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Author Topic:   Lost Speed

anthonylisske posted 05-05-2006 12:44 PM ET (US)
I have a 2004 Yamaha 225-HP Vmax on a 1973 OUTRAGE 21. When I dropped her in the water last year (light load for shakedown run) I got 61-MPH (GPS SOG) on a greasy calm day with a 21-inch prop at about 5,800-RPM. Brand new sanded, epoxied, and bottom painted bottom. Brand new Prop.
After I loaded her up with gear etc, she would get around 58 MPH (GPS SOG)at 5800 rpm WOT
I had her in Key west over the winter, and now she is back up and I am running her in LI Sound. I am only getting 50 MPH at 4900-5000 rpm WOT on a similar greasy calm day.
The prop has a few scrathces along the blade egdes. (these are light scratches, not dings, from slow idle in shallow sand bar) I know that the prop will cost me a few MPH, But 10MPH?
The bottom is clean, the engine has 75 hours on it, and the boat load is approx same.
any suggestions? I figured maybe the throttle cable stretched a little? I am going to change the plugs. Runs fine otherwise. Help would be appreciated.
Anthony
Tom W Clark posted 05-05-2006 12:52 PM ET (US)
Anthony,
I do not know what the problem is, but it is not the prop. 58 MPH at 5800 RPM is exactly the same propeller slip as 50 MPH at 5000 RPM and this is exactly what I would expect a 21" prop to with that motor (1 MPH for every 100 RPM)
I thin we can also rule out some unexplained and extraordinary weight gain as this would show up in a higher propeller slip number.
The motor does not seem to be producing the WOT power that it did for some reason.
rsess1 posted 05-05-2006 01:31 PM ET (US)
Try changing the spark plugs. Sounds like your down one cyliner.
VI Jamie 22 posted 05-05-2006 06:33 PM ET (US)
After the plug change and test run. If no improvement, pull the plugs and look at them carefully. If one is still clean, you found your problem. Also, check to make sure you have full throttle, with the engine stopped and the hammer down. good luck.
jimh posted 05-06-2006 06:58 AM ET (US)
I have analyzed your data using the Speed Calculator at
http://continuouswave.com/cgi-bin/crouchcalc.pl
My analysis is as follows:
Using your data of
HP = 225-HP
MPH = 61
and assuming a hull factor of about 200, I computed the weight of your boat to be
LBS = 2,400
Then, using the new speed of 50-MPH, I computed the new horsepower to be
HP = 151
It appears your engine has lost a significant amount of power.
bsmotril posted 05-08-2006 08:24 AM ET (US)
A loss of a cylinder on a V6 motor will generally give you a 1200-1800 rpm drop at WOT. First thing I would do would be pull the spark plugs and take a look at them. It is likely one will look a bit different than the other five, having more fouling. That is the cylinder that is not firing. From there, start troubleshooting either the ignition modules, or the carb for that cylinder. BillS
anthonylisske posted 05-08-2006 09:26 AM ET (US)
All,
Thanks for the help.
I was out this sunday and changed the spark plugs. As suggested, my number 6 Cylinder was fouled. (I could tell be the amount of build up.) The build up was not too severe, but right after I changed the plugs she ran tight and fast giving me 58 @ 5800rpm.
I have to admit, I think it was for two reasons:
First, I had never changed the plugs from the break in period with the 50/1 ratio. (Normal for my engine is 100/1) I had done all the recommended maintenance with that exception. (Plugs sitting in tool box)
Secondly, my parents had been using my boat in Key West and they are the "Idle Around" types and probably never opened it up in the three weeks they used it. I think the engine needs to "breathe" every once in a while to prevent fouling.
In short, thanks for all the advice. When I posted, I was a little concerned, but after the responses, I felt alot more confident that It was nothing too serious.
Anthony

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Author	Topic: Lost Speed
anthonylisske	posted 05-05-2006 12:44 PM ET (US) I have a 2004 Yamaha 225-HP Vmax on a 1973 OUTRAGE 21. When I dropped her in the water last year (light load for shakedown run) I got 61-MPH (GPS SOG) on a greasy calm day with a 21-inch prop at about 5,800-RPM. Brand new sanded, epoxied, and bottom painted bottom. Brand new Prop. After I loaded her up with gear etc, she would get around 58 MPH (GPS SOG)at 5800 rpm WOT I had her in Key west over the winter, and now she is back up and I am running her in LI Sound. I am only getting 50 MPH at 4900-5000 rpm WOT on a similar greasy calm day. The prop has a few scrathces along the blade egdes. (these are light scratches, not dings, from slow idle in shallow sand bar) I know that the prop will cost me a few MPH, But 10MPH? The bottom is clean, the engine has 75 hours on it, and the boat load is approx same. any suggestions? I figured maybe the throttle cable stretched a little? I am going to change the plugs. Runs fine otherwise. Help would be appreciated. Anthony
Tom W Clark	posted 05-05-2006 12:52 PM ET (US) Anthony, I do not know what the problem is, but it is not the prop. 58 MPH at 5800 RPM is exactly the same propeller slip as 50 MPH at 5000 RPM and this is exactly what I would expect a 21" prop to with that motor (1 MPH for every 100 RPM) I thin we can also rule out some unexplained and extraordinary weight gain as this would show up in a higher propeller slip number. The motor does not seem to be producing the WOT power that it did for some reason.
rsess1	posted 05-05-2006 01:31 PM ET (US) Try changing the spark plugs. Sounds like your down one cyliner.
VI Jamie 22	posted 05-05-2006 06:33 PM ET (US) After the plug change and test run. If no improvement, pull the plugs and look at them carefully. If one is still clean, you found your problem. Also, check to make sure you have full throttle, with the engine stopped and the hammer down. good luck.
jimh	posted 05-06-2006 06:58 AM ET (US) I have analyzed your data using the Speed Calculator at http://continuouswave.com/cgi-bin/crouchcalc.pl My analysis is as follows: Using your data of HP = 225-HP MPH = 61 and assuming a hull factor of about 200, I computed the weight of your boat to be LBS = 2,400 Then, using the new speed of 50-MPH, I computed the new horsepower to be HP = 151 It appears your engine has lost a significant amount of power.
bsmotril	posted 05-08-2006 08:24 AM ET (US) A loss of a cylinder on a V6 motor will generally give you a 1200-1800 rpm drop at WOT. First thing I would do would be pull the spark plugs and take a look at them. It is likely one will look a bit different than the other five, having more fouling. That is the cylinder that is not firing. From there, start troubleshooting either the ignition modules, or the carb for that cylinder. BillS
anthonylisske	posted 05-08-2006 09:26 AM ET (US) All, Thanks for the help. I was out this sunday and changed the spark plugs. As suggested, my number 6 Cylinder was fouled. (I could tell be the amount of build up.) The build up was not too severe, but right after I changed the plugs she ran tight and fast giving me 58 @ 5800rpm. I have to admit, I think it was for two reasons: First, I had never changed the plugs from the break in period with the 50/1 ratio. (Normal for my engine is 100/1) I had done all the recommended maintenance with that exception. (Plugs sitting in tool box) Secondly, my parents had been using my boat in Key West and they are the "Idle Around" types and probably never opened it up in the three weeks they used it. I think the engine needs to "breathe" every once in a while to prevent fouling. In short, thanks for all the advice. When I posted, I was a little concerned, but after the responses, I felt alot more confident that It was nothing too serious. Anthony