Boat slowed down

[rgeddes]

I have a 2005 Stingray with a Mercruiser 4.3 MPI with 200 hours. The boat has slowed down over the last couple of weeks. Last week, it took forever to get me up on skis.

I replaced to Distributor cap and rotor. That was expensive. I replaced the 21 prop to a 19 4 blade stainless prop. It was an improvement, but still slow.

I have a difficult time getting up the RPMs. With the old prop, my rpms at WOT were 3,500. With the new prop, it is 4,000 rpms.

The top speed of the boat was around 50+ mph. Now, the fastest it will go into 42 mph.

Any thoughts on what to check next?

 

[littlerayray]

Is there water in the bilge did you hit anything and it almost sounds like your not firing on all cylinders the motor doesn't sound rough do a compression check as well

 

[alldodge]

When the last time the fuel filter was replaced?

 

[rgeddes]

Did not hit anything. There is not water in the bilge. Boat runs fine. It has 40psi at WOT. Temperature is 160. Everything seems fine.

Should I replace the spark plugs next?

 

[littlerayray]

Your rpms seem really low by at least a 1000

 

[rgeddes]

The RPMs were higher earlier in the year. I took the boat out in May and it ran fine. It sat for 2-3 weeks before I took it out again. I'm afraid it might be the gas, or ethanol. It stalled several times when I started running it again. I used some Seafoam and it doesn't stall anymore. I am going to replace the fuel filter. When I change the spark plugs, I will check the compression.

 

[biggjimm]

Any way to temporarily hook up an alternate fuel tank? I have one of the 6 gal portable tanks like for a pontoon that I can hook up when I suspect a tank full of bad fuel is causing problems. Or just drain & re-fill your tank??? Good luck. Jim.

 

[rgeddes]

Boat still has the same problems after replacing the propeller, distributor cap, rotor, and fuel filter. I put filled up the tank 1/2 full with new gas, ethanol fee. I've run it down to a quarter of a tank. Still no improvement. Very slow to get on plane, then picks up speed as it gets going. I can barely pull a 120lb skier out of the water.

I checked the compression in all cylinders. They compression is above 90+ psi in every cylinder. One cylinder was at 90 psi. The others were 100+. As I replaced each spark plug, I tested the cylinder. One at a time. When I look at the Coil wire, one end is very clean. I can see bare metal. The other end if very dirty. You can not see metal. The coil wire broke when I took it off the coil. I need to replace it. Is this grease or a possible problem with the coil, or coil wire?

 

[Bondo]

I checked the compression in all cylinders. They compression is above 90+ psi in every cylinder. One cylinder was at 90 psi. The others were 100+.

Ayuh,..... That's a rebuildable core motor,...... a good runnin' motor will be in the 140 psi, 'n above range,.....

120 psi is a tired motor,.....below is a very tired motor,....

below 100 psi is a core to be rebuilt,....