CB400T Carb repair, etc

OK, I am still having cold start issues.
I checked my plugs, and the plugs that the local Honda dealer sold me are not the ones recommended in the owner’s manual.
They sold me NGK DR8ES plugs, and the manual recommends NGK DR8EA, which is what I ran successfully last year.
So, I just gaped the plugs I had in last year and I'll give it another try in a few hours.
Someone is still sleeping.....................
bob
p.s. - the olny way I can get it to start with the previous plugs is to open the petcock, start turning the engine over, and slowly pull the choke.
This works, but with these ES plugs it is very sensitive to flooding.
 
Just put in D8EAs. Dealer should have those on the shelf. No resistor inside the plug which may help with easier cold starts and less wasted spark energy during load.

You start the bike by pulling the choke all the way UP, petcock ON, and crank. Should start within 5-10 seconds of continuous cranking. Once it starts let it sit like this for about 5-30 seconds (depends on ambient temperature). The idle should be higher with the choke fully engaged. Especially if you blip the throttle. After this you move the choke to about 1/4 to 1/2 way position and you can start driving, or wait longer to get fully warmed up if you like.

Here is the starting procedure from the manual:

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1749127631133.png
 
Maraakate said:
Just put in D8EAs. Dealer should have those on the shelf. No resistor inside the plug which may help with easier cold starts and less wasted spark energy during load.

You start the bike by pulling the choke all the way UP, petcock ON, and crank. Should start within 5-10 seconds of continuous cranking. Once it starts let it sit like this for about 5-30 seconds (depends on ambient temperature). The idle should be higher with the choke fully engaged. Especially if you blip the throttle. After this you move the choke to about 1/4 to 1/2 way position and you can start driving, or wait longer to get fully warmed up if you like.

Here is the starting procedure from the manual:

View attachment 46276
View attachment 46277
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Yes, that is how I started the bike last year, but with the different plugs it just doesn't respond the same way.
I'll try the bike today with last years plugs, and pick up some new ones on my ride.
Thanks again!
bob
 
Maraakate said:
OK. Just FYI that coil will help with cold starts.
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Yes, I agree, and very much appreciate your guidance!
My wife and I are caught up in a few gardening projects right now so my time is spoken for.
trying to make our home easy to take care of because I'm not 18 anymore.
right now my back is out, so things are one hold.
maybe TMI?
bob
 
No, we're understanding of that here. In all fairness it's not a complete requirement. If the bike was running OK before on your previous plugs, then should be fine for now. Gotta take care of the wifes hobbies first before yours!
 
Maraakate said:
No, we're understanding of that here. In all fairness it's not a complete requirement. If the bike was running OK before on your previous plugs, then should be fine for now. Gotta take care of the wifes hobbies first before yours!
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well...........
I may have answered my question.
I took last years plugs, the NGK DR8EA's, gaped them, put them in.
Opened the pecock, pulled the choke a third out, hit the button, and.....
It started right away, so............
I'll be picking some new ones tomorrow.
Thanks again!
bob
 
Either that or D8EAs. Canada wanted DR8EAs to get it from 5K resistance to 10K. It really doesn't matter. You'll get a bit more spark output with the D8EAs. My dealer always has some in stock - maybe they will for you?
 
I orderd (4) D8EA plugs from Royal Distributing.
It was cheaper to order them and have them delivered than to pick them up at the dealer.
They will go in soon.
Thanks again!
bob
 
well...........
that settles it.
It was a bit cool this morning, and the bike sat for a few days, but..........
I pulled it out, pulled the chock half way, hit the button and it started right up.
It even seems to run smother with the D8EA plugs.
so..............
those DR8ES plugs were the problem.
Thanks again!
bob
p.s. - that cramp buster is great!
 
ya know guys..........
I figured something out today.
if your jeans are wet, and you put them on..........
then go for a long enough ride........
they will be dry when you get home.......
as long as you lift off the seat a few times at speed............
but, behind the belt is still a tad wet.
that's a problem for another day though!
starting great and running fine, thanks guys!
bob
 
Bobs twin said:
ya know guys..........
I figured something out today.
if your jeans are wet, and you put them on..........
then go for a long enough ride........
they will be dry when you get home.......
as long as you lift off the seat a few times at speed............
but, behind the belt is still a tad wet.
that's a problem for another day though!
starting great and running fine, thanks guys!
bob
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I don't know about where you are Bob, but around here in Florida it would have to be a short ride or the water-wet jeans would only briefly dry and shortly afterward would be sweat-soaked if you rode long enough, and especially if you had to stop in traffic for more than a couple of minutes :ROFLMAO:
 
ancientdad said:
I don't know about where you are Bob, but around here in Florida it would have to be a short ride or the water-wet jeans would only briefly dry and shortly afterward would be sweat-soaked if you rode long enough, and especially if you had to stop in traffic for more than a couple of minutes :ROFLMAO:
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yup, I hear ya.
When I went out here in southern Ontario it was just about a perfect day for sure.
also, the roads that I take are mostly through farm country, so there is very little traffic and not many stops.
later today it will be a lot more muggy, so..............
the bike will be parked.
now...........
on another note.............
it is hard for me to work up any form of sympathy for someone that lives in Florida, and gets a lot lore riding days tan I will ever see.
jus sayin................
:cool:
bob
 
Bobs twin said:
it is hard for me to work up any form of sympathy for someone that lives in Florida, and gets a lot lore riding days tan I will ever see.
jus sayin................
:cool:
bob
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If only you lived here for a few summer months Bob.... you'd be staying inside a lot more than you might imagine. I barely ride between late May and late October, and this (combined with typical 75% humidity on average) is why. My thermometer is in the shade just outside my kitchen window, and it's been like that here nearly every day for the last few weeks. Feels like a furnace in full sunlight.

heat.jpg
 
Out here is just the opposite. Yesterday it was sunny and in the low 70's, but the whole month of July has been cloudy, cold and windy. Last week it rained 5 days straight, never got to 70! Flannel shirt weather. The heat went on a few times.
 
wentwest said:
Out here is just the opposite. Yesterday it was sunny and in the low 70's, but the whole month of July has been cloudy, cold and windy. Last week it rained 5 days straight, never got to 70! Flannel shirt weather. The heat went on a few times.
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Wow, that's crazy.
 
We do get the hot here and the humidity is heavy. If I ride I go out before lunch as it is not comfortable after that. I live between Lake Ontario and Lake Erie, and the Niagara River is close, so huimidity is the norm. If I am thinking correctly, in Florida you can get in some good rides late in to the fall, and in to what we would call winter here, I am a tad north so I could be off on this thinking. But yes, I do understand the need to stay inside on those very heavy summer days. They are good days for fixin something that you can't get around to on other days.
bob
 
I went for a ride the other day with a friend and his HD Road Glide, which is a nice bike for sure.
But as the day went by I felt more and more comfortable on my CB400T, as compared to the larger touring bike.
My last bike was a Super Glide, but at my age this 400 is just about perfect.
It's easy and comfortable to ride and own, and with the expert advice and guidance I have received from many of you on this site, well, I smile a lot!
Thank you all very much!
bob
 
Bobs twin said:
If I am thinking correctly, in Florida you can get in some good rides late in to the fall, and in to what we would call winter here,
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Yes, my favorite riding time here is from late October to maybe mid-April, the coldest days in between aside. My gauge for riding temp is, if the sweat doesn't dry once you get moving then it's too hot to ride.
 
OK, I have a question.
High test gas or regular?
I have always run high test because I have been told that it burns cooler, and with an air cooled engine this is good.
I used to run 260 Sunoco in my S90, partly because I liked the colour of it.
Just thought I'd ask.
bob
 
I tend to use high test in motorcycles, because it has great resistance to pinging and knocking. These engines get really hot, and they have pretty high compression, too. And I suspect most of us don't ride so much that the extra cost is a factor.
 
Thanks!
One more question.
I have noticed that my bike, when I am above 65MPH, and at full throttle, will have little pauses, or dips, not sure how to word this.
It almost feels like fuel starvation.
Yes, it is a 400, and I am pushing it, but I just thought I'd ask.
bob
 
Bobs twin said:
it's around 7,000
the red line is 10,000
I usually ride between 5 and 6
bob
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OK, that rules out what I was thinking about. It's possible that it is cutting out intermittently at higher rpms, but you might not feel it as much in lower gears. Once, years ago, I had a bike that was cutting in and out sometimes, and it was that the level of fuel in the float bowls was slightly too low.
 
wentwest said:
OK, that rules out what I was thinking about. It's possible that it is cutting out intermittently at higher rpms, but you might not feel it as much in lower gears. Once, years ago, I had a bike that was cutting in and out sometimes, and it was that the level of fuel in the float bowls was slightly too low.
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I think I have the carbs working well.
I've followed all of the advice that LDR gave, which was very much appreciated.
The carbs started to work properly after I removed that pressed in metering jet and cleared those passages.
The bike just has a slight dip once in a while at full throttle in high gear under load.
I have a feeling I will just forget about it, as I do not take it on major highways anyway.
Bob
 
OK, I just got back from a ride.
The word I have been looking for is uneven, the acceleration in 6th above 65MPH is uneven.
But, if I take the bike up the 75MPH in 5th, then cruise in 6th at, 75 all is well.
also...........
I will try 87 octane next tank.
bob
 
Higher octane does nothing for these bikes. They were designed to run on 87. The 91/93 nomenclature in the manuals is based on the other formula for calculating octane. As per the 78 CB400 (same engine all throughout the CM400/CM450/CB450SC series with some minor additions in the 450 family):

1754662513841.png

Pump octane is likely what you're using at the pump. If you look closely you'll see the stickers mentioning the formula. I have been using standard E10 87 pump gas for over 15 years in all my bikes and lawn equipment. Simply put some fuel stabilizer in the tank every fill-up (yes, really) and it will fire right up again in the spring. No need to waste money on expensive ethanol free gas or high octane. Using higher octane from a regular pump might even be a detriment since it's used less which means there's a high probability of it being stale.

If you have pinging then you have an intake leak or an ignition problem.
 
Maraakate said:
Higher octane does nothing for these bikes. They were designed to run on 87. The 91/93 nomenclature in the manuals is based on the other formula for calculating octane. As per the 78 CB400 (same engine all throughout the CM400/CM450/CB450SC series with some minor additions in the 450 family):

View attachment 48173

Pump octane is likely what you're using at the pump. If you look closely you'll see the stickers mentioning the formula. I have been using standard E10 87 pump gas for over 15 years in all my bikes and lawn equipment. Simply put some fuel stabilizer in the tank every fill-up (yes, really) and it will fire right up again in the spring. No need to waste money on expensive ethanol free gas or high octane. Using higher octane from a regular pump might even be a detriment since it's used less which means there's a high probability of it being stale.

If you have pinging then you have an intake leak or an ignition problem.
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ok, sounds good.
I don't have any pinging, the bike runs well.
starts right up now with those plugs that you recommended.
I am just trying to figure out this higher speed uneveness.
I feel that I may have this figured out also, I'll just take the bike up to the speed that I want, then cruise in 6th.
It's been a while since I've had a smaller bike, they are a tad different, fun for sure!
but different.
bob
p.s. - I don't believe that any gas is ethanol free in Canada?
 
No idea about ethanol free in Canada. Have you verified the float height? If its a bit too lean could affect the mixture or is it only happening at cruising? Probably more of a Jim question as I work more on the autos than the manuals.
 
Maraakate said:
No idea about ethanol free in Canada. Have you verified the float height? If its a bit too lean could affect the mixture or is it only happening at cruising? Probably more of a Jim question as I work more on the autos than the manuals.
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Thanks, I've been pondering this since I read it yesterday. No brilliance to add yet.
 
LongDistanceRider said:
Thanks, I've been pondering this since I read it yesterday. No brilliance to add yet.
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The float levels are fine, it is a weakness somewhere.
I think I'll just use the 5th to speed then 6th approach.
Thanks guys!
I shouldn't really expect it to run like a new bike, it's 44 years old.
bob
 
In a different bike some discussion about using a thin washer to raise the needle just a smidge, which enriches the mixture at mid range. Whether this is relevant to your bike, I have no clue.
 
wentwest said:
In a different bike some discussion about using a thin washer to raise the needle just a smidge, which enriches the mixture at mid range. Whether this is relevant to your bike, I have no clue.
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I am coming to the conclusion that at higher speeds my bike is at it's limit.
I have no complaints it runs very well.
When I am at a speed that this uneveness happens, if I drop down to 5th it runs smooth and clean.
This leads me to believe that fuel starvation is not the issue, because in my opinion a higher rev and full throttle would require more gas.
It's ok, it gets me where I want to go.
Thanks guys!
bob
 
Something is not right. In looking at your first posts and pictures of the bike your headers have the blue hue too. Typically a sign of a lean condition and your plug colour will confirm if that is a problem. Yet as you noted your OK with issue at the top end of the speed band. I am of the opinion that these bikes are lean at mid and upper RPM. It is a lot of messing around to fix issues that can happen from the different gas formulas used today and the original jetting used back then.

I chased what turned out to be a very lean issue on my 1984 model with a different carb model than your running and resolved it with a slide needle shim.
 
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No. When you are raising needles on these carbs you are masking a deeper issue. It is not a "today's gas" type of issue. Blue headers is not just a lean condition. Excessive idling can also cause this condition. And Dave, it's been discovered the reason for your raising needles hack is because you have aftermarket jet needles in there. Which is something that was a mentioned many times as a possible cause. Just because a bike has 1000 miles on it means absolutely nothing. People screw with these things because they sit and want to try and get it running again and/or a quick sale and they buy a kit. Doesn't matter if it's the original owner or not.

The only lean issue on these bikes is the mid range jet could go up a number. It helps, yes, but it is not necessary.

Do the more/less air test and see if things improve. It's easy to do. Just tape off ONE of the two ducts on the air box lid with duct tape and go for a ride and see if it's any better. If it's too much and bogs down bad try taping it off about 1/2 way on that duct. Now try the opposite. Crack the airbox lid open and put something in there like a plastic screwdriver handle, etc. to keep it propped open. DO NOT just remove the air filter or the lid. That's too much of a change.
 
Maraakate said:
No. When you are raising needles on these carbs you are masking a deeper issue. It is not a "today's gas" type of issue. Blue headers is not just a lean condition. Excessive idling can also cause this condition. And Dave, it's been discovered the reason for your raising needles hack is because you have aftermarket jet needles in there. Which is something that was a mentioned many times as a possible cause. Just because a bike has 1000 miles on it means absolutely nothing. People screw with these things because they sit and want to try and get it running again and/or a quick sale and they buy a kit. Doesn't matter if it's the original owner or not.

The only lean issue on these bikes is the mid range jet could go up a number. It helps, yes, but it is not necessary.

Do the more/less air test and see if things improve. It's easy to do. Just tape off ONE of the two ducts on the air box lid with duct tape and go for a ride and see if it's any better. If it's too much and bogs down bad try taping it off about 1/2 way on that duct. Now try the opposite. Crack the airbox lid open and put something in there like a plastic screwdriver handle, etc. to keep it propped open. DO NOT just remove the air filter or the lid. That's too much of a change.
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the blue on the pipes came with the bike. (When it had the smaller Honda jets in it)
I changed the jets to Honda ones, the ones that LDR recommended.
It runs well enough for me, I don't plan on taking it to Bonneville.
bob
 
Yes, that's fine and normal to do. The mid range jet can benefit by going up a number for improved mid range cruising, but it is not necessary.

Also you are saying between gear 5 and 6. This cannot be right unless you have a 450 engine on it. 6th gear is an overdrive gear on the CB450SC/Nighthawk 450 and in turn they removed the kickstarter to make room for it. Do you mean 5th gear? Loss of power in 5th gear when you expect it most and then dropping down to 4 to compensate is a classic tired CDI issue. This is not to shoehorn myself into getting a purchase out of you, rather it is well documented. Another issue with the bad gas mileage and poor performance like this may be that the clutch pads need replaced. There might be some slipping going on and robbing you of power and causing you to use more gas to compensate.
 
Maraakate said:
Yes, that's fine and normal to do. The mid range jet can benefit by going up a number for improved mid range cruising, but it is not necessary.

Also you are saying between gear 5 and 6. This cannot be right unless you have a 450 engine on it. 6th gear is an overdrive gear on the CB450SC/Nighthawk 450 and in turn they removed the kickstarter to make room for it. Do you mean 5th gear? Loss of power in 5th gear when you expect it most and then dropping down to 4 to compensate is a classic tired CDI issue. This is not to shoehorn myself into getting a purchase out of you, rather it is well documented. Another issue with the bad gas mileage and poor performance like this may be that the clutch pads need replaced. There might be some slipping going on and robbing you of power and causing you to use more gas to compensate.
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Well, I have a 1981 CB400T, from Canada, and it has 6 speeds for sure, and uses em all.
Also, I just got back from a 65 mile ride and it is running fine.
I just won't expect it to go like a 1200 would.
As far as performance, this bike, after putting in the 110 and 75 jets, really gets up and goes, cruises fine also.
I am more used to a larger bike, so............
I don't have much of a need to cruise at or above 70MPH.
I just put my first tank of 87 in also.
I am getting between 60 and 63 MPG to boot!
All in all I am quite happy with this unit!
so, I'll stop whinning now............................
bob
 
Maraakate said:
Yes, that's fine and normal to do. The mid range jet can benefit by going up a number for improved mid range cruising, but it is not necessary.

Also you are saying between gear 5 and 6. This cannot be right unless you have a 450 engine on it. 6th gear is an overdrive gear on the CB450SC/Nighthawk 450 and in turn they removed the kickstarter to make room for it. Do you mean 5th gear? Loss of power in 5th gear when you expect it most and then dropping down to 4 to compensate is a classic tired CDI issue. This is not to shoehorn myself into getting a purchase out of you, rather it is well documented. Another issue with the bad gas mileage and poor performance like this may be that the clutch pads need replaced. There might be some slipping going on and robbing you of power and causing you to use more gas to compensate.
Click to expand...
The 1981 CM400 series had 5 speed gear boxes. The 1981 CB400T was a 6 speed.
 
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