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Discussion Starter · #1 ·
Hello

1978 CB400T Dream

It's never been a great starter

We've had the carbs stripped down and rebuilt by a proper mechanic
It still didn't start well

I recently had a rush of blood to my head and did a bit of home fiddling as well as sending things away to real people

Summed up below:
  • New battery, fully charged
  • Starter motor brushes and O ring replaced
  • New ignition coil, HT leads, spark plug caps (David Silver)
  • New spark plugs
  • New starter solenoid (David Silver)
  • New rectifier / regulator (David Silver)
  • New CDI (Rex Speedshop)
  • Stator taken out, sent away to re rewound, returned, refitted with rotor also put back in place
  • 3 fuses replaced
  • Fresh petrol / gas in the tank
Key in
Turn to ignition
Neutral selected
Press the starter
Starter motor springs into life
Engine still won't start

I said a few choice words

Any advice from anyone out there?

I also had to change the short fuel hose from the fuel tap
Will that have resulted in a loss of pressure?
Might be part of the problem?
If so, how to I overcome it?

Thanks in advance

Elwyn
 

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Oh my, you've been through a long list of replacement parts.

Verify float height, Google the "clear tube method" your bike may have the early style adjustable floats. Aftermarket carburetor parts can have critical differences and your float needles may simply be taller or shorter than stock resulting in wrong float bowl fuel levels.
Also aftermarket jets can be dodgy too, size not true to marking. I hope your rebuilds kept all of the stock hard parts in there and only replaced seals and o-rings.

Idle screw position should be set according to the Factory Service Manual.

Synchronization between the 2 carbies could be far off, Google "bench sync"

Your carb rubbers between carb and head or carbs to airbox could have air leaks causing a too lean condition. Spraying starting fluid (ether) on them while cranking the engine may suck some in through a crack or leak betraying its location.

There could be an issue with your exhaust system, over the years I've seen my share of mouse nests in mufflers, too much back pressure? Do you get similar puffs out both sides of the exhaust while cranking the engine?

Sorry to write a book of it. Good luck.
 

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Discussion Starter · #3 ·
Thanks
I'll run those google searches

It feels / sounds like a lack of spark or fuel starvation

Nothing's firing at all

Not even a splutter
No sound or feel of anything trying to bang
The rev counter is flatlined at 0

When I fitted the new spark plug caps to the new HT leads from the new coil, I didn't have much confidence that the cap was screwing into the centre of the lead (where the copper runs).

I'll try to start the bike tomorrow with the spark plugs out / touching metal earth to see if there are any sparks (or not)
That might be it?
 

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After attempting to start, do your plugs smell like fuel? If they do I'd chase spark.

Both plugs will need to ground to the engine at the same time for that test. Removing one at a time is easier without a helper.

If you have a test meter with a resistance setting, you can test your plugs, caps, coil secondaries and coil primaries independently.
This might help pinpoint a root cause.

Also before going to much trouble please remove your fuel tank and look for a bullet-connector on a black wire with a white stripe, this is your engine stop switch from the CDI.
Please make sure it is clean and tight. There will also be a Stop Switch test in the Factory Service Manual.

If you don't have that manual you can find one at the other Honda Twins forum,
Google it, it's the one that has Vintage as the first word of its name. They have a good manuals library and tons of members that know all of the ins and outs of these bikes.
Highly recommended.
Cheers.
 

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There should be one connection there hanging out conspicuously. Most Hondas have it but I'm guessing yours will too. It should be about 1/3 of the tank back from the front on the left side.
This will be just one black wire with a white stripe that exits the main harness, connects with male/female bullet connectors like a tail light or winner uses and enters the main harness again.
 

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Discussion Starter · #7 ·
No, nothing.
There's a bullet connector from the CDI, but that goes to the coil
There's another plastic connector (enclosed spades) between the CDI and the coil
The other end of the longer CDI leads are well away from the tank

Font Cable Automotive lighting Audio equipment Circle
 

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Sorry about that. I'll have to find that manual as well then. The connection I refer to is for mechanics working on the bike mainly. They undo the connection and it bypasses the engine stop switch so the ignition is disabled same as the stop switch turned to off, but can't be bumped back accidentally....

I'm off for the evening, I'll check back later on.
 

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Hi Elwyn, the rex CDI, the single wire on the left is the black/white ign kill wire, earth to kill ign.

If it is disconnected from the loom, the ign switches will not kill the ign, ie, you can't turn it off.

Invest in those red neon plug caps mentioned ages ago. You will see why when you use them.
 

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The whole ign system is a bit fragile and will not like a poor intermitant HT earth like a plug or two resting on the engine.

The cam cover is insulated.

Leave the CDI kill wire disconnected for now, but be aware, to stop the engine the wire needs to be earthed .
 

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Discussion Starter · #11 ·
Sorry, I get very easily confused

Are you talking about the bullet connector in the red oval below?

I took the old CDi off and replaced it with the Rex unit

I remade the connections, like for like as the Rex unit comes with absolutely no instructions

Have I understood that you're saying that the cable / wire below (red oval, bullet connector) has something to do with the kill switch?

On my bike (as above, removing and replacing, like for like), the bullet connector cable went to a receiving bullet connector cable / wire coming from the coil

Is that right, or do I need to make a connection from the Rex bullet connector (red oval below) to the killswitch somehow?

Won't that leave a cable / wire from the coil redundant, unconnected?

Thanks in advance
Font Audio equipment Cable Circle Gadget



Font Audio equipment Cable Circle Gadget



 

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Discussion Starter · #12 ·
Hello
I've just taken the tank back off
I was wrong
My memory is awful
The bullet connector connects to a corresponding bullet connector on a wire that disappears into the main wiring loom, that I assume connects to the kill switch
Still can't get the bike to start though
With or without that main loom (kill switch?) connection
Fully charged battery, starter motor doing its thing, plugs are sparking, fuel in the carbs and cylinders, but it won't fire at all
 

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Discussion Starter · #14 ·
I've been advised that this wire would be used on a 3-pin indicator relay, but as I have a 2-pin relay, it's simply not needed
One less thing to worry about
 

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Nice to see the indicator flasher unit upside down, as the right way up it fills with water !

You have a wiring diagram so know the CDI black/white wire is the means to kill the ignition via the main ignition switch, the one with the key, AND via the handle bar kill switch, earth to kill ign

So, everything indicated that the engine should run, but it refuses to start.

Are you Ryan ??

So, flywheel has its crankshaft Woodruff key ?

Cam timing correct ?

Cam chain tensioned ?

Balance chain tensioned ?

Valve working clearances correct ?

Compressions good ?

Carbs have fresh fuel from a clean tank and tap ?

Carbs clean, balanced, no air leaks, choke flaps work properly, dash pot pistons rise and fall and airbox filter serviced ?

Carbs getting fuel and float hieghts correct ?

Engine breathes ?

Yes to all above ?

You have a good battery ?

And you are not "Ryan" ?
 

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Discussion Starter · #17 ·
Hello
No, not Ryan
By flywheel, do you mean the rotor?
Part of the stator generator?
There’s no woodruff key
Only a bolt
The rotor locates onto the spindle by groove / runner
 

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You stated you had the stator rewound and put it back on. there is a woodruff key on the crank shaft too time the fly wheel to the motor . It goes in the groove. You might remove the fly wheel and check it. With out the key you might be way out of time. There are two small tits on the fly wheel that cause the ing trigger to fire at the proper time. With out the woodruff key the fly wheel could be late or early .

Bill H
 
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