Author Topic: CB400F won't start  (Read 390 times)

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Offline CB400Finhawaii

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CB400F won't start
« on: May 26, 2024, 12:37:04 AM »
I have a 1975 CB400F.  I don't believe the bike has been run in about 20 years.  I have had it for about 8 years but only started working on it 18 months ago.  Here is what I have done that would affect the bike's ability to start and run,

New ignition switch
New handle bar controls R&L
Rebuilt carbs
New battery
New plugs
Checked valve gaps

After doing the above the bike started but ran really rough.  I put about 3 miles on my bike.   I checked the timing but was not able to get the timing close.  I am not sure why. So I installed a Dyna S electronic ignition hoping this would fix the issue.  I didn't have consistent spark on 1&4, so installed new coils and caps.

Now, I can't get the bike to start at all.  I have spark on all 4 cylinders.  I double checked that the Dyna S was installed correctly.  The ignition timing is right on.  I swapped the wires from the 1-4 and the 2-3 coils, just to make sure they weren't installed incorrectly, and the bike didn't start (as expected).  I swapped the coils wire back to how I had them originally.  When I try to start the bike and pull the plugs, they smell like gas.  I've tried starting fluid, but the bike still wouldn't start.  Since I rebuilt the carbs, they are suspect, but the bike started before.  So even if the carbs need to be synched, the bike started before, so I don't think it is the carbs preventing my bike from starting now.  I have the stock jets in the carbs, but the stock air filter is not hook up yet.  I have never checked the compression, but since it started before, I don't think that is the problem now. 

Any ideas why the bike won't start and things I should be checking?

Mahalo
Mike


Offline bryanj

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Re: CB400F won't start
« Reply #1 on: May 26, 2024, 12:45:19 AM »
If it has stood that long its possible the rings are siezed in the pistons, do a commpression check and get back to us
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

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Offline Mark1976

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Re: CB400F won't start
« Reply #2 on: May 26, 2024, 06:44:03 AM »
   Let's back up a bit, if it was running ,albeit poorly, and now it doesn't and the plugs are wet. Ya gotta a number off issues, could be fouled plugs, could be no spark, could be poorly reconditioned carbs. Might be all three, go back to your basics, spark, fuel and compression. Stop replacing things until you can rule them out in the first place. Do your current set of plugs have spark? If they're wet maybe not (possibly fouled), check your compression if you'd like but I'm kinda leaning on poorly or improperly reconditioned carbs, overly rich condition or improperly set floats. More details on the carb reconditioning may be helpful, what kinda of parts (kits) were used. The dyna ignition isn't going to solve a thing, my perspective (your bike, your choice) is to go back to the points and condenser's (it ran with them before) and get it running properly with that set up. Make sure the battery is fully charged. One issue at a time.
Start with the end in mind...