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175 HP Merc / fuel injection / slow hole shot

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dhackney

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My new rebuilt 175 is placed onto my old 150XR4 lower unit. I have tried several props. The engine seems to load up with fuel rather than kicking up the RPM . The result is very , very slow to come to plane. Once on plane, the engine performs great. Any ideas? Thanks, David
 
Is it getting up to max rpms (5600'ish rpms) with whatever prop you have tried? but the hole shot just sucks.
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The props you are trying were originally on the 150 and you have just swapped up to the 175 powerhead or they were props for the 175?

How did the boat run and with what motor before this swap?

Need a little more history/info here to try and figure if it's a rigging problem, prop problem, gear problem etc...
 
I replaced with 175 block because my mechanic had one and would be cheaper than trying to deal with the oil injection problems in the 150XR4. I first tried the old prop ( 26 turbo for small lower unit ) was a bad hole shot, then discovered a bad power pack, so , I replaced both power packs, still bad hole shot. I then tried a 26 four blade , some what better, however , I didn't like the over all performance, and still bad hole shot. I found a deal on a new 24 four blade trophy that was made for the lower unit. First was still stalling and loading up. I attributed this to double oil, so , I switched tanks. Once the motor was good and warm the problem seemed to improve. Went fishing this past week and still bad hole shot, loading up as if the injectors aren't burning all of the fuel. If , ? , and when it plans it runs like a scaled dog, and I love the prop performance. There is so much lift that I am a little paranoid of over 5000 PMs , however I have no doubt I could get 6000 if I could keep it in the water, Thanks, David
 
What boat do you have this mounted on?

That is alot of pitch to initially get turning especially if it's on a heavier hull. I run a 19 pitch 4 blade on my 140 horse pushing a total displacement weight of 2400 lbs (1500 pounds of Mahogany hull with 900'ish pounds of motor/rigging/gear/passengers).

Now, I'm topping out at about 40 mph, but my hole shot is more than adequate and the motor doesn't load up trying to turn the prop. With 24 or 26 pitch I bet I could stall the motor if I thumped on the throttle (on my rig).

The point I'm getting at here is you may be way over propped. If you could make 5600 rpm with a 20 or 21 pitch that would still give the top end mph's you are looking for but it would be a whole lot easier to turn at lower rpms = better hole shot.

More pitch ONLY equals more speed until you reach your wot range - over that the pitch is wasted - in fact it can cause your motor to load up and create carbon deposits = early grave for the motor.

Unless you are running a very light hull, it really sounds like you have "too much prop"...
 
This is an 18 foot Sprint Bass Boat. This rig accelerates extremely hot and fast once on plan. It will also maintain a good plane at 2000 RPMs, and maybe less. If you trim and throttle at the same time the rig will hit 55 MPH before you can back off. I have not yet topped out, however I think it will run over sixty with the lift that this prop is providing. I have not yet seen over about 5200 RPMs. Also, it seems to give a better hole shot sometimes once the motor is good and hot, but not always. Thanks, David
 
Well it sounds like it's running fine and you definitely don't have too much boat for the prop.

It's possible that it's simply your expectation of the hole shot is not what your getting - might be nothing wrong at all (if you follow what I'm saying here).

If you normally "take off" with the motor fully trimmed down, try bumping it up a bit - you may experience some prop slip but that might be what you need to improve the low end.

A (perfect hole shot) is created when:

the prop quickly spins up
the quick spinning causes some ventilation (a layer of air around the blades)
the water finally collapses back against the blades causing them to "bite" and propel the boat forward

If the prop is too big to turn quickly and you don't get ventilation your hole shot will suck
If there is too much hull drag, when the prop "bites" it may not have enough thrust to overcome the drag sufficiently to give you a good hole shot (dirty hull, soggy hull from water intrusion through gel coat, too much weight forward of the center of buoyancy).
 
Its your lower unit .. the small gearcase Xr series are 1:78 ratio and the 175 EFI are 1:87. Thats why you had to drop from your original prop size as the 150 was carbed.
 
The 24 four blade runs really good once it is on plane. One solution that has been offered is to have the injectors cleaned. Do you think that the 24 four blade trophy prop is appropriate for this set up? If cleaning the injectors does NOT help, what would you recommend? Thanks, David
 
galamb said:
Well it sounds like it's running fine and you definitely don't have too much boat for the prop.

It's possible that it's simply your expectation of the hole shot is not what your getting - might be nothing wrong at all (if you follow what I'm saying here).

If you normally "take off" with the motor fully trimmed down, try bumping it up a bit - you may experience some prop slip but that might be what you need to improve the low end.

A (perfect hole shot) is created when:

the prop quickly spins up
the quick spinning causes some ventilation (a layer of air around the blades)
the water finally collapses back against the blades causing them to "bite" and propel the boat forward

If the prop is too big to turn quickly and you don't get ventilation your hole shot will suck
If there is too much hull drag, when the prop "bites" it may not have enough thrust to overcome the drag sufficiently to give you a good hole shot (dirty hull, soggy hull from water intrusion through gel coat, too much weight forward of the center of buoyancy).
Click to expand...

Totally agree. My fastest hole shots are with the engine parallel to the line of the hull or farther out. Same way with my last Ranger pad hull. As Graham stated, it allows the rpms to build fast (HP = rpms x torque x a constant of proportionality), get a little blow out assisting in that process of getting the rpms up and as soon as it reengages, the engine has increased in rpms several hundred or so and the result is a catapult forward and with repeated breakouts and engagements....boat takes off like a rocket, my hole show is just a few seconds; around 3.

I know nothing about your engine, but I do know that when you lug a 2 stroke it doesn't like it and yours to me is showing just that since once you get up, get the load off the engine and allow it to "run" that it does.

My simplistic advice is to prop for your WOT that you want to run. I personally run my Mercs over the 5500 rating usually up to 6k and have for years. Never lost an engine doing that and they love it. The 1994 and 1997 sales brochures I have for the 150 and 175 engines in 2 or 2.5 liter are all rated for 5600 WOT upper limit. (My current 90 is 5500 rated but as I said anywhere between there and 6000 is where I run it and sometimes, for short intervals with a different prop, I will run over 6k.)

Then, if dissatisfied with the hole shot, take your prop to a prop shop and let them vent it for you or do it yourself; I did mine on my drill press....SS is hard, believe me. Amazing what a 5/16 hole in the right place under the blade tip will do for your hole shot. A 4 blade allows you to better use your thrust produced by the engine, but the engine has got to be able to spin the prop to produce the thrust and for a pad hull type boat, in the hole, propped for a sizzling WOT that is asking a lot.

My 2c
Mark
 
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