240 timing differences

[siteunseen]

I've been working on a 240 that I never drive and am getting ready to sale.

Sunday I adjusted the timing and the carburetors.  It runs better than ever from what I remember.  The timing was at 5 degrees BTDC, I ran it up to 10 BTDC and it seems to run much better at 10.  Then I was reading the FSM this morning, I do things bass ackwards, and noticed the timing for a non US car is 17 BTDC.  Why is there such a big difference, 5 here and 17 in Japan?  What would the other owners recommend for the timing at 800 RPM?

[djwarner]

Pollution control differences.

I've always set timing at 17 BTDC with vacuum advance disconnected at idle speed. I arrived at this number by an old timers rubric of adjusting the timing at idle to maximize vacuum.

When reconnecting  a vacuum line from the manifold timing would advance to over 30 degrees at idle. Then I learned to use the vacuum port on my Weber Carbs and idle timing returns to 17. It turns out the Weber port is only active when decelerating and this is when you need the vacuum advance. Can't say what happens with SU carbs.

Never had a knock problem using these settings.

[Zed Head]

Retarded timing burns cleaner, apparently.  That's the basis.  One thing to consider though is that Nissan might have designed the advance curve to fit the expected initial timing.  Your initial timing setting will be added to total advance.  I have a distributor with "11" advance mechanism, 22 degrees, so if I set mine to 17 I'll end up at 39 total.  Probably not the best.  You need to know your distributor.

That's why some people set their timing to max advance desired, using a dial-back light or some other calculation.  You can make it run better at low and mid-range RPM but end up with lower power or detonation on the high end.

 

[sweatybetty]

would the USA and Canada distributors be different than Japan?

[Chickenman]

Delete

Edited June 22, 2016 by Chickenman