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Author Topic: #4 cyl won't fire  (Read 1015 times)

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Offline funkdr5

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#4 cyl won't fire
« on: November 23, 2009, 12:49:34 PM »
Ok, I started on this bike a few months ago, my first rebuild.  Changed the head gasket but when I put it back together one of the rubber seals that cover the head bolts had moved over.  So I took it back apart, this time I coated the head gasket with gasket sealer.  Now #4 isn't firing but actually blowing the gas back out of the air pod.  I took out the spark plug and it was coated in the gasket sealer, put a new one in but still not firing.  Any ideas???  I don't have a compression tester yet.  Anybody know if the $10.00 harborf. one works good?
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Offline funkdr5

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Re: #4 cyl won't fire
« Reply #1 on: November 23, 2009, 02:31:56 PM »
sorry it's a 82 650sc. I saw this picture somewhere else in the forum, is this specific to 550's? 
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Offline TwoTired

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Re: #4 cyl won't fire
« Reply #2 on: November 23, 2009, 02:41:16 PM »
I don't know if the 550 issue applies to the 650.

I'll delete my prior post.
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Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline crazypj

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Re: #4 cyl won't fire
« Reply #3 on: November 23, 2009, 03:00:34 PM »
If you didnt hold all the rocker arms up you may have bent a valve?
 I always loosen adjuster bolts and back them off level with bottom of rocker arm so it cant happen.

PJ
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Offline funkdr5

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Re: #4 cyl won't fire
« Reply #4 on: November 23, 2009, 03:02:25 PM »
Is there anything else I can check before taking it back apart?
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Offline crazypj

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Re: #4 cyl won't fire
« Reply #5 on: November 23, 2009, 03:03:38 PM »
Valve adjustment
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I fake being smart pretty good
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Offline funkdr5

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Re: #4 cyl won't fire
« Reply #6 on: November 27, 2009, 05:16:48 PM »
adjusted the valves and nothing.  finally got the valves out and they seem good.  any ideas??
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Offline crazypj

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Re: #4 cyl won't fire
« Reply #7 on: November 27, 2009, 06:45:47 PM »
Cam in backwards?
 Are carbs clean or is fuel flooding out?

PJ
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I fake being smart pretty good
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Offline funkdr5

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Re: #4 cyl won't fire
« Reply #8 on: November 28, 2009, 06:43:25 AM »
backwards cam?? is that possible??  the other 3 cyl. were running great. im sure the carbs need some tlc but it was spitting gas back out of the air pod so its getting enough gas right?  its my first build and i've not messed with carbs much.
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Offline funkdr5

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Re: #4 cyl won't fire
« Reply #9 on: November 28, 2009, 04:10:36 PM »
anybody?
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Offline crazypj

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Re: #4 cyl won't fire
« Reply #10 on: November 28, 2009, 09:46:31 PM »
If it was blowing fuel out of carb intake it has to be loosing compression which means valve isn't seating for some reason?
 There is a possibility its normal resonant reversion
Did you try swapping plug lead to number #1 cylinder? (and/or swapping plugs)
 The dual lead coils fire one plug center electrode to ground and the matching plug ground to center (to complete circuit)
It would be missing on both cylinders (1.4) if it was trigger units.
The coil has to fire both plugs although if one is fouled the other still sparks (same as grounding one lead)

PJ
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I fake being smart pretty good
'you can take my word for it or argue until you find out I'm right'

Offline funkdr5

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Re: #4 cyl won't fire
« Reply #11 on: November 29, 2009, 09:02:36 AM »
thanks pj. yes it had spark. i've ruled out bent valve, i'll check the valve seat next. i guess i should have done that already. my dilema is i didn't know if this could be a carb problem.
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Offline pinnacle

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Re: #4 cyl won't fire
« Reply #12 on: November 29, 2009, 10:27:43 AM »
for what it's worth i just went through the same dilema with my 78 cb550k.would cough fuel back through the carb so do your self a favor and do a leak down test and compression test as i found my #3 intake valave leaking like an open tap and the compression pulses of air were what was spitting the fuel back.
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1974 cb550, 1978 cb550, 1984 honda shadow vt750
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