bout boat fed up

[dondi]

3.0 mercruiser io cranks with hose attached and water on. dont have to give any gas. get to the water will not crank hard to turn over. what the heck is wrong with this boat???????????????

 

[hystat]

I'll assume by "cranks", you mean it runs and idles.
If an engine is tired (low compression), it can be hard to start when the exhaust is 12" or so under water as it is when your boat is floating. Start with a compression test.

 

[dondi]

would the timing be an issue?

 

[Docksidemarineservices]

2nd on the compression test.

 

[buckz6319]

I 3rd the compression test
Low compression, and low exaust pressure go hand in hand

 

[RicardoMarine]

it can be hard to start when the exhaust is 12" or so under water

At 33 feet depth, we scuba divers increase the pressure against our body by 1 Atmosheric pressure.
1 Atmosheric pressure = 14.7 psi.
14.7 psi divided by 33 feet = 0.44545454545 psi at 12" depth.
That's less than 1/2 psi of back pressure against the exhaust system.

.

 

[kghost]

At 33 feet depth, we scuba divers increase the pressure against our body by 1 Atmosheric pressure.
1 Atmosheric pressure = 14.7 psi.
14.7 psi divided by 33 feet = 0.44545454545 psi at 12" depth.
That's less than 1/2 psi of back pressure against the exhaust system.

.

Really????????????

Is this what boat advice is becoming..........

Maybe Stick with the dished pistons, more will understand that, not many but more...........haha

 

[Docksidemarineservices]

An engine with a slightly leaking, sticking or burnt valve will fire easier on the trailer.

 

[RicardoMarine]

.................

Really????????????

Is this what boat advice is becoming..........
Well, let me ask you a fair question.
Do you believe that this engine will not turn over due to the exhaust exiting at 12" below the water surface?


Maybe Stick with the dished pistons, more will understand that, not many but more...........haha
I hate full dished pistons. You should know that by now!

Perhaps you should stick with ''Motors".


.

 

[buckz6319]

At 33 feet depth, we scuba divers increase the pressure against our body by 1 Atmosheric pressure.
1 Atmosheric pressure = 14.7 psi.
14.7 psi divided by 33 feet = 0.44545454545 psi at 12" depth.
That's less than 1/2 psi of back pressure against the exhaust system.

.

Interesting

 

[turk]

At 33 feet depth, we scuba divers increase the pressure against our body by 1 Atmosheric pressure.
1 Atmosheric pressure = 14.7 psi.
14.7 psi divided by 33 feet = 0.44545454545 psi at 12" depth.
That's less than 1/2 psi of back pressure against the exhaust system.

.

This is true, but PSI is the key....I guessing the exhaust output is at least 6X6 inches...probably bigger. with at least 36 square inches to cover that puts 18 additional pounds of back pressure, (verse on the trailer) more if the exhaust is bigger. I've had this probably many, MANY times....Check to make sure your fuel is good, check the batteries are fully charged (takes more energy to turn over the engine, even in 12" of water), check your idle rpms, if your idle is where it should be out of the water then you need to adjust (most rpm specs are for in-water) and your engine, when set properly, will idle at least 300 rpms HIGHER out of the water....and PLEASE check compression.

Do not underestimate the exhaust back pressure! This is why all tuning of the engine, like RPMS, should be done in a test tank or on the lake!)