Another Honda CB400F cafe racer

Sorry about the damage, but at least now you know the main culprit and you can move on from here.

Keep at it, sir. She sure is a purddy scoot.
Thanks again Justin. Wow, I got lucky! I stopped by my neighbor's shop, he has all the proper tools and he touched up my valve seat over my lunch hour. I even had time to vote. He is an experienced motorcycle machinist and the good news is I do not need a new valve seat. With the touch up, the valve stem height only increased .004". He also offered to skim my cylinder head tomorrow too! All for the price of twelve hoppy and dank bottles of IPA. My kind of trade. He is setting up his shop, mills, lathes etc to only to do work on motorcycles. I will post his information in the coming months once he is ready to go back in to business.




After the head is skimmed I will reassemble the motor and hopefully this will resolve my idle issues. Onwards and upwards...
Hey guys, not to just barge in on the thread but I've been drooling over it for a few days now. An old guy near me has a 76 400f for $500. Missing the seat, bars and header (damn). Anyways it seems like a great bike all around especially for my girlfriend to ride and it's a Honda so it should be a fun time rebuilding, I guess I'm just wondering if there's any dark secrets about these bikes or anything i should know before i get knee deep in Honda parts.
Dave, no worries, these are great bikes, one of Honda's finest. They run like Swiss clocks (once tuned and synched), scream all the way up to 11,000 rpm's and are fast, light and extremely easy to handle. If you (or your GF) are taller or bigger I would consider a Honda 550. Most parts are available from Honda and some of the missing bits are available from David Silver Spares including new 4 into 1 headers. Used seats come up on e-bay often and new seat covers are around $70. Bars are available as is the right hand control. The left hand control is not offered by Honda anymore but you can find new ones from DSS or Japan or buy a used one. No real dark secrets, but make sure the cam chain and tensioners are within factory spec and the carbs are clean and in synch. Also, a stock airbox will make your life easier.

If I did not have a Gold Star to finish I would keep this bike in a instant. It will be difficult to sell this, but since I have found three before this one, another will come along in the future.

PM me your e-mail addy and I will send the original brochures, reviews and other information and links to the parts and service manuals.
Swan, are these the Hondas with the more set back foot controls? I seem to remember reading something (perhaps from you) about one Honda bike with almost rear sets for the first few years of the model run.
Worst CB650 Ever, yup, there were Honda's first production Cafe Racer and the 1975 and 76 models had rearsets. IN 1977 they were changed to be more forward. My bike is one the first 750 CB400f's built and has the early style rearsets.

I nearly finished rebuilding the motor last night. I still need to install the exhaust and carbs and run it tonight. With the valve seat repair and the cylinder head skimmed, compression in #4 is much, much better! I will post results after I ride the bike tonight.
Wow good to hear Swan, I wish I had the $$ to just buy this bike from you. I would fly to your place and just ride it home. I want one since I rode Justins and yours would be like buying a new one. Hope you get top dollar when you do sell her to put towards the goldie.


Maritime, thanks, this bike is going to be hard to sell. She runs and rides so well. The good news is I picked up another 1975 CB400f last weekend! It was cheap, titled, but a 500 mile round trip drive with a trailer wheel blowout, but worth it. I spent a few hours cleaning 30 years of dirt and barn dust off the new one, cleaned the carbs, new battery and put the tank from my last CB400f and she started up and ran well. A bit more fettling and a Dunstall replica muffler she went out for a ride. Runs great! I have not decided what I going to with the new one yet, Cafe or restore, keep or sell, hmmmm.... I will start a separate thread for this CB400F (my fifth one!):


Trailer wheel blowout but thankfully it was empty and on my way to pick up the new girl.

My current CB400F took a hell of a lot of carb work, tuning, tweeking, troubleshooting and synching to get it right. The machine and valve seat work raised the compression in cylinder #4 to the level of the other three cylinders but did not eliminate my idle problem completely. I have never had a problem with pods on a CB400F before, but this one gave me grief at idle, so I went back to the stock air system for a baseline comparison but it still had the same idle hang and richness at idle, therefore it was not the pods causing the problem. I am not the only one with this issue (Google "CB400F idle hang"...) I pulled and completely cleaned the carbs, idle circuit, mains, airways, emulsion tubes, raised and lowered the with the float levels 1 mm, played with #38 and 40 pilot jets, checked and reset valve clearances, retimed and verified timing advance bob weights were lubricated and working correctly, etc, synchronized with 4 gauge carb synchronizer, used Yamabond between the carb insulator boots and cylinder head to eliminate vacuum leaks, installed a new Honda Air filter, new air intake rubber boots, etc but still had an issue at idle. #@#%&!


I was getting frustrated but by the process of elimination I now believe the issue is with the aftermarket carb rebuild kit components themselves. The common belief is that the aftermarket needle and the stock Honda emulsion tube do not seat well together at idle, allowing too much fuel to pass, enriching the idle circuit causing it to rev up temporarily, then fouling the plugs, causing a drop down to a poor idle. Also, I measured the stock Honda air screw's diameter versus the aftermarket screw's diameter and found the Honda one is slightly (.005") larger. This may be also causing idle problems(???). So, I installed the OEM air screws.

Aftermarket top, Honda OEM stock air screw bottom.

Cleaned the holes of the emulsion tubes.

I cleaned the carbs from the new CB400f (#5 as I call her) and left the stock OEM Honda components in and installed them on to this CB400F (#4) and voilá, she runs great at idle and all through up to wide open throttle. I am unsure if my aftermarket carb parts are K&L or Keyster brand for they are in unmarked white boxes. I will dig through my receipts to see what brand they are and post so others can avoid them. A long hard lesson learned: use OEM Honda replacement parts in your carbs.

So, with a properly carburetted bike I have completed 80 shakedown miles and she runs and rides extremely well. I changed and examined the oil and filter at 50 miles and nothing was wrong. Thanksgiving in Minnesota was 63 degrees fahrenheit! Normally I go snowboarding, but I took the bike out for what may be the last time this year and rode nice an easy and then hit the empty back roads and opened her up. She does well at 80 mph plus, so smooth, great handling and by far the absolutely best sounding Honda I have ever heard. Back at the shop, I retorqued all the bolts, head, axle caps, etc and need to clean her up and try to sell her. It is a bad time of year to sell bike around here but I may try E-bay her or wait until spring to realize my reserve price of $3500. I did however order matching Honda carb emulsion tubes and needles from Honda (needle jet set OEM#16012-377-004) and will install them and test and synch the carbs one last time.

Here are some useful links to RichB's and other CB400f carb woes at idle:

Now that this bike is complete, time to think about CB400F #5 and I started on my CB750K4 last night. No rest for the wicked....
Alright, snow is here and it is time to work on bikes. My matched sets of replacement Honda needles and emulsions arrived las week and I installed them in the original carbs for this bike (CB400F #4). The difference is night and day. PERFECT idle, no more idle hang and I was able to synch the carbs in less than two minutes. The bike has never ran or sounded better. It is going to be a loooooong wait until spring. A long and hard lesson learned: use OEM Honda carb parts.

I broke and cleaned the carbs (again) and while I was in there, I tossed out the original phillips screws holding the arm plate to the throttle valve and replaced them with hex head screws. It is much easier to get inside the throttle valve with a thin 2mm hex wrench than a screwdriver.


OEM Honda needle and clip (top), after market (bottom). Dimensionally they are very close but note the color difference.

OEM Honda emulsion tube on left, aftermarket on right. Note the difference in the needle seat design.
Others have reported the brass used in after after market carb parts are softer and wear quickly.

I cannot take credit for this idea, somewhere on my CB400f carb research I read about replacing main jet springs with a spring and clip (Thank you Davis96 My jet springs were in really bad shape, they are no longer available so I went with the spring set up and it works great.


I will go over the bike one more time, re-tighten all the nuts and bolts, tweek the seat cover a bit, a good cleaning and then tuck her into her warm bed until spring. I will ride another 50 or so shakedown miles and then sell her. I think I am going to start on my other CB400F (#5) this week when my new seals and gasket sets arrive. I plan to strip it to the crank and restore it to stock factory condition and sell it too this spring. I'll do another thread for it soon. Happy holidays all!
I just picked up a 1975 400F SS that I am hoping to build up. It is in excellent running condition, but does need a little work. My plans with it are to replace the front master cylinder as the brakes squeak; clean out the engine, carbs; redo the entire wiring; remove the electric start; repaint the tank; and do some minor cosmetics. I am still getting caught up on this thread, but I came across your tank work, and I am curious where you got the Honda SS graphics. Can you give me some insight on this please?
reprodecals on Ebay. From Canada, good quality.

Took the first ride of the season yesterday on my Triton and the first ride on this CB400F today. Wow, I love this bike and she is so happy. Charged the battery, fresh gas into clean carbs and she fired right up into a smooth idle. I forgot how good this bike sounds and moreover how fun it is to ride. I went out and stretched her legs, blew dust off, broke a few laws, but nobody got hurt. Gonna clean her up and sell her. This is going to be a difficult goodbye...
Yea Swan, can we send our problem child bikes to you and have you rebuild them to your level of quality? ;D
Thanks guys, actually a friend dropped off a 72 BSA Lightning for me to go through the carbs, timing, chain, tires and hubs. I do not have a shop rate and do this soley for fun, but he was making hints about giving/selling cheap a 1966 Honda 305 he wants me to have, hmmmm, next project???

I would like $3800 for this CB400F. Mechanically sound, frame up paint, new spokes, tires, new seat, running beautifully etc. Way too much time getting the carburation perfect. The only issues are the front fender and a weird clear coat issue on the tank I am not happy with. I have not decided whether to go Craigslist or E-bay. Tomorrow.
I think we'd just like to see you do another build now that the Gold Star is coming to an end. The 305 is a lovely bike that would make a nice restoration, I'd think.
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