Topic: 1974 CB400CF trans noise

[4STROKE4SURE]

I bought a CB400CF. To my fortune the engine started fine, but has a knocking sound near the starter at idle. If I raise the RPM a bit it seems to go away. The front cylinder area sounds tight and quiet. I used a wooden stick to listen around the transmission casing for the area with the loudest knocking sound. So I am thinking the knocking is in the starter or clutch area. I did put it in gear, but the knocking acts the same as when in neutral.  I believe the starter motor on these bikes stays engaged to a gear, because there is no BENDIX type mechanism to engage it and disengage it after start up.  One more thing is that I was told that a complete gasket set for the CB550 will also work on a CB400. Is this true? Or, where can I purchase a complete gasket set for my 1974 CB400CF?

[Bodi]

Ummm... although first exhibited in Cologne in 1974 (at Intermot, fall motorcycle show) there was no 1974 CB400F: first model year was 1975.
And a CB400CF is... what?

[4STROKE4SURE]

Thank you for replying! The bike was sold to me as a 1974, and I just re-checked the factory dated neck ID label which states "CB400F 9/74", so it is tagged as 9/74 on the frame and also on the Pink Slip. The tank was originally Red, now metallic light blue. It has very little steel rust and aluminum oxidation. But I don't want to run it very long, until I locate the knocking sound in the rear case area. I will need a gasket set if I have to open the engine.

[MoMo]

Although it may be titled as a 74 , as Bodi said there is no such thing as a 74, model years ran 75-77. With Honda the model year was usually the year after the date of manufacture

 No way a gasket kit from a 500/550 would work. 

Adjust valves, set timing and synchronize carbs and the knocking may go away....Larry

[4STROKE4SURE]

Hi Larry, thank you for the clarification on the HONDA dating format, knowing specifically from 75 to 77 will make my parts searches more accurate. And I suppose off timing or off carb syncing could cause some surging through the drive system that could cause it to knock about at low idle. At least it is a good place to start, before deciding to split the cases. Thanks for your input. And thanks for the CB400 specific replacement gasket kit info.

[MoMo]

Keep us posted.  Hopefully a good 3000 mile service( full tune up and fluid change) will eliminate the noise...Larry

[hoodellyhoo]

Hard to know exactly what the sound is without being there but what you describe sounds to me like your carbs are out of sync. This can cause a kind of "chugga chugga" noise which I understand is clutch rattle. As said above, do a full tune up and carb sync and see if that helps.

[jakec]

My 400 makes a chugga chugga sound at cold idle. I figured it was out-of sync carbs as well. OR it could be that 1 or more carbs has the idle circuit a little clogged up. Pistons fighting each other in the cylinders would make that noise, wouldn't they? The only thing that's weird to me is that once I open it up (get the crank spinning above 6k for a bit) the idle clears right up and it'll run all day just fine. It's only when its cold.

[Don R]

 Check the serial number, it could be a really low number. I don't think right now there's any special significance to the parts or value but as time goes on low number bikes may become desirable. The early goldwings are seeing that recently.
 The 3,000 mile tune up is always the first thing to try to eliminate a running issue.

[jakec]

Sorry, I don't want to hijack this guy's thread. I know my carbs need work (especially #1, someone left it on the side stand). I think I will rebuild the carbs when the rain comes, and then do the 3,000 mile service.