90 Merc 150 XR4 smoking, running rough, won't plane

[plumber2]

I bought a 17 1/2 Bass boat with a 90 model Mercury 150 XR4. Seemed to run good hooked to a water hose but not in the water. Won't get up on plane, sometimes goes dead and smokes like a train when restarted. Will idle all day, I think a little rough and won't go dead when you give full throttle just chugs along and won't plane out, but has most problems at halfthrottle. I cleaned the carbs (really well), checked compression (120 on all 6), changed plugs and tested wires with a tester. Syphoned out all the gas and replaced with new premium and changed filter. Will rev right up on land and seem to run great. Has a Quicksilver 24 pitch prop that a local prop guy says is perfect. Oh yeah, doesn't run hot either. Where do I look from here?

 

[Elmer Fudge]

Re: 90 Merc 150 XR4 smoking, running rough, won't plane

check the fuel delivery system.

 

[plumber2]

Re: 90 Merc 150 XR4 smoking, running rough, won't plane

Forgot to mention that when I pulled a plug wire off either of the top 2 cylinders it didn't seem to make any difference in the way it runs. They have compression, spark, and fuel. Maybe the fuel pump isn't pumping enough pressure? Will get all the RPM's you want without a load though. Also all the plugs look black and oily even though they are new. Could it just be running way too rich?

 

[Clams Canino]

Re: 90 Merc 150 XR4 smoking, running rough, won't plane

I'd say the issue is with the carb that feeds 1&2<br /><br />Don't rev it too high out of gear.<br /><br />-W

 

[shipoffools]

Re: 90 Merc 150 XR4 smoking, running rough, won't plane

Fuel pump rebuild is about $15 for the kit and takes about 15 mins to complete the job. I had the same symptoms with my 70hp last season it gave me fits but a fuel pump rebuild solved the problem.

 

[plumber2]

Re: 90 Merc 150 XR4 smoking, running rough, won't plane

Thanks for the tip. I actually bought the rebuild kit this morning before I read your e-mail but its been raining here all day and didn't try it yet. But your response makes me feel a little less like throwing darts at a guessing board in the dark with a blindfold while spinning around. (very slight exageration) If its wrong at least it was a good enough idea for us both to think it. Thanks

 

[LubeDude]

Re: 90 Merc 150 XR4 smoking, running rough, won't plane

Sounds like what happened to my 150 when my stator went south.

 

[plumber2]

Re: 90 Merc 150 XR4 smoking, running rough, won't plane

Well I'm pretty sure I found the problem. A vacuum leak under the bottom carb. Repaired the leak and it smoothed out tremendously at idle and is very responsive. Hope that fixed it. Thanks for the tips.

 

[plumber2]

Re: 90 Merc 150 XR4 smoking, running rough, won't plane

OK OK OK, problem solved. It was a conbination of the vacuum leak and carburaters way out of adjustment. Took it to the lake yesterday and it ran great with a Laser II 24 pitch prop. If you find smooth water it will flip your eyelids back. Thanks again for the tips.

 

[Subforce]

Re: 90 Merc 150 XR4 smoking, running rough, won't plane

plumber2, Where was this vacuum leak at? Sounds similiar to my problem.<br /> Subforce

 

[plumber2]

Re: 90 Merc 150 XR4 smoking, running rough, won't plane

I don't know what you call it but on my motor there are two covers over the carbs. The bottom one (closest to carbs) has a check valve and a hose that goes to the motor under the driver's side of the bottom carb. Has something to do with draining out extra fuel that leaks out of carbs. Anyway, the check valve was bad and causing an open vacuum all the time. I plugged it at the motor and maid a huge difference. Good luck with yours.

 

[fostercasey]

Re: 90 Merc 150 XR4 smoking, running rough, won't plane

Sounds like what happened to my 150 when my stator went south.

how did yours run or act when the stator was goin out