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Author Topic:   Outrage 18 with 1988 Yamaha C 115-HP

frstevec posted 06-08-2010 09:56 AM ET (US)
Greetings--I have read many threads about propellers and concluded that the painted stainless K 17-inch OEM propeller was the correct one for my set-up [of a Boston Whaler OUTRAGE 18 with a Yamaha C-model 115-HP motor]. I weighed the entire rig: single axle, Galv trailer, boat, engine, and 1/2 tank fuel and one battery. The boat had a Aluminum T Top that I have removed, anchor chain and line-- total weight 2,750-lbs. Backing out stuff to estimate the hull [weight], I'm guessing 1,600-lbs. It does have bottom paint. I removed 80-percent of old paint and re-painted using Sea Hawk water based bottom paint.
The engine is mounted one hole up and runs 4,100-RPM with trim down; trimmed up to "3" on the scale, engine speed jumps to 4600 to 4,800-RPM, but the [boat speed] stays close to 31-MPH. Looking at the propeller chart the 17-inch at 4,200-RPM is 30-MPH. Running now with two adults and 1/2-FULL tank , T-top and 4,300 to 4,400-RPM [fasteest] without obvious cavitation. The propeller was on engine when I bought it last fall and I assume that it is original. [An engine speed of] 4,000-RPM is about my speed anyway. Should I look for a replacement [propeller] to increase [engine speed]? If so, which one? Thanks. Steve
Tom W Clark posted 06-08-2010 10:38 AM ET (US)
You're guessing your boat's weight because you did not fill the tank before weighing it (the only way to know how much fuel is in there) and not launching the boat after weighing and immediately returning to the scales to weigh the tow vehicle and trailer alone to get the tare weight.
It is very easy to be off several hundred pounds by guessing.
I don't think your slow speed is a propeller problem. The motor could come up one more hole with that propeller and it would help.
How are you measuring speed? GPS?
frstevec posted 06-08-2010 11:51 PM ET (US)
Thanks Tom,
I am using my Motorola Droid GPS Speed Tracker app to see mph. I tested it against my car speedometer and it is right on at 30 mph.
I think I will move the engine up another hole before I buy another prop-
Thanks for the way to get the tare weight; sadly, I'm 25miles from the nearest scales when the boat is splashed. I hope that I am not lugging the engine the way it is set up now.

frstevec posted 06-22-2010 10:21 AM ET (US)
Well, so much for my memory-- The prop is a 19K and the engine is Yamaha 115hp 1988. I have more time on the engine now and still see only 4100 rpms WOT. The speed according to my Droid GPS app is 30mph.
Is is worth changing to a 17K prop? I will raise the engine from one up to two up anyway. Tom? Thanks.
Tom W Clark posted 06-22-2010 11:17 AM ET (US)
I am confused. You are only able to hit 4100 RPM or 4800 RPM? That's a big difference.
Please clarify what your WOT RPM is.
Tohsgib posted 06-23-2010 11:26 AM ET (US)
Have you done a compression test? Are carbs good & clean?
Tom W Clark posted 06-23-2010 03:09 PM ET (US)
Yeah, again, I don't think you have the wrong prop, even a 19"
You have a motor problem. I think it is only running on three cylinders. There is no way that boat should be so slow.
That boat should be doing 38 MPH at 5000-5500 RPM.
frstevec posted 06-24-2010 09:01 AM ET (US)
Thanks for the input. I am getting 4100rpms tucked trim and only goes up to 4800 with trim so far out that it is obviously slipping badly and porpoising.
I pulled the plugs and top port side plug oily; the rest brownish and not oily.
Have not done compression ck. Idles 600-700 rpms.
I ordered new plugs and fuel pump. Will do a compression ck next.
I'm relieved not having to buy a prop but now in detective/diagnotic mode for problem. Thanks again. Steve
Tom W Clark posted 06-24-2010 11:32 AM ET (US)
An oily spark plug is consistent with a cylinder that has no spark but is getting fuel. The fuel is unburned so the plug is oily.
While new spark plugs *might* solve that problem by itself, you may have to investigate further to find it why no there is no spark in that cylinder.
Yamaha outboards of that vintage were rather notorious for having spark plug wires whose boots did not grip the plugs well. It is common to find the spark plug boots with zip ties on them in an effort to keep the boots attached to the plugs. You may want to check that out.
For the record, you still need a new prop, 19" is too much pitch. That boat/motor should be running a 17" pitch Yamaha Painted Stainless Steel, 16" Yamaha Performance Series or 15" Stiletto Advantage.
My point was that the prop, by itself, was not the reason for your profound loss of power and speed.
Also, never run WOT with the motor tucked all the way in. You would never operate the boat like that normally and it can create unsafe handling at top speed.
You trim the motor to the point where speed is maximized not to the point where the prop is loosing grip.
jimh posted 06-24-2010 08:10 PM ET (US)
To confirm Tom W. Clark's comments, I had a pair of 1987 Yamaha outboard motors. One of the first modifications I made to them was to use Ty-Wrap or zip-ties to help bind the spark plug wire boots to the spark plugs. Without the Ty-Wrap bindings, the spark plug wire boots would easily fall off of the spark plugs, causing the engine to lose spark in that cylinder and run poorly.
frstevec posted 06-25-2010 09:45 PM ET (US)
Greetings,
Today I installed a new plug in place of the oily one. Wow. Suddenly much stronger acceleration but inconsistent. I was unable to check WOT. After three hours runtime at various speeds, I pulled the new plug; it seemed dry and it looked completely unused. I thought it was firing; lots more smoke at startup but ? A new wrinkle is that now the engine sneezes and dies at low rpms. It surges and bogs too during acceleration, This is new (after I used up the old gas). I now have 50 gallons fresh gas in the tank. Will spraying Seafoam in carbs while running the engine, clean them? I already ran one can of Seafoam through the gas tank with the old gas( 20 gal) a month ago.
What should I do next? Thanks
Tohsgib posted 06-26-2010 10:59 AM ET (US)
For the second or third time....Have you done a compression test? Are carbs good & clean?
Tom W Clark posted 06-26-2010 11:27 AM ET (US)
How did you mix the oil with the fresh 50 gallons of gas?
How much oil did you add?
What type of oil are you using?
frstevec posted 06-26-2010 07:46 PM ET (US)
Today, I checked the compression. All four cylinders were 128psi.
I installed all the new plugs (old plugs were wet) and used Valvoline HD Carb cleaner; sprayed the entire can and added another can of Seafoam to the gasoline.
The idle is now much better, little smoke and when moved to full throttle, it does not stumble but makes a big air sound and accelerates slowly to plane. The WOT is 30mph by my GPS. I accidently unplugged my tach trying to wire my new VHF radio, so I don't know the WOT rpm.
Tom, I have automatic oiler. At the beginning of the season, I topped off the big tank in the console with one gal of Mercury tc 3w and added left over yammalube tc 3w less than a qt. I just added one gal of Cabelas semi syn tc 3w to the big tank Probably needs a qt to fill it completely. I did not think to record the amount of gas I put in. I think about 60 gal total.
Tom W Clark posted 06-26-2010 08:21 PM ET (US)
Automatic oiling? I thought the C115 was the premix model.
At any rate, you've now mixed three different types of oil? I have heard bad stories about mixing oils with the recomendation that you should draw down the oil level or drain it before filling with a new oil.
Is that a marine myth?
Tohsgib posted 06-27-2010 12:37 PM ET (US)
I don't see a problem mixing oils except it might make a funky color. I would not mix synthetics with regular oil though. They did not offer a C115 in 1988, not until early 90's I believe.
Engine is running on 3 cyls, start checking for spark. If you did not have fuel to 1 or 2 cyls you would have blown her up by now.
frstevec posted 06-27-2010 09:37 PM ET (US)
Tom,
I found out that my '88 engine is 115 because they did not make the C115 until the nineties as Tohsgib said. The Cabelas semi synthetic is a blend of synthetic and regular oil. I have read other places that the only critical issue for this engine is that it is TCW 3 compliant.
Tohsgib,
I have the $100.00! Service Manual and will check the ignition coils to see which one is faulty. Is that the logical solution for running on three cylinders? I mean after changing the plugs and making sure that the wires are making good contact with the plugs, what else could it be? Thanks for your help.
frstevec posted 06-29-2010 01:01 AM ET (US)
Sure enough, #1 cylinder ignition coil was way out. Resistance value is 3.7k ohms instead of 2.5k ohms. Ordered a new one and expect to be running on 4 cylinders soon. Thanks again.

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Author	Topic: Outrage 18 with 1988 Yamaha C 115-HP
frstevec	posted 06-08-2010 09:56 AM ET (US) Greetings--I have read many threads about propellers and concluded that the painted stainless K 17-inch OEM propeller was the correct one for my set-up [of a Boston Whaler OUTRAGE 18 with a Yamaha C-model 115-HP motor]. I weighed the entire rig: single axle, Galv trailer, boat, engine, and 1/2 tank fuel and one battery. The boat had a Aluminum T Top that I have removed, anchor chain and line-- total weight 2,750-lbs. Backing out stuff to estimate the hull [weight], I'm guessing 1,600-lbs. It does have bottom paint. I removed 80-percent of old paint and re-painted using Sea Hawk water based bottom paint. The engine is mounted one hole up and runs 4,100-RPM with trim down; trimmed up to "3" on the scale, engine speed jumps to 4600 to 4,800-RPM, but the [boat speed] stays close to 31-MPH. Looking at the propeller chart the 17-inch at 4,200-RPM is 30-MPH. Running now with two adults and 1/2-FULL tank , T-top and 4,300 to 4,400-RPM [fasteest] without obvious cavitation. The propeller was on engine when I bought it last fall and I assume that it is original. [An engine speed of] 4,000-RPM is about my speed anyway. Should I look for a replacement [propeller] to increase [engine speed]? If so, which one? Thanks. Steve
Tom W Clark	posted 06-08-2010 10:38 AM ET (US) You're guessing your boat's weight because you did not fill the tank before weighing it (the only way to know how much fuel is in there) and not launching the boat after weighing and immediately returning to the scales to weigh the tow vehicle and trailer alone to get the tare weight. It is very easy to be off several hundred pounds by guessing. I don't think your slow speed is a propeller problem. The motor could come up one more hole with that propeller and it would help. How are you measuring speed? GPS?
frstevec	posted 06-08-2010 11:51 PM ET (US) Thanks Tom, I am using my Motorola Droid GPS Speed Tracker app to see mph. I tested it against my car speedometer and it is right on at 30 mph. I think I will move the engine up another hole before I buy another prop- Thanks for the way to get the tare weight; sadly, I'm 25miles from the nearest scales when the boat is splashed. I hope that I am not lugging the engine the way it is set up now.
frstevec	posted 06-22-2010 10:21 AM ET (US) Well, so much for my memory-- The prop is a 19K and the engine is Yamaha 115hp 1988. I have more time on the engine now and still see only 4100 rpms WOT. The speed according to my Droid GPS app is 30mph. Is is worth changing to a 17K prop? I will raise the engine from one up to two up anyway. Tom? Thanks.
Tom W Clark	posted 06-22-2010 11:17 AM ET (US) I am confused. You are only able to hit 4100 RPM or 4800 RPM? That's a big difference. Please clarify what your WOT RPM is.
Tohsgib	posted 06-23-2010 11:26 AM ET (US) Have you done a compression test? Are carbs good & clean?
Tom W Clark	posted 06-23-2010 03:09 PM ET (US) Yeah, again, I don't think you have the wrong prop, even a 19" You have a motor problem. I think it is only running on three cylinders. There is no way that boat should be so slow. That boat should be doing 38 MPH at 5000-5500 RPM.
frstevec	posted 06-24-2010 09:01 AM ET (US) Thanks for the input. I am getting 4100rpms tucked trim and only goes up to 4800 with trim so far out that it is obviously slipping badly and porpoising. I pulled the plugs and top port side plug oily; the rest brownish and not oily. Have not done compression ck. Idles 600-700 rpms. I ordered new plugs and fuel pump. Will do a compression ck next. I'm relieved not having to buy a prop but now in detective/diagnotic mode for problem. Thanks again. Steve
Tom W Clark	posted 06-24-2010 11:32 AM ET (US) An oily spark plug is consistent with a cylinder that has no spark but is getting fuel. The fuel is unburned so the plug is oily. While new spark plugs might solve that problem by itself, you may have to investigate further to find it why no there is no spark in that cylinder. Yamaha outboards of that vintage were rather notorious for having spark plug wires whose boots did not grip the plugs well. It is common to find the spark plug boots with zip ties on them in an effort to keep the boots attached to the plugs. You may want to check that out. For the record, you still need a new prop, 19" is too much pitch. That boat/motor should be running a 17" pitch Yamaha Painted Stainless Steel, 16" Yamaha Performance Series or 15" Stiletto Advantage. My point was that the prop, by itself, was not the reason for your profound loss of power and speed. Also, never run WOT with the motor tucked all the way in. You would never operate the boat like that normally and it can create unsafe handling at top speed. You trim the motor to the point where speed is maximized not to the point where the prop is loosing grip.
jimh	posted 06-24-2010 08:10 PM ET (US) To confirm Tom W. Clark's comments, I had a pair of 1987 Yamaha outboard motors. One of the first modifications I made to them was to use Ty-Wrap or zip-ties to help bind the spark plug wire boots to the spark plugs. Without the Ty-Wrap bindings, the spark plug wire boots would easily fall off of the spark plugs, causing the engine to lose spark in that cylinder and run poorly.
frstevec	posted 06-25-2010 09:45 PM ET (US) Greetings, Today I installed a new plug in place of the oily one. Wow. Suddenly much stronger acceleration but inconsistent. I was unable to check WOT. After three hours runtime at various speeds, I pulled the new plug; it seemed dry and it looked completely unused. I thought it was firing; lots more smoke at startup but ? A new wrinkle is that now the engine sneezes and dies at low rpms. It surges and bogs too during acceleration, This is new (after I used up the old gas). I now have 50 gallons fresh gas in the tank. Will spraying Seafoam in carbs while running the engine, clean them? I already ran one can of Seafoam through the gas tank with the old gas( 20 gal) a month ago. What should I do next? Thanks
Tohsgib	posted 06-26-2010 10:59 AM ET (US) For the second or third time....Have you done a compression test? Are carbs good & clean?
Tom W Clark	posted 06-26-2010 11:27 AM ET (US) How did you mix the oil with the fresh 50 gallons of gas? How much oil did you add? What type of oil are you using?
frstevec	posted 06-26-2010 07:46 PM ET (US) Today, I checked the compression. All four cylinders were 128psi. I installed all the new plugs (old plugs were wet) and used Valvoline HD Carb cleaner; sprayed the entire can and added another can of Seafoam to the gasoline. The idle is now much better, little smoke and when moved to full throttle, it does not stumble but makes a big air sound and accelerates slowly to plane. The WOT is 30mph by my GPS. I accidently unplugged my tach trying to wire my new VHF radio, so I don't know the WOT rpm. Tom, I have automatic oiler. At the beginning of the season, I topped off the big tank in the console with one gal of Mercury tc 3w and added left over yammalube tc 3w less than a qt. I just added one gal of Cabelas semi syn tc 3w to the big tank Probably needs a qt to fill it completely. I did not think to record the amount of gas I put in. I think about 60 gal total.
Tom W Clark	posted 06-26-2010 08:21 PM ET (US) Automatic oiling? I thought the C115 was the premix model. At any rate, you've now mixed three different types of oil? I have heard bad stories about mixing oils with the recomendation that you should draw down the oil level or drain it before filling with a new oil. Is that a marine myth?
Tohsgib	posted 06-27-2010 12:37 PM ET (US) I don't see a problem mixing oils except it might make a funky color. I would not mix synthetics with regular oil though. They did not offer a C115 in 1988, not until early 90's I believe. Engine is running on 3 cyls, start checking for spark. If you did not have fuel to 1 or 2 cyls you would have blown her up by now.
frstevec	posted 06-27-2010 09:37 PM ET (US) Tom, I found out that my '88 engine is 115 because they did not make the C115 until the nineties as Tohsgib said. The Cabelas semi synthetic is a blend of synthetic and regular oil. I have read other places that the only critical issue for this engine is that it is TCW 3 compliant. Tohsgib, I have the $100.00! Service Manual and will check the ignition coils to see which one is faulty. Is that the logical solution for running on three cylinders? I mean after changing the plugs and making sure that the wires are making good contact with the plugs, what else could it be? Thanks for your help.
frstevec	posted 06-29-2010 01:01 AM ET (US) Sure enough, #1 cylinder ignition coil was way out. Resistance value is 3.7k ohms instead of 2.5k ohms. Ordered a new one and expect to be running on 4 cylinders soon. Thanks again.