03 yamaha t8 4 stroke

[saltchuckmatt]

I have a 2003 yamaha t8 four stroke that starts and idles fine but when you throttle up it bogs down. I thought dirty carb so I cleaned it twice and the same thing happened. Fuel pump is fine with 4 lbs of pressure. I put a new coil on it and still the same. A friend of mine had one he wasn't using so I exchanged all of the parts I could think of...(power pack, coil under the flywheel, flywheel, working carb) you name it and it runs the same. Compression test comes out good at 160 lbs with a 5 lb difference between cyl. Ran a leak down test and everything checks out..no leaks.
All I can think of now is camshaft or valve lash... just doesn't make any sense.

Have any idea's?

Matt

 

[raczekp1]

on working carb the same symptom?

 

[raczekp1]

did you change fuel pump?

 

[saltchuckmatt]

Yes, motor ran the same, no power. I did not change the fuel pump over but I did take it apart, squirted it across my driveway and it test to 4 lbs on my gauge. It's something else. I also disconnected the low oil override.

 

[raczekp1]

do you work on motor on the boat or on test stand in home?
to gets more rpm you need air and fuel in proprer ratio.
so you are geting to much fuel or to small fuel into intake inlet.
look at camshaft, and valves.
its easy to unbolt the head

 

[saltchuckmatt]

Ok pretty much looked at everything and or changed over parts that I know works. I guess I stumped everyone here. Valves adjustments were almost perfect but now they are even better. The only thing I can think of is some kind of internal issue or a crack in the intake manifold that I cant see or hear. Anyone know how to hook up a intake manifold gauge on a T8?

I think I'll just part it out.

 

[raczekp1]

you can buy used intake mainfold and change.
its god motor. its not worth to part it out.