Topic: CB450 getting stuck at 4k rpm... Help!

[urai]

I posted this over at caferacer.net but still have no idea so I figured someone here might have a suggestion:

I purchased a 73 CB450 awhile ago that wasn't running. After cleaning and rebuilding the carbs, changing the oil, and getting the right plugs for the bike I have been able to get it to start consistently and idle.

My problem is as follows: The bike idles around 1,200rpm but if I twist the throttle above 4000rpm the idle settles around 4,000 rpm and stays there. At first I thought the throttle cable was binding but the carbs return to resting on the adjustment screws so I don't think that is the case. If I turn the Kill Switch to OFF and let the idle drop below 2000 rpms... then turn it back to ON Before the bike dies. the idle settles back down to the 1200rpms I have it set at.

Oh and It isnt the float level because I set them both to 20mm as stated in the manual.

Any help would be greatly appreciated.  Thank you!

[mlinder]

Need more info.

Stock intake and exhaust?

Done a complete tune up? Checked your points? Is the advancer working properly? Are the carbs synched?

[lordmoonpie]

Hmmm, so you've done a carb rebuild - how extensive? did you take all the jets out? Sounds like this is sucking air somewhere so did you put the carb settings back to stock? Did you check the cabs were mounted corerctly and the carb stubs were not perished? Sounds like a minor setup issue to me...

[urai]

Thanks for the replies!

Sorry I have been busy and have not had time to work on the bike.  My carb "rebuild" consisted of taking the carbs apart and soaking them in carb cleaner for a day or two then rebuilding with a carb rebuild kit that replaced almost all the jets, the gaskets, and the float needle ect. The jets that I had to reuse and the carb passage ways were all sprayed out with carb  cleaner.

My bike is 100% stock.  I made an attempt to sync the carbs and the bike idles at 1200rpm and doesn't bog through the rpm range when the throttle is twisted.  My only problem is the getting stuck at 4000rpms. 

I purchased new points and a new condenser but have not replaced them yet because the points that are on the bike look to be ok still. 

I will have to tinker with the bike some more this weekend and see but any suggestions will be greatly appreciated.  Thanks again.

[tbpmusic]

Your carbs are probably not synched.

Go here and review the procedure.......

http://www.hondatwins.net/forum/viewtopic.php?f=29&t=537

Now, tight intake valves can also cause a 450 to hang up on idle like that, so be advised.......