7.4 mpi Not enough speed

[Captain Jack Sparrow]

I have a 2000 Crownline 266 br with a 7.4 mpi L29 Bravo 3.

The engine was recently rebuilt and when I got the boat was unable to exceed 32 mph. After replacing a bad fuel injector, the boats top speed with one aboard, 1/2 tank of fuel was 42+mph.

The boat comes up on plane immediately and without the use of tabs, there is absolutely no hesitation and sounds like it’s just purring along.

My question is, should I be getting more top end? If it yes, what can I check out.

 

[tpenfield]

Tell us what the engine RPM is at WOT (42 mph). It should be in the 4200-4600 range.

 

[achris]

What revs are you getting (measured with a calibrated tacho, not the dash tacho) at full throttle? And what's the pitch and style is the propeller?

 

[Walt T]

Need rpm, Drive ratio and prop pitch

 

[aimlow]

is the timing advancing properly?

 

[Captain Jack Sparrow]

I’m sorry, I did not mention that my tachometer is broken. As one of my projects I am looking to replace the tachometer. (It looks like it’s burried under the dark).

 

[achris]

Dash tacho is no good for these checks. You need a calibrated tacho, like the one in an advanced timing light.

 

[Captain Jack Sparrow]

That’s out of my expertise so I will wait for the Spring and ask my mechanic to run that test.

Do you agree that that it seems slow for the size engine and boat?

 

[achris]

You replaced a fuel injector, running a simple revs check is well within your capabilities.

Just go to any car shop and ask for a timing light with a built in tacho. Then you hook the red and black leads of the timing light to the battery, clip the sensor lead to any spark plug lead (and as you're just looking for the revs, it doesn't have to be #1 lead) and read the revs from the display... It's that simple..

Chris...

 

[tpenfield]

That’s out of my expertise so I will wait for the Spring and ask my mechanic to run that test.

Do you agree that that it seems slow for the size engine and boat?

Does not seem overly low for a top speed, but the RPM will tell the story.

 

[Captain Jack Sparrow]

Thanks all-

Chris, I will do that

 

[QBhoy]

Big heavy boats those, but I’d think closer to 50 would maybe be possible. Sorry to ask, but you will be trimming out at wot ?

 

[Scott Danforth]

since boattest has that exact boat with that exact motor doing more than 46 MPH.... ya got a problem

 

[aimlow]

There's an easy way to check the accuracy of a tach. A fluorescent light plugged into true 60 cycle current will "strobe" an engine timing mark at exactly 1800 rpms and 3600 rpms.

 

[alldodge]

was 42+mph.
tachometer is broken.

If your using the boat speedometer then you may be going faster/slower then what its displaying. Need a smart phone or GPS reading.

You could probably get a advance timing light or tachometer loaner for a auto parts store

 

[thumpar]

Crownlines are heavy but most in the groups are getting those to around 50. Make sure you are measuring speed by GPS like AD mentioned.