4stroke 15hp yamaha. no start

[jiggamurf]

hello there im a little lost. i have a 1999 f15eshy 4 stroke that will not run. i checked compression. i have 75psi on one cylinder and 80psi on the second. i have removed the carburetor and extra cleaned it twice. and the engine is hooked up to a brand new fuel tank with fresh fuel. i can visually see the fuel sprayed into venturi on carburetor. so now i am after the spark. i pulled spark plugs and put fresh set of plugs in. (NGK-DPR6EA-9) to be exact. the engine cranks all day but will not fire. it will not even attempt to fire. i put a spark checker and there is spark but it seems weak. i looked up specs and i believe as long as the spark jumps 9mm gap, its fine. is this correct? well the spark does indeed jump a 9mm gap.

so i have compression, fuel , and spark

any ideas?
thanks

 

[gss036]

Re: 4stroke 15hp yamaha. no start

Check the kill switch button, made pull the clip and reinstall it, check for grounds. Seeing that it is a 4 stroke, maybe try a little starting fluid to see if it will fire up with that.

 

[jiggamurf]

Re: 4stroke 15hp yamaha. no start

i did. unpluged kill switch. i still keep getting spark. but it seems weak. i sprayed starter fluid and doesnt change anything. it almost feels like its not sparking inside the cylinder. or the timing is off, it has one coil that sparks both the cylinders at the same time one at the exaust stroke while the other one is on the compression stroke and vice versa. i removed every single ground on the engine and 12v source on the engine cleaned all the way back to the battery terminals.

im out of ideas

i tested every ignition component and all tested good exept im suspicious on that coil. when i unplug the orange and black wires. there is continuity through the coil is that bad? i doesnt give me a spec on the book.

 

[jiggamurf]

Re: 4stroke 15hp yamaha. no start

update. i checked timing and its dead on 5d btdc. i phisically checked timing mark with piston tdc and its fine for both cyl. i put cyl 1 on tdc compression stroke and did leakdown test. found air totally blowing thru pee hole. put cyl 2 on tdc compression stroke and did leakdown test and air was blowing out cyl 1 spark plug hole. pulled head and headgasket was blown. cleaned head and found exhaust side very discolored. so my guess is it overheated and blew head gasket. compression still gave me 80psi on both cylinders. maybe that wasnt enough to run. does anyone know what compression is supposed to be on that motor? and when they overheat, what are the probable chances the head warped?

thanks

 

[99yam40]

Re: 4stroke 15hp yamaha. no start

Warped head is easy to check and correct on a 2 stroke, but I have not done it on a 4 stroke. Just put a piece of wet sand paper on a smooth flat surface like a thick piece of glass or Plexiglas add water and then rub the head in a figure 8 motion on it with even light pressure and see if it cleans all surfaces, if not keep going until it does, swapping positions and directions from time to time to make sure you are removing metal evenly. Or take to a machine shop. The block is a whole different thing if it is not flat them you may have to pull power head to correct.

 

[jiggamurf]

Re: 4stroke 15hp yamaha. no start

update-
performed a leakdown test on cylinder number one TDC compression stroke and all kinds of air came out cylinder 2 spark plug hole.

removed head. sent off to machine shop to get resurfaced, reinstalled, tested compression and cyl 1 was 160 and cyl 2 was 160. woohoo!

she ran like a champ!

thanks for all your help guys