Topic: CB550F won't run when hot below 2000 RPM

[Tim.]

Hey all - I've owned this bike for almost exactly one year, and am still working the kinks out.

First off, my carbs need to be cleaned, that's for sure.  However, I have done the tappets and timing.  That being said, here's my trouble.  The bike fires up no problem, and will burble along at about 1100 RPM (a little rough at 900 RPM).

Once the bike is good and warm (i.e. I've ridden for 20 minutes) it simply will not run below 2000 RPM.  The idle is also quite 'sticky' and will stick at 3000+ RPM when revved, even when still cold.  I'm constantly playing with the idle screw to bring things back down.

This makes riding unbearable, and was wondering if anyone had any thoughts.  I'm taking the bike into a mechanic who apparantly used to race old Hondas in the 60's and 70's in the Phillipines, and his son races too.  He works out of his garage.  I've had poor luck with mechanics in the past, and want to make sure I don't get lead down the garden path.

Any suggestions / comments would be welcomed.

[Gordon]

You need to synchronize the carbs.  99% sure that's what your problem is. 

Gordon

[Tim.]

Not that I doubt you or anything, but any reason this would only seem to appear when the bike is hot?

I will synch up the carbs, to be sure, just curious as to why it would manifest itself like this.

[Gordon]

You said yourself that the throttle was sticking at about 3000rpm even when cold.  This, combined with the hot idle problem is what tells me it's a carb synch problem.  I can't tell you exactly why this happens, it's just one of the quirks of a multiple carb system.  Once the carbs are balanced, set the air mixture screws.  This should get you a nice steady, slow idle. 

Gordon

[Tim.]

Sweet - thanks a ton.

[thirdman]

Just for a bit of collaboration, my 350/4 did a similar thing until I got my idle mix adjusted.  Had to do it the old fashioned way... turned 'em in all the way, and backed 'em off a half turn at a time until it ran right when hot.

Hope it works out for ya!!