75hp middle carb not working

hey i have a 15ft 66 chris craft with a 75hp chrysler 3 cylinder. after a lot fo work i just got it on the water this weekend. it always ran good outa the water and it ran good for a little while on the water. then i start cruisin almost full throttle and it was just die like it was losing fuel. i wait a few min and it started back up but ran rough. start crusing again and it would die again. after i got it back home i ran it on the muffs and it felt like it was missing so i pulled hte ignition wir off each cylinder and top and bottom stalled it out and middle did nothing. checked and had spark there though. next i went to each cylinder and turn the air/fuel mix screw in all the way and top and bottom cyl's stalled the motor and middle did nothing so i conclued theres a problem with the air/fuel mix on the middle cylinder. can some one help me with the carb dont no much about it or what can be wrong. thanks a lot guys really apreciate it.

Re: 75hp middle carb not working

Do a compression test.Get back with results.J

Re: 75hp middle carb not working

ok thanks ill do that. wont be till the weekend though. what are you thinking? why would compression effect the idle mixture not working. or maybe the idle mixture is working and theres no or low comp. in that cylinder?

Re: 75hp middle carb not working

also the middle carb controls the fuel pump right? so if it had low compression in that cylinder wouldn't the fuel pump not work or atleast not enough to run the other two cylinders?

Re: 75hp middle carb not working

any one?

Re: 75hp middle carb not working

anyone got any other ideas

Re: 75hp middle carb not working

so i took compression top cylinder 150 bottom 150 midle 50. i pulled apart what i guess is the head (the front cover were the spark plugs go. top and bottom cylinders look perfect still has cross hatching on walls middle cylinder walls are scored mostly on the bottom. what are my options is it possible i cna just clean up that cylinder and hone it real good and put a new piston and ring in it? or will i have to get the block machined and bored for an over sized piston? doesn't look like it got scored to bad but more like the poston and ring material i stuck on the walls. il get pics up asap

Re: 75hp middle carb not working

honing and re-ringing that 1 cylinder would work maybe. I would put rings on all cyl. Can't say how long this repair will last. The best bet is to rebuild the block. You would be much more satisfied with that

Re: 75hp middle carb not working

Post some pics.J

Re: 75hp middle carb not working

heres pics of the cylinder and one of the boat lemme no what you think thanks

Re: 75hp middle carb not working

Actually that doesn't look that bad.You will need to disasemble the motor and see what the condition the piston is.
Then figure out why the piston did that.
Carbon,carb set wrong,head blocked,bad gasket??J

Re: 75hp middle carb not working

hey thanks. youve given me the littlest sigh of releif haha, but it is what it is either way. im going to start tearing it down in the next week or two hopfuly. you think i can figure it out without a manual? im a full time auto mechanic and very mechanicly inclined but i dont know if theres anything crazy i should know about this motor before i do anything. also what are the cylinder walls and piston made out of? thanks alot jerry

Re: 75hp middle carb not working

hey so i started taking the motor apart today but i didn't get very far becuase i didnt remember my puller for the flywheel. and bolts are breaking left and right. i did pull the side cover off for the exhaust and i noticed one more bad thing. the middle cylinder is the one of the original pics but now i could see through the exhauts ports in the cylinder that the bottom pistion is pretty scored too although the cylinder walls on that one look fine so what does that mean? it also had 150psi compression. the top cylinder looks fine through those holes and alos had 150psi. what do you think? im worried this isnt worth tryin the fix with the time and money its going to take. and id hate to replaced the pistons with out knowing why this happened in the first place. thanks guys