Tach and prop issues

[further]

So i posted in the Force Forum and got some good feedback but figured I'd try to get more here. Got a 1988 Maxum 1700MA powered by a 1988 Force 85 HP. Had it out twice so far and runs great. First time out the stock tach didn't work. I bought a piranha prop 13.7x15 pitch per their recommendation. Got to about 27 mph. Bought a tiny tach and installed it. Had it out for the second time this past weekend. Miracuolously the stock tach started working. Hit a top speed of 27mph at WOT read by gps. Wierd thing is the stock tach read 4400 rpm at WOT and teh tiny tach read close to 7000 rpm at WOT. Something wrong with the tiny tach because it read 1750 at idle. I called and confirmed I got the correct one for my motor; however they said the red wire should be wound around the bottom cylinder spark plug wire not the middle one like i did so i will try this. However, my question is this, if the stock tach is correct, what can I do to get my rpm's up to 5000? if I'm already at a 15 pitch? Wierd because i think the original prop was a 19 pitch. Any input is much appreciated.
Thanks

 

[hwsiii]

Re: Tach and prop issues

Further, in my opinion you should be going faster than what you are right now. If you will fill this form out I will try to help you.

Iboats Boat and Motor Info
1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make and model of motor
7. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing and turn the motor until the tape lines up with each other, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. If you do not have a tach you can buy a Tiny Tach for $ 50
14. Are you at sea level or a higher elevation, give us the elevation in feet
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the forgoing could be the reason your prop is not attaining full RPM
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.

H

 

[further]

Re: Tach and prop issues

Ok, here's answers to as much as I can without being near the boat since its 2 hours away at my lake house. I've attached the spec sheet I obtained from teh manufacturer.

1. 1988 Maxum 1700MA
2. 16'8" overall length, beam = 7' 2", 1295lbs with 85 hp Force motor
3. 85 HP
4. Cruising, will be pulling tube and skiers, but not yet done so - only had it out twice - just bought it recently.
5. It's a runabout - open bow.
6. 1988 Force 85 HP
7. 85 HP and gear ratio is assumed at 2:1.
8. 4500 to 5500
9. Not sure on this one.
10. Not sure on this. It is a runabout not a bass boat - open bow.
11. yes, hydrafoil
12. Currently have a Piranha 13.75 x 15 pitch composite prop.
13. Stock tach measured 4400 rpm and tiny tach measured something like 7000 rpm at wot but I think I had the tiny tach set up wrong. Reached 27 mph by GPS only with myself and 6 year old daughter.
14. About 1000' above sea level in the poconos, PA.
15. I just tuned the motor - compression, all cylinders in teh 140's, new plugs, new impeller and housing, rebuilt fuel pump - drained old fuel and refilled 12 gallons of mid grade with appropriate oil and 1 bottle of seafoam.
16. This is a new prop - just got a 17 pitch to try as the piranhas are interchangeble so I can switch out as needed.
17. no damage.
18. trying to obtain correct rpms - arond 5200 would be nice.
19. Better top speed would be nice to.
Thanks for your help[.

 

[hwsiii]

Re: Tach and prop issues

Further, I ran the numbers on what prop you should be running and prop slip as well as prop change. Your prop slip is at 14% but with a composite propeller I don't find that exceptionally high and if you have to change prop pitch to raise your RPM to 5,500 RPM you would have to change to a 12" pitch and that is ridiculous. You are not reaching the speed that your boat and motor are capable of attaining which should be at least 5 MPH faster and it is not your propeller that is causing that in my opinion as your prop slip is not that bad.
There is a problem with your motor probably although I know you just checked everything out on it but please recheck the items in 15 above. The first thing to do is to raise the motor up 1 notch on the back of the boat and get rid of the hydrafoil for right now. Then take the boat out and run it and get me the new numbers and lets see where we are at then, and we will go from there.
i know this is not what you wanted to hear, but it is my opinion that you should have more speed left in that combination.

I have a 16' flats boat with a 40 Force on it and when it is loaded I carry as much weight as you do and I am getting 25 MPH with 3 adults, 1 teenager and 3 children. I have the same 2:1 gear ratio you have and I am running an Apollo SS 14" pitch prop on it, so that you have an idea of why I say what i am saying.


H

 

[Frank Acampora]

Re: Tach and prop issues

I suspect a good part of the problem is the combination of Hydro-Foil and composite prop. The Hydro-Foil alone will cost you about 3-5 MPH if it is not set correctly. Note that this is not an absolute given; some hulls do perform better with them. But by and large, they do have a well deserved bad reputation, so it could not hurt to try running without yours. I suspect that the composite prop will cost you another 2 MPH or so.

These engines seem to do best on the stock props or Michigan branded wheels. I have tried Vortex, made by Michigan and the same pitch prop will lose me 500 RPM even though top speed remains the same. They do like stainless props but many people balk at the cost.

However, You still need to check the carbs to be certain that the float level is correct. With the carb inverted, the float should be level with the carb casting. Then check your low speed needle setting. MOST of these three cylinder engines like to run at about one turn out from lightly seated. Since with any internal combustion piston engine, air is the limited factor, too lean will cost more power than too rich. Couple that with the fact that a too lean mixture is just begging for melted pistons.

Lastly, double check to see that the carb butterflies are opening fully at wide open throttle. I have seen a number of cases where they were set up incorrectly and full throttle was only putting the carbs in cruise position.

I suspect that with your hull and engine combo, a nice Michigan aluminum three blade 17 pitch will be close to correct and losing the "Whale-Tail" will boost both top RPM and speed. Save the composite props as emergency spares.

 

[bman1bpm]

Re: Tach and prop issues

Hey don't mean to hijack the thread but it seems to have relevent info to me.

If my throttle control is wide open and my butterflies don't open all the way, is adjusting the linkage from the towershaft to the carb linkage the proper way to do it?

 

[NMBuzz]

Re: Tach and prop issues

Further, in my opinion you should be going faster than what you are right now. If you will fill this form out I will try to help you.

Iboats Boat and Motor Info
1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make and model of motor
7. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing and turn the motor until the tape lines up with each other, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. If you do not have a tach you can buy a Tiny Tach for $ 50
14. Are you at sea level or a higher elevation, give us the elevation in feet
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the forgoing could be the reason your prop is not attaining full RPM
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.

H

May I ask the same favor?
NMBuzz

 

[NMBuzz]

Re: Tach and prop issues

I would appreciate you running this information to see if there is a problem or not. I will be glad to share any additional test data with you as well.
Thank you for doing this service for free!
NMBuzz



1. 1993 Larson 170 All American 17' OB Alpha 1 Gen 2 Sterndrive
SN OF 175784

2. Length 17.0', width7' 4", and base weight of boat 1760 lbs.

2a.What is the recommended HP for your boat- 155 HP

3. Number of people and gallons of gas normally on boat- 3-4, 20 gallons (full)

4. What do you use the boat for- sport, skiing, cruising the lake

5. Is it a Deep Vee and if so how many degrees of deadrise- Delta conic 18?, 12? transom angle Transom SN OF189152

6. Year, make and model of motor- 1993 Mercruiser 4.3L 2 bbl Alpha One
SN- OF116524

7. HP and gear ratio of motor IMPORTANT - 155hp, gear ratio 1.98R (not sure this is what is stamped on the top end of the out drive)

8. Manufacturer?s recommended Wide Open Throttle (WOT) range- 4400-4800

9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches- N/A

10. Is it a bass boat or does it have a pad bottom- no

11. Does it have a hydrafoil, dolefin or trim tabs-no

12. Make, model, diameter, pitch and whether SS or aluminum prop- attwood, Ballistic, 14 1/2 x 19?

13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. - 5,000 @42 mph, 20 gallons, 2 adults, 3 kids (~520 lbs total passenger weight) speed is from speedo not GPS (don't have one yet)

14. Are you at sea level or a higher elevation, give us the elevation in feet- ~4200'

15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the forgoing could be the reason your prop is not attaining full RPM- yes, yes, yes, all good.

16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop- ? just bought it this year, not sure about if it is the wrong prop or not

17. Does the prop show any damage that you can see- minor dings but no chunks or pieces missing

18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations- decrease the rpm's @ WOT to specified range (or even a little lower- I am not a hot rodder and I am trying to keep my good hole shot for skier pulls, but able to run WOT at times as for fun with slightly lower rpm's. Make sense I hope

19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.


Thanks again!

 

[hwsiii]

Re: Tach and prop issues

Buzz, the prop you need for your boat is the Solas Rubex 4 blade prop, it will bring your RPM down to about the middle of your recommended RPM range. It will increase your hole shot and acceleration through the whole range of your RPM. As a normal course of events people like the ride better, as with the 4 blades the ride is smoother because of the even number of blades and balance from it.


Price: $118.98
You Save: $38.97
Compare: $157.95
Discount: 24.7% Off
Add RUBEX 4 Aluminum Propeller Prop: 9513-143-19 Hub: RBX-102 To Your Cart

Propeller Specifications:
SKUrop #9513-143-19Hub #RBX-102
Manufacturer: Solas
Brand: RUBEX 4
Material: Aluminum
Diameter: 14 - 3/10?
Pitch: 19?
Blades: 4
Rotation: Standard (Clockwise)
Usually Ships Within: 1 Business Day



H

 

[sho3boater]

Re: Tach and prop issues

To compare I have a bayliner OB 16' with a force 85, it has a 19p SS MI wheel prop. I sharpened the prop and some other things managed a repeatable 43.1mph on gps with synthetic gear oil. I had a clamp on tach showing close to 6K rpm. I had the prop cupped and thinned by a shop, then bought a new tach, it now shows 5400 and sometimes 43 gps, sometimes low as 41 and change. But I still have to put the digital tach on and verify or adjust the new tach to be sure it is right. My speedo shows around 48 mph IIRC. It is running less rpm now. I figure 5500 to 5800 is best performance max rpm, just a guess. I run a smaller lake anyway so it is not pinned that long.

At one point I put a 20p laser prop on it and it would only pull 3800 rpm at some low speed. But it seems the motor is too deep to run that prop right, if it would even pull what is really a 21p equivalent prop. I have the motor about 3/4" spaced above the transom but still low for a laser type prop. It would pull a skier easily with the 19p it still takes off pretty good. I have a hydrofoil for it but if I trim it up some, it is on plane in a few boat lengths and will plane at a slow enough speed for me. This hull does have a pad, that might help in this area. Not towing, it planes slower with no trim.

I had a composite prop on another boat and was not real happy with it, though it worked ok and was cheap. It was a good spare prop.

 

[NMBuzz]

Re: Tach and prop issues

Buzz, the prop you need for your boat is the Solas Rubex 4 blade prop, it will bring your RPM down to about the middle of your recommended RPM range. It will increase your hole shot and acceleration through the whole range of your RPM. As a normal course of events people like the ride better, as with the 4 blades the ride is smoother because of the even number of blades and balance from it.


Price: $118.98
You Save: $38.97
Compare: $157.95
Discount: 24.7% Off
Add RUBEX 4 Aluminum Propeller Prop: 9513-143-19 Hub: RBX-102 To Your Cart

Propeller Specifications:
SKUrop #9513-143-19Hub #RBX-102
Manufacturer: Solas
Brand: RUBEX 4
Material: Aluminum
Diameter: 14 - 3/10?
Pitch: 19?
Blades: 4
Rotation: Standard (Clockwise)
Usually Ships Within: 1 Business Day



H

Thanks for that info. is this a SS prop? Where can I fing such an animal. At iboats perhaps?

Thanks again for the info. I am willing to giver her a try!

NMBuzz

 

[hwsiii]

Re: Tach and prop issues

Buzz, it is from Iboats and those are their numbers and it is aluminum.


H

 

[further]

Re: Tach and prop issues

Thanks for all the info. Planning on taking off the hydrofoil and rearranging the wiring of the Tiny Tach this weekend to try again and will post the results. I guess from what I'm hearing I should go and invest in a michigan aluminum prop and keep my composite as a spare.
Thanks again.

 

[hwsiii]

Re: Tach and prop issues

I will be waiting Further.


H

 

[further]

Re: Tach and prop issues

So took the "whale tail" off and put the composite prop to a 13 x 17p. Fixed the tiny tach so I'm getting good rpm readings. WOT is at 4550 RPM at 30mph. with 3/4 tank gas and just myself. Should I go down to a 15 p or maybe a 13p to get the rpms up. Boat is runnig great otherwise.
Thanks

 

[hwsiii]

Re: Tach and prop issues

Further, I could recommend a prop for your boat but I feel I would be doing you a disservice if I do that. You are showing the same RPM with either the 15" pitch or the 17" pitch prop and there ought to be about 600 RPM difference between the two. That tells me that your motor has a problem sine you took the hydrafoil off. When you get that fixed you should be able to turn the 17" pitch over 5,000 RPM and the 15" pith should turn right at 5,500 RPM.
Check the advance timing and the linkage to the carburetor, push the throttle at your controls and make sure the butterfly in the carburetor to make sure it is perpendicular to the carburetor throat and is opening all the way. Something is wrong with the motor and changing props does not fix the problem it only masks it.


H

 

[further]

Re: Tach and prop issues

Thanks HWSiii. I think you're right. I went back to a 15P and no change in rpm or top end. I think carbs and timing adjustment may be too much for me so I'll be taking her to the local marina tomorrow.

 

[hwsiii]

Re: Tach and prop issues

Please let me know the outcome when you get it back.


H

 

[bman1bpm]

Re: Tach and prop issues

I read the part frank wrote about taking off the whale tail off in hopes of gaining speed, I actually lost 5 mph with my boat! back on it goes.

 

[further]

Re: Tach and prop issues

And so the saga continues - rebuilt the carbs , actually think i did a pretty good job except had all kinds of problems and ended up taking it to my mechanic and after replacing my original carbs with some used ones, finally got her running again (mechanic actually complimented me on the carb rebuild but couldn't figure out why they wouldn't work). So my mechanic checked compression - around 125 on all three, good spark on all three and after the carb replacement he got up to 4600 rpm and 32 mph. This was on a 13 x 17p composite so i ordered a 13.25 x 15p michigan aluminum in hopes it will boost the rpms closer to 5000 and give me some more top end. The bottom paint on my boat is in pretty rough shape as well - can this affect rpms?? I assume it would certainly affect top end. Thanks