Not sure if it's running right, but the boat is slow!

[Mtarante]

Hi all, new to the forum, new to this boat...
2002 15ft sylvan aluminum side console with a same year 25hp mercury 2 stroke 2 cylinder.
Got the boat this spring, went through it all pretty well, new batteries etc, but the motor wouldn't fire.
Rebuilt the carb and it started up with the muffs on it, took it out to the lake and it fires right up, but isn't idling great (have to give it a little gas) but am pretty sure the low speed idle is a bit lean.
I've never gotten this boat to go faster than 14 mph (indicated by the depth finder), gonna try the portable gps next time I go out. That was just me and a fuel tank, but the boat has 3 chairs and decks, 2 batteries, etc.
To make sure the motor is running to spec I installed a tach, and am reading 5000 rpm at WOT.
My question seems to be is it capable of moving faster? Seems to be from what I read it should go at least 20-25, the max rating is 40hp.
Motor seems to be kind of "wimpy" but is running smooth, both plugs were changed and when I checked them, they were both light brown and seem to be firing well.
Is there a high speed mixture setting for this carb? Where is it?
Thanks for any help!
MT

 

[flyingscott]

I believe you should be closer to 6000 rpm with that motor. Is this a tiller or remote model? I would look to make sure the throttle is opening all the way. There is only one adjustment on that carb and that is for the low speed. When you rebuilt the carb did you get a full gasket set with the primer and fuel pump diaphragms? Did you check to make sure the check ball in the primer is seated and not jammed in the spring? What is the compression on the motor?

 

[Mtarante]

I believe you should be closer to 6000 rpm with that motor. Is this a tiller or remote model? I would look to make sure the throttle is opening all the way. There is only one adjustment on that carb and that is for the low speed. When you rebuilt the carb did you get a full gasket set with the primer and fuel pump diaphragms? Did you check to make sure the check ball in the primer is seated and not jammed in the spring? What is the compression on the
motor?

Thanks for the quick reply.
It's a remote.
Good catch on the max rpm, that could get more performance out of the top end, maybe increase speed a bit, not sure where I got 5k for WOT, Likely google, but I'll check the throttle linkage tomorrow.

I got the full rebuild kit with the new fuel pump diaphragm and the primer, which seemed to be centered and springing no problem.
I have yet to check compression, mission for tomorrow!

MT

 

[Scott Danforth]

if you didnt check top WOT RPM with a tachometer, you havent a clue what RPM the motor is turning. my pretty good calibrated ear cant tell the difference of a motor spinning 4500 RPM or 5500 RPM..... so man invented the tachometer

 

[Mtarante]

if you didnt check top WOT RPM with a tachometer, you havent a clue what RPM the motor is turning.

Thanks for the reply, my original post said I installed a tach and it is indicating 5k at WOT, the issue is what it should be.

MT

 

[Paddichuck]

I agree with flyingscott - should rev mid-high 5000s at least. Are you running a factory prop? Overpitching could be an issue.

 

[Mtarante]

I agree with flyingscott - should rev mid-high 5000s at least. Are you running a factory prop? Overpitching could be an issue.

As far as I know it's the original prop

 

[flyingscott]

Check the compression and the link and sync before anything.

 

[Mtarante]

Check the compression and the link and sync before anything.

Link and sync? Not sure what this is.
I just checked the throttle opening it was not opening 100%, turned the adjuster screw to get it all the way open and it spun up to near 6k with the muffs on, heading down to the lake now to give it a rip on the water with fresh gas. Compression tester on order.
Thanks!
MT

 

[flyingscott]

Muffs mean nothing and that is bad for the motor. What did you adjust that needs to be link and synced get the manual.

 

[Mtarante]

Success!
Just took it out on the water, 20mph verified with an iPhone and portable GPS. The speed sensor in the fish finder was off by 5 mph at full speed.
Adjusting the throttle got me from an indicated 9 mph to an indicated 15 mph, corrected by gps to 20-21.

Idles well, but will not start after shutdown without advancing the throttle to give it some gas (in neutral), would that still be low speed mixture adjust?

I have the Canadian version of the 15-30 hp merc 2 strokes (found online) and see no procedure indicating link and sync, is there another term to search on?

Thanks again
MT

 

[Paddichuck]

20 mph still seems slow for a 15' aluminum with a 25hp, but only by a few mph;

I have a 14' Lund with a 1991 25hp Johnson that'll do 30mph with only me in it.

regarding Link and synch:
http://forums.iboats.com/forum/engi...boards/390826-what-is-the-link-sync-procedure

 

[Mtarante]

20 mph still seems slow for a 15' aluminum with a 25hp, but only by a few mph;

I have a 14' Lund with a 1991 25hp Johnson that'll do 30mph with only me in it.


regarding Link and synch:
http://forums.iboats.com/forum/engi...boards/390826-what-is-the-link-sync-procedure

Thanks, that is very helpful.
I'm thinking this particular boat may not go much faster, the amount of wood decking and bulkheads makes me think it's a bit heavy, but agree it should be at least 25 mph. Previous owner said it could do 18 mph with 2 people when new, but just a datapoint

 

[Paddichuck]

Yeah, I don't think 20mph indicates there is necessarily an issue, just would have expected a few more mph. Could be a combination of heavy boat, less than optimal prop, etc. Sounds like it's now running the same as for the original owner if he claims it did 18 mph with 2 people.