1989 Force 85

[akboater]

This all started, because I wasn't paying attention. <br /><br />The boat is a 18' Bayliner Capri Cuddy Cabin. All was running last fall, when I pulled the boat from the water. In doing my end of season maint, I pulled the shift pin from the lower unit, instead of the drain plug.<br /><br />I replaced the lower unit with a rebuilt unit. Then noticed that I had a crack across one prop blade, that was about 1/2" from failure. So, I replaced the prop with a 15" cupped prop. (It had a 15" prop on it previously".<br /><br />All is well, acceleration, and speeds are about the same, but now wot is only 4200. It was 5400. I can't believe a cupped prop on this engine costs 1200 rpm, and 10mph !!!<br /><br />Compression and spark are good. I've decarbed, and to eliminate old fuel problems, am running on a portable tank, with new hoses and bulb, connected directly to the engine.<br /><br />I thought maybe something in the lower unit, but there doesn't seem to be any unexpected rotational resistance, and the oil doesn't show any metal ... so I don't think anything there is adding a load to the engine.<br /><br />Any suggestions .... would be GREATLY appreciated !!!

 

[roscoe]

Re: 1989 Force 85

You say 15" prop. <br />Is the diameter 15"?<br />Or is the pitch 15"?<br /><br />What was the diameter AND pitch of the old prop?<br />What is the diameter AND pitch of the new prop?<br /><br />If you increased the pitch by 5", your WOT rpm would decrease substancially, and your speed could possibley stay about the same.<br /><br />But you would be lugging your engine terribly.

 

[akboater]

Re: 1989 Force 85

The old prop was 13.5X15 uncupped.<br /><br />New prop is 13.5X15 cupped.<br /><br />Speed for both props was/is approximately<br /><br />22mph @ 3500<br />26mph @ 4000 per GPS ... <br /><br />Only thing is, it used to do about 38mph @ 5400 wot. Now wot is only 4200rpm.

 

[TomB]

Re: 1989 Force 85

Akboater,<br /> Did you ever find out what the problem was? I have a 1989 85hp Force that does the same thing. I can't get it over 26mph on a 16.5 Bassboat.<br />Thanks for any info<br /><br />Tom

 

[akboater]

Re: 1989 Force 85

No solution yet.<br /><br />But in thinking back ... a few years one of the kids jetskis had a similar problem. Was running good, but in the spring ... no top end.<br /><br />After messing with it for a weekend, I noticed the reeds looked pretty gummy ... so put a can of carb cleaner in the gas, and sent them to the lake. Ran around for a while, and top end started picking up. By the end of the day, it was back to normal.<br /><br />So, that's my next thing to try.

 

[lakeman1999]

Re: 1989 Force 85

If you replaced the lower unit, it is a possibility that the gearing in it is a different ratio.

 

[akboater]

Re: 1989 Force 85

Hi,<br /><br />I thought about gearing, but it checks out at 2:1 just like the old lower unit, and is what the book calls for. Also I get the same speeds for the same rpms as with the old lower unit.<br /><br />Thanks,

 

[akboater]

Re: 1989 Force 85

Ahhhhh .... come on. There's got to be more people than this out there with ideas / suggestions !!

 

[The Marine Doctor]

Re: 1989 Force 85

TBH<br /><br />I have a 1989 85hp Force sitting at the shop..doing the exact same thing...gets to 4300Rpm's and NO higher..be it we have a 15 pitch prop or a 19 pitch prop still the same Rpm.<br /><br />TMD is stumped

 

[The Marine Doctor]

Re: 1989 Force 85

I think on Monday I will pull the reed blocks again...and have a look.<br /><br />TMD

 

[akboater]

Re: 1989 Force 85

The latest is .....<br /><br />I bought a can of Berryman's B-12 Chemtool carb cleaner, and mixed up a fresh batch in an external tank. The idle rpm went up by 200 and the acceleration is much smoother, but still WOT is only 4200 rpm. Changed to a borrowed 13.5X17 prop, and WOT dropped to 3600rpm, top speed stayed about the same.

 

[The Marine Doctor]

Re: 1989 Force 85

I found the reason that the 85hp force would not work...Turned out to be the highspeed jets being too big for our elevation here..We put the new ones in and it pulls 5400rpm with the test wheel now.<br /><br />TMD

 

[akboater]

Re: 1989 Force 85

This motor has always been in the same area. And operated to 5400 rpm prior to changing the lower unit and prop. So, I don't think its the jets .... or maybe it just needs one

 

[The Marine Doctor]

Re: 1989 Force 85

Are you sure you installed the correct gears? 4cyl gears instead of 3 cyl gears.<br /><br />TMD

 

[akboater]

Re: 1989 Force 85

I'm relatively sure the gears are right. I bought the lower unit for reputable dealer. The gear ratio is 2:1 as per the manual. And the speed / rpm ratio is the same as it was previously, at lower rpms.