Idle problem

I bought my CB500 last January (2014) as a project so its been off the road since then. I took it for its MOT in January and to my surprise it passed but on the ride down there it kept cutting out. I found that the drain around the fuel filler had become blocked and I assumed had diluted the fuel so I cleaned the drain and emptied and refilled the fuel tank. As a precaution I also stripped, cleaned and rebuilt the carbs and have balanced them but I cant get the idle speed below 1700rpm without the bike cutting out.
My haynes manual says it should be 1300rpm +/-100.
Anybody got any ideas? I do know the baffles in my exhaust are shot which probably isn't helping but am I missing something obvious?

The idle speed is set with the bike hot and the choke off. Did you do that?

Yup up to full temperature but each time I take the idle below 1700rpm it cuts out

This is what happens if at least one of the idle jets is still blocked. Check if there is rust in the fuel tank; if not, another proper carb cleaning or replacing the two jets will solve the problem. Sometimes I need to clean the carbs twice as well as some dirt is intractable.

There are three bypass jets underneath the intake funnel as well, you may check them with compressed air or brake cleaner, too -one of them leads to the idle jet.

What Michael says sounds right to me, so I guess you'll be taking it all apart again!

Before you rips the carbs apart for another cleaning, you have reset the idle mixture screw to the correction position, haven't you?

Did it ride OK apart from the high idle speed?

Oh yes, well done for getting it through the MOT/back on the road (nearly!).

Bike rides fine apart from that but I didn't know anything about the idle mixture screw

Taking the carbs apart, cleaning them and not knowing about the idle jets?
Reading your original post, the adjustment (idle) is off and compensated by high idle.

Just curious, did you internally clean the carbs or only the outside? Not to offend you, but I had my share of carbs (cars and bikes) that malfunctioned and always ended up with small fuel and airways being blocked. So thourough cleaning after a long standstill can be a pain ....

Cheers,
Rob

I stripped cleaned and rebuilt the carbs both internally and externally. 
Its been along time since I have dealt with carbs but I was led to believe that the mixture adjustments was pre-set and not adjustable but obviously it is. It was a silly mistake to make but I'm quite capable of the task, I trained as an automotive engineer and up until 6 months ago worked as a service engineer for 9 years

OK, think you wil get them sorted then. The function is the same.
Sometimes the idle mixture screws are sealed. Main problem is there is a small o-ring that may leak and dirt may build up in the small holes they control.

Succes,
Rob

It's not allways a good idea to modify the setting of the idle mixture screws. Of course, if you disassemble the carbs, the setting needs to be done, and sometimes the setting is bad. But if a problem suddenly occurs, it is unlikely that the screws are causing it.

In case that the setting is needed, Honda recommends 2 1/2 turns out. From this position, turn each screw 1/4 out and check if the revolutions increase by 50 U/min or more. If so, turn out another 1/4 and so on. The problem is to judge if the idle increases by 50 revolutions. So, I found it usefull to take an exhaust emission tester and adjust them evenly to 1.5 percent CO. As most bikers won't have access to a tester, try 3 1/2 turns out, that will do for the moment.

The mentioned O-Ring isn't supplied by Honda (to be honest, it is, but only as a set for unbelivable 40 EURs). So I buy those parts as well as jets at www.motorradbay.de. They sell, for example, an idle jet for 3.50 EUR instead of eight. I found the O-rings at the pipe leading to the secondary air filter is prone to leak as well; those should be renewed every time the carbs are overhauled.