Topic: Progress on my '75 CB400F Garage Find

[Master_Moose]

For anyone who missed the thread in the intros, I picked up this bike for $250 from the original owner. The last time it was registered was 1982. It's been sitting in her garage ever since.

So far I've replaced the tires (+tubes & liners), the handlebars, the entire front brake system, the plugs, plug caps (NGK), the right switch assembly, and the fuel lines. I'm currently in the process of rebuilding the carbs, but I've run into a snag: the metal leaf springs don't fit on the replacement main jet sets. The diameter of the groove is larger on the replacements.

[Master_Moose]

Here's some more recent pics, with the new tires and more of the chrome & aluminum cleaned up.

[carnivorous chicken]

Keep the old brass and reuse it, clean it, replace the o-ring, and ditch the aftermarket jets. Problem solved and your bike will run better.

400Fs are great bikes. You got a hell of a deal, and that thing looks great. I'd dich that engine guard but that's just me. And make sure you do a complete 3000-mile tune up, change that oil, dribble a little oil in the cylinder before you crank it through.

[Stev-o]

Keep the old brass and reuse it, clean it, replace the o-ring, and ditch the aftermarket jets. Problem solved and your bike will run better.

400Fs are great bikes. You got a hell of a deal, and that thing looks great. I'd dich that engine guard but that's just me. And make sure you do a complete 3000-mile tune up, change that oil, dribble a little oil in the cylinder before you crank it through.

+1...nice work so far.

[SOHC4 Cafe Racer Fan]

Great deal and the bike cleaned up pretty well too.

[innovativems]

your 400 is looking great!

[MoMo]

+2 on reusing old jets, clean and new o-rings.  If your springs are bad I may have one or two....Larry

[Master_Moose]

They're sending me some Keyster main jets to replace the ones in the kit, but I'm a bit worried about using them based on some other stuff I've read. The only problem with reusing the original jets is that they had 35 years worth of varnish on them, so I gouged them up a bit while removing them. I'm not so worried about the edges, but what are the chances that I distorted them enough that the hole is no longer round?

Also, one of them has so much stuff in it that I can't even get the jet cleaner through. I have it soaking in chem dip now.

[Stev-o]

I wouldnt waste my time on Keyster jets.

Have you checked jetsrus.com?

[Master_Moose]

I finally got the jet cleaner wire through all the jets. They were pretty gummed up inside. I also chucked them into my drill and used it like a lathe to try to smooth out the edges. It seems like it worked pretty well, so I'm thinking of just using the original jets rather than any of the aftermarket ones.

[MoMo]

I finally got the jet cleaner wire through all the jets. They were pretty gummed up inside. I also chucked them into my drill and used it like a lathe to try to smooth out the edges. It seems like it worked pretty well, so I'm thinking of just using the original jets rather than any of the aftermarket ones.

do it, use the old ones as long as the inner diameter looks good and the outer seals well with a new O-ring

[Master_Moose]

do it, use the old ones as long as the inner diameter looks good and the outer seals well with a new O-ring

Is there a good way of checking the inner diameter? That is my only concern with using them at this point.

[MoMo]

do it, use the old ones as long as the inner diameter looks good and the outer seals well with a new O-ring

Is there a good way of checking the inner diameter? That is my only concern with using them at this point.

I'd rely on visual but I have seen charts that convert drill bit sizes  to jet sizes.

[Master_Moose]

The holes in the main jets looked ok to me, so I went ahead and used all of the original brass.

[Master_Moose]

Well, except for the float needles/holders. The replacement needles don't fit in the original holders so my options are to use the new holders and needles and worry that they're inferior parts, or to use the originals and possibly have worn out or sticky needle springs.

[MoMo]

Replacement float needles and seats  seem to be less problematic than jets.  Go for it

[Master_Moose]

It looks like I'll need to set the float height to 23mm, instead of 21mm like the manual says. It appears some others have had to do this as well due to replacement float needles being bigger.

Also, I had to make sure and measure both floats. It seems they were a little twisted somehow, so I was getting different readings on each side.

[Master_Moose]

I got it started for the first time today!

There are still a couple issues. For one thing, like I mention in the video, there's a rattling sound that I'm assuming is the valves being out of adjustment (or maybe just sticky after being idle for so long?).

The 23mm float height may not be good, because the carbs are leaking pretty bad out of their overflow tubes, especially carbs 1 and 2, and I took the bike for a short ride up the street and it's bogging down quite a lot.

By the way, when it dies, you can't see it, but I'm adjusting the throttle stop screw to get the idle down to 1200, but it just dies instead.

(Also, I left out the part where I spent a bunch of time cranking and finally getting it to sputter a little bit and then die repeatedly. I started recording after I was finally able to get the bike to run on its own for a few minutes, so when you see me hit the throttle don't be alarmed. The engine isn't cold!)

[carnivorous chicken]

That's good -- but you need to do the 3000-mile tune up before going any further to prevent possible damage. Valve adjust, points clean or replaced and gapped, ignition timed, etc.

For float height look up the clear tube method to verify you've got them set correctly. If they're still leaky, look at float valves, floats themselves, overflow tubes -- sometimes they have cracks.

[Master_Moose]

That's good -- but you need to do the 3000-mile tune up before going any further to prevent possible damage. Valve adjust, points clean or replaced and gapped, ignition timed, etc.

For float height look up the clear tube method to verify you've got them set correctly. If they're still leaky, look at float valves, floats themselves, overflow tubes -- sometimes they have cracks.

Fortunately this bike was converted to an electronic ignition by the original owner, so no points to worry about. Definitely the valves and timing need to be checked though.

I'll check into the clear tube method. Thanks!

[Master_Moose]

I just finished adjusting the valves and I'm not sure if I did it right. It was pretty difficult to get the .051mm feeler gauge in the space, because it's like a strip of foil. So I loosened the adjusting screw out several turns, put the gauge in, then tightened the screw down until the gauge could just move back and forth, but so it felt tight. I then tightened the lock nut and was pretty confident I had done it correctly, but was dismayed to find that the rattling noise is still there.

[MoMo]

Not sure if mentioned earlier but out of sync carbs and loose cam chain are likely culprits if the timing is right on...Larry

[Master_Moose]

I still haven't had a chance to remove the carbs and reset the floats. I ordered a Motion Pro SyncPro, but it won't arrive until next Monday.

Also, the timing might be off and, while I can set the static timing, without a working tach and the carbs being all weird, I can't set the timing with a light while the bike is running. It jumps around too much.

The frustrating thing is that the bike fires right up and idles nicely on its own. If it weren't for the rattling sound and the fuel dripping out the bottom I'd be tempting to just leave it as it is!

Anyway, I rode it to the bottom of my driveway and took some pics. I figure it's all I can really do for now.

[Sgt.Pinback]

Well done!

[Tenzrider]

It'll be worth it once the fuel dripping and excessive noise gets fixed for it. Nice work otherwise