Boyer problem--- running on one cylinder

Try a pair of new plugs first.

My Boyer equiped Atlas has started doing this too ,so I'm watching with interest .

If you have a Strobe connect it to the rhs lead and start the bike on the lhs no flash no spark.

Regards

Esme

Due to (thanks to) the 'wasted spark' principal of the Boyer system - assuming that the HT leads are long enough, simply swap them over (and the plugs) - this will test plugs, HT caps, leads and coils. If the problem moves to the other cylinder this implies an ignition problem. If it stays with the RH cylinder, your problem is probably elsewhere ... .

I had exactly the same problem, turned out the engine earth was compromised and would only take the current to support one spark, a new dedicated earth wire from head to battery cured it. With points you would not notice it but with wasted spark you do as the HT current is doubled. Its was a mk2A, the mk3 may have a better earth with the starter but the path from head to starter has a few joints to pass, my MK2A was reliant on the std wire from engine to Z plate.

Previously ian_condy wrote:

Previously mark_woodward wrote:

Due to (thanks to) the 'wasted spark' principal of the Boyer system - assuming that the HT leads are long enough, simply swap them over (and the plugs) - this will test plugs, HT caps, leads and coils. If the problem moves to the other cylinder this implies an ignition problem. If it stays with the RH cylinder, your problem is probably elsewhere ... .

Thanks for all your replies so far.

I have swapped plugs, HT caps, leads and coils already and the problem has stayed with the right cylinder and that's why I was wondering if there is a dedicated pickup coil for each cylinder on the stator plate in the timing cover?

Paul - thanks for your comment about the plugs - I did swap them over but I think sometimes you've to go back to basics with these problems.

When I turned the engine over with the plugs out both plugs appeared to be sparking normally but of course the RH one may not be sparking under compression.

I then removed the left plug and started the engine on the RH cylinder --- it ran but very badly although it would rev when the throttle was blipped - another check that carb slides/needles etc were ok.

Next step is the compression test later today and a check with a strobe ( thanks Esme for your reply).

Thanks again and watch this space!

Regards,

Ian

Did you take the pilot jets out and clean them? At least with the Amal premier carbs you can take the pilot jets out and give the carbs a good clean out with carb cleaner.

+1 I'd also check the pilot jet, esp as the bike has been sitting, is the rh cylinder getting fuel? Is the plug wet?

The original post says the RH plug is wet. I would check the primary resistance of the coils and compare with new ones if possible. also connect the battery to a charger while you are starting to ensure a maintained healthy voltage.

"The right plug was quite wet and when I swapped them over and restarted the right side was still not running only firing occasionally. I then swapped the HT leads but no change and finally swapped the 6v coils over but no joy."

Obviously the ignition aspects are not suspect since BOTH coil make the LH cylinder fire. A plug swap or new plug eliminates the plug as the last potential ignition problem. A temporary cure is usually enough to make the decision about the ignition while general trouble shooting down to major systems.

You have a mechanical problem or more likely fuel delivery problem.

Have you been running E-10?

When my 99 went onto one pot (Boyer) it was found to be a dodgy plug cap, an easy fix.

Well done for mentioning fuel, David.

'm still not sure about the Boyer -- it was fitted in 1982 -- I can understand the "wasted spark" scenario but what happens if a rotor magnet or coil fails on the Boyer pick up in the timing case? Can this affect the firing of one cylinder?

The Boyer box is a single switch, the timing of the switch is an average of the signals from both coils which is detects every 360 degrees, so it either switches or does not, there is no half way where it switches one coil only, it switches both or neither. If you only have one plug sparking then look elsewhere eg coils HT leads etc.

Not sure where to go with this now and does a 70 psi reading on the right side warrant a strip down?

Well first do a leakdown test, you want to find out if the lower compression is from rings or valves or a combination, then you can strip to fix rather than trying to find the problem later staring at what looks like good parts. During the leakdown you can hear which valve is leaking from listening to the open ports eg remove exhaust pipes and carbs if doing both cylinders, for rings you do a test without oil in the combustion chambers and then do it after adding some oil, which will for a short time stop the rings leaking, and check the difference.

I had a similar problem on the Spanish Rally some years ago, the cable to the right carb hadpulled through the crappy Amal plastic splitter under the tank.

Are you sure both slides are rising cleanly & together?

Cheers, Mike

I think you are correct to go down the compression track, 90 psi& 70 psilook awfully low to me. If I can think back to physics 55 years ago isn'tatmospheric airpressure 14 psi and if we multiply that by a compression ratio of 8.5:1 then according to my 1962 physicsO level that I've never ever used until this moment shouldn't you be looking for something in the region of 120 psi. Oh help me someone please.

I agree with the comment about putting oil down the bore, you should see an instant compression gain if the rings/bore are the problem and if not then it looks like the valves.

Hope I'm not sending you up a gum tree.

Regards

Bob

Swinging it over with a kickstart might only produce a low figure, starting it briefly will give a more realistic figure. Most compression testers are designed to be used with a starter motor.

Probably a silly comment but you have checked tappet clearances?

Hello please remember hairline cracks can come in the porcelain of the spark plug even new ones please check with care, yours annaj

One thing you could try, put Redex down the plug holes and do a leak down test. Then flood head with Redex and leave over night. Turn over engine ( plugs out) to clean out the Redex and repeat compression test.

I have been successful with this only once on a Hilman Minx but it did work restoring compression and stopping overrunning. It enabled me to take the Decoke kit back for a refund and saved a lot of work.

I must add at the time it was not my idea but my Fathers, one of many useful tips.

The Redex will not do any harm and will help loosen any carbon deposits.

Hi Ian,

Just read your post, and I had exactly the same problem as you.

I went through much the same process trying to find why my Commando was only running on the LH cylinder on tick over. The right was contributing nothing, silencer remaining almost cold. I eliminated the ignition as a possible cause.

I thought that it was either an internal carb problem or an air leak somewhere on the inlet manifold because the pilot air adjustment screw had almost no effect on the running. I had the carb on and off several times, fitted a new O ring between the carb and manifold and a new tufnol heat insulator between the manifold and the head although the originals looked OK. All to no avail. I also established that the pilot jet itself was not blocked

I have the original Amals fitted which differ from the Premier in as much as the pilot jet is fitted within the carb and is not removeable. Now, for some background info, check out the youtube video, link below.

https://youtu.be/jwDUplLn4Xg

The following makes reference to the attached jpg

I came across the video whilst searching for inspiration, having totally run out of ideas. Looked hopeful. Carb off yet again, removed the air adjustment screw, pushed the nozzle of a can of carb cleaner into the fuel passage, (the red circled drilling marked âgas(oline)â ), pressed the trigger, and nothing came out of the air screw hole or the two tiny holes at the base of the venturi. Bingo. Just as the smart chap in the video indicated, the fuel passage was blocked completely. Following his suggestion, I pushed a piece of wire into the red gas hole, working it up to the right angle and actually felt some resistance as it poked through the blockage. More carb cleaner injected and the spray came out everywhere it was supposed to. Carb back on, problem fixed! Now running cleanly on tick over. (Watch your eyes when using the carb cleaner, it can come out of some unexpected places).

The slight dilemma is that the Premier layout would be less prone to cake up at this spot because the removeable jet occupies the right angled bend. However, your symptoms are exactly the same as mine. Essentially there was no fuel supply at all to the slow running circuit so the cylinder was only pumping air with an occasional pop as some fuel found its way into the engine, presumably via the main jet.

You could try the same technique, using carb cleaner, to establish if the passages are clear. Also, donât ignore the carb float chamber, the red gas hole is supplied fuel via a drilling in an internal web from the bottom of the chamber. Check the float chamber gasket, make sure that the corresponding hole is clear. A bit obvious, I suppose but you never know.

If this is the cause of your problem, at least it will save having to dismantle the engine!

Good luck

Previously robert_haslam wrote:

Hi Ian,

Just read your post, and I had exactly the same problem as you.

I went through much the same process trying to find why my Commando was only running on the LH cylinder on tick over. The right was contributing nothing, silencer remaining almost cold. I eliminated the ignition as a possible cause.

I thought that it was either an internal carb problem or an air leak somewhere on the inlet manifold because the pilot air adjustment screw had almost no effect on the running. I had the carb on and off several times, fitted a new O ring between the carb and manifold and a new tufnol heat insulator between the manifold and the head although the originals looked OK. All to no avail. I also established that the pilot jet itself was not blocked

I have the original Amals fitted which differ from the Premier in as much as the pilot jet is fitted within the carb and is not removeable. Now, for some background info, check out the youtube video, link below.

https://youtu.be/jwDUplLn4Xg

The following makes reference to the attached jpg

I came across the video whilst searching for inspiration, having totally run out of ideas. Looked hopeful. Carb off yet again, removed the air adjustment screw, pushed the nozzle of a can of carb cleaner into the fuel passage, (the red circled drilling marked âgas(oline)â ), pressed the trigger, and nothing came out of the air screw hole or the two tiny holes at the base of the venturi. Bingo. Just as the smart chap in the video indicated, the fuel passage was blocked completely. Following his suggestion, I pushed a piece of wire into the red gas hole, working it up to the right angle and actually felt some resistance as it poked through the blockage. More carb cleaner injected and the spray came out everywhere it was supposed to. Carb back on, problem fixed! Now running cleanly on tick over. (Watch your eyes when using the carb cleaner, it can come out of some unexpected places).

The slight dilemma is that the Premier layout would be less prone to cake up at this spot because the removeable jet occupies the right angled bend. However, your symptoms are exactly the same as mine. Essentially there was no fuel supply at all to the slow running circuit so the cylinder was only pumping air with an occasional pop as some fuel found its way into the engine, presumably via the main jet.

You could try the same technique, using carb cleaner, to establish if the passages are clear. Also, donât ignore the carb float chamber, the red gas hole is supplied fuel via a drilling in an internal web from the bottom of the chamber. Check the float chamber gasket, make sure that the corresponding hole is clear. A bit obvious, I suppose but you never know.

If this is the cause of your problem, at least it will save having to dismantle the engine!

Good luck

Hi, I had a similar issue all last year albeit plug fouling in the mid range and went through everything already mentioned here eventually stripping the top end to replace the rings all to no avail. It finally turned out to be the new premier carbs I had fitted although I had checked all of the jets were right and the float heights in the first instance, turned out the needles although marked up the same had slightly different tapers! I eventually found it by swapping everything out of each carb over to the other side which is when the fault switched cylinders, then swapping things back one at a time. I would recommend you try this before stripping the motor as it is a lot less of a rave if the new premier carbs turn out to be the problem as mine did. Good luck, Al.