17 Ft Mako 140hp Johnson 4500RPM?!

[Chrisravosa36]

Hello, My maiden voyage on my 17ft restored mako didnt go as planned. It was well, the boat and engine did fine but I was planning on seeing some better #'s. I got 27mph @4500 rpm that was W.O.T. The motor is definitely lugging. Im guessing its supposed to be hitting at least 5250 - 5750. Its a 1972 Mako, with a 1988 140 Evinrude/Johnson. It was off a duel application, two 140s on a 24ft Mako. Im guessing the prop, it didn't propose until trimmed to high, so I believe the motor is at the proper level with the bottom of the boat? Any advice. I know with this motor and boat combo I should be hitting atleast 35MPH all day long. I did a compression test on the motor and it reads 120 on All 4 cylinders.

Thanks, Chris

 

[Sea Rider]

By proper level you mean the AV plate right ? If so, in reality doesn't say much as there's no instalation that's even with lower keel. Instalations are 10 to 25 mm, will depend entirely on OB manufacturer.

Boat should be trimmed to ride parallel or near parallel to water level when on plane, deck weight must be evenly distributed for boat to achieve that position. Check if prop ventilates, have back water splashes over transom, prop ventilates badly al tight close turns at speed on calm, no wind water cond.

Assuming it's an old prop, check that doesn't have already a spun hub or on it's way to become completely KO. If found OK check max achieved rpm as currently loaded, if too low, can maximize a less pitch prop to pull wot revs higher.

Happy Boating

 

[Chrisravosa36]

Assuming it's an old prop, check that doesn't have already a spun hub or on it's way to become completely KO. If found OK check max achieved rpm as currently loaded, if too low, can maximize a less pitch prop to pull wot revs higher.

Happy Boating[/QUOTE]


Il check for a spun hub TOMM. How do I test for that? Also the prop is a 14in dia. 17 pitch. If its 200 -/+ a pitch, and im hitting WOT light load 4500 RPM should I be looking at a 12 pitch prop? I go on the iboats website and see that they only have a 11 Pitch or 13 Pitch prop. I lreclall these OMC can go to about 6,000rpm but its best to stay below 5750 or at 5500. Any tips, Im going to take her out for another spin this week and report back. Other than this it ran good. I just want the most preformence from this motor, Its a great motor, healthy as the day is new! Id love to see about 35+MPH from it. How much Speed do you think I could gain from this prop size change, I would also be getting a Stainless. I think I might also go with a 4 blade, just because It will be an ocean boat, which would give better preformence aswell.


Thanks, Chris

 

[walleyehed]

This is a Cross flow design and it will do the best if set up for 5750-5800 with a normal load. My 1st question would be tach accuracy..
If tach is new and assumed good, I would be trying a 15P. 200+/- is ball-park but as the rpm comes up from 4500, so does the torque, so it can fool ya a bit.
Keep in mind also that with more speed comes less wetted surface and requires less HP to push it so more than likely you will gain a lot more than 200 per inch.
As for rpm, that model of X=flow will handle 6500-6800 with no issues. It's just a 90 deg. air pump. )
I'd try a 15P and have a known tach. That vintage Mako has a really cool (good) hull design and responds well to engine height changes.

 

[Chrisravosa36]

This is a Cross flow design and it will do the best if set up for 5750-5800 with a normal load. My 1st question would be tach accuracy..
If tach is new and assumed good, I would be trying a 15P. 200+/- is ball-park but as the rpm comes up from 4500, so does the torque, so it can fool ya a bit.
Keep in mind also that with more speed comes less wetted surface and requires less HP to push it so more than likely you will gain a lot more than 200 per inch.
As for rpm, that model of X=flow will handle 6500-6800 with no issues. It's just a 90 deg. air pump. )
I'd try a 15P and have a known tach. That vintage Mako has a really cool (good) hull design and responds well to engine height changes.

its a 140 Looper (Loop Charged motor) Flat Cylinder Heads, instead of groved. The tach was used, but I belive it is right, because Ive owned a few Johnson/ Evinrudes and I know what they sound like at WOT. This didnt sound like it. I also remeber on the back of the tachomterter there was some sort of adjustment screw, it had a few numbers on it, maybe 1, 2, 3, 4, 5, and 6? Its a OEM used OMC Tach. How would I test the tach just to be safe.

 

[Sea Rider]

What's the tach reading at idle ?

Happy Boating

 

[walleyehed]

Ok, this is the big-block 90 deg looper...several changes after the 85-86 era.. with that said, this eng likes 6K with a normal load and I wouldn't want anything less than 5700. This eng was rated at 140HP at 5500 I believe but that was also on 1988 fuel.
Sea Rider has a good point on Idle, that may give an indication of potential accuracy.

 

[Chrisravosa36]

What's the tach reading at idle ?

Happy Boating

im not sure, I recall cold start this april, the tach was about 1500rpm out of water, in neutrul with a little bit more oil than usually for the first start. it does seem like a high idle but on the lake, dropped into gear it had to be around 800rpm. im going to try to take her out one or so more times this week and report back with more #'s may go out tomm morning.

 

[Chrisravosa36]

Ok, this is the big-block 90 deg looper...several changes after the 85-86 era.. with that said, this eng likes 6K with a normal load and I wouldn't want anything less than 5700. This eng was rated at 140HP at 5500 I believe but that was also on 1988 fuel.
Sea Rider has a good point on Idle, that may give an indication of potential accuracy.

whats the 1988 fuel/ leaded fuel? also getting the motor to 5700RPM - 6000RPM, what prop would this require? a 15 Pitch like previously stated?

THanks, Chris

 

[Fed]

Should be easily seeing 40mph with that setup.
Not a spun prop as this would cause it to rev higher.
Not a bent prop as it would have to be so badly bent it would be blatantly obvious.
Not trim as you have tried it trimmed up with no improvement.

Slight possibility the motor is too low so just make sure the AV plate is not below the bottom of the transom.
Make sure the carb butterflies are fully open when the controller is at WOT.

After that your next question should be, "Why is my 140HP only putting out 70HP?".

 

[Chrisravosa36]

Should be easily seeing 40mph with that setup.
Not a spun prop as this would cause it to rev higher.
Not a bent prop as it would have to be so badly bent it would be blatantly obvious.
Not trim as you have tried it trimmed up with no improvement.

Slight possibility the motor is too low so just make sure the AV plate is not below the bottom of the transom.
Make sure the carb butterflies are fully open when the controller is at WOT.

After that your next question should be, "Why is my 140HP only putting out 70HP?".

lol, Il take a look at the buterflies tomm aswell. The AV plate seems to be right about dead even with the transom to be, trimmed up to the on plane position of the motor. I do thnk it very well could be the prop though, because I see an unsually slow plannng speed, maybe 20 seoncds before I get on a true even plane.

 

[Fed]

I have a very similar 17' boat as pictured (I hope) below.

It started off with a 70HP omc motor c/w a 17" prop which spun at 5000RPM for 30MPH.
I did for a time run a 15" prop on it, picked up a couple of hundred rpm but no increase in speed.

Now it has a 90HP omc motor c/w a 17" which spins at 5500 for 40MPH.

I've run lots of mildly beat up props that perform equally as well as perfect props and my numbers should tell you it's not a pitch issue trust me.
With a 140HP on your boat you may even be able to go to a 19" but as you say it's an ocean boat so being a little under propped is nicer.

Find out what's wrong with the motor.

 

[SkiDad]

I agree, it's the engine.

 

[Chrisravosa36]

I agree, it's the engine.

I think your all right, I checked the butterflies this morning, and they all have seemed to open up fine, I gave that the check. I went on to check the compression, the right side of the motor read evenly 130lbs and 129lbs, the left side was a big lower at 120lbs and 125lbs. I consider that to be acseptble enough for this old of a motor. After my outing, I put new plugs in and I forgot to check them out. I forgot which side each plug went in. I found 2 of the 4 plugs where black, and 2 were a tanish color. I think this is where my problem may be. Am I looking at a carb issue? or a spark issue?

 

[Chrisravosa36]

I just started it with a fresh pair of plugs this morning in the bucket, in neutral im pulling 2500rpm, and then it will drop to 1500 - 1000rpm off and off. I know it isnt the tach, because I can tell it's around 2500rpm. I guessing dirty carbs at this point, so ive went ahead and order 4 rebuild kits. Im not even sure when the last time they were cleaned on this was.

 

[Sea Rider]

Check that carb and time advance are well synched to deliver full HP. Don't forget an overdose of Power Tuner/Carbon Guard through the carbs at fast idle. Improves/restores lost power, will idle nicely and makes OB to run smooth. A must use with 2 strokes OB's from time to time.

If with doubt, perform a prop hub slip test, will know if prop is doing its homework or kaput...

Happy Boating

 

[Chrisravosa36]

Check that carb and time advance are well synched to deliver full HP. Don't forget an overdose of Power Tuner/Carbon Guard through the carbs at fast idle. Improves/restores lost power, will idle nicely and makes OB to run smooth. A must use with 2 strokes OB's from time to time.

If with doubt, perform a prop hub slip test, will know if prop is doing its homework or kaput...

Happy Boating

I will try a can of the seafoam, this has always worked for me in the past. Im going to also rebuild the carbs and check the timing this week. Luckly, ive got april break, so no school plenty of time to do this.

 

[Chrisravosa36]

I have just taken a look at the spark, and It seems to be acceptable. I used a cheap tester I got on amazon years back, it go between the plug and plug cap. I observed a orange spark in all of the cylinders. I left with rebuilding the carbs and a boat load of seafoam. Also should this now be moved into the Johnson/ Evinrude topic? Also let me explain the current situation ive got with fuel. I have two 12 gallon tanks that have 2 ft of line that connects to a y spliter, another 10ft of line under and around the deck, to the fuel water separator, then 6 inches to the pressure value, then the primer bulb, up to the fuel pump at that point. Could this be a lack of fuel situation? is the engine starving?

 

[Sea Rider]

Is fuel pump in good working order ? Hook a portable tank direct on engine and check if performs better. If so, fuel lines are too loooong. LOL!!

Happy Boating

 

[Chrisravosa36]

Is fuel pump in good working order ? Hook a portable tank direct on engine and check if performs better. If so, fuel lines are too loooong. LOL!!

Happy Boating

I will test with a tank tommorrow! How would I check the fuel pump?