Engine Tops out at 60% engagement of Throttle

CactusRose

2001 340 FV twin 340 mag mpi (300 hp) with Bravo III. Replaced port engine and since then hits WOT at about 60% throttle engagement. Have about 35 hrs on install. Shifter console and cables about 3 years old. New injectors installed with long block.  Can’t find any problem with linkage.  Any ideas?   Note starboard engine and control goes full throttle engagement at WOT.  Also props are in excellent shape and bottom clean. 

LaRea

When both motors are at WOT, are you hitting a normal speed?  So it's not a problem with power delivery, only with the position of the throttle controls?

CactusRose

No, port side lagging behind.  About 300-400 rpm lower. Also won’t sync unless I pull starboard back to match port position.  

aero3113

How old is your fuel filter? You might have an inline filter also. Is the distributor cap and rotor new? Spark plugs?

davidbrooks

I was gonna ask what did you move over from the old engine?

CactusRose

Fuel filter/separators replaced first. Spark plugs, injectors new. Fuel rail cleaned. Replacement engine was a new long block assembly.  Reused everything else. 

aero3113

It’s possible you have bad spark plug.
How about your spark plug wires?

CactusRose

Spark plugs wire and distributor all about 3 years old. Next time I am up at the marina will investigate condition.  Engine doesn’t appear to have any “misses” - runs smooth.  

CactusRose

Doing some research this morning and found an article on the TPS (throttle position sensor). Going to be testing to see if that could be contributing to my problem.  Any guidance appreciate. 

earl1z19

Did you check the travel of the throttle cables? Are they opening the TBI fully? They may have adjusted them at installation of the new motor.
When you say hits W.O.T what exactly are you referring to? The binnacle hits the forward stop or the motor wont rev any higher? What are the max RPM'S you are seeing?

CactusRose

Cable functioning properly. Shift handle all the way forward results in butterfly fully open. By WOT I mean the engine appears to be at “maximum” rpm at approximately 60% of full shift position.  Comparatively the starboard engine still has rpms and power to gain from 60% forward. As stated above rpms on port consistently 300-400 lower than starboard. Running 20p props so maximum is normally around 4600 (on starboard).  Getting around 4200 on port.  

aero3113

When you say distributor is 3 years old, do you mean cap and rotor? If yes, I would replace them and try again.

CactusRose

Yes.  I will add to the list.  Thanks. 

mattie

Twin 350 BIII Mags here. We had port motor stumble & multiple backfires couple weeks ago. Started acting up with no warning. Ran at about 60% power. Alarms going off. Wrecked a planned daytrip. Figured the worst had happened.

Motors idled fine, problem only appeared under load.

Had dealer techs come by & hook up laptop.
Long story short....2X caps, rotors & 16 sparkolators.......everything perfect. 

3 yrs is easily long enough for corrosion on the caps

davidbrooks

Dist cap, rotor, wires and even a slightly dirty fuel filter can easily pull an engine down 400rpm.  I am also wondering if any of the new fuel injectors is either clogged or just not working.

CactusRose

David Brooks that was one of my first thoughts. I did check to see that they were plugged in but didn’t have time to do anything else with them.  Not sure how to “test” them.  

YYZRC

Where are you getting your RPM numbers from? Analog gauges or digital?

CactusRose

Analog factory gauges.  Note had no issue with this before port engine was changed out. 

YYZRC

Might be prudent to swap the port/starboard connectors on the tach just to eliminate it as a source of error. 

davidbrooks

I heard a saying once "performance comes from paying attention to the little things. Not normally from just one big thing"

Black_Diamond

Check for a bad tach. 

CactusRose

Update, TPS checked out ok. Throttle cable readjusted. New plugs, distributor, and rotor. Both engines sync as they should up to and including WOT. 36 mph at about 4700 rpm.  Thanks for all the comments and help.