| Author |
Message |
    
Justin Mankowski
New member
Username: justinman
Post Number: 1
Registered: 07-2009
| | Posted on Wednesday, July 22, 2009 - 03:54 pm: | 
|
My repair shop doesn't know why I'm, only getting 3100 RPMs at WOT on my 30 HP mariner. I understand I should be getting around 5500. We did eliminate a few issues while trying to figure out my poor perfomance issues. He rebuilt the carbs so I know that is clean. I have good compression and spark in both cylinders. Fuel does not seem to be the issue. The prop was pretty dinged up so I replaced that. The diameter an pitch seemed to be appropriate for that moter according to 3 sources. I replaced the impellor. All season I've been trying to increase the top end speed of my boat. I have a 15 foot sylvan that tops out at around 7.5 mph and will not plane with 2 guys and a full tank of gas. With a light load I can get it to 13 or 14 mph. When the shop hooked up the timing light it revealed the 3100 rpms. Does anyone have any other suggestion i could try to increase my speed. I was told I should easily get a top speed in the low 20 mph range with 2 guys.
[IMG]http://i575.photobucket.com/albums/ss197/justinman_photos/DSCN7370.jpg[/IMG]
[IMG]http://i575.photobucket.com/albums/ss197/justinman_photos/DSCN7371.jpg[/IMG]
[IMG]http://i575.photobucket.com/albums/ss197/justinman_photos/DSCN7374.jpg[/IMG] |
Fastjeff
Senior Member
Username: fastjeff
Post Number: 6310
Registered: 09-2003
| | Posted on Wednesday, July 22, 2009 - 04:15 pm: |
|
Close to 30 mph if all is well.
Jeff |
Justin Mankowski
New member
Username: justinman
Post Number: 2
Registered: 07-2009
| | Posted on Wednesday, July 22, 2009 - 05:05 pm: |
|
That fast!?!? That would be awesome! I'm kind of a novice when it comes to motors in general so please forgive me if I ask stupid questions.
The timing light indicated everything was in working order except fot he RPM's. He showed me the reading on the for the RPM and it said 6200...he said that # should be divided by the 2 cylinders. Is that accurate?
Nothing happens when I squeeze the bulb at WOT, this would eliminate a fuel pump/pressure issue, correct?
I saw something on a similar thread about cleaning the exhaust port...Would this be worth a shot?
Reducing the pitch on the prop won't get me to 5500, so I've eliminated that as a solution.
The plugs seem fouled to me (black and wet) but my shop said they were fine and firing good. Could this be a big issue?
I thought it was the throttle cable needed to be adjusted but the flap appears to be wide open when all the way forward.
What else do you think I can do to get the RPM's /speed up? |
Bob Caskey
Advanced Member
Username: bobbyc
Post Number: 429
Registered: 10-2007
| | Posted on Wednesday, July 22, 2009 - 06:53 pm: |
|
Why was prop pitch ruled out...not sure about how accurately your RPM reading is...what angle is the motor set at and is it the correct shaft length for your boat?? |
Graham Lamb
Senior Member
Username: galamb
Post Number: 5782
Registered: 05-2007
| | Posted on Wednesday, July 22, 2009 - 08:42 pm: |
|
Yes, I would expect near 30 with only 2 on board. I run a 15 horse on a 14 foot Princecraft (full console) and on a calm day can get a touch over 20 with the wife and myself on board.
Carbon in the exhaust is usually an issue with a smaller motor (6/8/9.9/15) because the hole in the plate that lets the exhaust pass is very small (3/4" upto 1 1/4" on the 15) - the 30 has a fair sized exhaust (horn) and it would be unlikely that you could restrict it enough to drop 2000 rpms. If it did I would expect it to backfire as well.
I does sound however, like it isn't breathing properly. When they pulled your carbs did they take a look at the reeds? or make mention of them. A couple of stuck petals could account for your issue. So could a bad crank bearing seal (letting some of your air/fuel/oil mix excape before it gets to the cylinder. |
Justin Mankowski
New member
Username: justinman
Post Number: 3
Registered: 07-2009
| | Posted on Thursday, July 23, 2009 - 10:19 am: |
|
I just don't know that going much flatter on the pitch will make up 2400 rpm., Its gotta be something else. The motor appears to be mounted in the right place, the cavitation plate is even with the hull.
I don't remember about them mentioning anything about the reeds. I'm not sure what that is? I'll check on the crank bearing seal if I can figure out where that is. I need to get the manual. Does anyone know if the seloc manuals on online anywhere?
Thanks for you feed back! |
Derek Schulze
Member
Username: biffidum
Post Number: 33
Registered: 06-2009
| | Posted on Thursday, July 23, 2009 - 08:21 pm: |
|
Have you checked the stator? I would expect the RPMs to be a bit less if it was the stator, but you never know. |
Joe Kilpatrick
Member
Username: jlkilpatrick
Post Number: 7
Registered: 08-2009
| | Posted on Wednesday, August 12, 2009 - 10:54 pm: |
|
Make sure your are checking the timing with a Inductive timing light like a Snap On. You dont divide anything in half it reads the pulses off the plug wire giveing you RPM. If the light is showing 6400 and the engine sounds like it is over reving your have too small a pitch or diameter or combination of the 2 causing the low top speed however conversly your hole shot power should be really good for the first 5 seconds |
