Idles with minimum choke on

Hello forum, I recently just bought a 1981 Yamaha midnight maxim 650. The bike seems to work fine.

For starters I need to put the choke on and then gradually I turn it back off (not completely)once it’s warmed up, the idle goes around 1000rpm with a minimum choke.

The thing is that the bike doesn’t stay on with the full choke off.

In order to keep it in idle I have to slightly put the choke on, if I turn it off completely the bike struggles and then dies.

Is it ok on this bike to run with the choke slightly on?, or should it be completely off while driving.

The previous owner told me that he had only cleaned the jets and carbs only.

On my part I have completely cleaned the carburetors and put on a new set of jets. I’ve cleaned the carbs with an air compressor but didn't apply the carb cleaner solution because they look clean enough.

Also Could I fix this if I adjust the air/fuel mixture screws?

Thanks.

 

Choke should be off as soon as the engine is getting warm you put it off. You need a richer mixture to start the bike but you don't want it on choke when it is hot. It should not run properly on choke when hot. Look at the spark plugs firing ends what colour are they?

 

Seems like something wrong with one or more of the pilot circuits - so either clogged or pilot mixture needs adjustment.

 

Hi guys thanks for the reply. I just took off the spark plugs and they are black , like dry black. They are not wet.

 

It's running rich then.

 

Yes it’s running rich, I’ll clean the spark plugs and remove back the carbs and double check if something is clogged somewhere. In case that does not work I’ll adjust the air/fuel mixture screws.

Also, just to make sure before removing the carbs again, my jet numbers are:

Pilot jet: 43
Main jet: 112
pilot air jet: 195
Main air jet: 55 ( The book says 50, Can a 55 cause any problem?)