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Author Topic: Dying CB400/4  (Read 1853 times)

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Offline patlac

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Dying CB400/4
« on: March 08, 2011, 03:19:49 PM »
 Can anyone help me cure a problem with my 1977 CB400/4 .Having bought it with leaking carbs I cleaned carbs fitted new float valves set float height, fitted new air filter and plugs set pilot screw out 2 1/2 turns Compression is 110 psi on all 4cyls. The bike will rev ok in neutral or with clutch pulled in but riding it runs rough and wont rev over 4000 rpm. On removing plugs they are vert dry sooty. Bike converted to Boyer ign. Thanks for replies and suggestions.The bike has an airbox I ensured all jets clean but I will go over again and check boyer timing.
      I checked carbs today using a colortune and all 4 carbs are burning a nice deep blue.Dave500 suggested setting up boyer with a strobe. I have one I checked timing statically at TDC and it was ok Marks on Rotor lined up with Stator, At 4000 RPM the Marks are about1/2" anti Clock from Stator pick ups. What did he mean by turning plate to these marks then marking them I cannot move plate as it is at the end of travel.
« Last Edit: March 10, 2011, 08:13:27 AM by patlac »
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Offline DavePhipps

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Re: Dying CB400/4
« Reply #1 on: March 08, 2011, 03:24:16 PM »
does it have an airbox or pods?
In any case I would suggest a good cleaning of the carbs as they are in an unknown state. Check your jet sizes while you're in there.
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Offline MoMo

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Re: Dying CB400/4
« Reply #2 on: March 08, 2011, 05:26:31 PM »
When you cleaned the carbs,did you remove the mid-range needle jet and clean all the holes?  Every 400 four I have redone has had that jet clogged on at least one of the carbs. Is the timing set correct?...Larry
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Offline Joel

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Re: Dying CB400/4
« Reply #3 on: March 08, 2011, 05:33:29 PM »
I'd also suggest verifying the ignition timing.
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Offline dave500

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Re: Dying CB400/4
« Reply #4 on: March 09, 2011, 01:00:37 AM »
to time a boyer,use a timing light,its the only way,get it running then increase the revs and watch it advance,when it stops advancing adjust the plate untill the mark is on the full advance mark and lock it there.
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Offline Fred T

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Re: Dying CB400/4
« Reply #5 on: March 09, 2011, 04:39:03 AM »
Carb synch?
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Offline Deltarider

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Re: Dying CB400/4
« Reply #6 on: March 09, 2011, 10:54:36 AM »
Quote
Carb synch?
What makes you think that? The man says bike idles OK.
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Offline Tim2005

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Re: Dying CB400/4
« Reply #7 on: March 09, 2011, 01:21:43 PM »
This really does sound like blocked main jets or wrong float levels, but I wonder if this could be a fuel starvation problem, especially if the carbs are clean and jets are the right size, particularly the mains, and timing is set as Dave500 correctly describes. Fuel starvation could either be caused by a blocked fuel tap or blocked tank air vent.
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