Does not reach top speed

[rgeddes]

I have a 1991 four winns 180 with a 4.3 OMC engine. It runs fine, but will not reach its top speed of 42 mph. With just myself on the boat, it tops out at around 30-32 mph. It works great for water skiing, but I would like to go a little faster. What should I look at first for the top speed issue. The boat starts fine, and runs fine. It runs very well at 22-24 mph at around 3,000 rpm.

 

[Boomyal]

Re: Does not reach top speed

What is your WOT rpm? Are the throttle plates wide open? Is the boat trimmed right? Is the hull dirty and rough? Could you be waterlogged below deck? Is the motor worn and tired?

 

[rgeddes]

Re: Does not reach top speed

The WOT is around 4,000 to 4,500 rpm. The boat is trimmed up about 1/3 way up. The hull is very clean. The gel coat is in great shape. A few scratches, but that's it. There is no water in the bilge area. Recently, I had a problem with the wood around the gas tank. I tore it out and replaced it. I found some more rot around the ski locker area. I plan to replace that this winter. I had a leak a couple of weeks ago, but fixed it. The gimbel was worn down and rusted. Since replacing it, I have not leaks.

How can to see if the throttle plates are wide open? I have the throttle all the way down.

Before I put anymore time into the boat, I want to make sure that the engine and outdrive are working in top condition. If it can reach the 42 mpg. I plan to tear our most of the wood and re-fiberglass the deck. If I can't get it up to top speed, I'm not sure its worth it.

 

[alorio1]

Re: Does not reach top speed

Are you checking by Gps, make sure prop area is clear of fishing line. I found a wad of fishing line behind my prop that was slowing my engine and top speed down a few years back.

 

[Boomyal]

Re: Does not reach top speed

Just push your throttle lever all the way forward, then go look down the venturis. They should be straight up and down. There is a big difference between 4000 and 4500 rpm. Which is it? If it is 4k, then you are not propped right. With the rot you described could your flotation foam, below deck be like a watermelon?

 

[JJBoatr]

Re: Does not reach top speed

My brother has 1992 180 Freedom with a 4.3l and he is running the factory 14 1/2 x 21P propeller which puts it at 4200RPM trimmed up. His top speed is 46MPH on GPS(+/- 5m) What Prop are you running? Someone may have dropped the pitch way down for pulling a tube or skier. You should also verify that your tach is accurate and once you have done that, pay very close attention to it when you're trying to reach top speed and tell us EXACTLY what it reads. 1" of change in pitch can change your WOT throttle by 150 - 200RPM depending on your hull efficiency and weight. 3,000RPM sounds a bit high for 22-24MPH imho.

 

[rgeddes]

Re: Does not reach top speed

I checked the boat this weekend. 24mph at 2500 rpm. 34 mph at 4,000 rpm. It was wide open. I check the carb. The venturis was up and down. We used the boat a few more hours that day. Then, I had a major problem with my out drive. It no longer works. The prop just spins when in gear, forward or backward. I'm replacing the out drive. Do you think the out drive could have been the problem? Would the out drive prevent the engine from revving up over 4,000 rpm. The boat use to rev up past 4,000 rpms.

 

[alorio1]

Re: Does not reach top speed

Shift cable may have broke. Did the outdrive make any unusual sounds before it quit?

 

[rgeddes]

Re: Does not reach top speed

It made a loud bang nose that was heard at dock.

 

[Howard Sterndrive]

Re: Does not reach top speed

yes it could have been loading the engine. You might want to look into the SEI conversion to a Mercruiser Alpha style drive.

 

[alorio1]

Re: Does not reach top speed

Make sure you are replacing with the right upper drive gear ratio...........

 

[JJBoatr]

Re: Does not reach top speed

It sounds like your clutch dog assembly grenaded. Before that happened...Where you trimming up when trying to reach top speed?