CB400T cafe: Let's cut this thing into pieces

Finally getting started on this. God, I'm so sorry for the few of you that have seen my "idea" posts. I have a garage now so I can actually do this! Started taking my 1978 CB400T down to the frame today. Got all the small parts off now I need to start on the exhaust, engine and air box stuff. Hopefully that'll be done tomorrow. Maybe. I want to do something like Steel Bent Custom's CB400. Here's a picture of that!



Except I don't want mine to be white. And a couple of other things but this is my inspiration. As all of you know, the frame on the twin is HORRENDOUS. Grinder, meet frame. You won't be very good friends. I want to use DCC's hoop kit to create a good hoop for a short solo cafe seat. I also want to do an air box delete and use UNI filters, which will require rejetting (easy) and do a 2-1 exhaust similar to the one above. Then new shocks, custom wiring harness, hidden battery, etc. So the whole point is to lighten up the frame and get it to handle a little nicer.

As for the engine, I'm going to change some gears out to get some more torque at first and see where that gets me. If I'm not satisfied with that, we'll see where I go with it. I'm not too comfortable opening that up on my own so I'll get someone to help me with that. And by help I mean do it for me while I hand them tools and buy them beer.

So yeah! This is my first project with a bike and I need guidance! I'll be posting pretty regularly, I hope, with this. It'll be a weekend project thing seeing that I'm still in college and need to be a responsible student sometimes. I'll be buying parts sometime this upcoming week, I just need to decide what to get first. Any suggestions?

Thanks guys, stick with me, I want to make this thing one badass little twin.

Here are some pictures of the bike and where it's at now.

Any plans for the stock seat?

Not yet. I'll probably end up selling some of the stock parts

Jetting CV carbs with pods, and 2 into 1, exhaust is easy? Hmmm. You said this is your first bike project?

Maybe some flat or round slides...but CVs?

So I assume you test rode it before all this stripping down to establish a baseline to work from? What didn't you like? Popping the gearbox apart is fairly major work when you might be able to get away with changing the front/rear sprocket sizes instead.

gijoe13844 said:

Jetting CV carbs with pods, and 2 into 1, exhaust is easy? Hmmm. You said this is your first bike project?

Maybe some flat or round slides...but CVs?

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When I got the bike in the summer, I stripped to about where it is now and re-did the carbs. The jets are screw in jets and buying new jets isn't a huge deal nor is it expensive. Getting the carbs off isn't that bad either. Getting them on sucks though. When I say first project, I mean a complete rebuild. I've done other mechanical things before. Cars can be fun!

And Manxie, like I said, I've had the bike for a little over 6 months now, completely stock minus the handle bars. It doesn't have a lot of low end power, or not what I would like it to have, and the suspension is very soft. I know that's because this was supposed to be a cruiser bike but I don't want it to be a cruiser anymore. I've always like the cafe style and it would be about the same amount of money for me to sell this bike, buy a CB or something that doesn't have the diamond frame and get that the way I want. This will be more fun too. Well it'll be fun to look back on. I anticipate several moments of severe frustration.

I get how easy it is to change jets. The fact that you dont seem to understand how difficult they are to tune with pods tells me you don't really know what you are in for. Keeping midrange is near impossible and don't let those jet kits made for pods kid you. You will never get close to stock air box performance.

Not that much performance to begin with. Again, this is all up in the air and I'm open for any suggestions. I don't like how the seat is and I would like a more cafe look out of it. I'm not against re-doing the frame for this look, but I would have to figure out how to re-mount the air box and then get side covers that don't look like complete shit. I have tuned carbs before but they were flat slides, not CV's. I didn't know that CV's had such an issue with pods. Would a drilled air box do any good or just keep that all stock? As for seat, I know that some company makes seats that use the original seat pan, but they're based out of Vietnam and cost almost $300 after shipping. I don't want to do that. I'd be much happier either making a loop or cutting the mud guard mount off and setting up a kind of bratty looking seat too with low clip ons. Better direction there?

CV stands for constant velocity. They require a a smooth steady flow of air to keep the vacuum lift from fluttering. Pods dont create the flow that the stock velocity stacks inside the large space of the air box do. Cheap pods also block orificices in the mouth of the carb.

Flat slides don't rely on this steady stream of air and thus are easier to tune.


No amount of jetting will get your mid range back. You need to modify the the carbs themselves and only crazy pj knows that black magic. I would pm him.

If you are just chasing a look then ditch the air box and get pods but it will perform like shit. Which as you stated is nt great to begin with so it will be a miserable u reliable ride.

Well, let's get this thing to perform better then. I would love to have it cut corners like a pro and not start wimping out around 90 mph. Also acceleration sucks, but I think that has more to do with the weight of it than anything else. What if I did something like this but kept the airbox and got some light, mesh-industrial looking side covers for it and raised the back of the frame with longer shocks? (I know this is a 450 but it has the same style of frame)



So I could go for that really industrialism, Classified Moto look with an air box. Or I could buy Mikuni carbs and just be done with the stock CVs.

Or you could just spend the 200 bucks and get some mikuni round slides. I prefer the air box but some nice filters on mikunis has a lot of tunibility. And midrange would be more like 30 to 50 and you would a have a real flat spot there if you just go wi pods and no other upgrade.

What would be the advantage of the mikuni round slides over the stock setup? This isn't all about looks for me, I want it to be able to perform too by the end of this. How do I get my mid range to improve? I've talked to Sonreir briefly about this and he said the first two things I should do is to go down one tooth on the front sprocket and then lighten the whole bike up before taking apart my engine. That's what I plan to do in this build and see where that puts me.

You can't beat stock air box for STREET use, believe it or not, Honda knew what they were doing. Lighten the bike, change the sprocket, rebuild/replace/upgrade the old tech suspension HUGE BENEFIT and this includes front fork internals, customize rider position for yourself ie if you switch to clubmans or clipons then add rear set foot pegs, upgrade ignition, and rebuild/upgrade brakes.

If you are looking for track use then you can't beat the performance and tune ability of round slide carbs with velocity stacks. If you do this for street use you will spend more time rejecting for weather conditions and altitude than you will spend riding. Also you will have to rebuild your motors top end ever 500 miles.

A happy medium is flat or round slides with GOOD pods. KN or uni.

Here is a good read for you on cv carbs and pods.
http://www.hondatwins.net/forums/63-fuel-supply-carburation/23714-cb400-cv-carbs-pods-how-make-them-work.html

Thanks for the read. But I think I'll heed gijoe's advice and stay with the stock air box since this will be used exclusively for the street. As for front fork internals, where would I find these? I know that DCC doesn't stock replacement springs for the 400T. Would it be to my benefit to grab front forks off of a 550 or 350 and then put tighter springs in that?

calebacm said:

Thanks for the read. But I think I'll heed gijoe's advice and stay with the stock air box since this will be used exclusively for the street. As for front fork internals, where would I find these? I know that DCC doesn't stock replacement springs for the 400T. Would it be to my benefit to grab front forks off of a 550 or 350 and then put tighter springs in that?

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Only reason you should swap forks is for an upgrade. Ie disk brake vs drum or for thicker diameter tubes 37mm vs say 34. Otherwise just rebuild what you have. I don't know the best place for cb stuff but a quick Internet search for cb400t fork rebuild progressive should find you what you need. You will want to replace dust cover, main fork seal, cap seal, oil, maybe springs for progressive wound, and hardware if needed. Also get the copper washers for the lower bolt that releases your dampening rod.

I don't know what forks will swap but if you want to go for the best, a modern CBR would be a great upgrade. May require extensive mods to the stem and forks to make them work tho.

Others will know what works better than me, but whatever you do don't forget to replace the neck bearings with tapered ones From allballsracing or McMaster.

All in all you will probably have 100 bucks into everything and maybe more if you change to progressive springs and even a cartridge emulator if you want to go crazy.

Thanks man, I'll probably do a rebuild on the shocks and definitely keep the stock air box and make some kickin side covers for it. Something aesthetic that I'm foreseeing being a problem is the seat. Stock, the seat covers the bolt that holds the tank in place. I'm not able to figure out right now how to get a bratty or cafe seat to cover that without having to chop the frame. Maybe if I got a tank that covers it itself? Like the CB450 or a later 400?

Im not much help with cake decorating part but i am sure there are others who will know what tank fits with what seat on that frame.

I can't tell from the picture with your seat of, but if it is like my cb450sc it has that annoying frame step up that makes room for the tool box and also elevates the rear seat. I have seen two ways to get around it so here are the base options:

1. Break out the cutting wheel and start chopping: there are a few guys on the forum that offer seat hoops that are already bent, get some more frame pipe and some flat stock and create a new back section from stock. There are a fair amount of threads on doing this and it really gives you that one of a kind look while offering more suspension upgrade options.

2. Break out the craft foam: if you think of the seat cowl as just being cosmetic, and if you don't mind your seat cowl hanging lower that the seat frame in places, you can fiberglass a seat and cowl that will not only fit and mount safely and securely to your existing frame, but also achieve the look you desire while the frame is tucked up under the cowl. You can also utilize the existing seat mounting system. As before there a fair amount of threads on this, I recommend using woven glas.

You may want to start with #2 until you are really ready to change around your suspension and tire situation in the rear.

I think I'm going to go with option 1. I'm borrowing an idea from sbuagz's 450 tracker build but I'm going to style the frame a little differently. I'm going to mount the suspension the same way he did though. I've also decided to actually take an idea from classified moto and use perforated steel as side covers and some cosmetic flare. It'll be cool. I'm ordering the raw supplies tonight when I get home and I have a friend that fabricates and welds that's going to help me with it.

This weekend I'm going to cut the back of the frame off and take it to him so hopefully the big frame things will be done soon.


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