Spark trouble shooting

[hudson]

Hey guys, on my/5 I can’t get it to start. I know the three components are air fuel and spark. I pretty sure it’s getting fuel- I have re-bill and clean the carbs. and my air filter, it’s not brand new, but it’s good. So I’m statto think it’s a spark related. When I press the ignition switch it sounds like it wants to start, turns over Like it’s really trying so battery and starter are good. I have a Boyer ignition system checked all the wires according to the diagram, seemed good. I tested my coils, both the secondary and primary, they seem good. I check the ohms on my spark plug wires and they are good. So what gives?

I did take one spark plug out, left it in its cable and tried to start with it grounded against the cylinder to see if there’s any spark, and there’s not that I can see. I even used a new spark plug In case those ones were fouled out.

Any other suggestions? Does this sound like a spark or ignition to you? Is there anyway to troubleshoot the Boyer ignition? Any help is greatly

[Kurt in S.A.]

Snowbum discusses issues with low battery voltage and starting with Boyer ignition systems...near the bottom of this page:

http://bmwmotorcycletech.info/ignition.htm

Maybe you're afflicted with this issue:

http://bmwmotorcycletech.info/slash5cricket.htm

Kurt in S.A.

[Airbear]

Must be very frustrating. Sympathy attached. A few years ago I had real trouble getting my old girl to start. Sparks were weak and yellowish. I eventually bought a new set of coils - those things came packed full of crisp blue sparks and the old dear fired right up.

As well as air, fuel and correctly timed sparks you need sufficient compression. How long has it been since you checked valve clearances? Have you done a compression test?

[hudson]

The bike has been sitting for about a year. It ran fine, and then one day after it warmed up it would run very erratic. High rpm surging and it would start to smoke out the exhaust. The idle screws would have little effect on bringing down the RPMs. I focused on the carbs, re-cleaned, rebuilt, checked the flow. I thought maybe the slide was sticking or the float was overfilling. It would always start right up, and idol OK when cold, but after I rode it for about 10 minutes it would act up like this. the coils new from euromotor last year, and endurolast charging system. It ran fine, Started right up purred like a kitten, and the battery was charging fine.I even drove it to where I moved. But shortly afterwards just rides around town the symptoms started happening. Frustrated, I just let it sit for a year and I rode my other beemer.

Has a new Odyssey battery just installed. Valve clearances are good. I rotate the engine and the TDC for each cylinder is correct. I haven’t done compression test, because it was working fine. Probably will do one Anyway since that’s not a big deal to do.

The new charging system I put in last year wouldn’t have any affect on it what it?

I am familiar and have read snowbums article. Tested as much as I could from it.

From the information I provided, does it seem like a faulty ignition? I really think the problem stems all the way back to when the engine ran erratic. I was chasing the carbs. But most likely it was from something else.

If your bike had no spark and you check the coil’s and the cables ohms and the spark plugs, what else would you check? Not sure what else to do short of swapping out a new ignition system. What would you do?

[Airbear]

I would first ascertain that there truly is no spark. Try the test with plugs grounded on the cylinders in the dark. If you have a strobe timing light check the timing while running the starter.

I am not familiar with the Boyer ignition so cant help there. Maybe others could chime in.

The previous erratic running you mention might provide a clue. Could you describe this in more detail? Were you able to pin the problem down to one cylinder, for instance?

[SteveD]

Might help?

http://www.boyerbransden.com/faultfinding.html

[Rob Frankham]

Hi,

As you are satisfied that you have no spark, my advice would be to proceed as follows...

1. Use a test lamp or multimeter to test for battery voltage at the positive side of the coil. This should be a green or green/black wire and should not be the wire that goes to the Boyer Unit. With the ignition on, this should show a solid battery voltage.
   
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2. Once you have established that the positive side of the coil is hot, remove the connection that goes to the Boyer unit and test for battery voltage on the vacated coil terminal. this should also show battery volyage or very slightly less.
   
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3. Getting battery voltage at (2) above will establish that the primaries of the coils are (probably) good. Now connect a jumper lead to the vacated terminal on the coils and touch the other end briefly to ground while watching the grounded spark plugs. You should see a definite and reliable spark every time you touch the wire to ground. (Make sure you don't leave the lead connected to ground for any length of time as you could overheat and damage the coils, a brief touch is enough.
   
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4. If you can't get a spark at 3 above, then the assumption has to be a fault in the coils and/or plug leads and/or plugs. If you get a spark, then you need to check that the supply (battery and ground) to the Boyer unit is sound.

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If that gets you nowhere, the assumption has to be that the Boyer unit has failed... you don't say which Boyer you are using but in any case, at this stage, you are probably better off talking to Boyer themselves.

Good luck

Rob

[hudson]

Airbear - I did insert new plugs in the cables and grounded to the cylinders while cranking over. Nothing. When the erratic behavior started, it would start up fine, run great until about 10 minutes. Then at traffic lights especially, the rpms would rise and stay around 2 or so. I would play with the idle screws, turning them to bring it back down, they came down somewhat, but not all the way. It would smoke real bad, which my bike never really did before, perhaps a little after startup, but expected sitting on the kickstand. If I remember correctly, I would have to open up the throttle quite a bit to keep it from dying out. I would get home, the engine seemed pretty hot. I would let it cool back down with fans. I would have to re-balance things because the idle screws were obviously out of wack. I would adjust the mixture screw some, one attempt making it a little leaner, results the same. Repeated again making a little richer. Same results.

SteveD - Thanks for the link, I will look at the information and see what I can take from it.

Rob - I will get a test lamp and try your suggestions, but I will have to re-route a couple of wires because it is connected a little different.

The Boyer unit is micro digital for Pre 79 BMWs - red box.

The install is as in the attached diagram. I has the green wire from the loom attached directly to the green wire from the box. I did not install this, but it seemed to work before. I did take apart to re-route the wires some to make it a little neater, but the only wires I disconnected were the ones attached to the coils. As you can see a red wire (separate from the box) from the battery goes directly to the LH coil +. This would supply the power to the coil. The the piggy jumper between the coils are connected. The black from the box to the "-" of the RH coil is on and the brown to ground. There was no other wire that went from the RH coil "-" to ground/tach. Not sure what that is for? Note: On the second tab on the RH "-" coil, I put a wire on it from the Endurlast alternator rectifier unit/box as instructed.

I also tried these tests that were suggested by someone else: I also took a magnet, turned on the ignition switch and skimmed over the magnets on the pickup plate, which should give a spark to the plugs, when grounded to the cylinder. I also disconnected the two wires from the pickup plate and touched together which would also produce spark. Nothing in either case, if I did those tests correctly.

I will get a test light and do some more testing.

Thanks everyone!

[Rob Frankham]

Hi,

Just looked through the relevant Boyer instructions. The test I suggested before are still valid although, with the red wire hard wired to battery + you don't need to bother about the ignition switch. You do, though, need to check that the green wire goes live when the ignition switch is turned on.

Rob

[hudson]

10-4! Thanks Rob!