CB250T Running rich

[Noo_Noo]

Hey all, long time no chat, simply because I've been spending time as a smelly student and not as someone who needs to ride to work

Anyway, I have purchased myself a 1978 Honda CB250 to commute on. The only issue I have found with it is the fact that it appears to be running rich. Black sooty exhaust cloud, low mpg, popping on deceleration, the works.

I've given the air cleaner a clean, I've flushed the system with red-x as per the instructions, but I'm still getting black soot and shitty fuel economy (80 miles from a 12 litre tank ).

I'd take the carb apart in a heartbeat, and clean it thoroughly, but I've not had much joy finding a workshop manual that details the CB250t specifically, plenty for the plain old CB250 and the Superdream though, not sure they'd still apply however... I'd also be tempted just to wind the fuel mixture screw back a little as well, but again, I don't know what I'm doing , or indeed if there is a mixture screw on this bike.

Any advice appreciated, I can't afford to commute to work like this

[Noo_Noo]

DP to update:

I've just heard that the engine in the Dream and the 250 Superdream is massively similar, if not identical. Is this true?

[nighthawk250]

Do the carbs have a diaphragm, if so you need to inspect them, any holes and the slides do not move, which will alter the mi.xture

[Noo_Noo]

No diaphragm, it has a slider on a spring. Everything seems free in there, no signs of knackered parts or excessive wear.

EDIT: Found an exploded diagram showing the carb on this bike:

https://images.cmsnl.com/img/partslists/carburetor-cb250t-ii-1979-france_bigma000111e19_dd9e.gif

Also found that one of the throttle cables was not properly attached (the return one). Could this also be causing my rich running woes?

[Paddy Blake]

I am sure you will find the manual here.
https://www.bikechatforums.com/viewtopic.php?t=140295
Also get a new air filter if you don't know how long the one in there has been there.
Best of luck with it.

[Noo_Noo]