Knocking over 1500 rpm in gear only

[beach]

When in gear motor starts knocking about 1500 rpm, started knocking lightly and got louder last time out to where I haven't had it above idle again. Below that no knock. Out of gear can run it up to 3000 rpm smooth, no knocking. Any ideas? Could it be bad spark in 1 cyl or a carb needing cleaning?

1974 Mercury 850

1 152 psi
2 150 psi
3 151 psi
4 152 psi

 

[lilmandavis]

Re: Knocking over 1500 rpm in gear only

shift adjustment? is it doin it under load? only in gear or in neutral to?

 

[beach]

Re: Knocking over 1500 rpm in gear only

Knocking only in gear.

 

[lilmandavis]

Re: Knocking over 1500 rpm in gear only

figure out what part is knocking. the power head or the lower unit.

 

[gungalunge]

Re: Knocking over 1500 rpm in gear only

I walked away from my engine idleing off the dock it was sounding good . when i heard it in gear i knew going 3500 rpm it was disapointing . now i am rebuiling the lower end extensively , hope to see good results ..

 

[beach]

Re: Knocking over 1500 rpm in gear only

Seems to be comming from the top end. It starts knocking at 1500, if I try to increase rpm it starts shaking/vibrating so bad it wont run.

 

[beach]

Re: Knocking over 1500 rpm in gear only

I think the gears may be slipping or jumping out of place when I try to accelerate.

I took it out today and opened the throttle up, it started clanging as usual but when the motor got up around 3000+ the noise stopped and we weren't going anywhere.

What year and hp range can I look for a used lower end?

 

[roger3645]

Re: Knocking over 1500 rpm in gear only

beach e-mail me at rip3645@hotmail.com I may have all the parts you need. I run a 1975 and 1973 merc 850, I have extra LU parts. I'll check them out this weekend.