Tractor Carbs
Member
What should my advance look like with a timing light. 1943 M with magnito. I know they don't seem to have any advance weights to change with rpm. It runs fine with lots of power but sounds retarded at the 5 deg mark.
- Thread starter Tractor Carbs
- Start date
Bob M
Well-known Member
Unlike a distributor, a magneto has no centrifugal advance mechanism. Ie. there is no timing advance as RPM's increase. Timing is fixed at 30 - 35 deg before TDC across the entire operating range.
A mag DOES incorporate a fixed timing retard in the impulse coupling at cranking speeds. So static timing should be set to TDC. Then when the engine running adjust timing to where it runs best.
HOWEVER if your tractor is hand-cranked, static timing should be set a couple degrees AFTER TDC then left there for protection against backfire while cranking.
A mag DOES incorporate a fixed timing retard in the impulse coupling at cranking speeds. So static timing should be set to TDC. Then when the engine running adjust timing to where it runs best.
HOWEVER if your tractor is hand-cranked, static timing should be set a couple degrees AFTER TDC then left there for protection against backfire while cranking.
Its been my experience a lot of older low compression tractors that were designed to run on low octane distillate or tractor or drip fuel operated at maybe 30 to 35 BTDC run timing which in my opinion is a bit fast when burning gasoline where I prefer maybe 25 BTDC. However as Bob mentioned the static start/impulse timing cant be advanced before TDC or she can kick back. The trick is to get the start impulse at or a tad after TDC and the run timing where she performs best. I know how to do that on the Wico C and X mags but I'm not an IHC mag man.
John T
John T
gene bender
Well-known Member
The mags fire at TDC when the engine starts and runs the mag dgoes to around 33 deg
What pistons do you have in the M. When we put fire crater pistons in the M's we changed the impulse in magneto to have approx. 22 degrees spark lag. In other words, about 22 degree spark advance very close to the advance we used on battery ignition units when converting to fire crater pistons. I found that if the points get a little too close together with wear on the rub bar of points, that timing will get too late and the engine will labor at full throttle. Doesn't take much to really affect that shorter advance where the 35 degree standard advance it wasn't noticeable. You can easily put a timing light on it if you like and mark off the pulley in degrees to see what spark advance you actually have. 22 degrees is 1 7/16 on M pulley. Did enough of those to memorize that figure.
Similar threads
We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.
Copyright © 1997-2024 Yesterday's Tractor Co.
All Rights Reserved. Reproduction of any part of this website, including design and content, without written permission is strictly prohibited. Trade Marks and Trade Names contained and used in this Website are those of others, and are used in this Website in a descriptive sense to refer to the products of others. Use of this Web site constitutes acceptance of our User Agreement and Privacy Policy TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.
Yesterday's Tractors - Antique Tractor Headquarters
Website Accessibility Policy