CB400T Carb repair, etc

Bobs twin said:
Being as my coils, plug wires and ends are original, is it possible that I should check them to make sure I am getting good spark?
Is it possible that this may be why my bike is hard to start after it sits?
or is it just me in a learning curve struggling with cold start up?
bob
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Since your carbs have an accelerator pump, I'd try starting it cold with one or the other but not both together - either one twist of the throttle to give a squirt of raw fuel, or pull the choke up fully without twisting the throttle. From your description it seems doing both might be more than it needs.
 
ancientdad said:
Since your carbs have an accelerator pump, I'd try starting it cold with one or the other but not both together - either one twist of the throttle to give a squirt of raw fuel, or pull the choke up fully without twisting the throttle. From your description it seems doing both might be more than it needs.
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Thanks!
This will be my next attempt.
When it gets started it runs well, performs well on the road.
Another thought was that the gas that sat in it over winter might be a bit less cooperative, so I'll run it out in my next ride.
Fresh gas is always better.
I did put stabilizer in the tank in the fall.
Thanks again!
bob
 
mine does not have accelerator pump, but my starting procedure is FULL choke, no throttle, and all it needs is blip on the starter button even when cold. almost immediately the rpms will start climbing so I usually keep my hand on the choke and just use that to control the rpms at about 1000. after about 20-30 sec it stabilizes.

I have the Dynatek DC11-2 coil on mine, and if you are looking for something to upgrade this year, I join many of the others that recommend it. You have to make your own spark plug cables, so If you don't want to do that @Maraakate sells the whole kit with wires that he makes for you. It is one of the more pricey coil options for this model but worth it in my opinion if you plan to keep the bike long term.
 
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And if you do decide on the DC11-2 and already have one i can just make the cables and brackets separately. You'll still have to solder the green and yellow harness to the coil, but it's not too hard to do with a solder iron (don't use a gun).
 
I always give it a very, very minor amount of fuel when pushing the button. But yes, you could give it too much if you don't know the technique. Not really required with these bikes but used to other ones where it is a requirement.
 
Maraakate said:
I always give it a very, very minor amount of fuel when pushing the button. But yes, you could give it too much if you don't know the technique. Not really required with these bikes but used to other ones where it is a requirement.
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well.........
the last bike I had with carbs was a 1968 Norton 850, which required tickling before kick starting.
so..........
it's been a while.
I'll get there, it will just take me a while....................
bob
 
Bobs twin said:
Being as my coils, plug wires and ends are original, is it possible that I should check them to make sure I am getting good spark?
Is it possible that this may be why my bike is hard to start after it sits?
or is it just me in a learning curve struggling with cold start up?
bob
Click to expand...
You can check resistances easily.
Yellow - Green primary wires are under 1 ohm
Plug wire to plug wire w/o caps 8K ohms +/-.8
Plug end caps 5K ohms
 
Bobs twin said:
well.........
the last bike I had with carbs was a 1968 Norton 850, which required tickling before kick starting.
so..........
it's been a while.
I'll get there, it will just take me a while....................
bob
Click to expand...
I love float ticklers. Always start first "kick" on my mopeds with the bing carbs.
 
LongDistanceRider said:
You can check resistances easily.
Yellow - Green primary wires are under 1 ohm
Plug wire to plug wire w/o caps 8K ohms +/-.8
Plug end caps 5K ohms
Click to expand...
OK...........
I just tried to check the resistances, and...........
I disconnected the coils, zeroed my ohmeter and touched yellow and green, and it was under 1 ohm.
I removed the caps from the wires and didn't seem to be able to get any reading?
I put one lead in to one wire end, and the other in to the other end and didn't seem to be able to get any reading?
My tester was purchased in 1985, so..............
And being as I am niot very good with electrical.........
It is very likely that I did something wrong?
One reading out of three is where I am at.
bob
p.s. - one question....
do the plug wires thread out of the coil in the same way that the plug cap comes off of the wire?
I didn't want to try this in case I goofed something up, I'm a rookie at best when it comes to electrical.
 
I've decided to just buy new plug wires and plug caps for this bike.
The coil checked out OK for the first test, but my wires are getting hard.
the end caps have cracks in the gromets that are at each end and it makes sens eto put new ones on.
Unfortunatelt the parts place that I went to, Fortnine and PartsNmore no longer list an 83 CB400T, so I'll call the dealer when they open.
They have been able to get what I need in the past, and the parts are Honda parts.
when I have it apart I'l try the last two tests with a newer ohm meter also.
Thanks guys!
bob
 
You cannot get NGK XD05F caps any more from the dealer as NGK discontinued these about 2 years ago.

You snip back the wire with a pair of good scissors (or wire cutters) about 1/4 to 1/2" until you can see the inner steel (sometimes copper) core wire. This is part of a normal tune-up if you have the original coils.

You CAN get the NGK caps from David Silver Spares. There are also aftermarket versions now. If they work well and hold up as well as the originals... I have no clue... but probably. A few users here have used them and say they work just fine: https://www.amazon.com/TORCH-Replace-Phenolic-Kiloohm-SPARK_PLUG/dp/B0CP7HMT4P
 
Maraakate said:
You cannot get NGK XD05F caps any more from the dealer as NGK discontinued these about 2 years ago.

You snip back the wire with a pair of good scissors (or wire cutters) about 1/4 to 1/2" until you can see the inner steel (sometimes copper) core wire. This is part of a normal tune-up if you have the original coils.

You CAN get the NGK caps from David Silver Spares. There are also aftermarket versions now. If they work well and hold up as well as the originals... I have no clue... but probably. A few users here have used them and say they work just fine: https://www.amazon.com/TORCH-Replace-Phenolic-Kiloohm-SPARK_PLUG/dp/B0CP7HMT4P
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I did cut back about 1/4" then threaded the plug caps back on.
The bike runs well, I just think I would like to have new caps and wires.
Do the wires thread out of the coil?
If not I will be looking at a replacement coil, with wires.
The dealer has a Honda replacement coil with wires for $172 canadian, I just called.
bob
 
Wires do not come out of the original coil. Best thing to do is get a DynaTek DC11-2. Most eBay and Amazon offerings of aftermarket coils for these bikes are garbage AND/OR the wrong primary resistance and cause strange running. You should be able to source 7mm or 8mm spark plug SOLID CORE (NOTE: NOT CARBON!) wire.

I have a thread on how to do this: https://vintagehondatwins.com/forum...tructions-for-cb400-cm400-cm450-cb450sc.9178/

$172/CA will be cheaper than the DynaTek DC11-2 route. But only by a little bit. Either option is good. The DynaTek will allow a larger spark plug gap of 0.040" which is a smoother idle and easier cold starts.
 
Maraakate said:
Wires do not come out of the original coil. Best thing to do is get a DynaTek DC11-2. Most eBay and Amazon offerings of aftermarket coils for these bikes are garbage AND/OR the wrong primary resistance and cause strange running. You should be able to source 7mm or 8mm spark plug SOLID CORE (NOTE: NOT CARBON!) wire.

I have a thread on how to do this: https://vintagehondatwins.com/forum...tructions-for-cb400-cm400-cm450-cb450sc.9178/

$172/CA will be cheaper than the DynaTek DC11-2 route. But only by a little bit. Either option is good. The DynaTek will allow a larger spark plug gap of 0.040" which is a smoother idle and easier cold starts.
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What would your DynaTek DC11-2 cost me, if you wouldn't mind sharing that? I am in Canada also.......... Close to Niagara Falls.......
I believe from reading above it comes with wires?
Plug caps would be nice also.
Mine works, but like I said, the wires have lost theiur flexibility and my end caps have worn out seals on them.
Bob
 
Bobs twin said:
What would your DynaTek DC11-2 cost me, if you wouldn't mind sharing that? I am in Canada also.......... Close to Niagara Falls.......
I believe from reading above it comes with wires?
Plug caps would be nice also.
Mine works, but like I said, the wires have lost theiur flexibility and my end caps have worn out seals on them.
Bob
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I found this DynaTek at Fortnine, which is in Canada.
Our borders and customs are not what they once were anymore.
bob
 
Bobs twin said:
What would your DynaTek DC11-2 cost me, if you wouldn't mind sharing that? I am in Canada also.......... Close to Niagara Falls.......
I believe from reading above it comes with wires?
Plug caps would be nice also.
Mine works, but like I said, the wires have lost theiur flexibility and my end caps have worn out seals on them.
Bob
Click to expand...
It does not come with wires. Check summit racing, dennis kirk, or similar vendors. Hot rod car vendors probably have it. Not sure what options you have in Canada.
 
Make sure, and ask if you are unsure, that the wires are SOLID CORE. Do not get carbon core wires. The giveaway for carbon core wires is that they are USUALLY gray. This means you can't just run up to the parts store and get a cheap tune-up kit for a car and cut it to fit.
 
 
It's hard to tell. I don't think so, but I honestly don't remember if the bags came with 4 or 2 caps. I will look now and report back as I save the bags.
 
Maraakate said:
It comes with two bags of 4 caps and one bag with 4 terminals.
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This is the reply that I got from Dynatek about the DC11-2 coil

"Thank you for your interest in Dynatek ignitions.
Are you sure your bike uses a 0.5 ohm coil?
I seem to recall the CB400's in those years as using a 3-5 ohm coil.
In this case we would recommend our DC1-3.
I would suggest you verify the factory resistance specifications for your stock coil and then proceed from there.
For plug wires we would suggest our DW-200 for a solid core option.
Technical Support
Toll Free: 800-928-3962"

any thoughts?
bob
 
Maraakate said:
He's thinking of the CB400F. Tell him it's a CB400T/CM400T. You want a DC11-2. It is a 0.5 ohm coil.
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I let the Dynatek support people know that the coil recommended was for a CB400T, and that I am being told that the DC11-2 .5 ohm is the right coil for my bike.
this is what they said.......
bob

Well, it could be if it was ordered as a DC1-2 which would be the 2 coil kit version. My concern is more with the ohm rating. Can you measure your stock coil to verify or get access to a service manual for the specs?
Regards,
Technical Support
Toll Free: 800-928-3962
 
Excerpt from the Cylmers manual. Yes, I know this is frowned upon HOWEVER I think this qualifies as fair use because it is a single page and it is of low resolution.
Capture.PNG
 
From the CB450SC/Nighthawk 450 factory service manual (which uses the same exact system, the CDIs are interchangeable):
1746879711935.png
 
Bobs twin said:
Can you think of a reason why their support people would be so focused on a .3 ohm coil?
bob
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also, I found the DC11-2 coil on amazon.ca for $183.
this doesn't sound too bad, and would avoid the border concerns we seem to be facing at the moment.
bob

 
Maraakate said:
This is a two-cylinder parallel twin with wasted spark that uses true AC CDI.
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Just to be clear, the term "parallel" is about the cylinders being side by side and not a reference to the 360° crankshaft arrangement. The 350 and 450 are parallel twins with a 180° crankshaft. And yes, all 360° crankshaft Honda twin engines are a wasted spark system, as are the pairs of parallel cylinders on any Honda 4 cylinder engine - 1/4 are like a 360° twin with wasted spark, as are 2/3.
 
Bobs twin said:
Can you think of a reason why their support people would be so focused on a .3 ohm coil?
bob
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Because they aren't as familiar with these bikes as we are, that's all. I know you're old enough to remember the term "a little knowledge is a dangerous thing", and this is a good example.
 
ancientdad said:
Because they aren't as familiar with these bikes as we are, that's all. I know you're old enough to remember the term "a little knowledge is a dangerous thing", and this is a good example.
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Yup, turns out I am that old!
Thanks again!
I do trust you guys more than outside sources, even if they are the manufacturer.
I just posted what they said so that you would be aware of the info being given.
Have a great weekend!
bob
 
I just received this back from DynaTek, looks like they are on board now.
bob

Hi Bob,
Just to follow up I found this spec online that would indicate the OEM ignition is a CDI style so the DC11-2 should be OK.
The 1981 Honda CB400T uses an ignition coil with the following specifications135:
  • Primary Resistance: 1.5 ohms
  • Secondary Resistance: 13,000 ohms
Let us know if you need anything else.
Regards,
Technical Support
Toll Free: 800-928-3962
 
I dont know what their deal is. They measure out about 0.5 to 1.0 ohms on the bench. I know because as stated I've done a dozen of these. Just ignore them.
 
Glad you showed testing internal resistance of your probes first, I have seen some probes with a lot of resistance and it can make a big difference. that's good technique.
 
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