how fast should my boat go?

[yfz450guy]

i have an 88 bayliner bass trophy, 18ft., 125hp force, 13x19 3/blade prop.
i am asking becuase i can't get the boat to go any faster than 38-40 mph. that seems low for as small as the boat is and how big the motor is. my rpm's are in the 4200 range.
things i have done;
fuel pump, plugs, compression good at avg;133psi, new fuel lines, cleaned carbs, tank, have good spark on all 4 cyl., fuel fliter. and more.
i am about ready to put 20gals. of 115oct. race gas in it and drive it like i stole it. lol.
any ideas for more performance or things to check that may be bad that would effect the performance?
thanks in advance.

 

[WillyBWright]

Re: how fast should my boat go?

Forget the 115 octane idea. You'll be looking for a new motor before you burn up that first tank. Use regular unleaded ONLY! Best you're gonna get outta that package is lower 40s with a 19p aluminum prop and the motor mounted low, and mid 40s with a stainless 21p prop and the motor mounted higher. If it has conventional sparkplugs in there now, get surface gaps. There are gearcases with only snout exhaust behind the prop and combination thru-hub/snout exhaust. The faster one will be the combination. If you don't have that one, look for one. The way to tell is with the prop off. The combination will have a cavity in front of the prop, the snout-only will have a plate. Props are a bit difficult to find. They are unique and Force and Michigan Wheel are the only manufacturers I'm aware of for them. Make sure it's a pre-1995 model prop.

 

[kenmyfam]

Re: how fast should my boat go?

Forget the high octane gas and look more at the motor height, weight distribution, set up etc. Chances are you wont get much more from it.

 

[yfz450guy]

Re: how fast should my boat go?

the motor is as low as it will go.

By yfz450guy, shot with Canon PowerShot A95 at 2007-09-09

By yfz450guy, shot with Canon PowerShot A95 at 2007-09-09

 

[MWBROWN]

Re: how fast should my boat go?

I agree with the others. Use regular fuel only.

I have an original book from 1984, and it shows the prop as a 13 x 19, so you have that. It also show the HP range from 4500 to 5500 rpm.
According to your post, you are a bit low on rpm, if all is accurate.
I would think you should get a bit more speed with that set up. I can get 38 to 40 gps speed with my 1510 Fish and SKi with a 85 hp. I get about 5300 RPM.
I know not what to tell you to look for to increase your rpm.
You could raise the engine a couple of inch's according to your picture.

Good Luck,

Mike

 

[Ben Paquin]

Re: how fast should my boat go?

I'm getting a gps tested 40mph with 3 people on board on a rough water vee boat with a 115hp yamaha. And I think it should be quicker. It will go quicker once I put in the 17 pitch prop I ordered. My bet is something is wrong with the engine. Do you trim the engine out a lot ?

Bass boats with 115hp+ usually have 21-23 pitch props and are able to hit 50-55mph.

 

[Guest]

Re: how fast should my boat go?

It would seem something needs a tweek.Your not even reaching your hp developed rpm.5,000.I would raise the motor till venting becomes a problem.
Then go to a stainless prop.This may allow a little more height.Be sure it pumps water.Keep in mind when going stainless you usually need to drop in pitch.With your present rpm I would think 2 inches.You may want to go to the prop forum with all your boat and motor specs.Good idea to confirm the tachs accuracy and get a gps speed.

 

[rudedude]

Re: how fast should my boat go?

Iam getting around 38 -40 with my 86 capri 18-8 cuddy. RPMs for the 125 are 4400-5500. Make sure there all fireing.

 

[Ben Paquin]

Re: how fast should my boat go?

Good idea to confirm the tachs accuracy and get a gps speed.

The Speed and RPM vs prop he posted make sense. Definately a lack of power and don't doubt the speed is 40mph or lower with that RPM.

 

[Frank Acampora]

Re: how fast should my boat go?

I rebuilt the same combination this year. 1987 boat and engine. I left the engine right at the height you now have it. BEFORE the rebuild, the owner told me he turned a 13 X17 aluminum at 5,000, --unknown speed. AFTER the rebuild, the same engine turned the same prop at 6,000 and 40 MPH. I installed a Chrysler SS prop 13 X 19 uncupped and and rpms dropped --I forget, maybe 5,500 but speed was up to 47 mph. and this was with a hydrofoil on the cav plate. So I see that your speed and rpms are low for that combo.

Your compression is a little low, but I don't think it would account for that loss of power. Check to be sure your timing is at 30 deg BTDC at WOT and that your carbs are synchronized so they are both opening fully at WOT. Now, Michigan SS props are all cupped so you may need to experiment a bit --a 19 pitch cupped prop is going to load down your engine like a 21 pitch and may not or will not deliver the same speed. Aluminum will definitely be 2-3 mph slower in an equal prop. And I noticed on the prop forum that there are other props available--you just need to look for them.
Set the carb floats just a "smidge" high to be sure you are not getting a lean run, and be doubly sure that fuel delivery is acceptable. Example: on my 140 I have a re-cleanable fuel filter. When the filter gets slightly dirty (enough to slightly restrict fuel flow but not noticeable enough to cause major symptoms) I notice the (21 foot cuddy) hull top speed drops from 38 to 33 mph and the engine seems to be running normally. Clean the filter and the speed pops back up. So: you may be in a slight lean run condition and not notice it. Remember: Full throttle conditions in any internal combustion engine REQUIRE a richer mixture to produce full power.

And as for "racing" fuel, forget it. You are just wasting your money. Unless your fuel has an oxygen contributor like Nitromethane, the super high octane does nothing. The reason for the high octane rating is to prevent racing engines with 12 to 1 and higher compression from knocking and detonating. In a 9 to 1 low compression engine like yours, it does nothing. Regular 87 burns just as well--and a lot cheaper too.

 

[Nate3172]

Re: how fast should my boat go?

My 85 capri with the 85 HP Force does 38. Yours should definitely do more. Noticed no one on here asked if you confirmed that you are actually getting WOT at the carburetors. If you haven't checked it than that is where I would start. I use to only get about 34 to 35 with mine until I checked and realized that it was only getting about 3/4 of throttle.

 

[yfz450guy]

Re: how fast should my boat go?

any other ideas?

 

[yfz450guy]

Re: how fast should my boat go?

took the boat out this am and was able to launch where there was no "no wake zone". i warmed up the motor and idled away from the dock. when i felt it was safe i nailed the throttle and she shot out of the hole like i was launched from a canon! got her trimmed out and was able to hit 53mph and 5000rpm! im thinking holy cow now this is more like it. got to the other side of the lake and went fishing. went to leave a couple hours later and she ran like poop! i am convinced it is electrical. she ran good right off the trailer but once she was warm, she had a mis fire and i couldn't get past 40mph.

 

[rudedude]

Re: how fast should my boat go?

Coils?

 

[roscoe]

Re: how fast should my boat go?

Mis fire with a hot engine sounds like a coil is going bad to me.