1992 yamaha 40 excessive smokingrunning problems

"hi,ive recently purchased a 4

"hi,ive recently purchased a 40 hp yamaha,twin carb model and have just put it on my boat and ran the engine,it fires up first time but wont rev properly and dishes out loads of blue smoke,it seems to be only firing on the bottom cylinder,but if i pull the cap off the top cylinder wen its running and hold it close to the top spark plug it fires up and starts to run properly again on two but if i push it fully bak on it stops firing again,could this be just a duff set of plugs so the top cylinder is not burning the fuel<hence blue smoke>it will tick over,the guy we bought it off had put new carbs on,head,and exhaust plate,and said it was fine......guess ive heard that before eh!!!!!!!!any help or suggestions would be much appreciated.thank u in advance"

you are prob dumping fuel into

you are prob dumping fuel into your motor via fuel pump or stuck float . does primer bulb stay firm?

sounds like u need to adjust t

sounds like u need to adjust the carbs
what pre-mix are u running or using oil injection?

"hi,thanx for the reply guys,r

"hi,thanx for the reply guys,right im premixing the oil,about 60:1,ive just took the carbs off and the jets are dirty and theres crud all over em,so im gonna clean em right up and see how that goes,il keep u posted,thanx again,regards....jeff"

yep rebuild those guys
put a

yep rebuild those guys
put a set of new plugs in also

"hi,right ive cleaned up carbs

"hi,right ive cleaned up carbs and installed new plugs,engine runs,it is still smokey tho,at the moment im running it in a bin so culd the engine not be breathing properly??and im using motorcycle oil,i know i shuldnt be but its all ive got at the mo.culd that be the problem???the smoke seems to be coming from all over the place,but it is in a bucket.ive also checked the year on my engine and its actually 1983,now the guy who sold it to us told us it was a 1992ish and hes put 1998 carbs on it,wuld these be the same as the early ones...it starts fine,no probs but i want to be sure as i dont want to be stuck out at sea.the engine sounds fine wen running no abnormal bangs knocks etc.....please help guys......shuld i return the engine to seller????many kind regards in advance,jeff"

first is to find out what jets

first is to find out what jets u got in there
is the oil TWC rateded? probally not