cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

[snowman51789]

today i was testing the compression on my 92 3.0lx merc and i noticed that the spark plugs on cylinders 1 and 4 (assuming cylinder 1 is the front cylinder) were very dark/black (rich) colored while the plugs in cylinders 2 and 3 looked to be light colored (lean). i put new plugs in and ran it for about an hour and the new plugs showed the same thing. any thoughts as to what could cause that???

compression was #1 155 #2 145 #3 140 #4 135

resently replaced parts
plugs (begining of year and today)
wires
cap and rotor
rebuilt carb
replace all fuel filter's
checked fuel pump pressure

 

[Bondo]

Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Ayuh,.... I'd guess, 1/2 of yer Carb is boogered up....

 

[snowman51789]

Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Thats what I was originaly thinking but if I remember right, isn't the area under the carb and open area before the intake ports?? In other word, its not like one barrel gose to 2 specific cylinders and the other barrel goas to the other 2. And have you ever herd of this problem?

 

[snowman51789]

Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Bump

 

[Doernuth]

Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Could be a breach in the intake portion of the manifold gasket on the 2 and 3 cylinders. If it is sucking extra air through the gasket it will burn lean.

 

[snowman51789]

Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Hmmm that would make sence. Is there any way I could test that theory?

 

[littlebookworm]

Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Spray some WD-40 around the intake manifold with the engine running. If ther's a leak, the engine will speed up slightly when the oil hits the leak area. Hy

 

[snowman51789]

Re: cylinders 1 and 4 running rich but 2 and 3 are runing lean???????????????????

Oh I alread did that but I used starting fluid. N there was no change