Totally Stumped

[Larry Dikmann]

I own numerous Motorcycles and recently became enamored with Honda's CB 450 engine design. I purchased these two for 1000 and 900, respectively. The CB was in running condition the CL was not. Both had been sitting for 20 plus years. These are the photos of the bikes the day I bought them. So far I have cleaned the rusty gas tanks, Rebuilt carbs with new felt throttle shaft seals, replaced intake boots , set the timing with new points, set the valve lash, and changed the oil using 15-40 Diesel oil. My issue with both of them, is they start up immediately and within about 5 seconds rocket up to almost exactly 6000 rpms. If I close the choke, I can get them to idle down below 1k. I am also pretty this idle problem sure it is not caused by the advance mechanism as I have rebuilt both and even tried new springs. Additionally, I am fairly sure it is not an air leak in or right around the carb as I have sprayed carb cleaner all around the top caps and boot areas. The slides also go up and down very freely. Also, both bike have 200 plus psi on a wet compression test in both cylinders. Does anyone have any ideas what is causing this issue on both bikes? Totally appreciate any ideas....Thanks!

 

[ballbearian]

1st guess would be something identically wrong with both bikes float set ups. Nice thing is, when you find it, it will be an A-ha and a 2fer fix.

 

[Flyin900]

You scored there for sure. Great shape being California bikes. I can’t help with the bikes issues. Propane gas floated around the carb insulators is a little cleaner method to check for leaks.

 

[stl360+450]

My concern is that the throttle plates must not be sealing properly or are not fully closed if the choke makes a big difference. Did you confirm the bevel orientation on the plates when replacing the felts?

I assume cable related issues have been eliminated?

 

[MrPepper]

I also think sounds like a carb setup or throttle cable snag issue but going out on a limb and throwing exhaust manifold leak as something to check too

 

[Larry Dikmann]

1st guess would be something identically wrong with both bikes float set ups. Nice thing is, when you find it, it will be an A-ha and a 2fer fix.

Not being super familiar with these bikes, I looked at some photos of the relationship angle of the carbs going into the head and realized my angle was not as severe. I re-seated the carbs and got the idle way down to 900 and am working on carb synchronization just now. I feel a bit stupid but relieved.

 

[Larry Dikmann]

You scored there for sure. Great shape being California bikes. I can’t help with the bikes issues. Propane gas floated around the carb insulators is a little cleaner method to check for leaks.

Yeah I really scored on the CL which is a much nicer bike. It was an original owner bike that still had the original keys , toolkit , owners manual and only 9,000 miles. So far with the help of some aluminum foil I've been able to get most of the Chrome back to about 90 plus percent.

 

[wentwest]

Don't beat yourself up about the way the carbs were mounted. We all do that sort of thing, more than most would like to admit. It's called a hobby because it's supposed to be fun. And when the idle dropped to 900 I'll bet there was a big smile on your face.

 

[Larry Dikmann]

Update:

The CL is pretty much done. Lots of elbow grease with aluminum foil on the chrome pieces. The following was done as well with a total budget of 1500 US $ including purchase.

1. New Dunlop tires and balance beads.
2. Used a K1 seat pad and older seat cover.
3. Complete carb rebuild with felt seals
4. Reused all electronics with new plugs, set timing, adj chain and valve adj.
5. 15-40 Diesel oil change
6. Cleaned gas tank with screws and white vinegar. Used first baking soda then Diesel oil to condition inside metal.
7. Replaced both brake pads eve though old Honda ones were good.
8. New throttle cable. Re-routed to correct side
9. greased drive cables
10. Purchased k1 CL tank that I am in process of painting
12. Stripped and repainted fork ears and tail light.
13. Serviced forks with new "stock appearing" gaiters. used 20w oil Fork seals were still in great condition.