I recently acquired a neglected/abused 2000 Mercury 4hp 4 stroke that would only run with the choke on and very little power increase going past 1/2 throttle.
I cleaned the carb and got it so it'll idle decently (although there's is a bit of surging) but still can't get any speed out of it. It's on a small 12' fiberglass boat and while I realize it's not going to set the world on fire, I could paddle a canoe faster than this thing. It's just not reaching much RPM under load but revs fine in neutral.
I'm also using a good tank with new lines and primer bulb, which stays pretty hard and has no affect on WOT when I squeeze it.
Here's what I've done so far.
1. Cleaned carb and all jets, nozzles, orifices with cleaner then compressed air.
2. Checked all fuel lines.
3. Took off fuel pump and saw no obvious sign of problems but not sure of how to check for bad diaphragm.
4. Compression is well within spec @ 55psi
5. Spark plug looked good but gave it a good cleaning anyway and jumps a nice blue spark.
6. Throttle linkage all checks out and carb is fully opening.
7. Valve lash within spec.
8. I noticed a LOT of buildup on the back of the intake valve when checking the intake o ring so soaked it in Seafoam for a couple of hours, which seemed to help it idle smoother.
9. Carb gaskets and spacer look good.
10.Good air and fuel flow through inline filter.
I may have forgot something but am pretty much out of ideas so any suggestions are much appreciated.
Thanks.
I cleaned the carb and got it so it'll idle decently (although there's is a bit of surging) but still can't get any speed out of it. It's on a small 12' fiberglass boat and while I realize it's not going to set the world on fire, I could paddle a canoe faster than this thing. It's just not reaching much RPM under load but revs fine in neutral.
I'm also using a good tank with new lines and primer bulb, which stays pretty hard and has no affect on WOT when I squeeze it.
Here's what I've done so far.
1. Cleaned carb and all jets, nozzles, orifices with cleaner then compressed air.
2. Checked all fuel lines.
3. Took off fuel pump and saw no obvious sign of problems but not sure of how to check for bad diaphragm.
4. Compression is well within spec @ 55psi
5. Spark plug looked good but gave it a good cleaning anyway and jumps a nice blue spark.
6. Throttle linkage all checks out and carb is fully opening.
7. Valve lash within spec.
8. I noticed a LOT of buildup on the back of the intake valve when checking the intake o ring so soaked it in Seafoam for a couple of hours, which seemed to help it idle smoother.
9. Carb gaskets and spacer look good.
10.Good air and fuel flow through inline filter.
I may have forgot something but am pretty much out of ideas so any suggestions are much appreciated.
Thanks.
