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Old 09-28-2011, 11:54 AM   #1
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Default RPM's

I have a 2003 2700SCR with a 5.7 Merc and a Bravo 3. Every thing has been working fine this season until the last month. I cannot get the RPM's to go above 4000. I am now having trouble getting up on plan even using the trim tabs. I put gas treatment in every time I fill up. Plugs and wires were installed towards the end of last season. What should I look at?

On another issue, even when the RPM's were good if I have 6 people on the boat it takes time to get up on plan. A friend suggested changing the pitch of the props. Do you increase the pitch or decrease it?

I thank you all in advance for your help.
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Old 09-28-2011, 02:15 PM   #2
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Increasing pitch would lower max. RPM's. Decreasing pitch would increase max rpm's. However, before you start making changes, let's take a step back and look at what you're dealing with. You stated that "Every thing has been working fine this season until the last month".

What was the max. rpm prior to the beginning of last month? If it was much higher, and the pitch of the prop didn't change, then changing prop pitch to restore previous performance wouldn't really be the answer.

How does the bottom look? Is there growth? That will affect performace. How about the prop? Growth there will impact performance as well. Did you hit something? Does the prop look tweaked? Is there heavier than normal load on the boat?

Based on your description, changing the prop would be the last thing to consider.
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Old 09-28-2011, 09:36 PM   #3
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I agree about changing the prop. My thought on changing the prop was just overall better performance to help get up on plan not to fix the rpm problem. The beginning of August I could go up to 5000 rpm. I never kept it there. I would see it go to 5000 and I would back it off to 4500 to get up on plan. Once on plan I would reduce to around 3800. Once on plan I wold see the rpm's creeping up. We are not in salt water and there is zero growth on the bottom of the boat. It was painted in April. Zero growth on prop and props are in fine shape. Did not hit anything. I really notice the problem when we had 6 people on the boat and could not get up on plan. The next day the two of us took the boat out and had no problem getting up on plan but the rpm's would not go above 4000.
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Old 09-28-2011, 10:23 PM   #4
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I'd start with your fuel system.....if it was running fine..and nothing else had changed..by definition ..an outside factor is causing loss of rpms....so...check your fuel filter...replace if it's a spin on....
then start looking at your flame arrestor...is that blocked up???..then look at other things like plugs and distributor cap/rotor for any kind of corrosion....from there start checking plugs...do a compression test...is this a carbed engine??..if so it could be blocked up ports and jets....


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Old 09-29-2011, 01:37 PM   #5
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IMO, it will take a while to get a 2700 SCR up on plane with the 5.7 - just the nature of the beast, and even more so with 6 people and their gear aboard. My 2004 2400 SC3 with the fuel injected 300 HP 5.7 and B3, which is significantly lighter than your 2700, takes noteicably longer to get on plane with 6 people and their stuff.

Agree with S&S: if it was making 5k, and now it isn't, there's something amiss. I, too, think you need to get that sorted before considering chaning props. How many hours are on the engine? As noted above, check/replace the filters, clean/replace arrestor, check the engine timing. Plugs and wires were installed late last year - ensure none of the wires have come loose from the cap or the plugs. How about the distributor cap and rotor?

Dan
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Old 09-30-2011, 01:29 AM   #6
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start the engine at the dock. push the nutral button on the shifter and rev the motor up near 5000 for a a few seconds. see what the tack dose.

will make a rumble, but will not hurt the engine.

if you can pop over 4k, the its not your RPM limiter, which keeps you from going over your WOT.

drive it w/o six people.

i think you will find that you had a lot of load and the people were standing in the wrong place on the boat to get on plane. the engine was under a lot of load, and your boat was plowing in the water. put them in the middle near the driver or below.

lastly, water currents will give you funky performance, rpm will change if your trimmed the outdrive up to far and kinky the drive shaft.
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Old 10-10-2011, 12:52 PM   #7
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I did what you suggested and started the engine up at the slip. Let it warmed up and then put it in nutral and reved it up. It had no problem of going to over 5000. With two of us on the boat it got up on plan and the rpm's went up with no problem. I did notice that when I slowed down and cam off of plan then gave it gas that it was sluggish and had problems reving up again. I am pulling them boat for the winter in two weeks. I will have the plugs, wires, filter, everything replaced in the spring. Other then the normal winterizing Is there any other suggestions before I put it in next year????
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Old 10-13-2011, 12:51 AM   #8
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i think you will find a surpise under the boat when you pull it out of the water, like growth on the hull or a broken trim tab. when you tried to go back on plan i'm guessing you did not lower your tabs, or adjust your outdive trim.

the more empty the gas tank the more the boat will plow, becasue the boat is ligther by 8.lbs a gallon, opposed to having 800 lbs sitting on the keel to keep your hull cutting throw the water.

my advise is to leave the outdrive down all the way, because most people forget its up and use the prop as a fan.....

engine works don't fix it.....
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Old 10-13-2011, 01:44 PM   #9
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Do you normally run with 6 people? How about coolers with drinks and ice? Were they conveniently located out back on teh engine hatches. Was everyone sitting across the seating on the transom? I've had issues getting on plane under these conditions as well. It's the end of the season, I would not at all be surprised to see a layer of slime or growth on the hull as well. Even a thin layer of slime will cause a large amount of drag. Jsut a couple more thoughts.
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Old 10-14-2011, 02:22 AM   #10
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Is the fuel good? Are the fuel filters clean? Are any of the plugs damaged or fouled?

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