New Engine No Power

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KAM

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I fitted a new 28 Hp saildrive engine with folding prop to my 33ft 11,000 lbs fin keeler this season. Speed with the old 23 Hp was 7.5 knots. I can't get more than 5.5 Knots with the new engine. Can get 3700 revs out of gear but only 2400 in gear. Supplier says the 16 x 10 prop is the correct one for the boat. Have checked throtle and gear linkages. By passed the fuel system and run straight from a can. Checked underwater that the prop is unfolding. There is no fouling on prop or boat it's only been in water 4 months. Prop is anticlockwise which is correct for engine. Checked prop calc programs and the size seems to be about right. The old prop was 16 x 11. Engine starts easily, runs smoothly with no smoke. Beginning to think there may be an injection pump fault but don't see how this could be if I get 3700 out of gear. Boat is now back out of the water. Would appreciate any pointers as to what to try next particularly reccomendations on prop size from anyone with similar size boat and engine.
 
Is the gear box ratio the same as before or is it a new saildrive as well?

I have a 4.5t 34ft (so about 9,500lbs) a 2.5:1 reduction, 21hp and 16x13 2 blader and can cruise at 6.5kn with a shaft - if anything slightly over propped so yout prop sounds in the right range subject to ratio

Thought are there different forward and reverse ratios on your leg?
 
Is there black smoke from the exhaust under load at full power? This will have a large bearing on where to look next.
Just for starters, assuming no black smoke under load, check if the fuel is supplied to the engine at either the filters, lift pump or the injector pump via banjo bolts, check that the correct bolt has been fitted in the inlet lines as the banjo bolt on the return line may be fitted with a restrictor inside, which will greatly reduce the flow of fuel, but still pass enough to run the engine off load.
 
What revs are you doing at 6.5 knots compared with max revs out of gear.

No black smoke the exhaust is completely clean. On load and off. I have run the engine with the fuel line disconnected downstream of the engine mounted lift pump so the engine is just using the fuel in the filter bowl. It did not make any difference.
 
"Could a restriction in the leak off pipe back to the tank cause this problem."
Unlikely to be the problem.
It sounds like a fuel problem, your tests bypassing the system would have been my next step as well. When you ran from the remote fuel can you still had a couple of the banjo bolts at the engine mounted filter (is it plumbed in the right direction, no air leaks, and are you positive the element is clean) and the injection pump in the supply line- still worth a check here.
No pipes or hoses kinked or flattened? Is it possible to get a pressure gauge fitted at the injection pump, preferably at the bleed screw on the body?
What make of engine?
If it can make the max revs off load, its not so likely to be and injection pump problem, but anything is possible....
 
"Could a restriction in the leak off pipe back to the tank cause this problem. "

then again, Volvo (if it is one) put that restrictor in the return line for a reason, to keep the fuel pressure up in the body of the injection pump presumably, so maybe if its not restricted.....
 
I don't get full revs out of my 28hp engine in gear - as I kept the old sail drive and the gearing is a bit lower than a new sail drive.

It was explained to me that the engine was "held" by the prop - but the difference for me is that I'm upto about hull speed

Have you got new gearbox / saildrive as well ?
 
I changd the filter as a precaution. It seemed to be clean. Its a Beta Kubota. There are no banjo bolts it's just flexi pipes and clips on the filter. I may strip the pipework from the filter to the injection pump and look for foreign bodies. Problem is that the engine runs very steadily and smoothly.
 
It's a complete engine saildrive prop package. I supplied boat details and Beta provided what I hoped would be the correct combination. I think I'll physically check the gearbox ratios at the weekend.
 
OK I can't blame Volvo banjos this time!
Does the engine have a separate stop solenoid with a mechanical cable linkage to the inj pump, or it it internal to the injection pump? Adjustment on cable?
 
change of tack-
is it the original exhaust system, is there a valve on the transom that might not have opened completely after the new engine was fitted?
If it is the old flexy hose, it may have collapsed internally, maybe where it was pushed onto the new manifold, or any watertrap/ silencer.
This is going to keep me awake tonight!
 
When I re-engined three years ago with a Beta 13.5 hp I was assured by the Beta people that my old prop would be fine. The engine achieved full revs off-load but would not rev beyond 2000 under load. The engineer tried everything to try to find out what was causing the problem and eventually said the only thing left was the prop. He fitted a new prop and the engine behaved properly and has been perfect ever since.
 
I reckon its far more likely to be the prop than it is to be the Jap manufactured engine. And its easy to tell - just try another prop. A decent supplier would lend you one.
 
Its certainly keeping me awake! Its the original volvo box. It seems to be clear. There are no kinks in the flexi hose. I did not realise it could collapse internally. I'll give it a good internal check. The exhaust is well under water at cruising speed but this is the way it has always ben. I could try running with the exhaust disconnected. I dont mind the noise and fume but would it damage the engine.
 
My engines a bit bigger but I would be interested to know before and after speeds and prop sizes if you have that information.
 
I didn't take a note of before but after speed is approx. 5.5 knots @ 2600 rpm, flat sea. 3600 (full revs) gives hull speed of 6.5 but is noisy and wasteful. I have no information about size, pitch etc. Boat is Sadler 26.
 
KAM - the selection of props is not an exact science by any means but the design of engines is. The only thing that suggests it isnt a prop problem is the absence of smoke when under max load - this is what I would normally expect if the boat is over propped. Nevertheless, the prop is the first thing to eliminate simply because its simple to do. Incidentally, is there any way you can check the freedom of the drive train to rotate? On a shaft boat its easy just to turn the shaft by hand to make sure there isnt a serious alignment problem that is causing high levels of drag.

If it isnt the prop then the symptoms you describe suggest fuel starvation which could be anything from a collapsed / squashed pipe to blocked filters and a duff lift pump.
 
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