Asking an old, played question .....

Intermittent short in ignition and kill switches. Alternator charge is good but that energy has to get through the switches to the ei box. Run a jumper from battery neg to the white feed wire on the ei box and start the bike. It will take all of 5 minutes. I have a jumper made up with a switch and 20 amp fuse. Don't have to try to pull the wire off a running bike. First diagnostic test I do is clean the pilot jets, next is to bypass the switches. Every Brit bike I have has had either an ignition or kill switch failure at some point. On BSA it quit running going down the road, flicked the ign switch back and forth a few times and it took off, replaced switch. Bonneville wouldn't start, messed with the ignition switch and got it to fire, replaced switch. Commando running like crap, kill switch button was broken, rebuilt the kill switch. Trident wouldn't idle, ran better on choke, measured low voltage to ei, bypassed ignition and kill switch.
If the bike runs better with the jumper you need to find where the voltage drop is. Like I said the prime suspects are the switches but it could be a faulty connection in the harness. Points require just a minumum voltage to work correctly but ei's are more touchy. Have a read through on the article below. Pazon components are basically the same as Boyer. Especially important test is towards the end of article where you are looking for voltage drop when powering up the coils with the ei box disconnected.
http://vintagebikemagazine.com/technica ... -shooting/

Lannis said:

Has to be the pilot jets, right? Even though I drained the carbs before starting work last fall. So I took the carbs apart - they were clean as a whistle inside. Put the #78 drill through the pilot jets, there's nothing there, the drill bit is clean. Cleaned the passages from the "progressive" jet holes, nothing there, and carb cleaner shot through the jet comes out in two fountains from the progressive holes in proportion to their size.

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At the expense of stating the obvious this is meaningless – the T or Y section inside the pilot system of the carb body should also be clean and free of muck. The only safe way to ensure this is to remove the carbies and pilot jet and BLOW through with a 125PSI air jet at Both the pilot and air hole in the bellmouth end checking that it is freely blowing air downstream of where the slide runs up and down. HTH

Bernhard said:

Lannis said:

Has to be the pilot jets, right? Even though I drained the carbs before starting work last fall. So I took the carbs apart - they were clean as a whistle inside. Put the #78 drill through the pilot jets, there's nothing there, the drill bit is clean. Cleaned the passages from the "progressive" jet holes, nothing there, and carb cleaner shot through the jet comes out in two fountains from the progressive holes in proportion to their size.

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At the expense of stating the obvious this is meaningless – the T or Y section inside the pilot system of the carb body should also be clean and free of muck. The only safe way to ensure this is to remove the carbies and pilot jet and BLOW through with a 125PSI air jet at Both the pilot and air hole in the bellmouth end checking that it is freely blowing air downstream of where the slide runs up and down. HTH

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You can't exactly "remove...the pilot jet" from most Mk1 Concentrics, at least not without drilling it out as it's a pressed-in 'bush' also, the fuel side where the "pilot" jet/bush is, connects to the float chamber, not the intake.

htown's suggestion is a good one. I found my kill switch had very high resistance, so, having never recalled using it, I bypassed it and all the stock wiring so that voltage comes from my ignition switch, which is good, directly to the ignition module. Many unexplained problems solved.

When you changed from points to wasted spark EI you increased the load on the ignition system, you now have double the sparks so both coils and all the related wiring are working harder. If there are any marginal weak points in the LT or HT side including the earth routes then it can give you problems.

Do you have or can you borrow another set of carbs to try ?

Greg

gjr said:

Do you have or can you borrow another set of carbs to try ?

Greg

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My first thought was "Well of course not", then I realized that I've got the top end off of my BSA Firebird Scrambler, and those two carbs are just laying on the shelf.

Not sure what the jetting is relative to the Norton, though, but it probably doesn't matter if they're the same bore size, all I want to do is debug the problem .... Fuel fittings are different, I'm sure, I'll see if I can rig something up.

I need the bike on the road in 10 days; it's already been suggested that I just bag the Amals and put a Mikuni on it. I've always been able to make Amals work on anything I have so I've never made the conversion before, but this is getting old ...

Lannis

Lannis said:

Pazon ignition, using the same 12V coils as ran last year,

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Standard Commando coils are 6V (17M6) from '71 on.

Lannis said:

and which the Pazon instructions say to use.

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Pazon recommend two 6V coils (in series).

http://www.pazon.com/files/PDF/PA2.pdf

Ignition Coils
When using the standard arrangement of two ignition coils (whether 12 Volt or 6 Volt), they must be connected in series, as shown in the wiring diagrams on page 7. Do not connect the coils in parallel. For low compression ratio engines (less than 9:1) two 12 volt coils connected in series can be used, but we strongly recommend running with two 6 volt coils connected in series or one 12 volt dual output coil with a primary resistance of 3 to 4.5 ohms.

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Lannis said:

If something magic happened, it happened to both carbs at the same time. And since I didn't change anything about the carbs, now I'm looking at ignition,

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The same problem apparently affecting both carbs at the same time seems unlikely although not impossible.

Lannis said:

I'm running out of ideas here. It sounds like it HAS TO BE a carb problem, but I didn't change the carbs, then I cleaned the carbs in case they changed themselves with fuel varnish, and both of them are doing the same thing. Under the principal of "What Did You Change?", then the problem HAS TO BE the ignition, but absent just installing another EI, I'm not sure how to proceed

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Refit the points ignition?

he called me last night and we had a long chat. i told him as he has a bsa there to cannibalize parts from to try the boyer from it along with a few other things to look at as he removed the pazon. once again and old trick is to go back to what you had before you changed a part if it was running ok before you worked on it.

Lannis said:

I realized that I've got the top end off of my BSA Firebird Scrambler, and those two carbs are just laying on the shelf.

Not sure what the jetting is relative to the Norton, though, but it probably doesn't matter if they're the same bore size, all I want to do is debug the problem .... Fuel fittings are different, I'm sure, I'll see if I can rig something up.

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I don't know which year Firebird it is, but Firebird carbs are likely to be 30mm not 32mm.
There's also likely to be some differences in main jets and slide cutaways depending on the model year.

One problem fitting Firebird carbs to a Commando is they probably won't have the flats machined on the unused inner throttle stop bosses and also the carb flanges so they will clash.

You can over think things too and make false assumptions that eliminates simple tests.

One of my simple tests is the "spit test". If you can get your bike running, spit on the exhaust pipes. Your spit should instantly produce a puff of smoke if the cylinder is firing. Just because the exhaust pipe feels hot, doesn't mean that cylinder is firing. Your bike is compressing air and fuel, so it creates heat whether there's combustion or NOT... Don't be fooled by a merely hot exhaust pipe. It needs to be so hot that your spit will instantly produce a puff of smoke.

IF one side doesn't produce this puff of smoke, try a new plug in that side... since that would be a cheap stab at finding the problem.

The next thing I would look for based on your discription is an air leak, because you say the bike runs with the choke on... TO ME, this means that the ignition is most likely working. (but you can't conclude that yet) I would get the bike running, and spray carb cleaner around the manifolds and outside of the carburators and observe any changes in how the bike runs as you are spraying.

In the past, I've had a sticky slide body on one carb. I took both carbs off. I used some very fine grits of sandpaper to adjust the fit of the slide in question until it moved properly. When I reassembled the intake, I overtightened one manifold and put an invisible crack in it. It didn't take long for my bike to start running poorly. I found the crack (and the air leak) by spraying carb cleaner on the manifold as the bike ran. It would suck the fluid in when it hit the crack and the bike stumbled. I still couldn't see the crack, but repeated application of the carb cleaner fluid told me that there was an air lead there. When I diassembled the manifold, a piece of it tumbled free. When held together, the hairline crack between the two pieces was nearly impossible to detect with the naked eye, but it sucked air and made the bike backfire and run poorly... It was a simple fix. I replaced the manifold and the bike ran well again.

Do I have more war stories?... of course I do...

I've had a bad spark plug that tested good clamped to the head of the bike, but didn't fire under pressure mounted in the head. The fact that it tested good against the head, plus I thought the exhaust pipe was "kinda hot" on that side, made me assume it was firing in the bike. I worked for days trying to figure out why the bike didn't idle or run at low RPM. A friend asked me if I tried new plugs yet. I told him I didn't need to because I tested the ones I had and they worked. He bought me a set of plugs when he went out to buy lunch. I put them in and the bike fired on the 3rd kick and ran pretty well, which allowed me to start dialing in the idle settings and take some test rides. I assumed the warm pipe meant the cylinder was firing when it was not... but I learned how hot that pipe is suposed to be when the bike is firing... very hot, as I said above in the spit test.

It's amazing how one wrong assumption can take you down the wrong path... Good luck

Depends which is the easier to do so choice is.

Reinstall points.

or

Fit alternative carbs

Both will tell you if its a carb or ignition/wiring issue but with the A65 carbs possibly introducing a fake fault as they will be undersized and not jetted the same.

What are the odds of a carb fault appearing just as you fit EI. Not totally impossible but still unlikely.

Possible air leak in oil separator hose that leads to tee in crossover? Blank off tee and test.
Check supply voltage at EI module itself.
And yes, refit points, just to be sure it is the EI or not.

I once had an intermittent fault on a freeway ride, MK3 850. Bike suddenly died, tried starting again, fired right up, rode further, same thing. Eventually got where I was going and traced it to EI earth, fastener had come loose, at certain revs vibration broke connection, at others reconnected...
Worth a check on earth/power

johnny Lagdon said:

I once had an intermittent fault on a freeway ride, MK3 850. Bike suddenly died, tried starting again, fired right up, rode further, same thing. Eventually got where I was going and traced it to EI earth, fastener had come loose, at certain revs vibration broke connection, at others reconnected...
Worth a check on earth/power

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To this point mentioned above, Lannis, you HAVE replaced every snap connector on the bike, yes? I firmly believe all the Lucas jokes should be pointed at these often failed but hidden connectors.
http://www.britishwiring.com/category-s/266.htm

Lannis said:

auldblue said:

Lannis said:

4) Electronic ignition to eliminate an automatic advance mechanism that worked slick when OFF the bike, but very poorly when ON the bike.

......'\

The bike ran great last fall in all conditions, so there's nothing changed about the jetting or the float height.


Lannis

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Hi,
If it ain't broke don't fix it. Just wondering why if the bike was running great in all conditions on points why you felt the need to fit EI, I am having a slightly similar experience after fitting recon pump and I am thinking it is ignition timing that is out a bit going to strobe it and see what occurs. No doubt you have strobed yours. Or is it boil in the bag EI ?

Jg

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A fair question ... the bike ran great EXCEPT it wouldn't return to idle when the throttle was closed. I strobed it and found that the timing was staying advanced even when the bike was trying to idle, and would GRADUALLY return to retarded after a minute or two. I had the auto-advance mechanism in and out several times, it was like new and snapped right back when it was in my hand, but to be honest, I was tired of fooling with it. I have EI on my A65 BSA and I really like the fact that it doesn't start going out of tune the minute the engine turns over, like points with a rubbing block do. Plus you're guaranteed synchronization between cylinders just by the geometry of the trigger plate; NOT by some combination of points plate rotation and points gap setting.

So I went ahead while I was doing the oil system and installed a Pazon. I haven't had a chance to strobe it yet; on the other hand, on the 3 other Pazon and Boyer ignitions I've installed over the years, I've never changed the timing from the static setting based on a strobe test. The white dot in the middle of the circle is always bang on ....

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I remember YEARS ago that Lucas had a new spring set for the advance. As the stock springs get hot, they loose tension. So I think perhaps your springs are not pulling the advance off. If you put the points back in, why not replace your springs?

Lannis said:

So, when I was draining the old gas, I realized that one petcock was a “non-reserve” petcock with a standpipe, even though the tank has “saddles” and no crossover between them. That means that about a quart and a half of fuel is always unaccessible. So I turned the tank over to pour out the last quart, and out came sheets of old tank sealer and rust flakes. There are filters in the petcocks, filters in the line, and filters in the banjos, so none of this stuff had gotten to the carbs, and fuel was still flowing well, but I’ve got to get this sorted out before I run the bike any more ….

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I assume that you cleaned the petcock and banjo filters, and replaced or removed the in line filters?

Hello all and thanks to everyone who responded with suggestions. Every one of them COULD have been the reason I was having a problem with the engine running only on the throttle, dying when the throttle was closed EXCEPT when the choke was closed also.

Two paths to success -

1) Check COMPRESSION, IGNITION, AND FUEL in that order.

Valves were adjusted properly and leakdown on each cylinder was >70%. It has always been a good strong runner and I did not change the top end while it was down installing shocks, Pazon, and AMR anti-sump.

New Pazon ignition was checked with a timing light and with an induction test lamp. The ignition was firing on time even as the engine was coasting to a stop, and the timing was advancing and retarding perfectly with engine speed. Can't be ignition.

So fuel then.

2) If there's a PROBLEM, IT"S PROBABLY THE LAST THING YOU CHANGED.

Even if you didn't change anything, something might have changed. A tube was pulled loose, or ethanol plugged your jets, or oil drained down into somewhere you didn't expect.

Since the engine would not run at all at idle, but WOULD run on the throttle, it HAD to be some effect that was "overcome" by a large throttle opening. First guess was plugged pilot jets. I took the carbs apart twice and got them squeaky clean inside and out, no change.

Those of you who opined "Manifold Leak" were correct. Although I had carefully sealed the carbs and manifolds to the head, I had not realized that on the MkIII, there is a "breather tube" going from a tee in the manifold balance tube down to the oil separator for the engine breather. Something had gone wrong down there, and the breather tube was acting like a manifold leak. I took out the "tee", just ran a straight 1/4" fuel line between the carb manifolds, and the problem went away. I hope I'm not killing any whales or trees by disconnecting the manifold from the oil separator, but that's the way it's going to stay on THIS boy's MkIII.

Be that as it may, thanks for the help. Every answer, whether it's the actual answer to this particular problem, is useful!

Lannis

BillT said:

concours said:

Intake manifold crossover hose disconnected.

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If the bike will only run at full choke and over 2000 rpm, sounds like a vacuum leak.

I once started my bike and it backfired. Started right up next kick, but ran like crap - needed throttle and full choke to run.

50 miles from home and just a small screwdriver in my pocket. Checked the plug wires, played with the idle and throttle screws - everything seemed fine.
Noticed after 20 minutes of looking that the balance tube was not connected to one of the manifolds.

Found that - apparently - the backfire popped the crossover hose off one of the nipples.

Re-connected it and the bike ran right again

That was about 20,000 miles ago - still the same carbs

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You're welcome

Thank you Lannis for the followup.
It's nice when the original poster comes back to say what the problem was. It's a simple gesture, but often overlooked.

Glen