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Author Topic:   OR18 performance with 150 Evinrude
padrefigure posted 09-26-2002 05:01 PM ET (US)   Profile for padrefigure   Send Email to padrefigure  
Prop 14 1/4 X 19. 1987 engine, rebuilt powerhead in 2000. New plugs, new fuel/ water separator. The engine starts and runs well throughout the RPM range, but I only get about 41 MPH (GPS)and 4200 RPM's @ WOT. I have adjusted the throttle linkage to boost RPM's, but this did not affect the top end. Running Techron at the reccommended rate through a couple of tanks of gas did seem to help a little. Gleaning from other posts, I suspect that I should be getting another 1000 RPM and maybe mid to high 40's on the top end. Am I over-propped? Or are two cylinders along for the ride? How can I tell which one(s).
Peter posted 09-26-2002 05:58 PM ET (US)     Profile for Peter  Send Email to Peter     
You are not overpropped. I used to run a 14 1/4 x 21 to 5000 RPM. Have you checked for a fuel restriction?
Bigshot posted 09-27-2002 10:14 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Start at the most important a compression test. If not compression check spark. Then have carbs redone and it set up by a pro. How long has it been running like this?
padrefigure posted 09-27-2002 10:47 AM ET (US)     Profile for padrefigure  Send Email to padrefigure     
I have owned the boat for a little over a year. This is about the performance I got when I first bought it (although the tach was not working and I did not have a GPS to check speed.) It started running rough and being hard to start in the winter so I had it serviced. Both power packs were replaced, but the plugs were fine at that time. This summer, performance continally eroded to the point that I was only getting 3300 rpm and maybe 30 mph. That's when I changed the plugs and fuel/water separator and adjusted the throttle linkage. This gave modest improvements. Then I started adding Techron each time I added gas. One small bottle of Techron per 12 gal of gas (the reccommended rate.) I generally run 12 gals of gas every Saturday and Sunday so I am pretty sure that I do not have bad gas issues. While it would be nice to see what 50 mph feel like on the water, I am most concerned with dependability (which does not seem to be an issue right now) and keeping this 15 year old outboard running strong.
Seabrook posted 09-27-2002 10:55 AM ET (US)     Profile for Seabrook  Send Email to Seabrook     
I think Bigshot has the right idea on what to do. However, I hear a lot of people talking about size and pitch of props without mentioning, or maybe without knowing, if it is a cupped prop. Several manufacturers make cupped props that are double and triple cupped. Although they are not extremely common, they are out there. A double cup can make a 19 pitch perform more like a 20-21 and a triple couple could make it perform more like a 23" pitch.
hauptjm posted 09-27-2002 11:28 AM ET (US)     Profile for hauptjm    
I have the same rig on an '85 18OR with a '95 150 Johnson. Only difference (I assume) is I'm on a bracket.

For comparison purposes:

WOT 5600 RPMs, 53 M.P.H. I may be getting an extra 1-3 m.p.h. from the static set-up of the bracket.

Bigshot posted 09-27-2002 01:52 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
You either have a bad engine or gummed carbs, etc. Do a comp test NOW! If good we will procede.
padrefigure posted 09-27-2002 08:47 PM ET (US)     Profile for padrefigure  Send Email to padrefigure     
As instructed, I stopped by America's largest hardware store and purchased a compression tester. My test procedure was to pull the kill switch, remove one spark plug at a time and turn the engine over. After about 3-4 compression strokes, the needle would stop climbing. All cylinders measured between 75 and 80 psi. If there was any variability, the cylinders on the port side were slightly on the high side of the range. Also, the plugs at the top were blackened more than the bottom plugs.

One detail that I omitted in the original post was the fact that this engine is on a fixed set-back bracket. It is about 6" back and is mounted the equivalent of 3 holes up.

What's next?

padrefigure posted 09-28-2002 01:11 PM ET (US)     Profile for padrefigure  Send Email to padrefigure     
Checked the manual and 80 psi is low, so drove over to the neighborhood outboard mechanic to verify the test. Using the same test method, his gauge read 85 psi. He claimed that OMC had issued low compression gaskets in an effort to ward off piston burning. He was not sure if 1987 engines were affected.

Clymer says to remove all plugs and open the throttle full and test each cylinder. Clymer also says that minimum should be 100 psi, but the difference between cylinders is most important. Would the test method make that much difference in readings?

Off to the lake to test a 15" X 17" aluminum prop. Will report results this afternoon.

Dunk posted 09-28-2002 11:08 PM ET (US)     Profile for Dunk  Send Email to Dunk     
About your RPM. It has to be wrong. 41mph@4200 with a 19" prop thru 1.86 gears means you have slip rate of less than 2%. This is about impossible. 10% is about the norm. You said you replaced the tach? Did you set the dial on the back side of it to "6"?? Once you do that my guess is it will tell you the engine is running about 47-4800. If this is the case I'd be looking for bad coil of plug wire. If she's only running on 5 you'll loose 7-800rpms.If it's center piston on either bank she will still run smooth.

Yes, SOP on checking compression is a warm engine, throttle open and "all" the plugs removed. This gives you the max cranking speed with the starter. I can't believe an OMC mech checked one plug out at a time?? He was right about thicker gaskets to lower compression, but they stopped doing that in 82 when OMC went to the low ring pistons to reduce ring temps and reduce carbon problems.

If the engine hasn't been decarboned since it was rebuilt you might want to pick up can of OMC Engine Tuner, follow the instructions then recheck the compression. The compression sounds low and the engine could be carboned up. Those crossflow OMC's need decarboned every 50hrs if you want them to live.

padrefigure posted 09-29-2002 07:55 PM ET (US)     Profile for padrefigure  Send Email to padrefigure     
I think your tach advise is correct--it was not replaced, just "fixed." How do I isolate the tach problem--it must be the sender, the cable or the dial unit, right?

I ran the 15" X 17" and this is obviously not enough prop. It would not hold in a moderate turn and would blow out right on the edge of being fully trimmed out.

I run 10 to 20 hours per month, so I am well past the 50 hours between de-carbs. Can I do this procedure with muffs or do I need the back pressure of being in the water?

Thanks all for the advice.

Bigshot posted 09-30-2002 09:42 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Muffs is fine....Replace the darn tach if not sure. You can not fix tachs. You need a new mechanic. You can fix a 1960 corvette tach to the tune of $500-600 but for $60 you can buy a new one for a boat. I think somebody be pullin some wool!
padrefigure posted 10-07-2002 06:49 PM ET (US)     Profile for padrefigure  Send Email to padrefigure     
I de-carbed the engine (bottle of Techron in a gal of 50:1, ran engine on muffs for about 30 minutes, switched back to regular 50:1). Checked compression after de-carbing--it increased slightly to 85psi. There is little difference between cylinders. Took it out on the lake and still got only 38-40 MPH (GPS). I suspect that the tach problem is caused by a bad rectifier since I also have intermittent battery charge problems. Could this also cause power (speed) loss? Plan to change the rectifier in the next week or so.

Don't know what to think about the wool pulling. I appreciate your input.

Sal DiMercurio posted 10-09-2002 12:24 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Techron ?
Forget the techron & get some OMC Engine Tuner, or Seafoam & follow the directions.
Then you can be assured it's been decarboned.
Bigshot posted 10-09-2002 09:53 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Depends Sal....Yamaha trains their techs to run an outboard on 1 can of Techron with 1/2 gallon of gas. Before carbs run dry shut down engine, let sit overnight. This will not only decarbonize, it should unstick rings and clean fuel system. Kinda like shocking a pool. Do not recommend doing it annually but if in doubt.....
Smallfrye posted 10-11-2002 09:40 AM ET (US)     Profile for Smallfrye  Send Email to Smallfrye     
Steve, How is the motor running ? I talked w/ my motor guy who agreed with the other post on this subject; you probably have sticking rings due to carbon build up.
Using the techron shock treatment or just using decarb and soaking overnight may clean up the problem.
You may want to shift to synthetic oil once the carbon is gone. This will eliminate any future carbon issues.
padrefigure posted 10-11-2002 07:15 PM ET (US)     Profile for padrefigure  Send Email to padrefigure     
It runs pretty good--starts easily, smooth operation throughout the range. It is sluggish out of the hole--a slalom skier has to be pretty good to get up without drowning first and according to other posts, it is falling short on the top end. I intend to try to get another 10 years out of this OB, and I was just wondering if this is what I should expect.

Got your email and will be calling Allan soon for his opinion. Thanks.

tlynch posted 04-09-2003 11:33 PM ET (US)     Profile for tlynch  Send Email to tlynch     
Padrefigure, was there ever any conclusion to this thread?

Todd Lynch

Sal DiMercurio posted 04-10-2003 01:26 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Those 150s are not high compression engines to start with.
Most of the 1985 to 92s i'v checked were in the low 90 psi range.
I'd take Dunks advice as it's the same as I would give.
The rectifier sends 12 volts to the tach, he can check to see if theres 12 volts at the gray wire going into the tach, if there is while the engine is running his rectifier should be fine, if it's not 12 volts or higher, the rectifier is shot.
I believe he has the smaller charging system on that engine, the rectifier should cost around $65.00, if by chance he has the larger charging system, [ which I doubt ] it will cost $265.00.
The rectifier will not change the way the engine runs, it's just a charging system.
I'd give that engine a real good dose of engine tuner [ straight ] & leave it in overnight.
tabasco posted 04-10-2003 07:39 AM ET (US)     Profile for tabasco  Send Email to tabasco     
Hey Bigshot do you recommend putting a bottle of Techron in with a full tank of fuel (27 gallons) on a motor with only 50 hours? How often do you add a bottle to the fuel to the tank? I use it on my cars and am very happy with the results. Are there any negatives to using Techron?

PS: Costco is now selling it in a 4 pack under $10

Tom2697 posted 04-10-2003 09:42 AM ET (US)     Profile for Tom2697  Send Email to Tom2697     
Padrefigure, I don't know if this will work but I think it should. You can check your tach accuracy with an dwell/tach meter for a car engine. It has an inductive sensor that clamps around a plug wire (not important which one if you are only checking rpm) and can be adjusted to measure 4, 6, and 8 cylinder engines. Ask an old "motorhead" if he/she has one for checking the points on a musclecar. Or, you might be able to borrow one from Pep Boys, Autozone, etc. This will at least verify that your tach is bad without spending any money.
hooter posted 04-10-2003 10:47 AM ET (US)     Profile for hooter    
Not t'be a smartass, but about $7,500 for a new carbed OceanPro 150 installed with new controls will get you outta the garage and onto the water, replace the greese under your fingernails with good fish goop, and make you fall friggin' in LOVE with that 18' again. Don't care how big a motorhead you be, a 16-year old motor poopin' out like the one you've got there, is nothin but a barrel o'headaches. No offense intended, here.
Bigshot posted 04-10-2003 11:01 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Techron every 50 hours can't hurt. I usually just buy some decarb and do it before winterization every season. Now in FL I would do it every 50 hours or so because I do not winterize. I also run one in my 4 stroke every now and then.
Sal DiMercurio posted 04-10-2003 04:42 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
I think were beating a dead horse here, as the original post was Sept of last year.
Wonder what the final outcome was.
Outrage18 posted 04-11-2003 10:02 AM ET (US)     Profile for Outrage18  Send Email to Outrage18     
I have a 1982 OR18 w/ 1995 150 Merc.
Last summer the GPS hit 52-53mph with 2 people and slightly less then a half a tank.
At that speed things get a little hairy when you encounter some chop.


wildeone posted 04-14-2003 02:27 PM ET (US)     Profile for wildeone  Send Email to wildeone     
Maybe changing the subject, but I have an old 84 150hp Rude on my 18 (still runs great, smokey, but great!). Thinking of repower soon, either a new Jonson 150, or found a deal on a new 02 Merc 125 saltwater classic. Any suggestions on performance lost, if any? Thinking of the Merc for two reasons, weight, and that built in oil tank on cowling, need to save space in the splash well.

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