Topic: Check out my CB400F!

[oatmeal400f]

Hey there, i just biught a 75 CB400F and it is a beauty
Picture attached.
The guage is not responding too well, i will try to clean the cable and see if it will fix the problem.

Engine have to start with choke in down position, (off?)
When the choke is on, (up position)
The engine will lose power and eventually shut down.
The bike have to run with the choke towards the down position, or it will jerk on high speed axceleration.
Whyyyyy?

Also does my engine have a kncokung noise? i cant extinguish the noise from engine noise.

[DaveBarbier]

It's hard to hear if there's a knocking noise.

The choke is supposed to be lifted for starting a cold motor, then moved lower and lower until completely down and the bike idles on its own. You are not supposed to ride with the choke lever up.

I'm assuming down is choke off and up is choke on, but I'm not familiar with the 400F.

Nice bike, looks super clean.

[USMC5811]

My 750 did similar things, sounds like the carbs need a thorough cleaning.


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[flybox1]

^^+1
Clean the carbs.  You'll be able to SEE what the choke plates are doing when you actuate the choke lever 

[Bankerdanny]

It's not uncommon for these engines to sound like that, particularly if they have been neglected for a while. Set the valve clearances and adjust the cam chain tensioner, adjust the points and set the timing, clean and synch your carbs. I suspect most of the knock you are hearing will go away.

[kslrr]

Nice 400F!

[carnivorous chicken]

Choke lever down -- choke is off. Leave it that way unless you're cold starting. Nice bike, 400Fs are great.

[strynboen]

just klean the choker arm..and polish it..then there kleary is a indikator for choke on/off.(.up is choker on)..and must only be there for start up..and slovly bit for bit moved dovn ..as the engine is heating up

[oatmeal400f]

Thanks guys!
but is it normal that when the engine is warmed up, turning the choke on will disable the engine?
because that's what is happening.
I thought with choke on, there will be more fuel to burn, is it because when choke is on, the bike shuts off any air going into the engine?

Also, I have smoke/ vapor coming out of the left side cylinders, not too much tho, would that be a problem if I keep riding the bike? I want to ride it to the shop, but I don't want to damage it by riding it.

[carnivorous chicken]

Yes, when the choke is on (closed) and your bike is warmed up, it should run poorly or not at all, and die if you try to rev it.

Where, exactly, is the smoke/vapor coming from? Where the exhaust mounts to the engine? Off the outside of the cylinders themselves? If it's the latter, it's likely oil burning off, from a leak or being spilled. If it's the former, you need new exhaust gaskets.

If the smoke/vapor is coming out of the end of the left side exhaust (cylinders 1&2), then it could be a number of things -- oil burning from bad rings or valves, or water vapor burning off, or if the bike hasn't run in a long time crud in the exhaust burning off.

That being said, your bike came stock with a 4 into 1 exhaust system, and most replacements were also 4-1. Do you have an aftermarket 4-2 exhaust on there? Pitcures would help.

[MoMo]

^^ photo on first post CC

[That 70s Bike]

Thanks guys!
but is it normal that when the engine is warmed up, turning the choke on will disable the engine?
because that's what is happening.
I thought with choke on, there will be more fuel to burn, is it because when choke is on, the bike shuts off any air going into the engine? ...

Yes, a cold motor needs a higher fuel to air mix (choke on), after it's warmed up, too much choke can stall the motor with a too rich fuel/air mix...by yes, closing off the air source.
When viewing your video on the You Tube link there's the text: "CHOKE" (with an arrow pointing up) stamped on the lever.

[MoMo]

Choke on completely closes the air intake so it should stall out

[Don R]

I'd clean the carbs and do the usual 3,000 mile tuneup.

[carnivorous chicken]

^^ photo on first post CC

Derp, forgot about that first post. But still: vapor/smoke from where?

[Snowman1171]

I have the same bike , 75 cb400f.
Seam to have the same problem , as soon as I drop the choke down she wants to quit.

[MoMo]

I have the same bike , 75 cb400f.
Seam to have the same problem , as soon as I drop the choke down she wants to quit.

Do you mean it quits when the choke is off?   If so, clogged pilot jets and most likely blocked mid range emulsifiers...Larry

[thirsty 1]

Do you guys know how to set the low idle? There is a small brass screw/knob under the tank on the right side. This is the low idle set screw. Turning it in will increase idle speed and turning it out will decrease idle speed.