Boat won't go faster than 10 mph won't plane off.

Status
Not open for further replies.

Loganc

Recruit
Joined
Jun 12, 2013
Messages
4
I have a crown line 4.3 mercruiser. My boat won't go more than 10 mph and never plane off. Starts great doesn't miss at all. Just won't get to top speed or anywhere close. Has new plug wires and all. Any comments would be helpful.
 

callen369

Petty Officer 3rd Class
Joined
May 16, 2013
Messages
82
Re: Boat won't go faster than 10 mph won't plane off.

Has it set in water for along time? If so, check for marine growth, it can make a huge difference.

If this occured right after the plugs and wires, make sure all of them are connected properly. And verify you have them in correct position!That 4.3 will run on 3 cylinders/1 bank only, and not sound too bad, but will have no power. Yeah, I forgot to reconnect 1 bank after doing a compression check, took a bit to start, but ran. Would not plane out!
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Boat won't go faster than 10 mph won't plane off.

I have a crown line 4.3 mercruiser. My boat won't go more than 10 mph and never plane off. Starts great doesn't miss at all. Just won't get to top speed or anywhere close. Has new plug wires and all. Any comments would be helpful.

A little more information would be helpful...

Please Read This Before Posting A Question...-> How to Ask a Question....
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,465
Re: Boat won't go faster than 10 mph won't plane off.

I have a crown line 4.3 mercruiser. My boat won't go more than 10 mph and never plane off. Starts great doesn't miss at all. Just won't get to top speed or anywhere close. Has new plug wires and all. Any comments would be helpful.

Ayuh,.... Ya did leave the trailer in the parkin' lot, Right,..??
 

ktbarrentine

Lieutenant
Joined
Dec 12, 2011
Messages
1,296
Re: Boat won't go faster than 10 mph won't plane off.

Spun prop? What's your RPM at 10 MPH? (WOT?)
 

QC

Supreme Mariner
Joined
Mar 22, 2005
Messages
22,783
Re: Boat won't go faster than 10 mph won't plane off.

This is why we need more info ^^^^^. May be, but then he should report high RPM and no go. At this point we don't know if it reaches 1000 RPM or 10,000 :)
 

Loganc

Recruit
Joined
Jun 12, 2013
Messages
4
Re: Boat won't go faster than 10 mph won't plane off.

Never sat in water. It is backfiring a little bit. Warm up is around 5000 rpm but in forward only hits around 3000 wide open. Plug wires are new. Starts no problem and is running great not missing at all but still not going any speed.
 

Loganc

Recruit
Joined
Jun 12, 2013
Messages
4
Re: Boat won't go faster than 10 mph won't plane off.

Also seems to hit full power in reverse at about 5000 rpm or higher. Maybe carburetor ??
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
Re: Boat won't go faster than 10 mph won't plane off.

Props are not meant to be run in reverse with any efficiency. The RPM in neutral doesn't matter either since there is no load. Check your plug wires.
 

airshot

Rear Admiral
Joined
Jul 22, 2008
Messages
4,219
Re: Boat won't go faster than 10 mph won't plane off.

Hmmm...5000 in reverse, either you have a bad tach or you will soon be picking up parts to your engine. I would suggest you read carefully the "posting a question" sticky and give alot more info before any decisions can be made by the forum group.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Boat won't go faster than 10 mph won't plane off.

Also seems to hit full power in reverse at about 5000 rpm or higher. Maybe carburetor ??

Or timing advance, or compression.... Time to go back to basics....

Compression test, check timing (including advance), change fuel filters (including any in the carb)....

Chris........
 

ktbarrentine

Lieutenant
Joined
Dec 12, 2011
Messages
1,296
Re: Boat won't go faster than 10 mph won't plane off.

Never sat in water. It is backfiring a little bit. Warm up is around 5000 rpm but in forward only hits around 3000 wide open. Plug wires are new. Starts no problem and is running great not missing at all but still not going any speed.

Never in water??? Then how do you even get to 10 MPH, let alone on plane? 5000 warmup, then 3000 WOT? You are not making much sense at all. If not in water, then you are not getting to full power in reverse at 5000 (maybe full RPM by your reading), but you dont get "power" unless you are doing work...i.e., prop turning making speed.

Something about this whole thing is very fishy.

What is your prop diameter and pitch???
 

Loganc

Recruit
Joined
Jun 12, 2013
Messages
4
Re: Boat won't go faster than 10 mph won't plane off.

No I'm saying it doesn't stay in water. I pull it out every night. Never has set in water for long periods. No boat slips etc. Boat is at mechanic. Over my head. Thanks for all your help. Ill will post what the problem was when I know.
 

boatguy19

Petty Officer 3rd Class
Joined
Feb 15, 2004
Messages
94
Re: Boat won't go faster than 10 mph won't plane off.

5000 rpm is to high for that motor, should be no more than 46 to48 hundred rpm, it sounds like a carb problem. wouldnt hurt to check the gas filters.
 

Mariahshabah

Cadet
Joined
Jul 3, 2018
Messages
12
Did you ever find out what’s wrong. I have searched and searched and I am having the same problem with no answers. I’m lost.
 

GA_Boater

Honorary Moderator Emeritus
Joined
May 24, 2011
Messages
49,038
Did you ever find out what’s wrong. I have searched and searched and I am having the same problem with no answers. I’m lost.

Start a new thread. The OP started this one 5 years ago, replied 3 times and vamoosed. Don't expect an answer.

When you start the new thread, be more descriptive than the OP and tell us what you've done on her so far.

Closed.
 
Status
Not open for further replies.
Top