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Discussion Starter #1
Hey guys, Grant here again

So I've decided to start a project build thread for my recently purchased'75 CB400F (thanks to everyone for helping me figure out just what type of CB it was) which I plan on turning into a cafe racer (I also got a spare CB400F bike in pieces which I will either try rebuild in time or use as spares). My experience with riding is pretty good, but actually working on and fixing bikes is very limited, but I have a growing workshop and a fervent desire to learn, so hopefully that will see me through to the end of this build.

My intentions with the bike - get it running as smoothly as a 37 year old bike can run and then modify it to the look I want. In all likelihood it will be a daily run bike rather than a racer, but I sure wouldn't mind getting some real speed out of it and doing as many track days as my wife will allow...

As for budget, not really an issue, can pretty much spend whatever I need on it, you only live once right?

What has been done so far:

Before buying the bike I naturally took it for a good few rides, it felt great but did not idle. The previous owner blamed it on the carbs since it had been ridden mostly on dirt roads.

When I got the bike it wouldn't start, so I tackled the cleaning of the carbs first and nearly bust a gut trying to get the damn air box back on (any tips on a good way to do this without wanting to kill yourself?) and then charged up the battery.

Still wouldn't start.

So before I changed plugs, I decided to call the previous owner and ask if there were any "quirks" that I should know about. It was then that he decided to tell me that he had rewired the ignition switch to only start when on the "off" position. *sigh, coulda told me that before I pushed that bitch all over the suburb…*

Anyhoo, I set it to "off" and she started right up, although she doesn't idle for shit, so I will carry on just getting the basic maintenance checklist sorted out before trying to troubleshoot too much i.e. new plugs, new oil, checking the points and fiddling around with the carbs.

So that's it for now, would love to get your sage advice as I go through this project, will try not to ask too many stupid questions :)

Tx G

PS: for those of you that haven't seen it yet in my intro, here are some pics of the bike in its current state, more to follow in various states of undress as the days roll on...


 

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Grant,
I raced one of those for several years and put over 50,000 street miles on it. I bought it new in 1975. You can't get much more power out of one, so don't bother trying. Just get the engine running right and enjoy it. I had a pipe and K&N individual filters on mine. Spend your time and money on suspension and brakes. It has 33mm forks and a crappy front brake. I would upgrade to 37mm front end from a 87 -91 CBR600F and put the rear wheel on too. It will take a little fab work to get the rear disc set-up. Then run a 110-17 front and 150-17 rear tire.
Then get some rear shocks for it. Dresda used to make a swing arm for it and there may be some floating around. I would alos convert it to a 520 chain. The front sprocket from a XL500s fits as does the rear sprocket from a Suzuki GS500 if you switch to the CBR rear wheel. I had clip-ons and a solo seat on mine.


Ken
 

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Keep us posted on this build. I am picking up my 75 CB400F on Wed. What did you give for yours? I traded some powder coating work for mine. My buddy bought it at Barber 2 years ago for $300. He owes me around $400 for some powder coating so I told him to just give me the bike and I would call it even.
Ken, how much power are you talking about? My buddy built a race one with a bigbore kit and made about 130Hp. I'll definitely be getting his advise through my build. I'm been following the CB400F on CL and Ebay and they are far and few between and bring pretty decent money. One just sold on Ebay and didn't even run and went for over $1k.
http://cgi.ebay.com/ebaymotors/Honda-CB400F-/321030602907?_trksid=p3984.m1438.l2649&ssPageName=STRK:MEWAX:IT&forcev4exp=true#ht_500wt_1021
 

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That must have been a hell of a big bore kit to make 130+ hp. That's like modified GS1135 range.

Grant, that's a nice looking find there. I've always liked those sideswept header pipes, and yours don't look too rusty. The first thing I'd do with a bike that's idling funny and having the issues you're describing is clean the carbs. By that I mean take them off the bike, strip them down, and let them sit in carb dip for a few days to get all the crap out of them. My guess is you'll be amazed at how much crap comes out. See if you can't find new o-ring kits for the carbs as well; by now all the o-rings have turned to plastic and don't do much sealing anymore.
 

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With a 458 kit, big carbs, ported head, yosh cam and yoshima pipe might get you 45 hp, max. It will also have a very short lifespan if you rev it to 12k rpm, which you will need to to make that HP. At that rpm, the rings flutter and break the top off the top ring land. Of course you will also have rod and rod bearing failure in there, too.

Spend the money on suspension, tires and brakes.
 

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Discussion Starter #7
Ken, thanks for this goldmine of info, will certainly start doing some research around your ideas and figure out what kind of spares I can get my hands on out here. I am joining a few bike clubs in the area and will be attending as many swapmeets as I can to see what kind of goodies are on offer, so will keep an eye out for a Dresda arm if I'm lucky.

Marc, I bought it for $800 which I know is a lot for you guys, but bikes and cars are generally a lot more expensive out here. Watching US TV shows, I always curse at how cheap second hand vehicles are in the states and UK compared to here, but hey it is what it is. The bonus is that I did get a stripped down second CB400 in spares (minus the carbs) so that does lessen the hit somewhat...

Gearhead, yeah the pipes are in great shape, pretty much only surface rust, if any, on the bike in general. As for carbs, they were the first on the list for a cleanup which I did over the weekend and apart from a little bit of dirt in the bowls, they look to be in good nick. I could probably stand to change the seals and o-rings, but generally fine from what I can see. I don't think these are the original rings as the PO was fairly active with the maintenance, but once I have run through the basics like new oil, sparks etc I will then look at replacing all the rings and possibly the needles too if need be. Kinda feeling my way through, but having a significant amount of fun doing so :)

Suspension, tires, brakes. Check.
 

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quote:Originally posted by o1marc

My buddy built a race one with a bigbore kit and made about 130Hp. I'll definitely be getting his advise through my build.
I'm not sure I'd take his advice, because by the sound of it your buddy likes to tell you stupid shit just to see what he can get away with...

Oops, strike that, a buddy just pointed out it might also be using ram air on top of the big bore kit.

My bad.

:)
 

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Discussion Starter #9
hey chaps,

So I got some new plugs today and put them in, the old ones were really sooty and black, which according to the manual means the engine is burning really rich or the heat value is wrong. Would that be as a result of poor carb setup?

The plug from cylinder 3 was also quite oily from the look of it, does that mean the o-rings are shot?

Here is a shot of the 3rd cylinder plug:


Once the new plugs were in I started her up and she ran much better, even managed to idle for a little while but then died. I tried to start it up again but heard a strange squeaking sound on the left side of the bike. The bike has a fairly slow oil leak, so I'm a little concerned that it might be low on oil and that might be causing the squeaking and doing some damage, so going to clean her up real good to figure out where the leak is first, try fix that up and then change the oil.

Another thing that concerned me is that the plugs didnt seem to go all the way in, the washers still seemed a little loose, but the plugs were tight. I didnt want to tighten further and strip the cylinder head, so hoped for the best. It seemed ok, but if there are any thoughts as to whether this is normal or not?

Not terribly exciting reading just yet, but it idled for more than 5 seconds, so it's progress :)
 

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The oil leak on the left side between the cylinder and head is from a porous cylinder casting. There was a recall on them in the states in 1976 only on the early 75 models. Don't worry about it, it just makes a stain but really doesn't leak. Just looks bad. The recall was to install new cylinders. Not worth it.

The CB400F is very sensitive to a dirty air filter, which happens a lot because the crankcase vent plugs into the bottom of the airbox. There is a foam absorbent filter in the bottom under the airfilter and a metal mesh that gets soaked and soaks the bottom of the paper filter, causing the bike to run rich and your plugs look like the one you posted.

I suggest a compression check and and leak down test. I don't think of anything to squeak on the left side, unless the alternator stator or rotor came loose. Has it been crashed on the left side?
 

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I'll be seeing Jimmy soon and will get the details on that bike. He is a race winning rider and owned JIMSS (Japanese Import Motorcycle Sales and Service) Specialized in restoring CBX's. He definitely knows his shit.I witnessed $25K restorations of CBX's that shipped all over the world.

Brave, I don't know about the rest of the guys here but I think $800 for a CB400F and a basket case of spares is a great deal(Not as good as my $300-$400 which is why I tried so hard to close that deal ). They seem to be getting harder and harder to find. Here's what I found today:
There are no CB400F's on Ebay in the U.S or anywhere else that I know of. On Craigslist right now I found one in:
L.A. for $1500
N.Y. Original for $3000
N.Y. Cafe Racer, not run in 2 years $1500
Chicago nice stock one for $3200
I'd have easily given what you did for what you got. What do you others think?
 

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Discussion Starter #12
Ken, thanks for this, will definitely get those checks done and no, there is no crash damage on the left side or anywhere on the bike that I can see. Not sure I completely understand your notes on the air filter, but will come back to you if I can't make sense of it...

Marc, that's good to know - I was at a small indy bike repair shop around the corner from my place yesterday and they have another CB400F going for about $1,300 and it's in great shape...if they are becoming that sought after, maybe I should buy that too *evil grin* But wait, I'm getting ahead of myself, I need to prove that I can rebuild this bike before I get another one :) ... or do I... *practices evil villain laugh*
 

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Discussion Starter #13
Hey guys, so an update on how things are going with the bike so far…

I seem to be able to get it started fairly consistently by putting it into gear, slowly pumping the kickstart a few times and then switching the bike on and kicking it. Usually starts first time, but still doesn't idle.

As part of my "it won't idle" checklist, I opened up the contact breaker cover to check out the points and apart from quite a lot of dirt in the casing surrounds, I checked the contact breaker gaps and they are both 0.3mm which is in the range the manual recommends (it actually says 0.3mm - 0.4mm). The points don't seem to be burning or pitting, what does concern me though is that the breaker plate seems to be quite far from the pins that are used to stabilize the breaker when adjusting it. Could this be retarding the timing and contributing to the poor idle?

Here is an example of the 2/3 cylinder point plate in relation to the pins.



The 1/4 breaker is similar.



The "gasket" that the PO has put in was black silicon goop, not the standard cork gasket. Could this be contributing to the idle issue? I wouldnt think so, but would rather check…

Lastly, I gave the engine a good degrease and scrub down to try and locate the source of the oil leak. Ken, you mentioned that "the oil leak on the left side between the cylinder and head is from a porous cylinder casting." Not sure if this pic helps to show where it is coming from, but seems to be originating from somewhere around the starter motor. Could you check out this pic and let me know if you still think this is from the cylinder casting fault that you mentioned?

This is from the underside of the bike just a little underneath the starter...



On the topic of oil, the manual says to use SAE 10-30, but when I went to the bike shop, the guy there recommended a synthetic oil which he thinks is best for older engines, any thoughts on whether this is going to be ok for the engine? I heard that synthetic oils can be murder on the clutch of older bikes?

Here is a shot of the oil I bought, but haven't used yet.



Thanks for your help.
G
 

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The oil leak is not from the cylinder, it looks like the oil pan gasket is leaking. It is an easy replacement while you are doing the oil change. Never hurts to take a look at the oil pump pickup screen while you are in there. It always scares me when owners use silicone seal for engine gaskets since little worms of it always seem to get into the oil pan, looking for ways to get where they don't belong.

The oil you got will be fine, but is probably higher quality than you need.

The points look fairly normal, although the points plate is adjusted all the way to the end of its slot, so I wonder if the timing is set right on both sets of points. I would double check that. I suspect if it wont idle, then the pilot jet or idle circuits in the carbs are not clean enough, yet.

Have you adjusted the valves?

Ken
 

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Discussion Starter #15
Thanks Ken, been a hell of a week, haven't had time to much other than drain the oil while waiting for the gasket order to come through.

I haven't touched the valves yet, but did give the carbs a good clean, will be running them with carb cleaner when the oil pan gasket and new oil is in.

I wanted to get your guys thoughts on velocity stacks - I have done a crap ton of reading on them and obviously the stock airbox has its own stacks etc. I know too that most of you (or anyone else on most forums) feel that pods are any good for these old carbs, so I would rather keep the airbox than go pods, but I am intrigued by the idea of stacks. I must admit that it is largely for aesthetic reasons, but would love to get your opinions on whether I am asking for tuning trouble if I went this route?
 

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quote:Originally posted by braveg

This is from the underside of the bike just a little underneath the starter...

That leak could be from the O ring on the starter motor, or possibly from the gear shifter shaft or the output shaft seal behind the front sprocket. Take off the front sprocket cover to investigate further.
 

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Discussion Starter #18
Thanks Hillsy, I will be ticking off the potential culprits steadily, while the oil is drained I will check out the front sprocket cover...anything particular I should be looking out for once I remove the front sprocket cover? How will I know if the leak is coming from there or will it be self evident?

Thanks
G
 

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Discussion Starter #19
Thanks Hillsy, I will be ticking off the potential culprits steadily, while the oil is drained I will check out the front sprocket cover...anything particular I should be looking out for once I remove the front sprocket cover? How will I know if the leak is coming from there or will it be self evident?

Thanks
G
 
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