seems OK, but it never start again, since the first time ,very frustrating........!)so few hours ago I checked the timing (roughly with a spoke , but 8.7mm BTDC fully advanced!) and it look far away , unless I was too tired or too old ..........that why I imagine it could have slip!

my nearly finished Seeley MK2 , and down under the finished Atlas...........!

Very nice.

The timing can possibly slip, just to reinforce the discussions above.
And it does sound like it has slipped.

Sometimes it is necessary to use grinding paste on the taper between the aau and the magneto shaft,
so they have a clean surface to grip together.

Best to use a degree wheel to set timing....spoke in hole is too crude. There is a degree wheel that can be downloaded on this forum. Wedge a piece of wood or rubber tubing into the AAU to fully advance the unit. AAU springs should be new or known to be of proper tension. AAU should return to retard position without any sticking or hesitation before wedging.

Remove both plugs.. Look in left cylinder plug hole as you rotate engine in a forward direction with a wrench on the cam sprocket nut. When the left cyl intake valve comes into view, then disappears, the left cyl is coming up on compression stroke. Now use a spoke in left cyl and rock engine to sense when left cyl is at TDC. Now align degree wheel at zero with a pointer fabricated from stiff wire and attached to one of the stator mount studs.

Now remove magneto contact breaker center screw. Attach one lead of a volt-ohm-meter to the lug that secures the contact breaker spring. Find another point on the contact breaker that registers continuity when the points are closed, and open circuit when the points break, and attach the other VOM lead to this point.

Now rotate the engine backwards about 50 degrees, then slowly forward until the VOM registers point opening. Repeat several times to get an average reading.

Now rotate engine forwards 360 degrees and repeat the above procedure to get a reading when the right cyl registers point opening. The readings on both cylinders should be within 2 degrees....if not the cam ring will need centering..

Assuming both cylinders are registering points opening within 2 degrees, now re-set the AAU on the magneto shaft so the points open at 32 degree BTDC (factory spec for Atlas advance...you may want to set this to 30 degree or even 28 if you have high compression pistons), Check both cylinders to ensure both cyls fire within 2 degree of each other.

Replace center screw on contact block, remove wedge on AAU. Timing should now be proper and engine should fire up.

If cam ring is off center, reply for procedure to bring cam ring into center.

Slick

marinatlas said:

Hi, what amazed me is that it starts ,the first time, then I have to check the carbies to tune them , mainly the float height (they were flooding at the beginning, then the height was too low , then I went between and it seems OK, but it never start again, since the first time ,very frustrating........!)so few hours ago I checked the timing (roughly with a spoke , but 8.7mm BTDC fully advanced!) and it look far away , unless I was too tired or too old ..........that why I imagine it could have slip!

Click to expand...

Re;"but it never start again, since the first time ,very frustrating........!)"
Are you 100% sure that the pilot jet holes in the carbs & jet are not blocked in any way :?:

Hi Bernahrd, so some feedback:
yes the timing was way out , but it was not at the start .....why? after a full Sunday afternoon, I had found the cam ring was loose in the body , and when I took of the ally cover it protudes (just my guess!) and then get out the from that pion which locate it , thus the cam ring was out its place .........! cannot find another reason, so I refit it in the right place , retime the mag at 30° (commando piston), with the degree wheel, and was sure it will start ..........no way!
so today, I play again with the .04mm drill , and carb cleaner , I had tried different float heights , first above the bow level as recommended by Bushman one carb was flooding , then just at the same level , but now the tickler are too short.........end of the session for today !

Are you sure there is spark? Remove a plug, have someone hold it against the head while you kick it over. There should be an audible "snap" as well as a blue arc.

Has the magneto been rebuilt? A bad capacitor can kill the magneto.

More feedback please.

Slick

Hi Slick,
you should have something to do with synchronicity, as I am just back from the shed , and the Atlas starts ........YES!!!

so feedback now, it was (or should be ) a mix of several causes, as said before , I ha played with carbies and mag , to finally , retimed properly at 30° with degrre wheel, (the mag was freshly rebuilt from UK, but I know it could be not well done?), then redone the float height at just the same level with the top of trhe bowl, AND put a nail into the tickler, to improve tickling (which was poor, mainly when I played with float height!), then put the drill (0.04mm or 0.076") in pilot jet (done it maybe ten times ) blow air every where I can , carb cleaner , another set of new plugs (N7 Y)........what else
.....first kick , VROAAAM....now I have a fag (doctor won't be happy, but me I am!)
Thanx everybody for your support, it helps.........