Topic: 1975 Cb400F Problems

[gwallis]

I just started work on a 1975 Honda Cb400F that was sitting for over a dozen years.  The bike is in great shape but I have two situations that have me scratching my head.

1)  I replaced the burned out High Beam bulb and now the headlight does not work.  It did before the bulb replacement.  I check the usual suspects:  Headlight, Fuse as well as looking for lose wringing in the bucket with no luck.  I am stumped!

2)  The Tach is extremely slow to react.  The cable is moving as it should but the dial just creeps and never really reaches the top RPM.  Is this just because it was sitting so long?  Will it come around after it is ridden for a few miles?

Any help with these issues would be greatly appreciated.

[minimo]

1) Have you checked inside of the left electrical controls?  Check or clean the switch while you’re in there as oxidation on the contacts could be the result of no high beam. Also, check continuity on the blue and green wires, which I believe are specific to the high beam.

2) If you have the tach cable off, check for any breaks. If it’s intact, spray lube inside of the cable. When you put the cable back on, make sure the mating blade/slot align on the top cover end of the line. Also, be sure that the square end connector to the bottom of the tach engages. Also, be mindful of any extreme bends in your tach cable.


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[bryanj]

If you dont have a lights on/off switch on the rh side switch there is a link wire inside the shell that connects two different colour wires together, cant remember which OR by coincedence your starter button has fallen apart.
As to tacho, yes its because its been stood and no it wont get better

[Kevnz]

I've just freed up a speedo that was so seized you could only turn the mechanism over with a screwdriver fitted with a squaredrive head. Inverted the speedo and filled the cable input with acetone and let it soak overnight. Next morning it had freed up considerably, did the same for another night and normal service restored. Failing that, you may need to open it up. A dob of grease is used to dampen the action of the needle, and over years this has probably gone stiff resulting in the sluggish response. Carefully remove that and lube the innards and you should be good to go.

[gwallis]

Funny that you should mention the Starter Button.  The button has been sticking and engages as soon as I turn the key.  Is there some connection in that unit that would cause the lights not to work?

Enlighten me...parden the pun!

[gwallis]

I've just freed up a speedo that was so seized you could only turn the mechanism over with a screwdriver fitted with a squaredrive head. Inverted the speedo and filled the cable input with acetone and let it soak overnight. Next morning it had freed up considerably, did the same for another night and normal service restored. Failing that, you may need to open it up. A dob of grease is used to dampen the action of the needle, and over years this has probably gone stiff resulting in the sluggish response. Carefully remove that and lube the innards and you should be good to go.

Kevin.... Thanks for the input.  I just might try the upside down thing.  Thanks again!

[Don R]

  The start/headlight switch is combined in a plastic cage that often crumbles. I've owned 3 400F's and bought 3 new right controls.

[Flyin900]

Funny that you should mention the Starter Button.  The button has been sticking and engages as soon as I turn the key.  Is there some connection in that unit that would cause the lights not to work?

Enlighten me...parden the pun!

The start button plastic connection box inside that switch has possibly disintegrated and is causing the start button issue. It is a common issue on those old right hand control switches.

[Kevin]

The starter button is tied into the lights. When engaged power from the lights is diverted so the starter has more amperage.


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[PeWe]

Acetone might be too strong for paint, plastic. WD40 is thin and a good cleaner, deruster.

I lubricated the original screaming speedo on my K6 with the upside down method over night.
WD40 followed by thin oil but still thicker than WD40. I think it was lithium spray.

This was 2014. Have worked fine since then, around 30.000km.

[Bodi]

"Acetone might be too strong for paint, plastic. WD40 is thin and a good cleaner, deruster"

How do you get the inside of the glass clean afterwards? Anyway, I use 99% isopropyl.

[Kevnz]

I'm only talking about putting it in the speedo drive input, less than 1\4 of a teaspoon. Doesn't, or shouldn't get inside the guts. I tried penetrating oil, CRC, didn't work.

[PeWe]

"Acetone might be too strong for paint, plastic. WD40 is thin and a good cleaner, deruster"

How do you get the inside of the glass clean afterwards? Anyway, I use 99% isopropyl.

I was lucky to not get any oil inside dripping onto the glass.  I did not spray floods of it either. But for my speedo lubrication only make it stop screaming.

99% isopropyl must be a good alternative.
Used as cleaner on vinyl records back in those days. Or lock antifreeze for cars. Very special smell.

[gwallis]

If you dont have a lights on/off switch on the rh side switch there is a link wire inside the shell that connects two different colour wires together, cant remember which OR by coincedence your starter button has fallen apart.
As to tacho, yes its because its been stood and no it wont get better

You were absolutely correct!  I pulled the starter button out with needle nose pliers and the lights came on.  THANKS!

I love this Forum!

[Bodi]

My button guts turned super brittle and broke into many pieces. I bypassed the headlight switch and found a tiny button that fits in there just for the starter. Has worked fine for years and the added lamp power draw when starting hasn't caused any starting problem I can notice.

[Kenzo1979]

My button guts turned super brittle and broke into many pieces. I bypassed the headlight switch and found a tiny button that fits in there just for the starter. Has worked fine for years and the added lamp power draw when starting hasn't caused any starting problem I can notice.

+1  Just connect an SPST, Normally Open, mini push button switch like the one in the pic.  I prefer the type specified “plunger for cap”. Which means the part you push is part of the actual switch and not just a little cap that sits on a rod that can fall off and get lost at any point.  If you install a switch like this, just connect Black (ignition power) to the lighting wire on one contact (mine was black/red or pink), and your starter wire (yellow/red) to the other contact.  This will give you the setup that Bodi described.

[Kenzo1979]

Pulled out the switches I bought off Amazon last year to post some pics.  Fit pretty perfectly, works great and looks good to me.  If you can find the same switches you'll be happy.

[gwallis]

Pulled out the switches I bought off Amazon last year to post some pics.  Fit pretty perfectly, works great and looks good to me.  If you can find the same switches you'll be happy.

Thank you so  much for your post.  Do you know the specs on the switch?

I think that I found the correct ones.... 12 pack off Amazon for $17.00 delivered.

[Kenzo1979]

The seller I bought from no longer has it available, but the photo shows the specs from my purchase.  The link is what I found to be the same product from another seller.




https://www.amazon.com/dp/B07BD1MS18/ref=cm_sw_r_cp_api_glt_i_EQRYAXRCPJ5JNHP1X3RR?_encoding=UTF8&psc=1

[gwallis]

The seller I bought from no longer has it available, but the photo shows the specs from my purchase.  The link is what I found to be the same product from another seller.




https://www.amazon.com/dp/B07BD1MS18/ref=cm_sw_r_cp_api_glt_i_EQRYAXRCPJ5JNHP1X3RR?_encoding=UTF8&psc=1

Bless you...that is exactly what I needed.

Thanks again!