Boxerworks.com

Charles - I understand that the Boyer needs to be set at 4,000 rpm. I cannot currently achieve such engine speeds. What is your advice regarding where to set the magnets and stator plate in order to achieve ignition, as you seem relatively conversant with Boyer's system? Boyer tells me to set the stator plate in the middle of its adjustment range and then start it up. That does not work, so I was going with the "S" mark and making sure my magnets lined up with the stator plate when "S" was in the window. That also doesn't work.

Jean - It has never run with the Boyer. I have done the basic Boyer diagnostic tests, and the spark is strong and regular when not under compression, so I suspect the Boyer box is fine. I have considered a worn starter bushing as a possibility, for the reasons that you mentioned. Also, to be clear: it once ran with points. I have yet to put them back in and see if it runs now, post-rebuild. My plan was to put the points in and see if I can start it with the kickstarter, then try it with the electric starter, to eliminate the possibility of a bad starter. Compression before I rebuilt it was ~95 on each cylinder, so I have added a bit of compression with a new top end. I believe that the Boyer can't be used with a kickstarter, since their literature says you need at least 200 rpm to get spark. I'll check in in about a week. Thanks for the help.

I don't seem to remember that doing anything else but following the Boyer instructions, the magnets must be the right air gap or you would not be getting spark. How about rechecking the mounting of the magnet plate on the end of the camshaft.

Worth looking at timing with strobe running the engine on starter motor, with plugs out and grounded?

Other simple things to get wrong might include choke operation.
Try starting spraying easy start or similar into carbs
Making sure that battery voltage under load with starter operating is over 8volts.
Digital Boyers like to have resistor plug caps of 5000ohms.

Any other work done? Timing chain?

I'm a little confounded by the "200 rpm TO GET SPARK" statement. You 'd expect to have the engine start in 5 or 6 spark-strokes...the starter ought not have to run long at all. All the magnets/rotor do is provide a trigger signal to the spark electronics...Chasbmw said you need at least 8 volts with the starter running. I recommended 9.5-10 volts as that is my observation with my DYNAIII. My bike will start with the foot starter and the DYNA however.

Jean wrote:I'm a little confounded by the "200 rpm TO GET SPARK" statement. You 'd expect to have the engine start in 5 or 6 spark-strokes...the starter ought not have to run long at all. All the magnets/rotor do is provide a trigger signal to the spark electronics...Chasbmw said you need at least 8 volts with the starter running. I recommended 9.5-10 volts as that is my observation with my DYNAIII. My bike will start with the foot starter and the DYNA however.

That's a little weird to me too. I"m very familiar with FI systems not firing until a certain rpm and number of revolutions is achieved, but I've never seen it in carb engines.

Perhaps a Boyer-GURU will speak up to illuminate us...

Boyers like most other electronic ignitions, will turn off power to the coils if the engine is not turned within say 5 seconds and require a signal from the rotor to switch power back on when the engine is turned. this stops the coils overheating if the ignition is left on.
This may be where the Boyer does not trigger under 200 rpms comes from.

Motobins used to list Boyers as being unsuitable for kick starters, this has always puzzled me, because probably 90% of Boyer production has gone into kick starter only British bikes, it may be because before Boyer revamped their electronics, Boyers would revert to full advance under low voltage conditions.

This can cause kickback which can be painful and on certain machines fitted with sprag clutches on retro fitted electric starters such a Godet Vincents the kickback will break the sprag clutch.


My advice to the OP is to use his strobe to take a look at timing, running the engine on the starter motor will plugs out and grounded, this should enable him to see if he is anywhere close on static timing and adjust accordingly. Failing any success with this to refit points and see what happens. It is quite possible that something apart from timing is preventing this bike from starting.

There's aleays the chance that the flywheel is not ON in the correct position.
THERE. I said it.
Even the nearby OFFICIAL BMW shop has been known to get that wrong!! (can you believe?)

And I've got one sitting in my garage like that...it's 1/5 position off. (NO, I did not do that. It happened that either the PO or the local workshop did it.) Got points tho, and it runs good. SOMEDAY I'll fix it...not on my #1 priority list tho.
I'd try to get it running on ONE set of plugs, with the points and old coils installed, and check the timing marks. Once it DOES run again, and you KNOW the carbs are doing their thing, THEN fit the Boyer system up and see what happens.

Back to trying to figure this out. I had only a couple hours today and didn't get much done. I did check compression and found that it was 125 psi in both cylinders. Seemed kind of low for a new top end. I had the carb-to-airbox tubes disconnected for the compression test, but I didn't have the throttle wide open (sorry Duane, but I did follow the advice from your website for the rest of it, I just airballed on the throttle), which may have depressed the reading a bit. In any event, the fact that I got equal readings on both sides, and that those readings were 125 each, confirms that lack of compression is not causing the non-starting.

Jean - the flywheel is on so that when TDC is reached, the OT mark is dead-nuts on the notch in the window. I checked this with a degree wheel and a piston stop - twice.

Since I have compression, I decided to try and kickstart it with the Boyer. No luck.

Tomorrow I will time it with the plugs out and grounded while holding the starter button down. This should confirm (or not) that spark is arriving at roughly the right time. My light was shot today. I haven't used it since a VW rebuild a few years ago, and it was old then. It is a cheap plastic job that was made in the USA - that ought to indicate its age:)

First Question: If my starter bushings are shot (a definite possibility on an original Bosch from 1973) then I should not be getting spark under compression, right (starter sucks so much juice that not enough gets to the plugs)? In order to test whether or not I need to replace the starter, I was going to leave the plugs in but not connected and then ground two live spare plugs to the heads. If these plugs spark when I depress the starter button, then my starter is not the problem. Is this a reasonable diagnostic test for the starter under compression?

Second Question: Do 5K caps make any difference when kicking vs. electric starting? I've got only NGK 5K caps.

Back to it in the morning. I've got compression, and I think I'll soon know if I have spark (see question 1). Maybe I'll come back around to carbs soon.

Do you have a Multimeter...? What we are calling the "bench meter"?
Connect it across the battery terminals while you operate the starter and read the battery voltage. That tells you how much is left to fire the Boyer unit.

Spark Plugs in/out: It takes more voltage to fire the plugs in the compressed atmosphere. It also takes more starter moxie to turn the engine over with plugs IN. BUT...if you have a set of plugs in the engine and get a really snappy spark on the spare set you "probably" have enough spark to ignite the fuel.

HOWEVER...you said earlier that you got wet plugs out when you tried to run the engine with the plugs in, so it is important to check the voltage during cranking...Starter bushings get worn out from milage and use, not age. The rest of the starter could be showing signs of age tho. Maybe a dirty commtator, or dirty insides causing drag.

If the Boyer is getting firing voltage and the plugs are getting gas, I'm surprized you are not getting some kind of "firing noise" or at least a backfire by now.

If you are getting 125 psi from a cold engine, and with the carbs still in place, the top end is probably not your problem.

What's your voltage at the battery, no load? Has it gotten run down with all this testing? Look for 12.4V or more, if not, give it a charge before you dick around with other stuff.

There's a wee piece of Airhead wisdom that runs like this: "It's the battery, it's always the battery."