Topic: Removed muffler - now bike (CB400F) won't start. Help requested.

[obrut]

OK, removed the muffler on my CB400F last night to repack it.  It took some effort to get it off.

Now the bike won't start???  Lots of fuel in the tank and I've checked the fuel tap and it flows.  I have spark on all cylinders (although it may be looking a little weak).  Pods are clean so I have air.  The freshly charged battery cranks the motor at speed and it sounds like its trying to fire but won't run.  No better with the kick start.

The wiring on this bike has seen better days.  I'm planning on fixing that after some frame mods are completed.

I assume I have disturbed something whilst wrestling the muffler off. 

The bike was starting and running fine before I removed the muffler.  I would welcome some recommendations as to what to check etc.

Ps.  In case it is relevant - the main 15A fuse got very hot (didn't fail) either during one of the extended cranking sessions or during the charging of the battery.

[d3buttz]

check the wiring that goes to your points. start there and trace back to where they connect in the bundle with the rear brake switch.  your wires run along the bottom of your frame and could have been rattlled loose from the pipe wrestling. good luck

[obrut]

Thanks, will try and report back.

[obrut]

Can't find anything loose.  Fuses all ok and I have power in the black wire from the points to the coils.  However, spark is a little weak/patchy.

Can anyone describe how to check out the coils?

Still don't know how this ties in to the muffler removal though???

[KingCustomCycles.com]

It doesn't tie into the muffler removal.  Think back, you did something else.  Hooked up a battery charger, bumped the kill switch, shook the headlight housing, unbolted a ground unknowingly, etc...

[obrut]

"It doesn't tie into the muffler removal.  Think back, you did something else.  Hooked up a battery charger, bumped the kill switch, shook the headlight housing, unbolted a ground unknowingly, etc.."

I agree - I did hook up a battery charger (and the battery has charged up correctly).  Petcock is set to flow, tank has fuel.  Gearbox is in nuetral (indicator light confirms).

I have checked the handlebar kill switch and it is in RUN.  Are there any others?

Can't find any grounds loose.

The really strange part is I appear to have fuel, air and spark - but no start??

[Kong]

If you have spark then you must not have fuel.

[obrut]

Ok, this is getting strange...

At first I had weak spark on 1 and 4, then really weak on 2 and 3 and now no spark anywhere.  I have power going to the blue and yellow wires (which cycles on and off when you turn the motor over).  The 1/4 coil is also getting much hotter than the 2/3 coil.  I also have power in the black/white that leaves the coil.

The kill switch appears to be working correctly.  Fuses are ok.

What else could kill the spark??  What test would you do next?? 

[KingCustomCycles.com]

Your battery died suddenly,  test it under load and I bet it drops to 11 volts or less with the starter engaged. A shorted coil will also load the battery and drop your voltage.

[obrut]

Firstly, thanks for your help KCC.

This is getting stranger:  If I remove a plug, insert it in a lead and ground the plug against the motor, then I get little or no spark when I crank it over on the starter (using the charged bike battery or jumper cables from the battery of a running car).  However, if it pull the plug away from the motor by a 3-5mm then I get a good blue spark at the electrode which jumps to the motor.

Grounding the plug against the motor seems to be killing the spark.  Any idea what would cause this??

[KingCustomCycles.com]

I would suggest you need to test the coils and wiring per the manual.  Usually I can give a guy some short cuts I have learned but this is back to basics troubleshooting.  It was a coincidental electrical failure with the muffler work, in my opinion.

[HawaiiMike]

If it turns out not to be an electrical issue, pull the muffler and check it out.  When I read your first post it crossed my mind that maybe you blocked the muffler with too much baffling.  If the exhaust gases aren't getting out the bike won't run.

[KingCustomCycles.com]

+1, didn't think of that common problem, thanks!

[obrut]

Thanks guys, I thought of that too and have already checked that the muffler still has a free passage down the middle.  It also won't start with the muffler off altogether.

I got some new plugs, coils etc on the way and will then get back to elec trouble shooting.

[obrut]

It runs!

Back to basics - pulled, cleaned and regapped the plugs, recharged the battery, checkhed fuel to the carbs, checked all the earths.

Still don't really know what caused it to refuse to start - best guess is really fouled plugs.

[camelman]

The 350F and 400F are very susceptible to fouled plugs and low batteries causing starting issues.  If in doubt, then charge the battery and clean/replace the plugs.  I use Seafoam to clean my plugs if I don't have a spare set handy.  As long as the plugs are newish, they should clean up and work again.

Camelman

[Gaither]

obrut

If you did all that at one time, you'll likely never know which item/s fixed it. But, who cares? Just be glad she's running good again.

'Glad you hot 'er going (and it wasn't too expensive).