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Direct Link To This Post Topic: Prop wrong, or engine problem?
    Posted: 05/22/2011 at 9:02pm
I'm new to boating. I bought a used 1999 Crestliner 20 foot pontoon with a 1993 Johnson 90 horse 2 stroke. The auto oiler is missing, so I mix the oil and gas.
I just had the boat in the water for the first time, and find I can't go over 3000 rpms without cavitating. We played with the tilt/trim and found the boat does the best with the trim about 80% down. The boat will cruise at 15 mph at 3000, but bump it to 3200 rpm and it starts sucking air. We had three people on board and about 12 gallons of gas, and not much else.
Am I doing something wrong? It would seem I should be able to run at 4000 or 4500 rpm if I need to. Where do I start looking? Any advice would be appreciated.
 
Thanks for helping a newbie.
 


Edited by ressless1 - 08/14/2011 at 12:10pm
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Direct Link To This Post Posted: 05/22/2011 at 9:25pm
Should be running max WOT is 4500-5500. When you say sucking air - please define what you mean. What sucks air? What shape is the prop in? (please post pic of prop) also post pics of the placement of your motor. What size prop is on the motor? Reason I ask is that you have a 99 boat, but yet has a 93 motor on it, so we need to know what the motor use to be (like on a bass boat?) so it could be its the wrong pitch. Should be a 14x11 or 14x13.
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Direct Link To This Post Posted: 05/22/2011 at 10:26pm
Is it cavitating?  Or blowing out?  Blow out is sucking air where it suddenly overspeeds the engine and loses speed.  Just had a similar thing.  Last year i could run 5300 (max of 5500) WOT no probs.  Added a CMC PT 35 Tilt/trim unit this spring and could not go above 5000 without getting Blow Out usually around 5200 rpm.   Found that we needed to re-rig the engine by tucking it under to get more prop under the boat so to speak.  Now we get 5300 - 5400 WOT and an extra 2 MPH.  I can still trim up and cause Blow Out but no need to except for not using my head.  My 2 cents.

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Direct Link To This Post Posted: 05/22/2011 at 10:51pm
Mike,
What I get sounds a lot like what you describe as blowing out, but a lot lower rpm.
 
Charles,
The prop looks kind of beat up, I don't know the pitch. I'm thinking about a new one and keep the old one as a spare. I'll get the pictures in the next couple days.
 
Many thanks.
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Direct Link To This Post Posted: 05/22/2011 at 11:34pm
Also pic's of your motor and transom may help.  The relationship of the ventilation plate to the bottom of the transom would be nice.  Dumb question - are you at full throttle or near it at 3000 rpm?

Mike
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Direct Link To This Post Posted: 05/22/2011 at 11:43pm
If the prop is beat up, that'll tear your lower unit and motor up over time - not good. Yes, definitely pics of your motor (out of the water is fine) but we need shots of the cavition plate area with it also showing the motor pod and tubes (toons). Look at the markings on the prop and let us know what they are.
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Direct Link To This Post Posted: 05/23/2011 at 7:03am
On my 20 if not loaded right will have the same problem. I even have the same thing happen in ruff water, only use it as a work boat so we did not look into it yet
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Direct Link To This Post Posted: 05/23/2011 at 9:12am
I know a gu that had a Chrysler motor.  He said he could remember how many time he repaired/replaced the oiler and finally threw it away and started mixing his oil.  He ran it for years like that.  From what I went thru, remounting my motor recently, I'd guess that yours may not be mounted correctly, but yours may be too high.  Mine was too low.  I also wonder if yours is running right.
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Direct Link To This Post Posted: 05/23/2011 at 7:20pm
Mike, 3000 RPMs is about half throttle, it has some left, but asa soon as the motor revs up, the low oil warning light comes on.
 
Here is a picture of the prop. I can't find any markings except for a number 3832528.
 
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Direct Link To This Post Posted: 05/23/2011 at 9:00pm
I can almost guarantee that a new prop (or having that one reworked) will solve alot of the problem.
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Direct Link To This Post Posted: 05/24/2011 at 9:21am
If I clean up the burrs and rough spots with a file and sandpaper, will that help me through the weekend?
Can anyone share where to look for reasonable prices on a new propeller?
 
Should I go with a 14 x 11, or a 14 x 13?
 
Is stainless steel worth the extra money?
 
Thanks again,
jerry
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Direct Link To This Post Posted: 05/24/2011 at 9:36am
I just did a quick look in the BPS Marine catalog and aluminum props for an OMC90 were about $100 but didn't see any 14's. I think you should be able to get an aluminum one in the $100 range but expect to pay 3 times more for SS. There are alot of places online. I bought a SS online for my 50HP very reasonable but don't remember the place. Personally I think the aluminum is fine if your operating in an area without rocks , lots of stumps or freshwater. I think the SS is worth the money otherwise and have put them on some of my boats. Just remember you can replace the aluminum one again or twice for what 1 SS cost but the SS probably won't ever need replacing.
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Direct Link To This Post Posted: 05/24/2011 at 9:40am
I've had good luck at iboats for new props. Look at the turning point props, they're nice! 13-3/4 x 15 should be about right. Should be able to hit it for under $100.
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Direct Link To This Post Posted: 05/24/2011 at 10:33am
Got mine from the same place we have for the prop calculator
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Direct Link To This Post Posted: 05/24/2011 at 12:59pm

I have a similar engine on my boat. I run between 5000 to 5200 rpm @ WOT. Yes, it looks like you could eliminate a lot of worries by first replacing that prop. I got a new one from the Prop Calculator guy/Prop Wizard too. It shipped quickly and fit great.

Note: the install instructions that come with the prop make it a point to say; “do not bend the carter pin back across the bolt, bend out slightly” …I see in your pics that your pin is bent all the way back…..Don’t know if that makes a hill of beans or not?

Anyway good luck, happy Toon’in    

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Direct Link To This Post Posted: 05/24/2011 at 2:08pm
This is the place I ordered my last prop from. They were great people and about $15 ceaper for the same prop from the above suggested place.
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Direct Link To This Post Posted: 05/24/2011 at 2:18pm

For your motor the cheapest place appears to be the place that Vermillionfox suggested above. Not sure what shipping is though.

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Direct Link To This Post Posted: 05/24/2011 at 2:29pm
A quick google search showed an iboats coupon code for 5% off (FACEBOOK5). Shipping to me for a prop (I'm in St. Louis) showed to be $9.85, not bad.
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Direct Link To This Post Posted: 05/24/2011 at 10:25pm
OK, I have a new prop ordered, along with a Johnson service manual. Smile
Iboats seemed to have the best sale price. I went with the 13.75 x 15 pitch.
 
Thanks everyone for getting me pointed in the right direction.
 
If it still has a problem, I'll get pictures on the lake.
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Direct Link To This Post Posted: 05/24/2011 at 10:34pm
Originally posted by Carolina Blue Carolina Blue wrote:

Note: the install instructions that come with the prop make it a point to say; “do not bend the carter pin back across the bolt, bend out slightly” …I see in your pics that your pin is bent all the way back…..Don’t know if that makes a hill of beans or not?

Anyway good luck, happy Toon’in    

 
I pulled the prop this evening and found the pin and the nut were loose. Needless to say I ordered a new nut and keeper along with the prop.Big smile
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Direct Link To This Post Posted: 05/24/2011 at 10:55pm
Good idea on the nut and keeper. And I think you'll have pretty good results with the new prop. That's the same pitch I run on my 20'er with a 90 HP Merc. and it's just about right.
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Direct Link To This Post Posted: 06/13/2011 at 10:34am
Finally got the boat out with the new prop and the boat seems to have a better feel to it.
Putting both old and new prop side by side, the new prop appears to be less pitch. Speed does not appear to change much, but I think it pulled the tube better.
Motor at WOT still only turns about 4300 rpm.
I'm wondering if it is opening all the way. I'll try to look at that this weekend.
 
Thanks to everyone for your help.
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Direct Link To This Post Posted: 07/11/2011 at 1:00pm

I need to revisit and update this post. Some of my original problem appears to be lack of familiarity with the boat and not trimming the motor down enough.

We have been out a few times with the new prop, 13 7/8 and 15 pitch, usually with 4 people on board.

Now WOT I get about 4000 rpms. The boat seems to pull ok.

We

 

Speed reads about 20-21 mph, although I'm not sure of the accuracy of the speedometer or the tach.

What next?

Should I try a lesser pitch prop to get the engine RPMs up.

Does higher rpms mean using more fuel?

 

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Direct Link To This Post Posted: 07/11/2011 at 1:56pm
First use a GPS, its the ONLY accurate indicator of speed as speedo's are highly inaccurate. You should try using a 14x11 prop for your motor which is the norm (or 14x13) and yes on higher RPM's means more fuel, but if the prop isn't right, you're not efficient at the fuel you're burning now
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Direct Link To This Post Posted: 08/08/2011 at 11:12pm
The motor is a 1993 Johnson 90 HP purchased with a boat last winter. We have been on the lake about 10 days this summer and the motor has performed well. There is no auto oiler, so we mix the oil.
 
This weekend the motor developed a flutter, or miss, and low speed and mid range. It seems to run OK at higher RPMs.
 
I bought a manual, but I do not see this problem addressed.
 
I'll start with new spark plugs tomorrow, but I want to ask if anyone has experienced this problem, or if this engine has any common issues I am not aware of.
 
thanks
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Direct Link To This Post Posted: 08/08/2011 at 11:20pm
Ok, I have has a couple days to play with props and tried a 14x11. WOT now gets the motor to 4900 rpms, and the motor seems happier at WOT.
Top speed is the same, at 21 mph by the GPS.
 
Cruising at my target of 3000, I loose a couple MPH.
 
Tubing is better, but cruising is worse. I am thinking of trying a 14X13 to see if that would be a good compromise.
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Direct Link To This Post Posted: 08/08/2011 at 11:45pm
You're on the right track with replacing the plugs first. Since it has been performing well, then it's a good bet that could be the problem. Always best to rule out the simple (inexpensive) things first..
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Direct Link To This Post Posted: 08/08/2011 at 11:49pm
I think a 14 X 11 would be underpropped on a 20'er with a 90 HP. I run a 15" pitch on mine. And I'm surprised your wide open RPM's are so low with the 11" pitch. Should easily hit 5800 with it. Wonder if there's something else going on with the engine causing that. 
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Direct Link To This Post Posted: 08/08/2011 at 11:52pm
Also, have you checked the setting on the back of the Tach? Should be set in the "6" pulse position.
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Direct Link To This Post Posted: 08/13/2011 at 12:17pm

I have touched on this subject in a couple other threads, which I will compile into this thread.

 Background, last week, I had an engine miss, bad at 2500 – 3200 rpms, where I like to cruise, but not at WOT. I replaced the plugs, and fixed a slight fuek leak at one internal hose fitting. I went for a testing day at the lake yesterday. The boat is a 20 foot Crestliner, with a 1993 Johnson 90 hp. The load is two people, 20 gallons gas and a cooler of ice and drinks. Speed is determined via GPS. I checked the tachometer for different settings, but see nothing to adjust. I can cruise at 3000 rpm for about 3 ½ hours on 12 gallons.

First hour out is with prop 14 X 11 pitch. The motor is a lot better than last week, but I still detect an occasional flutter at mid throttle. At 2800 rpm it is a turtle, 8-9 mph. I can cruise at 3200 rpm and get 12 mph. WOT the motor sounds good, rpm is 4800 and speed is 20-21 mph.

At the landing, for the second hour, I change props to 13 5/8 X 15 pitch. The change in feel is immediate. Now I am cruising at 2800 RPMs, and 14-15 mph. but WOT only gets to 3900 rpm and 21 mph. Also, the engine feels good; the occasional miss is not there.

What next? Do I have an engine problem, wrong prop, or just being too anal?

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