Help

[CraigBarnard]

I have a mercruiser 120 hp 4cyl. carb i/o.

Ran fine last year.

This year i cannot get it to rev over 2000 rpm and has a massive lack of power.

I checked the spark plugs and numbers 2 and 3 are running Rich but 1 and 4 seem fine, proper colour.

Runs fine at idle.

I have some seafoam sitting in the carb, hoping its just some gummed up crap in the carb.
Used the fuel pump to pull straight from the can until the engine died.
Not sure if that will be effective but easier than removing and disassembling the carb.

Any ideas?

 

[heyyou325]

Re: Help

Have you checked the choke? That's a real easy fix. If not, check the fuel lines. How much black smoke do you get from the exhaust? Is the air filter plugged? It could be a lot of things. Going to the regular forums in the merc inboard section, a lot of people there who know them better than I do, but I've mentioned some easy things to check.

 

[CraigBarnard]

Re: Help

Choke fine
No black smoke.
Posted in merc forums too.
Thanks
Just really curious why only the two center plugs are running rich.

 

[dozerII]

Re: Help

Have you checked the points and advance plate for rust?

 

[CraigBarnard]

Re: Help

No points. Converted to electronic system.
Havent checked the advance, will do that tonight.

Thanks

 

[airshot]

Re: Help

Choke fine
No black smoke.
Posted in merc forums too.
Thanks
Just really curious why only the two center plugs are running rich.

Do a compression check on your motor, if compression is low in 2-3 fuel will not burn and show fouled plugs. The 4 cyl motors have a reputation for blowing head gaskets between cyl 2-3. A proper compression test will give you an indication of the general health of your motor.

Airshot

 

[heyyou325]

Re: Help

If the plugs aren't firing hot enough, they won't burn clean. You could check the gap. If they were missing, you'd notice 2 missing. Not firing hot enough wouldn't cause it to not rev up. I'm assuming it's an older engine since you list a 65 chieftain as your boat. I don't really understand the fuel injection. But if the floats are stuck or the needle valve it could cause it to run way too rich, or lean, either could do that. Too rich and plugs not firing properly I would imagine could cause your problem. maybe