Topic: CB400F on't fire up and run

[seabird]

Advice and Ideas sought for this problem:

Restored 1975 CB400F. 

I have sparks (Electronic Ignition), Fuel to cylinders as shown by wet plugs, the engine turns over with the electric foot and with the K/Start, yet it won't fire - won't even backfire.

What I've done:  Checked the ignition timing (got to get it running before I can re-time with a Strobe) - set at the "F" timing mark as per the instructions.
Fuel enters cylinders (wet plugs) - fresh fuel.

New battery.

Will re-check valve clearances tomorrow if my hands don't freeze solid (only -4 degreesF in my garage today, and snowing).


What's next?  Valve timing? (Oh No!!  )  What else?

She's ready to go except for this little hiccup.

Thanks fellers!

Seabird

[supersport_CB400F]

I’d check all my timing marks again If I had the engine apart.

[TwoTired]

An engine requires Compression, Fuel, and timed ignition to fire.

How have you verified compression?

Fuel on the plugs verify that ingredient.

The mere presence of electronic ignition does not verify properly timed spark.
Did you see the spark plugs sparking across the electrode gap?

Did you verify sparks occur after compression stroke when both valves are closed and near TDC?

Was your spark advancer assembled 180 degrees out of phase?

Cheers,

P.S. Is your electric foot a recent addition?  And, won't mister Roboto miss the loss?

[GroovieGhoulie]

All timing: valve, ignition, etc.

Also, (prolly a dumb suggestion) make sure it's getting air.

air
spark
fuel
should mean a running engine.

If all else fails, check the flux capacitor to make sure it's fluxing.  

[seabird]

An engine requires Compression, Fuel, and timed ignition to fire.

How have you verified compression?

Fuel on the plugs verify that ingredient.

The mere presence of electronic ignition does not verify properly timed spark.
Did you see the spark plugs sparking across the electrode gap?

Did you verify sparks occur after compression stroke when both valves are closed and near TDC?

Was your spark advancer assembled 180 degrees out of phase?

Cheers,

P.S. Is your electric foot a recent addition?  And, won't mister Roboto miss the loss?

Compression is good on all four pots - new pistons/ring sets fitted, no discernable wear in the cylinders.

The plugs spark like Christmas tree lights - fat blue sparks.

Spark Advancer not touched during rebuild - but PO reports 'bike ran up OK before being stored.

I'll lift the rocker cover and verify/re-adjust the valve timing - when it's warmer....

After that I'll re-gap the valve clearances and re-fit the Carbs - (which giant brain designed the cabs to hang off the cylinder son rock hard rubber)?

Thanks guys!

Seabird

[Bob Wessner]

Fuel to cylinders as shown by wet plugs,

Seems like you are saying everything appears to be OK otherwise, but when you say wet plugs, how wet? Even with a spark, if they are really wet, they will/may not fire. Is the cause of the wet plugs because of a lack of ignition, or too much raw fuel??

[seabird]

Hi  Bob,

The plugs are certainly _not_ dripping with fuel, but are obviously damp - they're easily wiped dry by finger pressure alone.
The spark can be easily seen in daylight, but the spark is seen both on the central electrode and arcing across to the threaded body of the plug as well.  I've only checked the 1 and 4 plugs - both appear the same - all four are the correct type fort the 400F and are new.

It's just occurred to me that I've only reset the timing on cylinders 1 and 4 - I should also have re-adjusted cylinders 2 and 3, but the cold and growing darkness pushed me indoors to thaw out before I could do this, so I'll check the inner two cylinders' timing tomorrow morning.

It just seem ro me that I have all that's needed for the motor to run, i.e., sparks, fuel and air, it's just that they're not occurring at the same time; damned frustrating!

Seabird

[Tim2005]

but the spark is seen both on the central electrode and arcing across to the threaded body of the plug as well. 

Time to buy some new plugs- when they're arcing like that then they've had it. Set 2 & 3 timing too & I'll bet it'll fire right up.

[supersport_CB400F]

The insulators break down with time that’s why the have time/miles and then replace limits

[Bob Wessner]

But seabird indicates the plugs are new...

all four are the correct type fort the 400F and are new.

Maybe his thoughts on the timing of two and three are on the right track. If warm it may run rough on two, but doubt you can start it on just two.

[GroovieGhoulie]

I just adjusted my ignition timing a few weeks ago and the timing was retarded as all hell due to points wear, however, the 2&3 timing was still advanced, so I had to advance the whole plate, then retard the 2&3 timing to get it all synced up.

What's weird is that she purred and ran great before and while it runs better now, the difference is not night/day.  More like just a bit smoother.

Syncing the carbs was more useful in helping smoothness.  Got rid of the clutch rattle as well.

[supersport_CB400F]

I still think the timing is the issue....

[GroovieGhoulie]

I still think the timing is the issue....

I would tend to agree.

[seabird]

For anyone who isn#t sick and tired of this thread yet...

Found the (probable) cause(s) of the lack of action here...

1.  The spark plug in #3, supposedly fitted by my son after helping to lift the engine in - wasn't.  It is now.

2.  Most likely cause:  When I had the head removed and refurbished by a "motorcycle engineering company", whoever rippped the head off cunningly severed the trigger lead to the lecky ignition.  On the advice of the manufacturers' Techie department, I soldered the matched end (tricky - those wires are like hairs) of the four cut wires.  Obviously my soldering talent is near to non-existent, because although 1 and 4 have great sparks, #2 and #3 have no spark whatsoever.

since the Electronic Ignition kit is at least 15 years old, I reckon I'll bite the bullet and shell out for today's version.

Thanks blokes - your help and ideas worked again!

Seabird

[GroovieGhoulie]

Any possibility of putting a Honda igniton in?  Once set up properly, the points are pretty good.

[supersport_CB400F]

I just got the Dyna S from Z1 cost about 82 quid with postage and took 10 days…… the advantage is it’s self contained so you have no box of electronics to keep dry. I just need to find an advance retard plate now....anybody got a spare 350F one to sell or a 400F one with the 13.5mm shaft?