Engine knock at wot throttle on 1975 25hp johnson

[g3 1436]

Hi I'm having trouble with my 1975 25hp johnson. It's my first time posting so forgive me for newbie mistakes. I'm a little lost I believe that I advanced my timing to much and may be having pre detonation. It starts up great it idles all the way down. But when I open it up all the way in gear..As I reach top speed it starts to make a noise similar to a dull knock.. Any advice I change almost all the ignition components.And a few other things ..... Ive put may hour on this motor and am positive that it has nothing to do with the gears.. Any advice anyone thank you

 

[racerone]

Remove the 2 bypass covers and inspect pistons and rings.---Also allows you to look for loose bearings.

 

[g3 1436]

I'm sorry I'm unfamiliar with the bypass covers..Do u think it would be that..With it running so smooth and not making the noise thus out the whole throttle range?

 

[Bosunsmate]

If you have a timing light you can check to see if the timing is going too far.
If you have a compression gauge now would be the time to use it,
you can also bring the pistons to top dead centre and then with a screwdriver with some cloth on it check on the piston head for any excessive play in the bearings/ any significant difference between the two pistons will indicate somethings up with them.
Best to check all that too make sure but might just be too early timing like you say.
The bypass covers are the two little covers on the opposite side of the exhaust cover. Removing them means you can access the pistons and check the rings are springy, ie not broken. You then need to replace the gaskets but they are only 2 or 3dollars each

 

[racerone]

OK , so did you torque the flywheel after the ignition work ?

 

[g3 1436]

Ok I didn't torque the flywheel. But I put it on pretty tight and I've took it off a few times it definitely hasn't moved, from being loose.I also did compression test and checks out same as before 115 on both..As for checking the timing I dont have a light but am willing to go get on.. But my clymer book says I have to check it at 1000 rpm.. And I have no tack currently at hand.. Im contemplatingon buying a tiny tach do you have any information on doing the timing without one..? Thank you guys for all the help this things driving me crazy.

 

[Bosunsmate]

http://forums.iboats.com/forum/engi...4008-joe-reeves-wot-timing-procedure?t=228183

Ive never used a tach, but im not saying they are wrong