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Chad_in_PDX 
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 Topic: B won’t start
Posted: 01 Sep 2022 at 11:20pm |
I picked up a 1940 AC B at the beginning of the summer. Supposedly a “ran when parked” situation. Well, unfortunately it was parked outdoors for some time. Amongst many other things, I’ve rebuild the magneto (FMJ4B3) as well as the Zenith carb (10698A). When I crank the engine it never fires though I do occasionally get a pop of fire that shoots out the manifold. I seem to have a good spark from the plugs, good flow of gas through the carb main jet, air cleaner isn’t restricted, point gap is correct, valve gap is set, valves lapped in, compression is good, manifold/intake is free of holes, new plug wires installed correctly, new plugs gapped. Really don’t know what’s keeping this tractor from starting. Rechecking the carb again tonight I found a hole that does not pass air. What is the passage for and is it supposed to vent elsewhere in the bottom half of the carb?  Next is a strange problem with the throttle. No more movement is achieved at the carb throttle valve once the throttle handle is moved forward of this position. Carb is at WOT in the picture. I’ve tried starting the engine in just about every rearward throttle detent, to no avail.  One last thing is my inability to get the dimpled tooth of the magneto gear to rest at the 12 o’clock position. The closest I can get it is to about 1 o’clock. Is this normal? Obviously, this makes getting the C on the plastic gear meshed with the dimple trickier. Though I think I’ve got the two gears meshed at the correct position.  Any ideas getting this thing started would be greatly appreciated. I’m at my whits end. Thanks Chad
Edited by Chad_in_PDX - 02 Sep 2022 at 1:18am
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WF owner
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Posted: 02 Sep 2022 at 5:50am |
Welcome to the forum!
If you are getting "a pop of fire that shoots out the manifold", it sounds like your timing is off, either inside the magneto or the mag position or plug wire placement is wrong. This link may help:
EDIT: If you are having problems getting the beveled tooth in the correct position, it's possible that someone has moved the timing gears under the front cover, which would throw your timing off.
Edited by WF owner - 02 Sep 2022 at 5:54am
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MACK
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Posted: 02 Sep 2022 at 6:05am |
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Out of time, mag or plug wires. MACK
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steve(ill)
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Posted: 02 Sep 2022 at 9:14am |
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FIRST the mag has to be TIMED internally... As WF has posted... Then it has to be INSTALLED and timed right to fire at TDC mark on the crank. ( NOT the FIRE MARK).
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Chad_in_PDX
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Posted: 02 Sep 2022 at 9:37am |
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Everyone, thank you so much for the replies. WF, I had not come across that page. Wish I had earlier. Great info.
Can anyone confirm that that one hole in the carb is not supposed to pass air or fuel? A blind hole.
Chad
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steve(ill)
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Posted: 02 Sep 2022 at 3:17pm |
I think you are pointing to the IDLE port.. Gas gets sucked up that hole into the TOP COVER and is controlled by the IDLE SCREW... You cant push a wire thru it with the long brass tube in place.... maybe you can blow air thru it..
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steve(ill)
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Posted: 02 Sep 2022 at 3:20pm |
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and when you TIME a mag to the tractor, you are getting it to SNAP at TOP DEAD CENTER, right ?? The IMPULSE will move the timing to the fire mark , after the motor is running..
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Chad_in_PDX
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Posted: 02 Sep 2022 at 11:25pm |
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Small update.
The hole in the Zenith carb that is noted with the arrow is supposed to pass fuel. Mine was clogged. If anyone else runs into this issue, a 0.032” thick piece of spring steal wire can be used to push through.
BUT, this didn’t seem to be keeping the B from starting. Put the carb back together, buttoned everything back up, tried to start it but no luck. Could be wrong but it seems like the carb is not the issue now.
Moving over to the timing, my wife spotted CENTER on the flywheel. A tiny bit more cranking and the magneto clicked. Steve, is that the way it’s supposed to be?
Chad
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JCSinPITTS,PA
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Posted: 03 Sep 2022 at 7:23am |
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i had a problem where in put the wire in firing order but thought the magneto turned the other way so it fired on 2 clyinders. post of pic of the back of magneto with wires in
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steve(ill)
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Posted: 03 Sep 2022 at 8:21am |
Chad, you should hear the SNAP right at TDC.. Dont get too far away from that point.. The closer the better... Loosen up the mag bolt and rotate toward or away from the motor 1/8 inch and retest...
ALso as JC said, you have to have the right PLUG WIRE when you hear the snap.. I put a 1/4 inch hose up against the #1 ( front) spark plug hole and feel for air coming out as you rotate the motor toward CENTER... If you dont feel the AIR, your on the exhaust stroke and need to rotate the crank all the way around again... When you feel the air coming out, keep rotating till the SNAP at CENTER.. and see that the #1 plug wire has a spark ( plug in the wire and grounded to motor) .. Which ever wire SPARKS, that is #1 ... If you want a different plug wire to be #1, you have to pull the mag, rotate the motor to the next snap and reinstall.
Edited by steve(ill) - 03 Sep 2022 at 8:22am
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Chad_in_PDX
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Posted: 03 Sep 2022 at 11:01pm |
OK, so it’s sucking air on cylinder #1 then that spark plug fires. At the end of the compression stroke for cylinder #1 I lined up FIRE in the timing window. Then I took the cap off of the rotor (see picture). Looks like #3 is about to fire. So I’m 90 degrees out of sync from where I should be? I read how to correct things when 180 degrees out of sync but I’m not sure how to correct 90 degree? Or maybe I’m just not understanding things. Thank you all, your help is invaluable. Chad 
Edited by Chad_in_PDX - 04 Sep 2022 at 12:11am
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WF owner
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Posted: 04 Sep 2022 at 6:19am |
If the timing is 90 degrees off, one of two things are wrong.
As I said before, someone may have turned the gears in front of the magneto drive so they aren't timed properly.
The other possibility is that the spark plug wires are not inserted in the correct position in the magneto. #1 spark plug wire should be between 10 and 11 o'clock as you are sitting on the seat looking at the mag. If the timing gears are not timed correctly, although it isn't the right way to do it, you could move the wires on the magneto one place. Turn the engine to TDC on the compression stroke. Put the #1 spark plug wire in the terminal where the rotor is pointing, then, going clockwise, insert #2, #4, then #3. (Firing order is 1,2,4,3)
Edited by WF owner - 04 Sep 2022 at 6:26am
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steve(ill)
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Posted: 04 Sep 2022 at 8:24am |
Turn the engine to TDC on the compression stroke. Put the #1 spark plug wire in the terminal where the rotor is pointing, then, going clockwise, insert #2, #4, then #3. (Firing order is 1,2,4,3)
YES... you can just move the plug wires to the next hole on the cap... If you WANT to keep the wires in the holes they are in now, remember that the motor is a 4 stroke... the MAG turns HALF AS FAST as the motor....
With the mag OFF and #1 wire and plug installed, rotate it so it SNAPS and you know 1-2-4-3 ..... So #1 FIRES, then you continue to turn and hear 3 SNAPS... then #1 you will see fire again on the 4TH SNAP... now rotate 3 SNAPS again and you know #1 will be the NEXT ............ now install the MAG on the motor.
Dont have the motor at TDC when you install the MAG... that is a common problem... Have the motor about 30 degrees BEFORE TDC ...Thats when the MAG starts to wind up and will fire when you rotate to TDC.
Edited by steve(ill) - 04 Sep 2022 at 8:36am
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steve(ill)
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Posted: 04 Sep 2022 at 8:41am |
Read #4.... if you install the MAG when at the 30 degree FIRE MARK, that gives the mag time to WIND UP and SNAP when you rotate to the TDC mark....
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Chad_in_PDX
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Posted: 04 Sep 2022 at 9:01am |
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Thank you WF and Steve!
The plug wires are installed by the book. I’ll do more investigating tonight.
WF when you say “gears in front of the magneto drive“ are you talking about the way the fiber gear and the dimpled steal gear are meshed? Or are another set of gears entirely?
Chad
Edited by Chad_in_PDX - 04 Sep 2022 at 9:12am
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steve(ill)
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Posted: 04 Sep 2022 at 9:14am |
the mag does SNAP and FIRE your plug ( you saw the spark , right ???).......... so the mag is assembled correctly.. If there is no FIRE at the plug, its internal..
your problem is installing the mag on the tractor in the right position to get the SPARK at #1 on compression.
Edited by steve(ill) - 04 Sep 2022 at 9:17am
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Like them all, but love the "B"s.
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WF owner
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Posted: 04 Sep 2022 at 9:35am |
 Chad_in_PDX wrote:
WF when you say “gears in front of the magneto drive“ are you talking about the way the fiber gear and the dimpled steal gear are meshed? Or are another set of gears entirely?
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I am talking about the gears in the engine (governor). If I remember right, when you have the engine at TDC on the compression stroke, the "slot" where the governor drives should be slightly off level (if the timing gears are right), but tilted slightly down on the right side. If your slot is near vertical, something is wrong with the timing gears.
Again, If I remember correctly, you can access and turn those timing gears by taking the cap off the front of the governor on the front of the engine.
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Chad_in_PDX
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Posted: 04 Sep 2022 at 10:57am |
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Steve, yes, I have a strong spark at each of the spark plugs. I’m still trying to get up to speed on what you are saying. Thank you for the detailed responses. I’ll do some work on the tractor this evening and report back.
Right now my firing order seems to be 3124 instead of 1243. With #1 at TDC on the compression stroke.
Chad
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steve(ill)
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Posted: 04 Sep 2022 at 12:33pm |
take your mag and put in a vice in the shop.. Put a plug and wire into #1 PORT.. Ground the plug to the mag....
Grab the input tang with a pair of pliers and turn it to WIND UP THE SPRING and then it will SNAP.... keep doing that until #1 plug FIREs.... if you do it 3 more times ( 2-4-3 not seen).. then #1 will FIRE AGAIN....... Then turn in 3 more times ( 2--4-3 not seen) and NOW ITS READY TO FIRE #1 .... go put it on the tractor..
The tractor should have the CRANK set at the FIRE MARK ( 30 degrees before CENTER) and you install the mag..... This is where it will FIRE when the motor is running.
When you were turning the mag on the bench and it was WINDING UP THE SPRING, that is what will happen now as you ROTATE THE MOTOR TO TDC... When you get to CENTER, the mag will SNAP and fire #1 plug....
When the motor starts, the springs inside are overcome by weights and WIND UP no longer occures... The MAG will fire at the FIRE mark.
The MAG is mounted with two bolts in slotted holes and you can ROTATE it inward or outward a few degrees to get the SNAP right at the CENTER mark.
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Like them all, but love the "B"s.
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Chad_in_PDX
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Posted: 04 Sep 2022 at 10:51pm |
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Got the tractor started up tonight. First time running in seventeen years. It drove really well! The final drive gears were a little noisier than expected. Is that just because they are straight cut gears?
Steve, your detailed response about getting the magneto in sync was super helpful.
Thank you everyone for the help on getting the B running.
Chad
Edited by Chad_in_PDX - 05 Sep 2022 at 1:14am
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steve(ill)
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Posted: 05 Sep 2022 at 8:49am |
GREAT !!
Some of final drives do make noise... I have a couple that are pretty quiet.. i have one that i rebuilt and it whines going down the road in 3rd gear.. Bearings are new and proper set... You COULD have some bearing problems...that would be normal for 70 year old tractor... hard to tell ... some do make noise even when properly set.. You can remove the oil pan, clean and put a quart (??) in each side to help..
GOOD JOB !!
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Like them all, but love the "B"s.
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