Topic: CB400F - Dialling it all in

[parm94]

I got a 400F from a fellow who had it restored for him in 2008. The bike was overhauled completely including the motor. He put about 1600 miles on it but it sat around for the most part. I believe motor was bored out to 466 but I still need to talk to the builder about that. Runs and rides okay, however I've been wrenching to get her running like she looks.

First up was valve adjustments and timing. I'm wondering if I might need to deviate from factory valve clearance specs.



Next up is the dreaded 400F cam chain tensioner bolt, it doesn't look like it will be stuck.



The brake was seizing so the master and calliper were both rebuilt with DOT 5. Someone assembled the caliper with regular grease so ended up all over the brake pads. I've substituted it with the renowned Dow Corning High Vacuum Grease. My favourite upgrade is my new stainless line. It's a single piece from SlingShot Cycles and what a world of difference on the brake lever, wow.



Tires were cracking and 10 years old. The hubs were already glass beaded and spokes chromed. Now the wheels are getting trued and some new Avon rubber. Furthermore, the worn sprockets are being replaced, along with a new chain.



The paint the builder used on the motor is melting off and peeling on the valve cover which is a total bummer. So far the problem is isolated around the tappet covers. The valve cover will come off sometime in the winter to resolve this.




Miscellaneous: New plug boots as the old ones were out of spec. Changed the fork oil, liking the feel of 10Wt. I've also ordered the correct tank decal for the 75 model but the current looks is growing on me. I'm tempted into taking the carbs off to have a peek inside. I've become well aquatinted with doing exactly that whilst tuning my 550F. Lastly, Im considering the upgrade to electronic ignition. Hoping to have all this done to get in a local vintage motorcycle show on Sunday.

[MoMo]

Nice looking 400, only one of the photos shows-last one, all the rest have a negative bar inside a circle....Larry

[SOHC4 Cafe Racer Fan]

Yep, no pics. 

[parm94]

Yep, no pics. 

Nice looking 400, only one of the photos shows-last one, all the rest have a negative bar inside a circle....Larry

Put your glasses on guys! Google photos was glitching

[MoMo]

pics up now

[parm94]

Wow, what a difference truing the wheels makes. With the addition of new sprockets and chain everything feels more nimble and tight on the road. Also, I was successful in adjusting the cam chain tension which eliminated clatter.


I took a peek at the plugs after a long ride. I found that perhaps cylinders 2 and 3 are running too lean. I understand the cylinders in the middle trap more heat, could this account for the white plugs? In comparison, 1 and 4 are both coated with a nice brown.



I've also run into an issue with my brake light switch from Slingshot Cycles. The switch is defective and leaking fluid which apparently no one else has ever complained about. Shaun has sent me a new one but these seem to be the same thing sold from China for a couple bucks on fleabay. I'm real glad about the switch to DOT5 now. Does anyone know of a more quality product?

[parm94]

Got some ride time on the bike and clocked nearly 1000 miles in 2 days going to Vancouver Island. Everything ran stellar and even got up to 95 mph.

The plugs after the trip are still white in cylinders 2 and 3 whereas 1 and 4 have a brown tinge. After the trip I moved the main jets up from 80 to 85 but still see white plugs in 2 and 3 after a chop. I'm running a David Silver Spares repro muffler with stock airbox. The rest of the carb set up is stock. Top end power is all there but I'm concerned about running lean. Coils are in "spec". Perhaps fuel level in the bowls?

My butt dyno tells me low end power is also lacking some but I haven't ridden any other 400 before. Haven't read plugs in those ranges yet. Need to get a hold of the engine builder to ask about the internals.

[calj737]

Clear Tube test the actual fuel level in all 4 carbs.

[flatlander]

re. valve clearance:
use stock spec unless it's a performance cam in which case you need to use the specs of the manufacturer. did the builder say if he put in some non-stock cam, or why do you ask?

re. carbs:
check fuel level first as cal says, it's the easiest thing to check and fix.

the 400 can be fun. my neighbour used to have one and i rode it once in a while.
not sure what bikes you're used to but low end power won't be great. this thing can be revved high, it needs it and likes it.

[parm94]

Clear Tube test the actual fuel level in all 4 carbs.

All four levels are like this, I did set the bowls to spec when I last had the carbs out.

re. valve clearance:
use stock spec unless it's a performance cam in which case you need to use the specs of the manufacturer. did the builder say if he put in some non-stock cam, or why do you ask?

The PO wasn't sure about the motor build. Spoke with the builder today and it's all stock.

Spark looks strong to me, plug caps are new, spark plugs are correct. The DSS repro muffler isn't very free flowing either. Still baffled why a stock 400 has white plugs after increasing two main set sizes. I know these are self cleaning but this doesn't seem right lol. Will post any new developments.

[MoMo]

Are you sure the timing is not advanced on two and three?

[parm94]

Are you sure the timing is not advanced on two and three?

Yep, timing has been set correctly. Haven't figured it out yet. May do some more experimenting soon since I've already got the jets to play around with.

[parm94]

Have been getting some clutch slip when winding out after 6k rpm. The revs shoot up but acceleration decreases. Looked in the basket after making adjustments didn't help. The plates are good and I didn't notice any warping but I did see grooved ridges in the basket fingers. Could this be problem? For now, I have some stiffer EBC springs that I'm going to pop in.