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Author Topic: CB550 Cylinder number 3 not firing  (Read 177 times)

Offline bergers

  • Posts: 46
CB550 Cylinder number 3 not firing
« on: Nov 07, 2017, 17:04:47 »
Hey everyone, I've been working on my bike on and off for the past year and have replaced a lot of parts and checked over stuff while going through it. The list is as follows:

NEW
carb kit for all 4 (floats, float valves, jets, seals, o-rings, etc.)
fuel lines
coils
spark plugs/wires
battery

CHECKED
carbs hydrodipped and cleaned thoroughly
bench synced(used something like an eighth inch drill bit under the slides and brought them to all the same height)
intake/exh valve lash
compression (bike cold, between 125 and 140psi for all 4)
point gap
spark(ok/strong on all 4) 

I ran the bike off of a small temporary tank, it starts fairly easily with a shot of starting fluid, once warm it starts without it. The problem is cylinder number 3 is dead cold, I can put my hand the exhaust header at the head for number 3 while If I did for the others I would get a nice 2nd degree burn. A bike needs 4 things to run; compression, air, fuel, and spark. I know I have spark, I have compression and air, so I assume at this point it's some elusive fuel issue. All bowls have fuel(some overflow periodically), so I'm not sure if it's a float height issue or a carb body needs to be replaced. Any help is appreciated
« Last Edit: Nov 07, 2017, 18:01:36 by bergers »

Offline coyote13

  • Posts: 1151
Re: CB550 Cylinder number 3 not firing
« Reply #1 on: Nov 07, 2017, 17:30:25 »
Is there an accelerator pump on #3?  If there is, might check that the diaphragm doesn't have any tears or pinholes and isn't pinched.  Also make sure the slide is synched correctly with the other three carbs, I had a lock nut that kept backing off on my CB750 and chased my tail on it for quite some time before I realized the slide was wide open all the time
Half the fun's in the get there...

Offline bergers

  • Posts: 46
Re: CB550 Cylinder number 3 not firing
« Reply #2 on: Nov 07, 2017, 18:13:47 »
Is there an accelerator pump on #3?  If there is, might check that the diaphragm doesn't have any tears or pinholes and isn't pinched.  Also make sure the slide is synched correctly with the other three carbs, I had a lock nut that kept backing off on my CB750 and chased my tail on it for quite some time before I realized the slide was wide open all the time

Nah its a 74 550, so no diaphragm. And I corrected the original post, I meant to say I synced all of the slides to each other with the drill bit, not the butterflies.  I would think that should at least put me in the ballpark of having them synced.

Offline cxman

  • DTT SUPPORTER
  • *
  • Posts: 2337
Re: CB550 Cylinder number 3 not firing
« Reply #3 on: Nov 07, 2017, 19:00:58 »
squirt a bit of starting fluid in #3 carb when the bike is running

does it pick up? if it does then you know the slow jet circuit or ? sync? is whacky

if it does not swap the plug with another cylinder or a new one restart




1978 CX650 Super Deluxe
1979 XS1100 Special
1974 xl350
1983 cx650 Custom
1973 cb750
1980 cb750
1981 cb650
1982 cb900 c
1974 kawasaki 350 bighorn
1983 GL1100 aspy full dress
1983 GL1100 Nekid
and a bunch of others

Offline bergers

  • Posts: 46
Re: CB550 Cylinder number 3 not firing
« Reply #4 on: Nov 07, 2017, 19:41:41 »
squirt a bit of starting fluid in #3 carb when the bike is running

does it pick up? if it does then you know the slow jet circuit or ? sync? is whacky

if it does not swap the plug with another cylinder or a new one restart


That's a good idea, I'll try to do that tomorrow if it's not raining.

Offline coyote13

  • Posts: 1151
Re: CB550 Cylinder number 3 not firing
« Reply #5 on: Nov 08, 2017, 16:30:33 »
Suppose it could also be carb -> head vacuum issue.  Check to make sure that carb is fitted properly in the insulator boot and that the boot doesn't have any cracks.
Half the fun's in the get there...