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Old 09-29-2014, 07:47 PM   #1
Jai
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Default HELP! Bsa lightning only running on one cylinder.

Hello,
I've browsed through old posts and found similar problems but never anything that was resolved.. I'm not a mechanic, but I'm building a up 69' lightning (twin carb) for some reason I can't get the left cylinder to fire. It was backfiring here and there for a bit but now only running on one cylinder (it runs fairly smoothly on the right).

Here is what i've done..

-new pistons/bored cylinders
-boyer ignition
-podtronics regulator/rectifier/capacitor
-12v dual coil

I've tried...
-held hand over right air intake... motor dies
-held hand over left intake.. nothing happens
-switched out plugs.. no change
-switching plug leads.. it still runs on the right cylinder
-flip flopped carbs... still runs on the right
-adjusted valves.. (not a mechanic and never done this) pretty sure did it correctly, tight enough that the next size up feeler will not fit.

Any suggestions are much appreciated!!
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Old 09-29-2014, 10:26 PM   #2
Sturdly
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Default Re: HELP! Bsa lightning only running on one cylinder.

What does one need for an internal combustion motor to run? Spark, Pull the wire on the dead hole spark plug, insert a screw driver. start motor holding screw driver !\8" or so from ground. Got spark? No. Ignition problem. Compression, remove plug from dead hole and check it. Compression too low, check that valves are closing. Is the plug in the dead hole wet? If not it's possibly a fuel delivery problem. Check if the carb has gas, etc.
Thats the basics to troubleshoot any engine.
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Old 09-29-2014, 11:05 PM   #3
MountinAsh
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Default Re: HELP! Bsa lightning only running on one cylinder.

Jai I noticed your not running a battry in your system. But you do have a boyer installed. You didnt mention anything about upgradeing your rortor and or stator. Check the output voltage from your stator when the lump is running and make sure its at least 11 volts. Anything under that and your boyer may not fire like it should.
I chased that gremlin for weeks on my 64 lightning with a compleat(brand new out of the box) Sparx system.
if your rotors magnets are weak.it does happen. your boyer will not be happy.
If you can, just for a test. Slide a fully charged battery into your system and give it a kick. I bet your gonna fire on both barrels.


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Old 09-29-2014, 11:10 PM   #4
greasystain
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Default Re: HELP! Bsa lightning only running on one cylinder.

well your first problem was using that electronic ignition stuff when first getting a bike going. that stuff is next to impossible to physically diagnose any problems on! if you had points youd be riding this bike right now and banging your neighbors hot daughter behind a tree someplace over the bike. ive had a little to drink tonight, but seriously, are you getting spark with the plug pulled out of the motor and sitting on the head? if you are its most likely not firing at the correct time 360 out.
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Old 09-30-2014, 12:41 AM   #5
Jai
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Default Re: HELP! Bsa lightning only running on one cylinder.

Thanks for the replies!
-Ive got good spark from both plug wires.
-Both cylinders are at 155psi
-plug in the dead cylinder getting fuel
-I haven't tested the rotor/stator running, but I will tomorrow.
-Before I put in the boyer I started it on the points and it ran the same, thats why I ended up switching to EI.

So it's sounding like timing or rotor?
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Old 09-30-2014, 02:11 AM   #6
greasystain
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Default Re: HELP! Bsa lightning only running on one cylinder.

is it a single coil single fire system? or dual coil independent spark?
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Old 09-30-2014, 11:40 PM   #7
Mr.Pete
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Default Re: HELP! Bsa lightning only running on one cylinder.

The Boyer box, coil and plug leads are working fine, if one cylinder is firing. If the alternator wasn't supplying enough power to the Boyer, no cylinders would fire.
It could still be a faulty spark plug, but you've tried that too. You could always try that again with a new plug.
Swapping carbs didn't help, so it's probably not a carb problem. It would be a terrible carb to totally stop the cylinder firing, you'd usually get something even if you had to tickle the carb to get it happening.

It could be a sticky valve. It wouldn't show when you did a compression test, but if the guide clearance is too tight it could tighten up as soon as the engine starts running. You might find out more if you start it with the rocker cover off.

A totally blocked exhaust can stop one cylinder too. Worth checking, but unlikely. Also check that no-one left a rag in the intake port.
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Old 10-01-2014, 05:54 AM   #8
Lester
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Default Re: HELP! Bsa lightning only running on one cylinder.

Swap plug wires on the coil and see what side fires...
just a thought...

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Old 10-02-2014, 12:54 AM   #9
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Default Re: HELP! Bsa lightning only running on one cylinder.

Jai sez~"-plug in the dead cylinder getting fuel"
are you 100% CERTAIN of this?
you`v got 155psi in both cyls,
spark in both plugs
really only leaves one thing!
simple test,remove air filters, fire and run on the existing cyl, open throttle some and spray dead cyl w/carb cleaner [dont drown it!] if you hear a few good farts from that cyl , clean the main jet.
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Old 10-02-2014, 12:42 PM   #10
Jai
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Default Re: HELP! Bsa lightning only running on one cylinder.

Wanted to give an update on this.. I got it going!! I ended up pulling all the wiring and requiring everything. I've got a hunch I had it run as negative ground.. Anyways.. It runs great. Thanks for all the help!
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Old 10-02-2014, 12:43 PM   #11
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Default Re: HELP! Bsa lightning only running on one cylinder.

(Rewiring)
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