ok what would you check next?

davidbrooks

So at the beginning of spring i was able to get up to 39mph and 44-4600 rpm.  Now i can barely hit 30mph and i am really struggling to get up on plane. At best i get to 4000 rpm. Seemed to do act the same with 1/4 tank of gas or full tank. I checked and i don't have any codes on the pcm and it is full power available.  I just did a tune up with plugs, wires, rotor and cap. The old plugs looked pretty uniform. I have a 2003 342 with Merc 350 engines with 450 hrs on them.  
I felt a little bit of growth on the bottom but not too bad.  I would also think that it wouldn't have an affect of 10 mph like i am seeing.  Throttle cables?  If so what advice do you have on how they should be adjusted.  Compression?  I would of thought i would of seen something different on the plugs? Air leak?  Ugh.  You know you are frustrated when you start thinking about just buying new engines.  

youstolemybeer

Scrub the bottom and see

aero3113

Check your props also for growth, you'll be surprised what a couple of barnacles can rob you. 

Ransnan

Just scrubbed the bottom of my 342 yesterday,  probably 3 knots or so faster at 3400 rpm's

davidbrooks

Props are clean and sides are as far as i can reach.  Ordered a mask and snorkel today so i will have to look at the bottom next week.  This just seems like too much for barnacles.

craigswardmtb

That does seem like a lot.  I would check compression.  It seems awfully early in the season to have enough growth to slow you that much.  Unless you had the totally wrong kind of bottom paint and were therefore more susceptible to growth.  Our waters are still cold here in CT, so that seems to limit growth in my area too.  Not sure if its the same down your way.

Wildboating

For 2 years I have been trying to figure out the same thing.   I struggle to make 30 mph and 3800-4000 rpm wot.  If you figure it out please let me know....!!!!

davidbrooks

@Wildboating I was able to hit 39 mph in May so it is a pretty new development.  But this really bugs me.  What have you done to figure it out?

Dream_Inn

@davidbrooks - the barnacles are really bad this year, so don't count that one out.  They started very early.  My boat was in the water on the Rhode in February and was in/out a couple times and at 10 weeks had tons of little barnacles that slowed my boat almost to not get on plane.  This is with bottom paint, but after pressure washing I put some new bottom paint on.  I'm glad I'm on the lift now cause that was a real pain!

Wildboating

@davidbrooks. Everything!!  See the thread -smarty pants I really need your help.    I can't imaging what the last 1000 rpm will be like.  39 vs 29 mph..  my wot is what my cruise should be. 

davidbrooks

@Wildboating I have been following or trying to. Wow you have really been digging in and getting some amazing support. Last I heard you were going after possible air leaks. I am just getting started.

Wildboating

I shot the motor again with carb cleaner.   Never found any air leaks.  I have some more testing to do this week.

davidbrooks

@Wildboating So i went back through and reread your entire saga.  I changed out my plugs and wires. Bought the wrong cap and rotor so waiting on the new ones.  The plugs look like they are running a little lean to me.  They all looked the same. Early this spring i had an IAC sensor go out.  Ran a code and actually put the boat into guardian mode with only 78% power available.  I replaced the sensor with a new one but in my typical "Bull in a China shop" mentality i split the IAC gasket.  Glued it together with some gasket glue and put it back in.  Just ordered two new gaskets.  I was thinking.  When you do a block and swap out the attached parts that is a lot that can go wrong.  In my case i only messed with one thing so i am starting there.  If that doesn't help then i am looking at fuel.  I replaced the fuel water filter but not others.  After that......I am going to do the balance test.  Then hmmm.  Drink heavily and get used to going slow.

reneechris14

I did my injectors on the port motor a couple weeks ago that motor running very strong now.yesterday left for a long trip and the starboard motor has issues,thinking same problem.Did cap,rotor,plugs no help.when it started acting up the tact was bouncing 3200 3600 then she went down to 3000.going to do injectors and starboard motor.weird to have this issue with in 5 hours run time.2005 350mags 312 hours no codes on pcm

reneechris14

My plugs look like that too.all pretty unifrom

davidbrooks

Finished up tune up.  Plugs, wires, Cap, rotor and fuel filters.  Engines run and definitely start better.  Much stronger easier start.  I went out fishing yesterday and ran it pretty hard.  Not a big change in top end though. Weather started getting rough...cue Gilligans Island song.... and i was Hauling A#$ home and i noticed that my rpms would only go above 4100 when i trimmed up the outdrives.  I have been leaving my out drives alone as they have become problematic. One in particular seems to only want to go up.  Then i have to take it all the way up to trailer mode before it grudgingly  will go back down.  After that it seems to cooperate.  Sort of.  Well i trimmed up a little and after a while of full on WOT i got a solid tone. Shut down and go into neutral and it goes away.  Start back up and continue home.  I put on my Rinda and read it out and my rpm history had 0 time above 4500 rpm but history showed an Overspeed and temp alarm.  Overspeed at below 4500 rpm?  Is this right? Normal?  Temp may be due to a partial obstruction in the Y pipe.  I replaced flappers in the spring and i believe that the old ones were disintegrated.  So now i get to figure out how to clear the pipe.

davidbrooks

Just got back from an outing with a dive mask and a paint scraper.  If i didn't do it myself i would of never believed the difference.  The barnacles were not all that bad.  They were only on the back 6-8 feet of the hull, few on the flat surfaces of the outdrives and a bunch on the trim tabs.  But what a difference. Boat jumped up on plane, only needed 3/4 throttle to keep it at 30 mph and i could keep going faster if i wanted to.  To everyone that said scrape the bottom.  Ding you gentlemen were spot on.  I will definitely not skip bottom painting again. 

Handymans342

David, I had everything painted on my boat. Put in Solomon's slip on April 15. By May 30th, the props were totally covered with barnacles. 

Liberty44140

Really glad to see this outcome David, great that it was simple!

Dream_Inn

Glad to he's it David. As I said, the barnacles are the worst this year.