Cylinders #2 and #3 Rich #1 and #4 normal

[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?

 

[Bondo]

Re: Cylinders #2 and #3 Rich #1 and #4 normal

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?

Ayuh,.... Yer avoidin' the inevitable,.......

 

[CraigBarnard]

Re: Cylinders #2 and #3 Rich #1 and #4 normal

So are you suggesting that the carb will be the problem?

 

[NHGuy]

Re: Cylinders #2 and #3 Rich #1 and #4 normal

Yup, just rebuild it. Or if you have the cake buy the exact OE replacement. Don't muck around with other than OE unless you are carburetor smart. CFM, jetting, linkages, gaskets, choke connections - all that stuff is designed into the OE as a system.

 

[PeterB26]

Re: Cylinders #2 and #3 Rich #1 and #4 normal

Before you go too crazy with the carb check that the ignition coil is good. And put new plugs in. I had something similar on a V-6 4.3L and after thousands of bucks and countless hours on carb work it turned out to be a coil.

Merc uses a strange set up for the coil too. They often have a resistance link wire to the coil that delivers less voltage to the low volts side once things are warmed up. The idea is that when the motor is cold you get a bigger spark. This part is best troubleshot by just jumpering it out with a regular piecve of wire. But don't run that way for too long because the coil will eventually be damaged due to overheating.

Peter

 

[CraigBarnard]

Re: Cylinders #2 and #3 Rich #1 and #4 normal

Update.

Accelerator pump only squirting out of one port instead of two.
Looks like the diagnosis is heading towards a plugged up carb.