Topic: 1975 Honda CB400f Project - Beginner

[gjunkie]

Hello everyone,

This is my first post on here. My intro to the forum was RickB's project - http://forums.sohc4.net/index.php?topic=51957.0 with the same bike as mine... amazing story what he had to go through.

I've recently purchased one myself in much better condition than what RickB had to start with, thankfully. I got it for $1200 USD from a friend of a friend who's moving out of the country. It is fully registered, and this past weekend I took the safety course. Once I get my certificate I'll be heading to the DMV to get my license.

I'll be posting my progress here as I attempt to build my very first Cafe Racer. So here she is:



Known problems:

• Rust - You'll see from these photos that there's a decent amount of rust throughout.
• Dents/Scratches - Its obviously been dropped a few times. The exhaust is pretty scratched up, as is the motor.
• Air Leak - We tried to pump the front tire to no avail. You can hear it leaking through the valve.
• Oil Leak - The seller informed me that there's a small leak on the right side of the motor. We haven't pinpointed the exact spot just yet.
• Dead Battery - No longer a problem, bought a new one.
• Chain Tensioner - Seller informed me that it is slightly bent from a previous owner trying to do some work. I haven't gotten to it yet, so I don't know the extent of the damage.
• Old Tubing - The tubing from the petcock, through the filter, and into the carbs was pretty old. We also didn't know how old the filter itself was so we replaced them. There's still plenty of old tubing to replace tho.
• Idling - It takes a good 10 minutes or so of revving it at about 2500 rpm to get it warm. Even with the choke on, it won't idle by itself at first. After 10 minutes she idles just fine. Not sure how to fix that.
• Transmission - We were able to ride it up and down the street to get a feel for it. When shifting to 3rd and 4th gear (haven't gotten it to 5th yet), it sounds like it floods a bit, struggles, and then catches on. Not sure if that's just the nature of an older bike? Aside from that, it seems to function fine.
• Gas Tank - It's not properly bolted down. Right now the only thing holding it in place is the seat and its own weight.
• Seat - It doesn't clip on... you can freely lift it from one side to get underneath. Not that big of an issue of course.
• Missing Side Cap - The cover on the battery side is missing, but I plan on moving the battery below the seat anyway.

The seller gave me a few spare gaskets, sprays and such. The front fender is also removed, but I have it.

When we first bought the battery, we were surprised to see that it was a DIY battery. We had to fill it with battery acid, let it sit for 40 or so minutes, then charge it for a couple of hours. After that, we still had issues starting her up. We could get fuel through the petcock when in Reserve mode, but not on On mode... little did we realize that we just simply had to put more fuel in the tank... live and learn.

We also semi-tested all the spark plugs to make sure they all fire. I don't know their actual condition, but they do fire. We just put them up against the motor and looked for a spark when starting it up.

Here are some closeups of its current condition.


























And here's a picture of me riding it for the first time this past weekend. My buddy has an old school helmet which we're using while testing this beast. Funny thing is that it has no visor at the moment, and the bike doesn't have the front fender attached... and it was wet and rainy when we tested it... water in the face....


Next Up: Getting the front wheel air leak fixed. We want to get it in good enough condition to get it to my buddy's dad's shop, about a 30 min ride away. I wouldn't want to ride it any longer before doing some real work on it. In fact, I'm a little freaked out by just that ride...

After that we'll be taking everything off and cleaning it all thoroughly. From there, see what needs to be replaced. Once we know that I'll be shaving off latches and such from the frame that I won't be needing and getting it powder coated.

Updates to come....

[gjunkie]

Here are some electrics under the tank and the carbs

[Mugen_Stumpo]

it's nice to see another 400 build...

the bike is in not so bad condition too... what kind of coil do you have in there?

[RickB]

They're the DYNA coils. Says right on the side.

You're on the right forum for help should you need it.

Good luck!

[gjunkie]

They're the DYNA coils. Says right on the side.

You're on the right forum for help should you need it.

Good luck!

Thanks RickB! You're my inspiration over here.

Currently I'm storing the bike at a friend's garage. He's letting me keep it there and actually turn his small garage into a mini workshop. This weekend we're going to the hardware store to get some tools and some lumber to build ourselves a few work benches, shelves, etc. I'll post a picture once we have it complete to give you an idea of the space.

[Randawg77]

Sweet bike,  looks like a good deal for twelve hundo,  what with the Dyna coils and clubman bars already on there.  A good start to a killer cafe. 

[Tews19]

1200 for any running cb in Cali is a steal! Nice buy and ride! Subscribed.

[Apexxn]

Good luck with it and focus on one issue at a time and you'll get it done.

If the po didn't change the jets for those pods then it's not going to run right and could possibly cause some damage because of the lean condition. I've never had a bike that leaned out as much as this one when increasing air flow.

[jas67]

Welcome to the 400F owner's club!

I'll be watching your build.

[jneuf]

Welcome to the 400F owner's club!

I'll be watching your build.

^^^

What he said!

[gjunkie]

Hey guys! Thanks for the warm welcomes. A couple of updates:

Wheel: So in my excitement of having a new bike, I rode it a couple of times without checking the air pressure, which lead to pressure on the air valve. That's why air was leaking... I broke it So today we took the front wheel off and took it to a local Honda shop. Had it fixed in an hour with a new tube. However, when we got back to the bike we noticed that the brake pads had locked shut. Without a proper bike stand it was a complete pain to put the wheel back... Kept putting things back in the wrong order and then not able to fit certain screws, etc. We bled out some break fluid to open the pads (without first realizing that we could've just loosened the caliper, I think it's called, it would've been easier). So we got the wheel back on, but now I have no front brake... getting some DOT 3 brake fluid in the morning, and finally it will be rideable.

Leak: From what we can tell, the leak is actually coming from the left side, not the right, of the motor. We think taking off the cap and putting a gasket in there could help, so that might be my next immediate project before starting to take the whole thing apart.



Also, we went to the Honda shop cruisin' by the beach in this 1950 Mercury. Awesome...

[gjunkie]

I've been thinking a lot about relocating the battery, but I can't seem to find a perfect solution. I'm in love with seats like these, but I can't for the life of me figure out where the battery is in this CB750, "Brownie":



They've got the flat seat, but no battery in the usual spot... Can anyone tell me where the battery is? I've seen some sealed racing batteries that are very thin, and I suppose it can be laid down under the seat... but these are usually something like 2.6 Ah, and my current battery is 12... not sure if these small batteries would last longer than a single ignition.

This one also has a 4-4 exhaust which looks amazing here. I was considering doing something like that... at least a 4-2. Kind of a fan of the exhaust wrap too... sorry purists!

[Felix]

If I'm right, they've placed it on the swingarm. Can't find a picture of it though.

[gjunkie]

If I'm right, they've placed it on the swingarm. Can't find a picture of it though.

That makes sense. It looks like I may have enough room for a small battery in the same spot, but I'd have to cut some things off the frame... once I start taking it apart I'll be able to better see what I do and don't need.

Heading out today with my buddy to get him a 79 Yamaha XS750. I'm sure pics of that will come.

[gjunkie]

The current battery the bike has is a 12v, 12Ah capacity. I'm wondering if I want to use a smaller battery to be able to hide it better, could something like this work?
http://www.stuntsteel.com/ballistic-battery.html

They're a little higher voltage, 13.6 charged... not sure if that would fry my fuses...

Essentially I'm looking for an option to hide the battery above the swing arm/below where it currently rests. Am I looking in the right place?

[swan]

Welcome to our little weird corner of the world. CB400f's are fantastic bikes and you got one at a good price for California. I have restored 5 of these now and hit me up if you have questions, need part sources, images, manuals etc.

Before you do anything else, pull the carbs and thoroughly and completely clean them one at at time. Your need for a high idle indicates your idle jets are clogged from varnished gas and other gunk. Please report what number main jets and idle jets you currently have. Stock is #75 mains and #40 idle jet and most CB400F's with pods have #80 or larger main jets, #38 idle and the needle raised one clip.

Next, clean out your tank and petcock and install an inline filter before you feed your freshly cleaned carbs fuel. Now you should get the bike to idle correctly. Run it for a while and then do a compression test on each cylinder. This will tell you the state of your motor before you open it up. Your PSI should be even across all cylinders. If not, then you either have bad valves, valve guides, bad rings and or bores and/or a head gasket leak. A leakdown test will help pinpoint any of these problems.

Your front brake issue, like nearly every old Honda, is caused by an old and failing brake piston o-ring, which causes the brake piston to stick. I highly recommend buying a new master cylinder kit ($30), stainless steel replacement brake line kit ($70-80), a new brake piston 0-ring from Honda ($5) and possible an new brake piston ($40). Also replace your brake pads with new ones. The OEM Honda brake pads sucked in their day and more so when wet. This set up makes your bike brake better than it did when it left the factory.

Ride your bike in stock condition for a while to get a feel for what you like and what you would like to change. Then worry about the modifications and cosmetic changes.

Good luck and keep the images coming!

[gjunkie]

@Swan Thanks for the detailed info! I was wondering what my first steps should be, and this all sounds like very sound advice. The motor right now is a big question mark, so this should start giving me a better idea.

Side note, my buddy picked up a Yamaha XS750 yesterday. Really good condition. $1320. Not bad at all...



I'm off to get my license!

[swan]

No worries. Here is a link to CB400f parts manual and Tim Boughen's CB400F carb notes and images 
http://ebookbrowse.com/cb400f-pdf-d17480625

Here is one more recent CB400F build threads http://www.dotheton.com/forum/index.php?topic=39976.msg487340#msg487340

[ampsrampstramps]

I've been thinking a lot about relocating the battery, but I can't seem to find a perfect solution. I'm in love with seats like these, but I can't for the life of me figure out where the battery is in this CB750, "Brownie":



They've got the flat seat, but no battery in the usual spot... Can anyone tell me where the battery is? I've seen some sealed racing batteries that are very thin, and I suppose it can be laid down under the seat... but these are usually something like 2.6 Ah, and my current battery is 12... not sure if these small batteries would last longer than a single ignition.

This one also has a 4-4 exhaust which looks amazing here. I was considering doing something like that... at least a 4-2. Kind of a fan of the exhaust wrap too... sorry purists!

It's mounted under the swing arm off of existing bolts on the engine.

[gjunkie]

@Swan - Thanks for the links!

@ampsrampstramps - Interesting. I'll have to see how I can pull that off.

Updates:
Today was quite a day. I rode the bike for the first time for an extended period of time. First thing to note, I can't get her above 45mph. Second thing, the bike died on me about 20 minutes into the ride. When I pulled to the side of the road, there was a lot of oil leaking from the left side of the motor, right from under the heads. The motor had almost no oil left. Walked to a gas station, got some oil, and filled her up. From there, she seemed to function a bit better, but still was unable to get past about 45mph. I'm guessing this is purely due to the leak issue... bad compression.

We rode to Deus Ex Machina in Venice, which is close to the garage I'm storing it at, and had a coffee... when we were done, the battery was dead. I should note that the lights are always quite a bit dim, even after a full battery charge. Not sure if this is due to an old headlight bulb or a bulb of low wattage...? The interesting thing is that I hadn't started up the bike in about a week and a half and she started up just fine today... but after riding it a bit, the battery died. Could there be a power leak of some kind? Side note: how does the bike charge up the battery? Does it have an alternator?

We had to push the bike and drop the clutch into second a few times until she started and was able to ride it back to the garage.

I won't be riding it again until I take off the carbs for a complete clean up job, and figure out the leak. I've got a bunch of extra gaskets... not sure that's all it will need...

Here's a picture of the leak when I pulled to the side of the road... You can see how clean the heads are and how much oil is coming out from below.

[SOHC4 Cafe Racer Fan]

Unfortunately, it looks like pulling the motor and replacing the head gasket is in your future. 

You also appear to be suffering from a charging issue.  You may wish to get a multimeter and check for (internal) breaks in your wiring harness.  I had a similar issue with my first 750K7.  We initially thought it was the rotor, but I was still getting insufficient current back to the battery after we replaced it.  It turned out to be a bum wire in my harness.  I ended up gettting a spare harness from 754 (since K7 and K8 harness were not then being reproduced).  I'm not sure if anyone sells reproduction wiring harnesses for the CB400f, so you might have to repair it, IF that IS the issue.  I would diagnose the wiring issue BEFORE you pull the motor, while the bike is still operating to check the recharging current.

Deus Ex Machina has some beautiful bikes on display, and decent coffee, too.

[gjunkie]

Unfortunately, it looks like pulling the motor and replacing the head gasket is in your future. 

You also appear to be suffering from a charging issue.  You may wish to get a multimeter and check for (internal) breaks in your wiring harness.  I had a similar issue with my first 750K7.  We initially thought it was the rotor, but I was still getting insufficient current back to the battery after we replaced it.  It turned out to be a bum wire in my harness.  I ended up gettting a spare harness from 754 (since K7 and K8 harness were not then being reproduced).  I'm not sure if anyone sells reproduction wiring harnesses for the CB400f, so you might have to repair it, IF that IS the issue.  I would diagnose the wiring issue BEFORE you pull the motor, while the bike is still operating to check the recharging current.

Deus Ex Machina has some beautiful bikes on display, and decent coffee, too.

Thanks for the help!! I agree, since the bike is in "running" condition, I should test as much as possible before taking it apart. I dont know the first thing about multimeters... is there one you would recommend? I see Amazon lists all kinds.

As for the leak/gasket issue, we figured that was gonna be something we had to do, so I'm ready and willing. While I'm at it I'm just gonna clean every inch of this bike.

** EDIT **
Bought this: http://www.amazon.com/gp/product/B000EVYGZA/ref=oh_details_o00_s00_i00

[SOHC4 Cafe Racer Fan]

I got mine at Home Depot. Any simple one will do.

[gjunkie]

Multimeter has arrived! Bought myself a carb synchronizer kit as well but that won't arrive for another week.

Question: Gasket sealant. Can I use any type? Is there a specific brand/type I should stick to?

I'll be taking the motor/carbs off sooner than I thought I'd get a chance to... Within the next couple of days. I'm pumped.

I'm also looking to sell off the current stock exhaust and get this one: http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-exhaust-systems-black-cb400f-mac-4-into-1-system-201-0501.html
I hear good things. Any opinions?

[swan]

I would NOT sell your stock exhaust. Mac exhaust are fair, not terrible, but not great. The graceful, swoopy, sweepy and sexy stock OEM 4 into 1 exhaust is what makes CB400f's look and sound so good. Macs have more geometric hard turns and look clunky and black is ugly compared to nice chrome. You can buy new pattern stock pattern exhaust parts, pipes, etc from David Silver Spares if your originals are ratty. Used CB400f exhaust headers go for good prices on ebay and NOS headers go higher than what you paid for your bike. The prices have come down quite a bit since DSS offers really nice  replacements for a reasonable price.