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Author Topic:   Non-Boston Whaler Boat with 70-HP

jjbrab posted 08-10-2010 01:03 PM ET (US)
This year I purchased a 15-foot WAHOO boat--identical to a Boston Whaler boat--with a Johnson 70-HP engine. The [non-Boston Whaler-boat] will only do about 24-MPH at wide open. I read early about propeller size here and inspected mine. The propeller almost touches the [anti-ventilation] plate. Could the propeller size affect performance that much? Do I have a more serious engine [malfunction]? The engine runs smooothly and the boat [reached hydroplane] easily, but [the maximum speed is] just not the speed I expected!
Sal DiMercurio posted 08-10-2010 07:16 PM ET (US)
How many rpms will she twist at wide open throttle? you gotta tell us the maximum rpms she turns. What size prop is on it the prop is stamped either on the outside of the hub, or inside the exhaust hole, such as 14 x 17 or 14 x 19 or 14 x 21. The rig should twist a 19 pitch s/s prop and get 42 - 46 mph.
What year is the engine ?
If the prop is a 14 x 19, that should be very close to right, and I would than expect the [Power Pack] to be bad, as [Power Pack] has a low speed mode that will allow you to only go about 25 mph and turn about 3500 rpms & the high speed mode will allow the engine to rev to near 6000 rpms with a 19p prop and low to mid 40s speed.
When I first got my engine only ran on the low speed portion, and when I put a new [Power Pack] on her, she went to 6000 rpms and 42 - 43 mph. 1997 Johnson 70 hp. with 14 x 19 sst OMC prop.--Sal
jimh posted 08-10-2010 08:37 PM ET (US)
Propeller diameter, pitch, number of blades, and blade shape will all affect performance. Generally a propeller is described by giving the diameter in inches, the pitch in inches, the number of blades as an integer, and the general type of blades by various descriptors. It is unusual to define a propeller in terms of how closely the blades come to the anti-ventilation plate, so a description of that dimension does not convey a lot of information about the propeller.
jjbrab posted 08-11-2010 10:23 AM ET (US)
It's a 1994 engine. The propeller is 14 x 19. I need to go out and check the [engine speed] at [maximum throttle]. Thanks for the information. Not sure what a [Power Pack] [costs] but [buying a new Power Pack and replacing the existing Power Pack] might be a good place to start. I also had the problem where the engine will run all day just fine but if you shut it down and sit for a while till it is cool it has trouble restarting.
Tohsgib posted 08-11-2010 12:08 PM ET (US)
Have you done a compression test? If not you might be wasting your money. I would do compression check and if all looks pretty even, then clean carbs. Then check for spark if still bad.
Sal DiMercurio posted 08-12-2010 09:55 AM ET (US)
Nick is 100% right, the very first thing you do is a compression test or leak down.
Those 3 cylinder engines have the tendancy to score the middle cylinder if run lean, but are by far the best engines "EVER" made by OMC.
Sal
jimh posted 08-14-2010 08:31 AM ET (US)
I an not familiar with an OMC Power Pack where there are two modes of operation, one for high-speed and one for low-speed. A Power Pack is just a name for a capacitor discharge ignition system. Problems with an OMC Power Pack are fairly common. As electrical or electronic devices, they are not infallible, and it seems like too much heat--the bane of all electronics--can cause them to fail.
If the engine running characteristics are being affected by the Power Pack, you typically see a rather abrupt change in the run characteristics. The electronics seem to either work normally, or abruptly change to work abnormally. I had a problem with the Power Pack on my V6 Evinrude engine which affected only one-cylinder. The problem would suddenly appear and then often just as quickly disappear. However, because of the cost of the Power Pack, about $300, before I replaced the Power Pack I went through a thorough process of eliminating all the other elements in the spark ignition circuit for the affected cylinder. It was only after I tested the spark plug, the spark plug wire, the coil, and all the connections by swapping components from one cylinder to another, that I decided the Power Pack was the culprit.
In any case, a discussion in PERFORMANCE assumes the engine is running properly, and the topic of discussion is optimization of the performance by engine mounting adjustments, propeller selection, and other techniques. If you think your engine is not running normally, you should begin a new discussion in REPAIRS/MODS, and seek advice on how to repair the malfunction in your engine. Once you have the engine running properly, you can return to PERFORMANCE and seek advice on optimization of the boat, motor, and propeller.
jpgbu1 posted 08-16-2010 10:42 AM ET (US)
I think the LOW RPM version they are talking about is the S.L.O.W. mode designed with overheating and low oil res in mind.is the engine alarm working? could be as simple as low oil reserve or something triggering that feature as well. PS don't use the internal tank on that boat with new E gas! it will = disaster.
Sal DiMercurio posted 08-16-2010 09:06 PM ET (US)
No, it' wasen't slow mode.
Obviously it killed 1 of the 3 cylinders, which allowed the engine to start & run, but not get more than 3500 rpms.
I ordered a new Power pac from Boat fix for 1o9.00 [ if I remember correctly ], installed it & 6000 rpms on the tac.
Jim, your right, there is no high or low rpm on the power pac, it just goes lower when no juice is getting to 1 or more cylinders.
Some engines still run, & others wont even pop if the power pac takes a hike.
It [[ JJs post ] sounds like a pp to me, because it runs normal most of the time, & other times it happens after running good all day.
Sal
Tohsgib posted 08-17-2010 11:42 AM ET (US)
EVERY powerpack I have blown happened while sitting. Obviously that is incorrect and it probably blew the first rotation from the starter. You are sitting there going....it ran fine yesterday!!!
brisboats posted 08-18-2010 06:58 PM ET (US)
My old 1986 Wahoo 16.2 limited would do 46.1 mph turning a 13 x 19 OMC sst prop with a well tuned 1986 56.1 cu. inch OMC 70 hp. Something is definitely wrong here but I would probably start with the fuel system after the compression test.
Powerpacks are expensive and not returnable, best to start with the simple stuff first. Pull the airbox and make sure the throttle plates are horizontal at wide open throttle. Make sure the timing advance arm is also moving fully forward against the stop. Get a spark tester and check spark at each cylinder, put in a new set of spark plugs too. I have had a few powerpacks and switchboxes go bad on me and it has always been poof, done, dead, last rights read. A cylinder dropping out may just be a coil.
Brian
brisboats posted 08-18-2010 07:06 PM ET (US)
Forgot to mention my 16.2 Wahoo! limited was later rigged with a 2003 40hp Johnson and still did 32mph. You are obviously not even getting one half the power out of this engine. If the motor is indeed running smoothly yet hard to start a leak down and compression test will tell all.
Brian

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Author	Topic: Non-Boston Whaler Boat with 70-HP
jjbrab	posted 08-10-2010 01:03 PM ET (US) This year I purchased a 15-foot WAHOO boat--identical to a Boston Whaler boat--with a Johnson 70-HP engine. The [non-Boston Whaler-boat] will only do about 24-MPH at wide open. I read early about propeller size here and inspected mine. The propeller almost touches the [anti-ventilation] plate. Could the propeller size affect performance that much? Do I have a more serious engine [malfunction]? The engine runs smooothly and the boat [reached hydroplane] easily, but [the maximum speed is] just not the speed I expected!
Sal DiMercurio	posted 08-10-2010 07:16 PM ET (US) How many rpms will she twist at wide open throttle? you gotta tell us the maximum rpms she turns. What size prop is on it the prop is stamped either on the outside of the hub, or inside the exhaust hole, such as 14 x 17 or 14 x 19 or 14 x 21. The rig should twist a 19 pitch s/s prop and get 42 - 46 mph. What year is the engine ? If the prop is a 14 x 19, that should be very close to right, and I would than expect the [Power Pack] to be bad, as [Power Pack] has a low speed mode that will allow you to only go about 25 mph and turn about 3500 rpms & the high speed mode will allow the engine to rev to near 6000 rpms with a 19p prop and low to mid 40s speed. When I first got my engine only ran on the low speed portion, and when I put a new [Power Pack] on her, she went to 6000 rpms and 42 - 43 mph. 1997 Johnson 70 hp. with 14 x 19 sst OMC prop.--Sal
jimh	posted 08-10-2010 08:37 PM ET (US) Propeller diameter, pitch, number of blades, and blade shape will all affect performance. Generally a propeller is described by giving the diameter in inches, the pitch in inches, the number of blades as an integer, and the general type of blades by various descriptors. It is unusual to define a propeller in terms of how closely the blades come to the anti-ventilation plate, so a description of that dimension does not convey a lot of information about the propeller.
jjbrab	posted 08-11-2010 10:23 AM ET (US) It's a 1994 engine. The propeller is 14 x 19. I need to go out and check the [engine speed] at [maximum throttle]. Thanks for the information. Not sure what a [Power Pack] [costs] but [buying a new Power Pack and replacing the existing Power Pack] might be a good place to start. I also had the problem where the engine will run all day just fine but if you shut it down and sit for a while till it is cool it has trouble restarting.
Tohsgib	posted 08-11-2010 12:08 PM ET (US) Have you done a compression test? If not you might be wasting your money. I would do compression check and if all looks pretty even, then clean carbs. Then check for spark if still bad.
Sal DiMercurio	posted 08-12-2010 09:55 AM ET (US) Nick is 100% right, the very first thing you do is a compression test or leak down. Those 3 cylinder engines have the tendancy to score the middle cylinder if run lean, but are by far the best engines "EVER" made by OMC. Sal
jimh	posted 08-14-2010 08:31 AM ET (US) I an not familiar with an OMC Power Pack where there are two modes of operation, one for high-speed and one for low-speed. A Power Pack is just a name for a capacitor discharge ignition system. Problems with an OMC Power Pack are fairly common. As electrical or electronic devices, they are not infallible, and it seems like too much heat--the bane of all electronics--can cause them to fail. If the engine running characteristics are being affected by the Power Pack, you typically see a rather abrupt change in the run characteristics. The electronics seem to either work normally, or abruptly change to work abnormally. I had a problem with the Power Pack on my V6 Evinrude engine which affected only one-cylinder. The problem would suddenly appear and then often just as quickly disappear. However, because of the cost of the Power Pack, about $300, before I replaced the Power Pack I went through a thorough process of eliminating all the other elements in the spark ignition circuit for the affected cylinder. It was only after I tested the spark plug, the spark plug wire, the coil, and all the connections by swapping components from one cylinder to another, that I decided the Power Pack was the culprit. In any case, a discussion in PERFORMANCE assumes the engine is running properly, and the topic of discussion is optimization of the performance by engine mounting adjustments, propeller selection, and other techniques. If you think your engine is not running normally, you should begin a new discussion in REPAIRS/MODS, and seek advice on how to repair the malfunction in your engine. Once you have the engine running properly, you can return to PERFORMANCE and seek advice on optimization of the boat, motor, and propeller.
jpgbu1	posted 08-16-2010 10:42 AM ET (US) I think the LOW RPM version they are talking about is the S.L.O.W. mode designed with overheating and low oil res in mind.is the engine alarm working? could be as simple as low oil reserve or something triggering that feature as well. PS don't use the internal tank on that boat with new E gas! it will = disaster.
Sal DiMercurio	posted 08-16-2010 09:06 PM ET (US) No, it' wasen't slow mode. Obviously it killed 1 of the 3 cylinders, which allowed the engine to start & run, but not get more than 3500 rpms. I ordered a new Power pac from Boat fix for 1o9.00 [ if I remember correctly ], installed it & 6000 rpms on the tac. Jim, your right, there is no high or low rpm on the power pac, it just goes lower when no juice is getting to 1 or more cylinders. Some engines still run, & others wont even pop if the power pac takes a hike. It [[ JJs post ] sounds like a pp to me, because it runs normal most of the time, & other times it happens after running good all day. Sal
Tohsgib	posted 08-17-2010 11:42 AM ET (US) EVERY powerpack I have blown happened while sitting. Obviously that is incorrect and it probably blew the first rotation from the starter. You are sitting there going....it ran fine yesterday!!!
brisboats	posted 08-18-2010 06:58 PM ET (US) My old 1986 Wahoo 16.2 limited would do 46.1 mph turning a 13 x 19 OMC sst prop with a well tuned 1986 56.1 cu. inch OMC 70 hp. Something is definitely wrong here but I would probably start with the fuel system after the compression test. Powerpacks are expensive and not returnable, best to start with the simple stuff first. Pull the airbox and make sure the throttle plates are horizontal at wide open throttle. Make sure the timing advance arm is also moving fully forward against the stop. Get a spark tester and check spark at each cylinder, put in a new set of spark plugs too. I have had a few powerpacks and switchboxes go bad on me and it has always been poof, done, dead, last rights read. A cylinder dropping out may just be a coil. Brian
brisboats	posted 08-18-2010 07:06 PM ET (US) Forgot to mention my 16.2 Wahoo! limited was later rigged with a 2003 40hp Johnson and still did 32mph. You are obviously not even getting one half the power out of this engine. If the motor is indeed running smoothly yet hard to start a leak down and compression test will tell all. Brian