Prop Question

[Jiggz]

You would have to limit your throttle to no more than 5500 RPM before something catastrophic happens. However, you need to validate your tach is accurate and inline with speed based on GPS. So far you have yet to post your actual GPS speed with concurrent engine RPM. I understand you mentioned more than 6K rpm but not the actual GPS speed.

 

[fishnski14]

You would have to limit your throttle to no more than 5500 RPM before something catastrophic happens. However, you need to validate your tach is accurate and inline with speed based on GPS. So far you have yet to post your actual GPS speed with concurrent engine RPM. I understand you mentioned more than 6K rpm but not the actual GPS speed.

Ok..Today I went out to an open lake to see how the boat responded with the 4 blade prop. I used a phone based app for the speed that was pretty accurate, compared it to my speedo three different times 20-40mph, 40-55mph, 60-70 mph and it was only off by 1 mph each time so I thought it was accurate enough to determine the speed of the boat.

At 5k rpm's the boat ran at a blazing 34 mph...

.. between 3/4 and full throttle.. after adjusting the trim I would pick up an extra 2-3 mph but then the rpm's would gradually creep up around 5500 rpm's..

Jizzy, I'm thinking along the same lines as you that I would just have to limit my throttle to 5k rpm's before something bad happens.

I also noticed something really weird..there were a couple of times that the motor seemed as if it was slipping and would thump.. sorta like the gears wasn't locking in good..

 

[Jiggz]

34MPH at 5K RPM is about normal. So what was the GPS speed at 5500 rpm? I got a 19.5' Ski Boat with a Force '89-125HP and my WOT speed is around 5200 RPM with a GPS speed of around 40 MPH (with 3 people onboard), using a 13"-17P 3-blade SS prop. The thump sound could be an indication the clutch dogs are starting to slip and would need a little bias in the forward by adjusting the shift rod. The same slippage can actually cause an increase in rpm without any significant increase in GPS speed. Could it be the reason behind your high rpm is due to slippage?

 

[fishnski14]

34MPH at 5K RPM is about normal. So what was the GPS speed at 5500 rpm? I got a 19.5' Ski Boat with a Force '89-125HP and my WOT speed is around 5200 RPM with a GPS speed of around 40 MPH (with 3 people onboard), using a 13"-17P 3-blade SS prop. The thump sound could be an indication the clutch dogs are starting to slip and would need a little bias in the forward by adjusting the shift rod. The same slippage can actually cause an increase in rpm without any significant increase in GPS speed. Could it be the reason behind your high rpm is due to slippage?

34 mph was the top speed at 5500 rpm I would really have to be careful when trimming the engine because it would gradually increase in rpm and speed. I'm just surprised with that engine I would only achieve a top speed of 34 mph on such a smaller boat..??

I had been reading some threads about adjusting the shift rod..Is there a certain way this should be done..??

 

[SkiDad]

If you are hitting 5500 rpm with a 21 pitch prop you should be around 50 mph. Something is wrong. How long does it take you to plane with the 21 ?

 

[fishnski14]

If you are hitting 5500 rpm with a 21 pitch prop you should be around 50 mph. Something is wrong. How long does it take you to plane with the 21 ?

I didn't time it buts a lot slower getting on plane than when I had the 3 blade 13x19.. A friend of mine said I should be hitting around the 50 mph mark as well. I am new to boats and really don't where to start making adjustments. Jiggz made a suggestion that I should make a shift rod adjustment when I described to him what happened yesterday.

I am going to look over my throttle linkages and find a thread on how to adjust the shift rod... The old family john boat with a 15 Johnson is faster than my boat now.. Goodness Gracious..!!

 

[SkiDad]

While the engine is off and key off, put the boat in forward gear - then go back and spin the prop to the right - if it slips you need to adjust it. The adjustment is 2 nuts on the shift rod below the carbs - make sure you put a large towel over the red wires below the starter so you don't zap yourself - those red wires are hot even with the key off. Don't forget to take the towel out when done.

Mark the nuts so you know your starting spot. Then you just loosen top nut 1/4 turn then tighten the bottom one so it's tight again. Loosening the top one pushes the rod down further so it's it going further into forward. You then get a friend to put into gear (with engine off) and see if the prop locks when you spin it to the right. Just don't go too much on the nut adjustment as you might loose reverse. I would say a 1/4 or maybe 1/2 turn will be all you need. just my opinion though - but always make marks like I said so you can put it back if you don't like the results.

 

[fishnski14]

While the engine is off and key off, put the boat in forward gear - then go back and spin the prop to the right - if it slips you need to adjust it. The adjustment is 2 nuts on the shift rod below the carbs - make sure you put a large towel over the red wires below the starter so you don't zap yourself - those red wires are hot even with the key off. Don't forget to take the towel out when done.

Mark the nuts so you know your starting spot. Then you just loosen top nut 1/4 turn then tighten the bottom one so it's tight again. Loosening the top one pushes the rod down further so it's it going further into forward. You then get a friend to put into gear (with engine off) and see if the prop locks when you spin it to the right. Just don't go too much on the nut adjustment as you might loose reverse. I would say a 1/4 or maybe 1/2 turn will be all you need. just my opinion though - but always make marks like I said so you can put it back if you don't like the results.

Ok Mitz, I think your right. Today I put the lever in forward and the prop was still able to be spun I took a screw driver and pushed on the arm a little and wasn't able to spin the prop so I do need to adjust the shift linkage just a little. I tried to make the adjustment at the cable but it did nothing. I don't think anyone has ever made an adjustment to the shift linkage. I decided not to do it today as the wrench I had was to short.

I don't think my carbs are opening WOT either. Should the butterflies be 180 degrees at full throttle?

 

[SkiDad]

Should the butterflies be 180 degrees at full throttle?

yes. There is a Link and Sync FAQ at the top of the page on how to fix that

 

[fishnski14]

yes. There is a Link and Sync FAQ at the top of the page on how to fix that

Thanks Mitz..I read it and I know I will have to eventually do it.. Is there a FAQ or something related that details shift linkage adjustment..??

 

[Jiggz]

No Title

Here's what typical shift adjustment nuts looks like. As Mitz mentioned, you do a 1/4 or a 1/2 turn at a time to do the adjustment after you made sure you marked it first where you are starting from. For forward biasing, you need to the rod to push down a little bit more, hence loosening the top nut first and then tightenening on the bottom nut next. Test and re-do as required.

 

[fishnski14]

Here's what typical shift adjustment nuts looks like. As Mitz mentioned, you do a 1/4 or a 1/2 turn at a time to do the adjustment after you made sure you marked it first where you are starting from. For forward biasing, you need to the rod to push down a little bit more, hence loosening the top nut first and then tightenening on the bottom nut next. Test and re-do as required.

Awesome...You guys know exactly what to do to help out. I should be able to make some adjustments later this week and I will let you know how that went.
I noticed some rough (little rust) spots on the nuts for the shift linkage. Do you think using some penetrating oil on those nuts will be ok?

I will also be ordering some new cables. The cables that came with the engine are a little too long for my boat. Maybe that will work out some of the problems as well.

Are there any performance enhancements that could be made to this particular model motor?

 

[pnwboat]

Those adjusting nuts are kind of hard to get at, but with a little patience it's not that bad. Penetrating oil should be fine if you think you need some.

As far as performance enhancements.... there's not a lot you can do to the motor itself that will give you a major performance enhancement. It's a two stoke so to make any changes to the air/fuel induction system requires grinding the By-Pass ports and or replacing the Reed valves with aftermarket ones. The performance enhancement from the aftermarket reeds is not a lot.

The one area that you can make a noticeable improvement is changing the lower unit gear ratio. The 125HP motors usually come with a 1.73:1 ratio lower unit. Switching to a 2:1 ratio lower unit will help generate more "Pull" at lower RPM's so you'll accelerate faster and may add a few MPH to your top end. You will have to switch props though. For example, if you are using a 17 pitch prop, you may have to go to a 19 pitch because the motor will now rev higher at a given speed. All of the later model Force 4 cylinder motors have lower units with gear ratios right around the 2:1 range.

 

[fishnski14]

Those adjusting nuts are kind of hard to get at, but with a little patience it's not that bad. Penetrating oil should be fine if you think you need some.

As far as performance enhancements.... there's not a lot you can do to the motor itself that will give you a major performance enhancement. It's a two stoke so to make any changes to the air/fuel induction system requires grinding the By-Pass ports and or replacing the Reed valves with aftermarket ones. The performance enhancement from the aftermarket reeds is not a lot.

The one area that you can make a noticeable improvement is changing the lower unit gear ratio. The 125HP motors usually come with a 1.73:1 ratio lower unit. Switching to a 2:1 ratio lower unit will help generate more "Pull" at lower RPM's so you'll accelerate faster and may add a few MPH to your top end. You will have to switch props though. For example, if you are using a 17 pitch prop, you may have to go to a 19 pitch because the motor will now rev higher at a given speed. All of the later model Force 4 cylinder motors have lower units with gear ratios right around the 2:1 range.

Roger that...I sprayed the bolt and nut down, going to let it sit and hopefully they are not to bad to adjust...I was reading a thread a few from earlier this year and one of the members said in all his time working with the Force he only had to adjust the linkage once.

I had a feeling there wasn't much that could be done. I will be putting some reeds on soon, what are some decent ones (best bang for the buck).

I was searching ebay looking for lower units, I think it would be a good idea to have one sitting in the corner on standby. Which year make and models come with the 2:1 ratio..??

 

[pnwboat]

I had a feeling there wasn't much that could be done. I will be putting some reeds on soon, what are some decent ones (best bang for the buck).

Cost wise, not sure any of them will qualify as "best bang for the buck", but Magemarine on Ebay is probably the cheapest by a little bit. Chris Carson is also a reasonable alternative and very good customer service. Both sell complete sets for $70 - $80. Boyesen is also another one but more expensive. As far as performance, they're all about the same. All of the aftermarket reeds are made from a composite or carbon fiber material. I don't know how long they will last, but I've seen some original reeds from the 1988 125HP motors that were original and looked almost brand new.

I was searching ebay looking for lower units, I think it would be a good idea to have one sitting in the corner on standby. Which year make and models come with the 2:1 ratio..??

You can also check any of the local auction sites for good deals on Force lower units too.

1988 - 1989 85HP motors are 2:1 ratio. Note: The earlier 85HP were also 2:1 ratio but you have to check to be sure.
1990 - 1994 90HP - 120HP are 1.93:1 ratio. Note: Some of these units have a two piece drive shaft with a coupler. You need these for it to work on your rig.
150HP were all 1.93:1 ratio
1995 - 1999 120HP are 2.07:1 ratio, but I'm not sure that they will fit your motor as that are the Mercury style lower and use a different adapter plate on the bottom of the motor.

Note: When purchasing a lower, always check the gear ratio. You can do this by putting it into gear and turning the drive shaft. Put a mark the propeller or propeller shaft and the drive shaft. Turn the drive shaft until you see the propeller or propeller shaft start to turn. This takes up the slack in the clutch dogs. Put another mark on a lower unit case that lines up with the one on the drive shaft and another mark that lines up with the one on the propeller or propeller shaft. Turn the drive shaft. If it takes two turns of the drive shaft to make the propeller or prop shaft turn one time, you have a 2:1 ratio. If it takes 1 3/4 turns of the drive shaft to make the propeller or prop shaft turn one time, then you have a 1.73:1 ratio lower. You get the idea.

 

[fishnski14]

Cost wise, not sure any of them will qualify as "best bang for the buck", but Magemarine on Ebay is probably the cheapest by a little bit. Chris Carson is also a reasonable alternative and very good customer service. Both sell complete sets for $70 - $80. Boyesen is also another one but more expensive. As far as performance, they're all about the same. All of the aftermarket reeds are made from a composite or carbon fiber material. I don't know how long they will last, but I've seen some original reeds from the 1988 125HP motors that were original and looked almost brand new.



You can also check any of the local auction sites for good deals on Force lower units too.

1988 - 1989 85HP motors are 2:1 ratio. Note: The earlier 85HP were also 2:1 ratio but you have to check to be sure.
1990 - 1994 90HP - 120HP are 1.93:1 ratio. Note: Some of these units have a two piece drive shaft with a coupler. You need these for it to work on your rig.
150HP were all 1.93:1 ratio
1995 - 1999 120HP are 2.07:1 ratio, but I'm not sure that they will fit your motor as that are the Mercury style lower and use a different adapter plate on the bottom of the motor.

Note: When purchasing a lower, always check the gear ratio. You can do this by putting it into gear and turning the drive shaft. Put a mark the propeller or propeller shaft and the drive shaft. Turn the drive shaft until you see the propeller or propeller shaft start to turn. This takes up the slack in the clutch dogs. Put another mark on a lower unit case that lines up with the one on the drive shaft and another mark that lines up with the one on the propeller or propeller shaft. Turn the drive shaft. If it takes two turns of the drive shaft to make the propeller or prop shaft turn one time, you have a 2:1 ratio. If it takes 1 3/4 turns of the drive shaft to make the propeller or prop shaft turn one time, then you have a 1.73:1 ratio lower. You get the idea.

Thanks for that info. I'm going to be looking keeping an eye open for those year make models. I just want to have one on standby in the mine breaks. I looked on ebay, those guys have some proud prices. I think I read where Jiggz said you could find them used for around $200. I haven't seen one as of yet.

I adjusted the linkage and I think it worked. I have to put it in the water when it warms up some. I want to do some small mouth bass fishing this year.

What are the best plugs? And are the plug wires able to be changed?

 

[fishnski14]

Anyone have a link to a tach for an 1985 Force 125

 

[pnwboat]

What are the best plugs? And are the plug wires able to be changed?

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Either Champion UL18V or NGK BUHX, but it's kind of a personal preference thing. These are both surface gap plugs without an adjustable electrode.

You cannot change the plug wires on the coils on the Prestolite ignition system. Only thing you can change are spark plug boots and the metal clip on the end of the wire. If you change the metal clips, make sure the replacements are made from stainless steel, otherwise they'll rust in no time and cause more problems.

Anyone have a link to a tach for an 1985 Force 125

You can Google "Force 20 pole outboard tach" and see what you get. They're getting harder to find these days. Just make sure they have a "20 pole" setting.