1989 Yamaha 175 - Power loss and High Rev

[OnLine]

Have a 1989 175 Yamaha on 20' Mako CC. <br /><br />SYMPTOMS:<br />Earier in the season, while running at 4000 RPM's and above the engine would jump up a 100-200 RPM's every few seconds. Below 4000 RPM's it would run fine. 2 Weeks ago I brought the throttle up to 3k RPM's and the engine would rev high but the boat wouldn't move. Backed off the throttle to idle and pushed up again, everything seemed fine. This weekend, the boat wouldn't go over 1800 RPM's without high rev/loss of power. Boat goes in and out of gear with no abnormal noises from the lower unit.<br /><br />QUESTION:<br />Does this sound like a spun prop hub?<br />Could it be the lower unit? Seems like a slipping clutch plate.<br />What should I check besides the prop?<br />Could it be no oil in the lower unit?<br /><br />Thanks,<br /><br />OnLine

 

[OnLine]

Re: 1989 Yamaha 175 - Power loss and High Rev

Also - Anyone know Max RPM's on this motor?

 

[John from Madison CT]

Re: 1989 Yamaha 175 - Power loss and High Rev

Hmmm, sounds like it could be a slipping hub on that prop..<br /><br />Max RPM's are 5500RPM's.<br /><br />John

 

[OnLine]

Re: 1989 Yamaha 175 - Power loss and High Rev

John,<br /><br />Thanks for your reply! I'm going to get the prop rebuilt 1st. Very concerned it could be the lower unit, but everything sounds ok, the motor just revs up like there's no resistance.<br /><br />I never need to run the motor beyond 4800 RPM (about 40mph) and was curious how high it would go. Is it bad for the motor to run WOT?

 

[Solittle]

Re: 1989 Yamaha 175 - Power loss and High Rev

Runnin WOT will only hurt your gas card.

 

[suzukidave]

Re: 1989 Yamaha 175 - Power loss and High Rev

It sure sounds like a spun hub. <br /><br />You need to make sure you run your motor in its recommended WOT range. running a 5500 rpm wot at 4800 rpm max means you are lugging the motor, especially when you run below 40mph. That will carbon up your motor and cause other problems. If 40 mph is the max speed you want, you need a lower pitch prop or to switch prop designs to a 4 or 5 blade so your rpms are closer to 5500 at 40 -- this should also mean your boat will get out the water faster.

 

[orca]

Re: 1989 Yamaha 175 - Power loss and High Rev

If you are worried about the lower unit remove the lower oil fill screw and check the oil, it will be obvious if there is a problem. If you see metal filings on the fill screw magnet you have big trouble.

 

[OnLine]

Re: 1989 Yamaha 175 - Power loss and High Rev

Thanks for the responses!<br /><br />suzukidave,<br />Have no problem running the motor above 4800, just thought it was best not to push it. Once the prop is fixed (I hope that's what it is), I'll run it WOT for a few minutes. Is this long enough to clean out the carbon buildup? Should this be done everytime the motor is run?

 

[suzukidave]

Re: 1989 Yamaha 175 - Power loss and High Rev

Online, 2 strokes should run as much as possible within their recommended rpm range -- gunning it once in a while to get up there is not the answer. You need to confirm the minimum recommended rpm for your boat and then consider whether to reprop. Might be a good idea to do this before you spend money fixing the current prop.

 

[OnLine]

Re: 1989 Yamaha 175 - Power loss and High Rev

I assume the minimum recommended RPM is for the engine? How would I find this?

 

[OnLine]

Re: 1989 Yamaha 175 - Power loss and High Rev

Pulled prop today, rubber bushing was all mashed up. Should have it repaired in a day or two.<br /><br />Thanks for the help!