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Back cylinder not working, PLEASE HELP!

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Old Jul 15th, 2011, 01:13 PM     #11
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Re: Back cylinder not working, PLEASE HELP!

Quote: Originally Posted by BillMull View Post
Hey Glider, can I test to see if I have a leak around my intake by using carb cleaner by spraying it around it while its running. If the bike responds to it, that means I have a leak? Is that correct? Is there any chance the problem is the coil?
The spray would give you a definitive answer if the intake is leaking or not.
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Old Jul 15th, 2011, 01:52 PM     #12
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Re: Back cylinder not working, PLEASE HELP!

Quote: Originally Posted by BillMull View Post
Is there any chance the problem is the coil?
I am not saying this is your problem (it probably isn't) but here is some info regarding your question about the coil.

I never had a HD dual fire coil in my hand to see how they are made, but if they are made like the schematic represents, you can have an issue with yours. The reason I say that is this. On dual fire, the spark plugs are in series with ONE secondary winding which has no center tap to ground. When you pull one spark plug wire, BOTH plugs should stop firing because one plug provides a ground path for each other. One plug is firing with positive polarity and the other plug fires with negative polarity.

If you pull a plug wire, you must connect that wire to frame ground in order for the remaining plug to fire. Now earlier you said when you pulled the front plug wire, the bike continued to run. And when you pulled the rear plug the bike died.

ASSUMING YOUR NOT DEALING WITH AIR LEAKS OR MIXTURE ISSUES,,, the bike should have died when you pulled either plug if the coil is actually made like the schematic represents.
If the secondary is completely isolated from frame ground and the primary windings, the above would hold true.

With coil still mounted to the bike, take a meter and check to see if ANY continuity exists between a spark plug tower terminal and FRAME ground & either primary wire stud. You should read infinity between either coil tower to frame ground and either primary terminal if my theory holds true.
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Old Jul 15th, 2011, 05:22 PM     #13
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Re: Back cylinder not working, PLEASE HELP!

Pull front spark plug wire=engine dies.
Pull back spark plug wire=engine runs.
Wouldn't this mean something wrong with back cylinder?
Am I missing something?
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Old Jul 15th, 2011, 07:11 PM     #14
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Re: Back cylinder not working, PLEASE HELP!

Quote: Originally Posted by wilks3 View Post
Pull front spark plug wire=engine dies.
Pull back spark plug wire=engine runs.
Wouldn't this mean something wrong with back cylinder?
Am I missing something?
Only true if the ignition is a single fire ignition OR if it is dual fire and the coil secondary winding does have a center tap.

I am 95% certain that the OP's ignition is dual fire and the coil does not have a secondary center tap. The schematics I have seen so far reflect this but I don't have a 1996 Sportster manual to know for sure.

When you pull a plug wire on a TRUE dual fire system with no center tap secondary, it kills both plugs, not just the one you pulled. If you ground the wire you pulled, the other plug will then fire.
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Old Jul 15th, 2011, 08:18 PM     #15
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Re: Back cylinder not working, PLEASE HELP!

Ya, I don't know either on the coil set-up. It just seems odd pull wire on front, engine dies, pull wire on rear, engine runs, but rough. So something in the ignition is still firing and engine will run on front cyl, but not back cyl. Would still like to know the compression on back cyl.
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Old Jul 16th, 2011, 12:34 AM     #16
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Thumbs up Re: Back cylinder not working, PLEASE HELP!

Thanks guys for the replies....I may of confused you guys....If I pull the wire on the back cylinder it continues to run.....If I pull the wire on the front cylinder it dies.....Today I was fooling with it some and got me some carb/choke cleaner to test it. I started the bike and let it idle and of course it was idling very rough as expected with front cylinder only working. While idling I revved it up and then let go and a blue flame shot out of the rear cylinder exhaust pipe. When I rev it up it seems the rear cylinder kicks in like normal. I then tried holding up the choke while it was idling and it made the back cylinder run like normal. It sounded great!!! I let go of the choke and it went back to the back cylinder not firing again. Pull the choke and it went to normal state again...I got so excited thinking I was on something and came back in and forgot to spray the carb/choke cleaner to test the intake seals......Guys, I dont know how to say thanks enough for you all trying to help me....It means a ton to me...If I can ever repay you guys with some info someday consider it done....BUT, I dont know much about Harleys just yet....BUT, I will be a life long friend to ya!!!!!!
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Old Jul 16th, 2011, 10:14 PM     #17
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Re: Back cylinder not working, PLEASE HELP!

Today I went out to fool with my bike some more. I started the bike and the back cylinder still not working. I guess I just expect it to heal itself overnight...

While it was running I pulled the choke and held it there and the bike ran great and the back cylinder was working fine and it sounded normal. When I let the choke back down it went back to its normal state of the back cylinder not working. Also, while it was idling I revved it up and let the throttle go and it shot a blue flame out the exhaust pipe of the back cylinder. This was NOT while I had the choke pulled just normal idle and then rev and then let go. Can I use carb and choke cleaner to check my intake seals?
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Old Jul 16th, 2011, 10:27 PM     #18
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Re: Back cylinder not working, PLEASE HELP!

Have you checked the compression on both cylinders yet? Almost sounds like burn't or hanging open exhaust valve on rear cylinder.
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Old Jul 17th, 2011, 10:56 AM     #19
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Re: Back cylinder not working, PLEASE HELP!

I would be doing a compression test next, if you have a blown head gasket or as Wilks says a bad valve you will not have fire in that cylinder
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Old Jul 22nd, 2011, 11:08 PM     #20
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Re: Back cylinder not working, PLEASE HELP!

well, it works great with the choke pulled or revving it up....I did the carb cleaner test on the intake and the bike changed drastically when I sprayed it on there...So, im trying to replace the gaskets on the intake...Lets pray that helps!!
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