P11 Won't Start

A guy dropped off a P11 as it quit on him and won't run.

What I have checked:

1. Ignition: it is fitted with a Mk 4 Boyer, battery is right up, good spark, plugs look relatively recent, base timing seems correct.

2. Fuel: it tickles up fine, and there is fuel getting into the cylinders - enough that it should at least fire with the spark that it has. Gas is fresh-ish - should burn. Or at least get a "chuff" out of it. I have resisted giving it a shot of vitamin "E"...

3. Compression: 160-165 psi on both cylinders within about 4 compression strokes - healthy...

It should at least fire, or give some indication of life, but it is just dead to the world.

I have never had one beat me before and I have revived a huge number of left-for-dead engines in my lifetime. This one has me at a loss.

I had this bike in the shop last year for a bit of work (bad coil) and it was a 1-kick bike when it left.

Thoughts?

Do you have race rollers available? Makes life a whole lot easier on a balky bike. Did you clear the crankcase of oil? I've seen wet sumping strangle a kick. Let us know when you find the fault.

I suggest you take off valve covers and verify valve operation. Maybe the camshaft is "shot"?

- Knut

I would have thought that the 165 psi of compression would have cleared the valves.

Is there any possibility the ignition timing is out 180 degrees?

Fuel and spark is usually enough to get a puff. Should puff with a flat cam too, but not run worth a hoot.

Was the Boyer ignition in there last time you saw the bike, or is it a new addition by the owner?

P11 is guess work on "all in" timing when the primary cover is on. Static can usually be close and it will still light up.

180 degrees out on the timing would take a slightly confused person because the piston would be at the bottom of the stroke. Both go up and down together and Boyer is wasted spark so both plugs fire at the same time. Not trying to learn anybody anything, just talking.

It is possible that the timing is set wrong side of TDC making it 32 degrees retarded. That would also require some confusion.

The P11 Red book gives 32 degrees fully advanced, and a measurement for what I think is the piston position relative to something. 8.69mm (.343") Might be a gizmo the screws into the spark plug hole. Bring it up to TDC and back it off to that measurement. Not sure, because I don't use that method for timing.

Resistor plugs if installed don't need the resistor caps.

If it has a podtronics reg/rec they can't take an electrical short and work properly afterward.

What the others said.

Got nothing to add really.

I almost asked if it was a wasted spark system or not.

The Boyer has been It for years. The owner does no work on his bikes at all (wish he would just by a Honda… lol).

I swapped the box to a Mk4 last year (had one that I took off my own bike when I switched to a TriSpark.) Ran good after the swap. Knowing how little love this bike gets, I figured it would be a bit more forgiving for the owner.

I was thinking timing too, maybe it had slipped. From what I can see, with the plugs out, they are sparking pretty close to top dead centre, just slightly before, spinning it over as slowly as I can with the kickstart and still have the Boyer fire. Seems close enough that it should do something.

May have to pull the primary cover, and put the degree wheel on it…

I thought about the race rollers, but no room and no budget for those…. Besides, if it is tuned right, it should start easy.

Taking the P11 primary off should be a final desperation step because it is a not so much fun job. Particularly if still using flat head screws to hold the cover on. Messy and that wire going through the inner cover is a PITA. The thin gasket is also a challenge to deal with. Maybe I'm just getting old and grumpy.

As Jerry mentioned a full sump will slow the crank down. Should still fart a little though.

A little off topic: Where is the Boyer ignition located on that P11? Is it a distributor bike? Or does it have a Commando engine in it?

You might want to consider taking the timing cover off and looking at the cam chain tension after checking to be sure the Boyer rotor and stator plate are still in the right positions before taking the primary off.

It could be carburetion or bad fuel even if the ticklers are working. Especially if it has been sitting around with ethanol fuel in it for months. That stuff needs Stabil in it if any motor is going to sit a lot.

If lucky, you'll spot a loose wire somewhere before you have to really dig into it.

Good luck

It is a distributor bike, crankcase is drained. Trust me, I am not looking forward to disturbing the primary. I too was thinking that pulling the timing cover maybe a better course of action, and may actually be more informative.

I have set it aside for now while I rebuild a transmission in a buddy's 850 - think on it a bit more.

I have a couple of things i want to try. Dropping the float bowls is on the list, as well as maybe a different set of plugs.

Thanks, @Schwany

A Hill .

Simple things first eh , make sure gas will run your mower or , whatever , looking , smelling not a test ….

Derek Wilson said:

It is a distributor bike, crankcase is drained.

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Boyer Mk4 in a Lucas 18D2 distributor? That's odd. Normal set-up would be an AMC points housing and two large (2") MA6 coils clamped to a bracket at the seat tube.

- Knut

mdt-son said:

Boyer Mk4 in a Lucas 18D2 distributor? That's odd. Normal set-up would be an AMC points housing and two large (2") MA6 coils clamped to a bracket at the seat tube.

- Knut

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Excuse the use of colloquialisms by us less rested types - you are very correct, sir - it is indeed an AMC points housing. Please accept my apology for the misnomer.

I finally got back to the P11 today. Checked the ignition timing, it was still in time.

So I threw a different set of spark plugs in it - started right up!! Looked like it had good spark with the original plugs out, but I guess not with them in the cylinders…. Oh well…

Great when things start working like they should.

Nortons sure are spark plug sensitive. I've had several similar experiences messing with different older spark plugs on my Norton.

As a kid I had a Honda 70. One day I stripped out the spark plug hole, oops! So dad nd I took the cylinder head to town and a machine shop in town "fixed" it by boring and tapping the hole for a 90 plug. After that, I could never get a spark plug to last for more than an hour or 2 of running time. After that the engine would quickly get harder and harder to start until finally it would not start at all. Replace the plug with a new one (always NGK) and it would start first kick.

The removed plug looked fine, and no amount of cleaning,--no matter how you cleaned it, wire wheel, sand blaster, bead blaster, whatever--it would never run again. I never have heard a satisfactory explanation of why that would happen. 35 years later it remains the eternal motorcycle mystery in the back of my mind.

Junglebiker said:

As a kid I had a Honda 70. One day I stripped out the spark plug hole, oops! So dad nd I took the cylinder head to town and a machine shop in town "fixed" it by boring and tapping the hole for a 90 plug. After that, I could never get a spark plug to last for more than an hour or 2 of running time. After that the engine would quickly get harder and harder to start until finally it would not start at all. Replace the plug with a new one (always NGK) and it would start first kick.

The removed plug looked fine, and no amount of cleaning,--no matter how you cleaned it, wire wheel, sand blaster, bead blaster, whatever--it would never run again. I never have heard a satisfactory explanation of why that would happen. 35 years later it remains the eternal motorcycle mystery in the back of my mind.

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Depends on which "90" plug you were using maybe? Early Honda 70's used a NGK CR7HSA (my friend down the street had one).

C=10mm R =Resistor 7 =heat range H =Length of plug S =copper core A =special firing end construction (whatever that means)

The early Honda 90s used the same plug. Later 90s had the bigger diameter plug, but I see some use a BR7HS (14mm) - no A

Maybe it is that A that makes All the difference?

Went from a C series plug to a D series plug. The original was probably a C7HSA, I don't remember what the D series plug was, though obviously it would have to have the H in common, and the heat range was probably 7 or 8, (both were much more common than a 6 or a 9 where we lived), so that gives us D7H, S seems most likely to have been the next digit, (can't imagine what else it could have been). So D7HS is most likely what it was.
Someday I'll have to build a test engine and see if I can replicate the issue.