Engine struggles

bazza

280 300hp vp 2010
engine sweet at low speed when trying to get on plane fades back to low revs for a short time changed plugs distributor cap and rotor with new leads and new fuel filter.
I have found the exhaust blocked at the prop but ok above so I think this is the problem boat in water most of the time so animal groth any tips for clearing whilst still in water?
any suggestions gratefully accepted.
thanks Bazza

212rowboat

there is nothing there but a steel passage that leads to a boot at the hinge, and then again a steel passage to the Y.  

get a coat hanger and make a hook on the end, and have at it.  

the boot, aka the accordion exhaust bellow, ought to be swapped out for a 'tube' instead... the premise is the exhaust is routed through the prop at idle and below plane, but up on step (plane)?  She breathes, and sounds good too. 

exhaust bellows/boots should be done drive off and on the hard. 

bazza

Thanks for help rowboat will give it a go
bazza

bazza

Rowboat a thought would you think this blockage could cause the power problem?
thanks Bazza

212rowboat

without doubt... the exhaust needs to breathe.  just like an air intake restriction, an exhaust restriction will limit performance, and just like intake, it'll happen when it reaches the point it can't pull or push anymore in/out.  

there is a term that's tossed around that isn't accurate- back pressure.  some will say that some 'some' back pressure is good, but that isn't true.  'scavenging' is good, and it is related to exhaust restriction too, but it isn't back pressure.  scavenging is the conveying of exhaust pulses down the path, one drawing the other behind it by convection of heat... a bend of proper angle/diameter heats up as hot as the exhaust pulse itself and pulls the pulse toward it... that is good so long as the path beyond it is less restrictive than the pipe in front (or another hot spot introduced further down the path), otherwise you get a 'wall' of denser (cooler) air the next pulse has to push through- creating back pressure.  

low in RPM range 'back pressure' SEEMS to assist in building RPM's faster- as the exhaust stroke doesn't purge the cylinder completely due to resisting pressure. the engine sucks in fresh air in the intake valve and it encounters the spent air that reenters the cylinder before the exhaust valve closes, and it makes like thunder as the cooler intake air is rapidly warmed- expanding but not to the point of detonation- it presses the piston downward in an 'assist' that allows greater RPM's to be achieved faster.   that 'air', though, is already depleted of o2, so the 'burn' isn't near as stout as it should/could be, and it doesn't need near the fuel as the injection is providing... so... you're losing performance and wasting fuel. 

properly designed- less restrictive intake and exhaust- an engine 'seemingly' revs with more effort- extending the rate/timing of building RPM's- but each of those strokes matters more as they're generating more power.  

builders 'play' with this concept to get what they want from an engine.  an engine with a camshaft profile intended for low end and mid range power curve isn't impacted as much as a profile intended for high end performance- it builds the power and has the power to move the prior exhaust pulse out of the way- the high end engine will labor more to get to the high end than the low end profile as it isn't designed to touch into the power range until later. 

Marine engines touch into the power band early and provide it up until the valve trains design of 5500 max, starting to fall off after 5k rpm... fortunately the exhaust path on these engines is short, and there is some argument that washing through the prop at speed actually creates a vacuum for the pulses to escape far beyond what is possible otherwise...

your exhaust being even partially blocked is costing you power... 

aero3113

You can check your exhaust flappers also. There's a chance they broke off and are obstructing the exhaust.

Liberty44140

Easy to check the flappers with a hair dryer, check my thread from March on how to do it 

bazza

I can not thank you all enough the knowledge and will to pass on that knowledge is beyond what could ever be expected .
 I will pull the boat out in the next week or two look at it myself or maybe a marine mechanic.
 I will post the results 
thank you Bazza

reneechris14

I used an endoscope to check mine. This a mercuiser.
This could help to see if there is obstruction.

bazza

Good idea to check with wifi scope I do have one, I assume that a blockage in the prop exhaust is something that happens to many outdrives? I must say I have never heard about this happening before after years of boating, stories about this would be very helpful and would assist me in my hunt for the obstruction.
Thanks Bazza

aero3113

bazza said:

Good idea to check with wifi scope I do have one, I assume that a blockage in the prop exhaust is something that happens to many outdrives? I must say I have never heard about this happening before after years of boating, stories about this would be very helpful and would assist me in my hunt for the obstruction.
Thanks Bazza

Yes, has happened to me. Do an internet search and you will see other posts about it.

bazza

I have done internet search and did not find exactly what I was looking for ,my fault I am sure. could you please confirm that the exhaust gases and water should be coming out of both the centre of duo props and exhaust flat tube just above props on my DPS-A duo prop VP 300 HP V8 2010. before I take it out the water.
Many thanks 
Bazza

bazza

It looks like I was wrong about a blocked exhaust, out of water and all was perfectly clear, so back to original suspicions FUEL, I have had some bad fuel in the past month water and muck in it stalled the engine a few times while I was out on the water, worked it through to get back to marina changed fuel filter/ water separator lots of water in filter, two weeks boat standing in water used it again and the present fault occurred, changed filter again also while I was at it I changed distributor cap rotor plugs and leads, and checked outdrive as I explained, so back to square one, the high pressure fuel pump is a lot noisier than it used to be I checked running fuel rail pressure it was steady at around 50 psi upon first putting on the ignition it runs up to 60 psi the shuts off, I have eliminated fuel tank pick up strainer its ok, I am considering ordering up a high pressure fuel pump kit, engine 300 hp v8 VP 2010 raw water cooling.
Advise most gratefully accepted.
Thanks Bazza.