Re Visited Prop for 1988 150 hp 20 ft Sea Ox

[Steve135]

Hi I just took out my boat for the shake down run. I purchased this boat this year. The prop on the motor is a 15 1/2x15 thats what they put on it when the motor was rebuilt last year.It had a smaller prop on it. I can't remember what size it was. The WOT is only turning 4200 rpms way to low. What should my next try be. I think I have a 15x17 I will try this week. I'll let you guys know what happens. But in the mean time plase if someone is running the same combo on this type boat let me know what your running. <br />steve

 

[lowbud]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

stinky2<br /><br />I have a 1982 150 hp 20 ft Sea Ox. The Johnson 150 replaced a 140 hp. I bought it used several years ago. I will check my prop info next time I am at the boat, but I am pretty sure it is a 15x19. <br /><br />Now it gets interesting....I max out at about 3400 rpm. I get on plane and do about 25 mph at about 3100-3200 rpm, and if I go above 3400 rpm I start to cavitate. I too think these rpm's are low, but the boat works fine.

 

[Dhadley]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

A 19 would be about right depending on which model 20'er you have. However, something isnt right. At even 4200 you'd have to drop about 8 inches in pitch to get into the ballpark. If this is the true top rpm, youre lugging the motor and that will kill it. <br /><br />Naturally the first thing you want to do is make sure the motor (in both cases) is running correctly. The easiest way to seperate the boat and motor is have the dealer run it on the test wheel. If the r's come up to where they should be then you know the problem is in the set up and/or boat.<br /><br />If youre sure the motor(s) are running correctly then look at the tach(s). Make sure the tach is an OMC or BRP tach and is set on position 6.

 

[Steve135]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

Ok guys I made a big mistake on the current prop thats on the motor. I took it off today and its actually a 15 1/2 X 15 prop. I just replaced it with a 15x17 I haven't run it yet. It doesn't sound as if it running at rpms greater than 4200 either? But I too questioned the tach!<br />steve

 

[Dhadley]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

If youre truly only getting 4200 the last thing you want to do is put a bigger prop on. <br /><br />Is the tach set on 6? What brand is it?

 

[Steve135]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

The tach has been on the boat probally since it was new in 1980, but may have been changed at some point.The motor and boat has been together since it was new The 15 1/2 x 15 was what the marina put on when the guy got it rebuilt. The hole shot is poor and the tach only reads 4200 rpms. I know enought about motors to know it wasn't turning fast enought. I did change cables this year could it be out of trim? I have done this before and never had problems adjusting cables. I did just put this boat in Monday and haven't yet had time to see if the tach is acting weird. I gave it a good run to the mooring and thats all I got on the tach.Dhadley what size should I try to see if the rpms increase?

 

[Dhadley]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

Is the tach set on 6? What brand is it?

 

[lowbud]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

Dhadley & Stinky2,<br /><br />I have a 14 /2 x 19 prop. An OMC Tach #174206 with the setting at 6.<br /><br />For years I have run the boat at 3200 rpm on plane. Whenever I start to exceed about 3400 it starts to cavitate and the rpm's shoot up to 5000+. Again, I do about 20-24 mph. The boat is a Sea Ox 200C, a 20' walk around. Pretty heavy boat.<br /><br />I have always thought that when the last owner put the Johnson 150 on the boat that the tach was not match up correctly, but I guess it is? <br /><br />Should I be looking at changing something or leave well enough alone? Thanks for the help.

 

[Dhadley]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

Lowbud - is your prop worn at all? Is it ss or aluminum?

 

[lowbud]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

S.S. prop. Blades in decent condition. Also have spare prop of same dimensions but aluminum. <br /><br />Boat also came with a smaller prop, maybe off the previous 140 hp. Not sure.

 

[Steve135]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

Ok to answer the question on my tach its a teleflex tach before they were setable. This motor boat combo have been together since 1980, boat and motor new. I have ordered a new tach to eliminate it as I saw it pin out at 8k at some point. I tryed the 15 x 17 for fun and found it to run less rps. Like I figured it would. My main question was what speed the boat was exspected to do and what prop anybody else was uning on this type boat. I know what rpms should be at WOT. but 20-24 is slower than my boat runs I was at 26 mph from gps and I really needed to trim more down and couldn't get it anymore. Yes these are very heavy boats! <br />steve

 

[lowbud]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

Stinky2,<br /><br />Is your Sea Ox a cuddy or center console? I make sure I put as much stuff up in my cabin to get the weight off the back end. I am not sure if the pitot tube speedometer is more accurate or not than a gps.<br /><br />Although these boats are a little heavy, they are comfortable to be in when it is a little rough.

 

[Steve135]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

Lowbud I have a center console. I ran it today for its first of the season fishing trip. The other outings were just test drives. The boat ran great for about 45 minutes and then just wouldn't throttle up. But since the tach went completly out now, I can't even be sure of what the top rpms were at the time. I was thinking it might be related to the low speed limiter caused by heat. that would cause the low throttle setting (2500) but we continued on and trolled for 3 hrs and no problems when it was time to go it worked fine. Maybe I had some gunk in the fuel filter or fuel pumps. I am changing filter tomorrow. I will get back to you all when I get the tach.

 

[Steve135]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

Ok guys I put the new tach on the boat Teleflex set a 6p and the 15 1/2 x 15 produces 4000 rps at WOT this isn't good! But its so far away from where it needs to be,should I look somewheres else first before the prop. I changed the fuel filter but havetn't run it yet. I am also going to see if the fuel pumps picked up any particals from the tank.The boat sat for 5 years I checked to see if linkage alows movement to all mechnical stops. This motor runs really good has only about 30 hrs since the new power head was put on it. I am thinking that one of the fuel pumps could be bad? Maybe I will rebuild both as the were probally dry for all those years!<br />steve

 

[lowbud]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

Stinky2<br /><br />Glad to see you are making some progress. Don't have any recommendations on how to further increase your rpms. <br /><br />When I purchased my Sea Ox it had been setting for 7 years with only 20 hours on the new outboard. Previous owner had cancer and passed away. I had to rebuild all three carbs and then she ran fine. Now I am slowly rebuilding the whole thing as they break.<br /><br />I hope you disposed of all the old fuel and replace with new. I use 89 octane with lead additive. Again I have a 1985 Johnson 150.<br /><br />Did you say that your throttle plats open all the way up?

 

[Steve135]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

update I got some info to check the coils as I could have loss one and not know it. I found one plug wire no off but pulled back pretty far. This made some improvement in the rpms they are 4500 rpms at WOT and the boat sounds better and moves faster. I am going to clean up the wire terminals at the motor end to see if that helps any? As far as the gas it only had 5 gal in the tank I took as much as I could out I started with 60 gals of fresh gas with fresh start added. It still could be a fuel pump problem thats for this weeks work.<br />steve

 

[Steve135]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

Ok when out today and heres what happened. The boat ran 4200 rpms and 25 mph most of the day.<br />On the way back in something burped and the motor sounded better. When I went WOT I had 5100 rpms and 35 mph I trimed to 5400 rpms and 37 mph. This lasted 1 mile and the motor slowed and stalled. The ball was full and hard.I was able to restart and go but I had wasn't able to go fast due to wake zone and I wanted to be headed in rather than out! After 2 miles at 1500 rpm I was able to open it up to 5200 rpms and 35 mph and it did the same thing, this time the motor was slow to crank? I switched to both batteries ands it started again. The max rpms was 4200 I ran it several times and got mixed results from 4200 to 5000 but never was able to obtain 5400 again.The battery thing didn't seem to matter as I went back and forht between 1,2 and both. The motor sounded ratty at low rpms . I pulled each coil at idle and found a change to the rpms. I called it a day and found that the motor had a big sound differance above 3000 rpms and ran ruff at lower rpms almost like a bad ping. Any help would be great!

 

[lowbud]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

stinky2,<br /><br />You may want to start a new thread on this one?

 

[MGuckin]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

Better to not start a new post. Keep it togetther seeing as it is the same problem motor.<br />You said you heard a "burp" and a "ping". Just a suggestion. Verify link and sync. Check flywheel key.

 

[Steve135]

Re: Re Visited Prop for 1988 150 hp 20 ft Sea Ox

Ok I used the word burped and maybe thats the wrong word. I push the throttle up and the motor reacted, then without throttle movement there was a change in engine rpm and sound <br />(hick-up) the motor ran better from that point on. This was after 4 hrs running that day.This is only the 4th outing with this boat for me! I will pull the plugs tomorrow. I still haven't rebuit the fuel pumps yet1<br />steve