73 merc 650

[Great Dane]

I need help!!!!!!!!!!!my motor is getting a spark and fuel to all 3 cylinders, however it will not start. After a lot of trial and error i have found that the motor will start with both cyl 1 and 2 but as soon as the 3 cylinder is plugged in it backfires and WILL NOT START!!!!!<br />also the prop turns when the engine is in neutral.....is this normal?<br />I am new to boats and boating so i need any help I can get. <br /> thanks in advance!!!!!!!!!

 

[JB]

Re: 73 merc 650

Howdy, Great Dane.<br /><br />Welcome to iboats. <br /><br />Sounds like you may have a sheared flywheel key or a couple of the plug wires mixed.<br /><br />If you can turn the prop easily with her in Neutral it is not unusual. If the prop is "locked" to the driveshaft you may have a shift linkage adjustment out.<br /><br />Good luck.

 

[Great Dane]

Re: 73 merc 650

fyi.....all wires are getting spark ........and they are numbered on the block and the wires....1+2+3 top to bottom....<br />also the prop makes a clicking sound when turned CW, and it seems to turn the pistons when turned CCW......all while the shifter is in neutral and the engine off!

 

[Great Dane]

Re: 73 merc 650

could it be a bad wire???????? event though the plug is getting a spark?

 

[CATransplant]

Re: 73 merc 650

I'd run a compression test. A holed piston will backfire badly, as you describe.<br /><br />If the test comes back with zero compression on that cylinder, it's time to pull the head and take a look.