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Author Topic: cylinder 4 not firing?  (Read 787 times)

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Offline wilson889

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cylinder 4 not firing?
« on: July 04, 2011, 05:51:19 PM »
Hey all, I went to ride my bike today, 1975 cb750k and after the usual warm up, I noticed that 4th cylinder wasn't hot like the other 3. I recently installed new coils and wires as well. I pulled the 4th plug out and there was some oil on it.. not necessarily black though. Just a little oil.

Any suggestions as to what's wrong?

Thanks
kevin
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1975 Honda CB 750K

Offline sick_seven_fifty

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Re: cylinder 4 not firing?
« Reply #1 on: July 04, 2011, 06:51:29 PM »
If it really is oil, and not fuel mixed with a little carbon, then it might be a leaky valve seal.  It would allow a little oil to pool on the cylinder while the bike isn't running, it could foul the plug when you start it up.
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Offline wilson889

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Re: cylinder 4 not firing?
« Reply #2 on: July 04, 2011, 09:46:34 PM »
Quote from: sick_seven_fifty on July 04, 2011, 06:51:29 PM
If it really is oil, and not fuel mixed with a little carbon, then it might be a leaky valve seal.  It would allow a little oil to pool on the cylinder while the bike isn't running, it could foul the plug when you start it up.

ok i guess ill throw in another plug and give it a  go..
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Offline sick_seven_fifty

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Re: cylinder 4 not firing?
« Reply #3 on: July 06, 2011, 07:03:30 AM »
If you put another plug in it, watch for a puff of blue smoke when it first fires.  That's a sign that your valve seals are leakin.
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Offline wilson889

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Re: cylinder 4 not firing?
« Reply #4 on: July 06, 2011, 11:36:54 AM »
ok, thanks man! I really appreciate the help.
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Offline wilson889

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Re: cylinder 4 not firing?
« Reply #5 on: July 06, 2011, 05:54:33 PM »
Quote from: sick_seven_fifty on July 06, 2011, 07:03:30 AM
If you put another plug in it, watch for a puff of blue smoke when it first fires.  That's a sign that your valve seals are leakin.

Well I put the new plug in and no blue smoke.. and i didnt see oil this time around, but might be what you said about fuel/carbon.
any other suggestions?? i mean the bike seems to be running normal other than the other 3 pipes are running much hotter than the 4th. 
Im clueless.. :(   
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Offline WarwickE36

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Re: cylinder 4 not firing?
« Reply #6 on: July 06, 2011, 06:01:38 PM »
bad wire to 4, restricted idle jet.
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" Why does anyone get offended by what someone does to their own bike? I dont get it. "

You made me think about it after I cheered knowing someone else would like to know what these control freaks are up to.
 Every time any owner strips whatever precious Honda part the horrified purists parts go up in value. That's not the part that bothers them.
 What bothers them is they sat up late at night, their breast full of wonder and estrogen, unable to sleep, dreaming about their lovely darling and all her glory... and next thing you know someone else doesn't share their emotional deluge and their reaction is they must spread their mind museum as far as they possibly can, taking over as much of the real world as possible.

Drink fast, drive slow, but ride it like you stole it

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Offline Psychonaut

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Re: cylinder 4 not firing?
« Reply #7 on: July 06, 2011, 06:03:00 PM »
Is this a quick touch with the hand or actual pyrometer temp? If it's a measurable difference, could be low compression in just one cylinder, doubtful but possible. Could be idle air screw adjustment but I would think a sync issue first if this is only at idle.
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Offline wilson889

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Re: cylinder 4 not firing?
« Reply #8 on: July 07, 2011, 08:26:22 AM »
Psychonaut:  its a touch with hand and spit test. It doesn't get hot enough to sizzle. Lol. I don't think its a bad wire, I just a bought them new from a forum member who said it was all inf working order. I haven't checked carbs yet, I assumed that when I had them cleaned and rebuilt and synced those would be fine.(done last year but hasn't ran with them til now) but I guess ill have to take it back to him and have him fix it/look it over. I hope its not compression problem. :(
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