won't idle low=too much timing?

[greg brillus]

Without stating the obvious, when setting the timing....did you actually lock the ATD on full advance first, that is hard around clockwise, or else you may be starting and trying to idle on full advance, and then the engine advances more...to which I suspect the engine would detonate badly if you try to ride it.....60 to 70 degrees.....a tad too much. Only reason I ask is because it was not included in your original question.......Cheers......Greg.

 

[Bill Thomas]

I have been thinking about your trouble, And saying to my self, Carb' Carb' Carb', Then I remember I once had a Mag' fail in the same way ! I rode it to a race track, Raced, Then it went like yours, And had to keep the rev's up all the way home, Got nicked Three times in one go, Bad day !! Cheers Bill.

 

[koggg]

Check tre slip ring, if renewed.
The wrong type gives difficult sparking on one pot.
Mats

 

[clevtrev]

I carry an appropriate metric ruler in my toolkit, on the back of which I've taped timing measurements of every British bike for which I could find data (the print is tiny, but I also carry an eye loupe in the toolkit). It's not that I don't love the English system of measurement, but it's a lot easier to determine TDC on an engine to a tenth of a mm with the ruler, then add that number to that the timing spec. for the engine, to determine where BTDC needs to be, than it is to quickly and accurately add, say, 13/64" to 7/16" to help someone set his timing when kneeling on the side of a muddy road in the rain as cars whiz by.

p.s. note in the above table that the difference between, say, 34-deg. and 33-deg. is 0.021", i.e. 1/2mm. It is easy to determine the positions of the piston at TDC and BTDC to better than this, which is why the ruler method works just fine. Even if you have the world's best protractor and TDC-Locator in your garage for setting the timing to the nearest 0.0001 deg., it's unlikely you will have those instruments with you on the road. If you do need to set the timing of your engine while on the road you will be quite happy to be able to do it to the accuracy a ruler gives you.

You should travel with a piston stop, set for that machine, on your travels if you are that pedantic. You can even use it in the dark !

 

[Kansas Bad Man]

We all know different fuels burn at different speeds when they have the right fuel air mixture, we also know the oxygen in the air changes from day to day, we know the more the oxygen the faster the fuel burns, the start of the burn can not be a set in stone degree number for best setting, to many variables. It is a matter of preference not a number for the best volumetric efficiency of your bike, having said that, there will be days that the bikes tune will be almost spot on .

 

[Magnetoman]

You should travel with a piston stop, set for that machine, on your travels if you are that pedantic.

Odd, but the people who I've helped over the years to get their bikes running again using that ruler actually expressed gratitude for me having it in my toolkit. Although none of them called me a pedant, maybe they were just too polite to say it.

 

[Kansas Bad Man]

The ruler is only as accurate as the piston crown shape permits , if the crown does not create a 90 o flat to the sparkplug hole , the measurement is camed giving a false reading as the crank is rotated.

 

[Magnetoman]

The ruler is only as accurate as the piston crown shape permits ,.

That's true, but...

Most engines allow the thin machinist's ruler to be inserted fairly close to parallel with the direction of travel. Even if it is angled by 10 deg. the fact the piston only moves ~1/2" down from TDC means the tip of the ruler will not slip very far across the piston top so this error is fairly small for all but highly domed, high compression pistons in an engine where the spark plug hole is very near the side of the bore. Also, although I can't remember who wrote it,

the start of the burn can not be a set in stone degree number for best setting, to many variables. It is a matter of preference

someone pointed out that, especially with today's variable gasoline mixtures, the no. of deg. BTDC where the timing needs to be set isn't such a well defined number that setting it to better precision than this is called for anyway.

 

[Martyn Goodwin]

You mentioned that the ATD is a bit old. Check my thread on my experience with a worn ATD - the pivot pins for the bob weights worked loose and I was having a devil of a time getting a stable idle. Repaired the ATD and things became better.

 

[usefulidiot]

update: tonight i spent the last couple hours re-setting timing. first thing i did was check where it was at from using my rod-timing method. It was way off....it was so far off i'm embarassed to say the numbers and i'm surprised it was running at all. This did give me my ATD"s range of 36 degrees which i understand to be 2 more than it should. It took me forever to get the ATD locked on the taper without the armature rotating in the process. I ended up making a little line with a marker on the cam ring and the cam heel to see where the points were breaking using the cigarette paper method. That way i could easily see if it moved during the process I set it at 36 degrees fully advanced so that i could be at or close to 0 with no advance. Checked it again after everything was locked down. Bike started second kick and sounds much crisper right off the bat. At that point i called it a night. Still have to re-tune the carburetors in the morning but i'm confident i should be able to get it running happily. Just in time too...looking forward to the Dania Beach Vintage Motorcycle Show next Saturday. Thanks for all the ideas and i'll update again should i successfully get the carbs tuned.