Questions on Prop and perfomance on 88 Force 125

I took my boat out to the lake today, for the first time with a new tach on it, since there wasn't one before. I am only running about 4600 RPM's at WOT and trimmed up. On the engine it says it should be run between 4800-5800 RPM's. I don't know what the size of the prop is that I have on the boat. I took it off and all it says on the hub is Michigan and part number is 071031. I went to their website and searched for this part, but can't seem to find it. I did find a simalar number from another site that stated 310, so I think it may be the same, and it showed this part number as a 13"X19. Can anyone tell me anything about this prop? <br /><br />The boat seemed to perform well today. I took 12footers advice about using the Deep Creep, decarbonization method, and from about 3 weeks ago on the boat, I was topping out at about 32.5 on GPS and today I was up to about 36.2 on GPS. <br /><br />Also, there is probably about 10 gallons or so of old gas in the engine. Does anyone know what about how fast I should get this boat up to with this engine? <br /><br />Thanks,<br />Bryan Cox<br />MTU

Re: Questions on Prop and perfomance on 88 Force 125

What kind of boat and what size?

Re: Questions on Prop and perfomance on 88 Force 125

88 Bayliner Capri 19.5 Foot<br /><br />Thanks,<br />Bryan Cox

Re: Questions on Prop and perfomance on 88 Force 125

Does anyone have any ideas on this?

Re: Questions on Prop and perfomance on 88 Force 125

Hi, Bry.<br /><br />Sounds like you are way overpropped. That B'Liner should use a 15" to 17" prop with a 125 (prop rated). I have heard that Forces were crank rated at one time. You may have one of those, or you may have a very weak engine that isn't going to turn any prop up to 5800.<br /><br />Has your package at any time performed properly, or has it been that way since you bought it?<br /><br />Is there a chance that your tach is off? 36mph sound like a good WOT speed for your rig.<br /><br />

Re: Questions on Prop and perfomance on 88 Force 125

JB,<br />I just found that the Prop that is on the boat now is a 13" x 17 Michigan Prop. I had never had a tach on the boat until as of the past month, so I don't know what it used to turn. I have had the boat about 2.5 yrs now and it has run up to 42 in the past. Right now I have some old gas mixed in the tank with some new stuff, so its still not running on good fuel, so I think that may add to it running a little slower. It is now running faster than it was 4 weeks ago, it only got up to 32.3mph on GPS and yesterday it was up to 36.1 on GPS. <br /><br />This is when I found that it isn't getting into the correct running RPM's yet, so now I am trying to play with the prop to get into the operating range of the motor.<br /><br />Thanks,<br />Bryan Cox<br />MTU

Re: Questions on Prop and perfomance on 88 Force 125

The more I think about it, Bry, the more I think your tach is in error. Not certain, though, because if it gets to 36mph at 4600, 42mph would require it to get to about 5300rpm and you said you had seen 42mph with the same engine, same prop..<br /><br />I think it is time to give your engine a physical. Compression check, carb cleaning, decarb and feed it fresh fuel. If you have lost 6mph you have dropped 700rpm at WOT.<br /><br />

Re: Questions on Prop and perfomance on 88 Force 125

I think part but maybe not all is in the prop pitch. <br /><br />You might test drive a lower pitch prop (14 or 15) to figure out what's up. If you get a dramatic change in rpm (more than 300 rpm per inch) then you are currently badly overpropped. If the change is in the 2-300 rpm range per inch then I suspect you may still be overpropped but that you are really making better than 4600 revs right now -the problem may also be in your tach and you will want to check it out too. As JB says your speed doesn't sound too bad.<br /><br />I start with the fact that I would have thought that 4600 rpm is too low for w-o-t on your boat with a 125 and a 17" prop unless your bayliner is heavier than normal bayliners or you have a motor or trim problem (or the prop has been repaired to so as to get a different pitcj). Also, if decarboning it made 4mph difference (=400-500 rpm) then that would mean you were running it three weeks ago at only 4100-4200 rpm. You should definitely have noticed when an engine is revving that far under its performance band. It would sound and handle wrong. That all suggests your tach is wrong.<br /><br />However, the tach might be right and you must have been badly carboned up to get such an improvement in speed which is often a sign you are overproppred and lugging the motor.<br /><br />I just repropped my boat and from trial and error I found that my motor/boat combo has a comfortable prop range within which rpm changes about 200-300 rpm per inch of pitch. When I went one inch beyond that range I suddenly lost 700 rpm in one step. That might be your problem since I can't think why else you'd be at 4600 rpm at 17" (which would normally mean you should drop all the way down to a 13" prop for optimal use) Too find out if that's the problem, try a lower pitch prop as suggested.<br /><br />One tip, when messing with different prop pitches make sure you trim and load the boat the same and run it in the same place in the same coniditons to ensure you aren't comparing apples and oranges.

Re: Questions on Prop and perfomance on 88 Force 125

Thought you guys might find this article interesting... <br /><br /> http://popularmechanics.com/outdoors/boating/1997/9/Comparison_Boat_Props/index.phtml <br /><br />It goes into some good prop detail and shows just how much difference the prop can make.<br /><br />rgds<br /><br />Frank

Re: Questions on Prop and perfomance on 88 Force 125

Bry, I had a 1987 Trophy with the 125 Force (yes it was motor, not prop HP rated back then), and I ran a 17 pitch SS prop on it. I think your tach is wrong too, because 35-36 mph was around 5700-5800 rpm for me. I had other boats confirm the speed too.<br /><br />I think you will find that the 17 pitch is what you need, unless you load the boat super heavy. I usually fished 3 guys in that boat, and could hit 35 mph on a calm day.

Re: Questions on Prop and perfomance on 88 Force 125

I have been trying to find another way to measure the RPM's, with a shop type tach. The only problem is that they don't seem to work right on this engine, due to the 20 Pole Alternator.<br /><br />Does anyone have any other ideas?<br /><br />The tach is brand new and this was the first time that the boat has ever had one in it. It is the beede tach, that supports up to the 20 pole alternator. It seems to be correct, except at top end, just buy the sound of the engine.<br /><br />Now, I have found that it seems there may also be a problem with my carbs as stated in one of the other posts on here. They seem to leak when I pump primer bulb, then gas will drip out instead of stopping. I checked and it seems the gasket on the bowl, is worn so I ordered the carb rebuild kits from the dealer and should be in next week. I am hoping that this will make a difference.<br /><br />This engine had never been decarbed until I did it this past weekend, with the Deep Creep, which worked awesome. <br /><br />To tell you the truth, this boat ran like it was a new boat to me, it has never driven and purred as good as it did sunday. Even the time that it got up to 42, it didn't handle as good or purr as good as it is right now.<br /><br />I am thinking about trying to get the Hustler 17 pitch prop to see if maybe my prop has some damage, it does have some dings in it, and I have been planning on a new prop. I guess ill give that a shot and try staying at the same prop size, I can always get another one that goes down a size to 15 pitch.<br /><br />I have been told that on this boat, I should beable to get to about 40-45 MPH with that engine running correctly. And I know it has gone 42 in the past, it was about a 2 yrs ago that it did that though.<br /><br />Thanks for all you guys help,<br />Bryan Cox

Re: Questions on Prop and perfomance on 88 Force 125

I have now replaced the reeds with Boyeson reeds and put a Hustler 17 pitch prop on the boat. I now am able to get about 4800-4900 rpms at about 40 MPH, with Garmin GPS 12.<br /><br />The boat is now running stronger than ever. I also found that I was not getting WOT out of the carbs, due to a incorrectly adjusted Throttle cable. It didn't have enough spring to pull idle back down to about 1000 RPM's when it was set for WOT to open all the way up. I would get about 2500 rpms, due to it not closing the carbs.<br /><br />It now really runs like a new engine, and has never run this strong or sounded so perfect before. I was ready to get a new engine, but now I'm extremely happy with this Force now. I also replaced the Spark Plug caps with NGK screw on caps, and that helped a bit to.<br /><br />Hope this will help someone else, with bring life back to that old Force. It is like a totally new boat, the way it handles now to me at least, lol.<br /><br />I can also plane out faster and then drop back and run in plane at about 1300 rpms no problem now.<br /><br />Thanks for all the help.<br /><br />Bryan Cox