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Offline flybox1

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#2 not firing....steps to take
« on: May 24, 2014, 07:20:24 PM »
#2 doesn't get hot. Just warm from the others. I  can grab the header when all others are scalding hot.  I just finished this rebuild.  Hone, re-ring, valves lapped.  Everything was tight and within spec as noted in Hondamans book. 

#2 Plug sparks when held against the head, and Plug caps are all new, but #2 read @ 5.24
Swapped 2/3 coil wires.  #2 still doesn't get hot.
I meticulously cleaned my carbs, but will verify cleanliness and choke butterfly operation in the morning...

What else should I check.  Thanks.
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

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Offline goldarrow

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#2 not firing....steps to take
« Reply #1 on: May 24, 2014, 08:49:18 PM »
Check the pilot jet again, try new spark plug.  I had new plug that was bad before.  Check plug wire is good, not internally broken. That's all I could think of right now
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Offline Jimsun

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Re: #2 not firing....steps to take
« Reply #2 on: May 24, 2014, 08:54:35 PM »
I had similar issue with my cb550. The culprit for me was my emulsion tube being clogged. After i cleaned them, cyl 2 header is as hot as the others.
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Offline flybox1

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Re: #2 not firing....steps to take
« Reply #3 on: May 24, 2014, 09:07:38 PM »
I will pull my carbs to verify, but I disassembled and cleaned them for winter storage, and recently put them all back together.  They were still spotless and shiny.
Clean filtered gas, too.
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline goldarrow

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Re: #2 not firing....steps to take
« Reply #4 on: May 24, 2014, 09:14:36 PM »
On a 750, just drop the bowls and see the jets
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Life Is Full Of Challenges - And My Backyard Is Full Of SOHC4's

CB550 K0
CB750 K0, K2, K23 JDM, K45, K5
And the little ones z50r, xr50r, st90


750k5 http://forums.sohc4.net/index.php?topic=114817.0

Offline ekpent

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Re: #2 not firing....steps to take
« Reply #5 on: May 25, 2014, 05:20:03 AM »
A bad plug can still get spark when just laid on the head but may not work correctly under full compression.
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Offline Vinhead1957

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Re: #2 not firing....steps to take
« Reply #6 on: May 25, 2014, 06:17:57 AM »
+1 on ekpent
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Offline flybox1

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Re: #2 not firing....steps to take
« Reply #7 on: May 25, 2014, 06:42:18 AM »
Ok. I'll try this first, but I gotta wait till the neighborhood wakes up ::)
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline Stev-o

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Re: #2 not firing....steps to take
« Reply #8 on: May 25, 2014, 08:31:10 AM »
Quote from: Vinhead1957 on May 25, 2014, 06:17:57 AM
+1 on ekpent

+1....time to wake up the neighbors
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Offline flybox1

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Re: #2 not firing....steps to take
« Reply #9 on: May 25, 2014, 09:45:40 AM »
#2 still cold with new plugs.   :-\  Carbs coming off for a re-check
Other ideas welcome and appreciated.....
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline Tetter

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Re: #2 not firing....steps to take
« Reply #10 on: May 25, 2014, 10:09:59 AM »
As mentioned above... pilot jet.
I had the exact same issue after my rebuild.  :o


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Offline flybox1

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Re: #2 not firing....steps to take
« Reply #11 on: May 25, 2014, 10:30:39 AM »
Hope that's it. Meticulously going thru mine...again  ::) ;D
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline TwoTired

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Re: #2 not firing....steps to take
« Reply #12 on: May 25, 2014, 10:50:15 AM »
Sometimes the float valves stick, starving the bowl for fuel.  Check the drain screw for #2.  Tap on the bowl to see if mechanical shock will dislodge the float/valve.

Or remove the carbs...
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Offline jamesb

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Re: #2 not firing....steps to take
« Reply #13 on: May 25, 2014, 11:52:10 AM »
Mine was just doing that but on #1. I changed plugs wires  he ked everything then finally dropped the bowl on that carb to see I there was a problem and low and behold it must have been because it hasn't had any problems since. So I'm thinking it washed some debris out of there
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Offline fire113

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Re: #2 not firing....steps to take
« Reply #14 on: May 25, 2014, 12:16:07 PM »
...check the vacuum screw at carb #2

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Offline flybox1

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Re: #2 not firing....steps to take
« Reply #15 on: May 25, 2014, 12:20:36 PM »
Ok. Still not firing on #2
Each carb was inspected, broken down and reassembled. 
No blockages in any of the jets.  Passages blown clean. Float heights verified correct.
Carbs back on bike....Bowl drain screw on #2 opened allowing gas to flow.
When tightened, float valve shut off fuel.  Carbs are operating as they should as far as I can tell.

Next option.... :-\
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline flybox1

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Re: #2 not firing....steps to take
« Reply #16 on: May 25, 2014, 12:22:25 PM »
Quote from: fire113 on May 25, 2014, 12:16:07 PM
...check the vacuum screw at carb #2
Ok...
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline flybox1

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Re: #2 not firing....steps to take
« Reply #17 on: May 25, 2014, 12:28:54 PM »
« Last Edit: May 25, 2014, 12:33:07 PM by flybox1 »
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline fire113

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Re: #2 not firing....steps to take
« Reply #18 on: May 25, 2014, 12:50:32 PM »
...try a shot of start pilot spray at carb #2 to be sure that something explosive is in cyl. #2 and see if pipe #2 is getting hot. If not do a compression test on cylinder #2.


 
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Offline TwoTired

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Re: #2 not firing....steps to take
« Reply #19 on: May 25, 2014, 12:52:16 PM »
  Do the plugs get wet after cranking with full choke and the kill switch blocking spark?

Inspect the valve operation through the inspection/adjustment ports, verify they all move full travel.
Compression check.

Fuel/air, compression, spark = must run.
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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 flybox1

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Re: #2 not firing....steps to take
« Reply #20 on: May 25, 2014, 02:13:58 PM »
Quote from: TwoTired on May 25, 2014, 12:52:16 PM
  Do the plugs get wet after cranking with full choke and the kill switch blocking spark?

Inspect the valve operation through the inspection/adjustment ports, verify they all move full travel.
Compression check.

Fuel/air, compression, spark = must run.
Exactly...so, I pulled the new densos I put in this am, and im pretty damn embarassed ::) but I'll post here and take my lumps.    ;D  I added four 1" screened airbox powerholes and I didn't account for this change.

Holy isht those are lean  :o
After going out 2 turns on my mixture screws, they are just starting to tan. And #2 is warming up.  Certainly not hot like the others, but noticeably warmer after 2-3 min idle.
#42 pilots are on order...
Thanks for the input guys. 
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline Duanob

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Re: #2 not firing....steps to take
« Reply #21 on: May 25, 2014, 07:11:58 PM »
Hey Rob, it wouldn't be a good story without a few bumps along the way ;)

I would throw the ND plugs in the trash and go get some NGKs. I had the same problem earlier this year with 550F. It was  bad plug and it was fairly new.

Also:
Did you recheck your valve tappets? Maybe #2 is too tight? No comp, no fire.

Are you sure you have OEM spec pilots? I had that same problem as well with the F.

I hope you get it on the road soon, but today is a good day to wrench in a nice dry garage.
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Offline disco

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Re: #2 not firing....steps to take
« Reply #22 on: May 26, 2014, 01:51:54 AM »
+1 to what Fire113 said.....a bit of starting fluid thru the carby will firstly determine whether your problem is fuel or spark. Then tackle the problem once you have narrowed it down.
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