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Mercruiser Alpha One 5.0L in 2005 Crownline 206LS - SLOW PLANE Reduced Top End!

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bp316

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We have a (purchased new) 2005 Crownline 206LS with a Mercruiser 5.0L v8 Alpha One, 260HP engine. This boat has 36 hours on it. It's used only a few times a year and is otherwise out of the water, dry docked in our dock at Grand Lake, Ok. Each fall it is 'winterized' by a local marina and each spring it is 'dewinterized'. Oil is clean, new gas etc....

When I picked up the boat (brand new) in 2005 it easily reached 50mph but still had a slow plane time. EVERYTHING is stock, I do not know what the size and pitch the prop is (stock too). Fast forward to the last few years.... This summer it was barely able to reach 40mph, the time to plane is painfully long. In fact it takes about 15-20 seconds to pull an experienced skier out of the water. I have been boating my whole life and know how to trim properly to get the boat planed and to cruising speed.

I was going to consult the marina and put a power prop on it, however, with the 'new' top end I was afraid cruising speed would be impacted even more.

I'm at a loss, the boat's in mint condition, the engine is even still shiney! but it runs so slow. While running there is no misfires, no hesitation, it's just slow. Any thoughts, I've been reading your forum for a while and wanted to ask your opinion.

Other info: I can maintain around 30-32mph at 4000rpm. I seem to max out at 5200rpm

Engine serial: (I don't know 100% what I have, but I do have correct serials straight from dealer) 0w065927
Drive serial# 0w553149
transom serial # ow178930

Thanks in advance!
 
How old is the fuel? When did you last change the fuel filter? It may not be running correctly on all cylinders...dirty or fouled spark plugs or dirty injectors. See what the plugs look like and check for bright blue spark at each plug. Clean the spark arrestor.
 
If you are hitting 5200 rpm and the prop is in perfect condition and the prop hub is not spun, your propeller is under sized.

Also Check that your drive is able to tilt all the way down/in.
 
How much weight is in the boat? Look at the Coast Guard placard for the limit. If you are hauling over nourished passgrs. that could be why it won't plane. A 21' boat w/260 HP is about correct. What RPM does it reach before it gets on plane? High RPM at that time could mean the coupler is going out.
 
Docksidemarineservices said:
If you are hitting 5200 rpm and the prop is in perfect condition and the prop hub is not spun, your propeller is under sized.

Also Check that your drive is able to tilt all the way down/in.
Click to expand...


Thanks for the great replies folks!

The fuel was old, one year. However, I ran that out after adding fuel treatment in one afternoon then filled up with a fresh tank of 87 octane.

I will get with the marina for service records however We have instructed them to do all recommended mainentance and recommended intervals. I'll check all the plugs while I'm down there next.

The passengers are normal weight and we didn't exceed weight limits. We had 8 people max but when trying to pull a skier we'd have 3 people get on the SeaDoo leaving mainly women in the boat while I drove. We did test with as little as three people in the boat with no skier and there was only a marginal improvement.

We checked trim and prop, all functioning normally and prop is in good shape (maybe one tiny ding)

When I hit the throttle to plane with trim down I get to about 3500 rpm, once it hits around 20mph it starts to plane. When I trim up as it approaches 25mph the rpm increases and the boat almost slingshots up to 35mph. If I keep the throttle full open ill hit around 5200 rpm and 36-39mph.

Appreciate the help !
 
Also by trim up I mean proper trim, i forget the term, but it is not shooting water toward the surface :)
 
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Based upon your WOT of 5200 RPM and cruising at 4000 RPM I don't think you have a major problem. Give the engine a minor engine tuneup. As for slow planing I suggest that you get a 4 blade prop 1 pitch lower than what you currently are running.
 
Hi have you got any closer to solving the problem? I have a similar problem with a 2005 5.0L MP1 Brovo3 with 78hrs Serial No: 0W328030 Model No: 4M42037TT which came with the Rinker 232 Captivia as new. It was serviced at end of year, kept on a trailer. Unfortunately we have only had the weather to take it out twice this year in the last two months, all new fuel. It is a lumpy tick over and would stall when going from reverse to forward coming off the trailer and then seemed to take longer to get out of the hole and then going to Cowes week lost power. The Mercruiser main dealer mechanic is having problems sorting, its ticking over at 525-560 rev he says should be at 600 he thought it was the IAC valve as he didn't think it was controlling the airflow correctly to increase the revs but it didn't make a difference but it was chucking carbon out in the exhaust water. looking at plugs found they were black with carbon and didn't correspond to what should be in there. Carbonised plug etc indicates running rich which is either too much fuel or not enough air. He checked the rotor and cleaned it up fitted new plugs and leads checked with a timing light on each lead that there was a signal. Tried again still same new plugs covered with carbon, then he checked the fuel pressure found it went up to 90psi (which he had never seen before) he said should be around 32-38psi took the regulator of at the cooler 3 and found a ring of paint had come off the housing and was stuck across the regulator he removed that and it performed better the revs came up but the pressure was still gradually building up to around 50-55psi so he thinks the regulator part below is faulty. Typical best two weekends of the year and engine is playing up. I am waiting to see if he can get the part separately i see you can get it separately in US for around $90 so they should be able to get it over here.
 

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kj-GB said:
Hi have you got any closer to solving the problem? I have a similar problem with a 2005 5.0L MP1 Brovo3 with 78hrs Serial No: 0W328030 Model No: 4M42037TT which came with the Rinker 232 Captivia as new. It was serviced at end of year, kept on a trailer. Unfortunately we have only had the weather to take it out twice this year in the last two months, all new fuel. It is a lumpy tick over and would stall when going from reverse to forward coming off the trailer and then seemed to take longer to get out of the hole and then going to Cowes week lost power. The Mercruiser main dealer mechanic is having problems sorting, its ticking over at 525-560 rev he says should be at 600 he thought it was the IAC valve as he didn't think it was controlling the airflow correctly to increase the revs but it didn't make a difference but it was chucking carbon out in the exhaust water. looking at plugs found they were black with carbon and didn't correspond to what should be in there. Carbonised plug etc indicates running rich which is either too much fuel or not enough air. He checked the rotor and cleaned it up fitted new plugs and leads checked with a timing light on each lead that there was a signal. Tried again still same new plugs covered with carbon, then he checked the fuel pressure found it went up to 90psi (which he had never seen before) he said should be around 32-38psi took the regulator of at the cooler 3 and found a ring of paint had come off the housing and was stuck across the regulator he removed that and it performed better the revs came up but the pressure was still gradually building up to around 50-55psi so he thinks the regulator part below is faulty. Typical best two weekends of the year and engine is playing up. I am waiting to see if he can get the part separately i see you can get it separately in US for around $90 so they should be able to get it over here.
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The regulator needs to be changed. Sometimes you can clean them and sometimes you can't. If has never seen the pressure that high, it's time to find a more experienced mechanic.
 
You'll want to own two propellers for this size hull and for your usage....... one for tubing/skiing, and one for cruising.
To begin with....., 8 people is pushing it on a 20 foot hull, IMO.

I'll go with Chris on the fuel pressure......., and perhaps also have the ignition module checked in that it is delivering the correct progressive spark lead.
Substandard fuel pressure for an FI system, and substandard ignition advance will cause an engine to perform poorly.


As for the compression test, you'll want the throttle plate fully open, not fully down... and be sure to cycle each cylinder several times... perhaps four.


.
 
kj-GB said:
Hi have you got any closer to solving the problem?
Click to expand...


Nope, we're four hours away from the boat. I'm waiting on a call back / fax /email from the marina that services the boat. I requested full details of maintenance history so I can determine last replacement of fuel parts and plugs. I'm hoping they have the prop specs off the top of their head so I don't have to run down and find out.

I have noted everyone's recommendations and based on their past service I'm going to instruct them to go ahead and do a little over haul.

A friend of mine who does all his own engine work also wanted me to check the exhaust to make sure nothing is obstructed.

I love reading all the input from everyone, I wish I had a chance to run back down and try a few things out right away.
 
Guys thanks for the info, now I have to decide which regulator to change the one on the cooler 3 or the one on the fuel rail, as they are both joined by a rubber tube, then to find where i can get them from easily in the uk. In USA seems to be so much easier to locate and obtain.
 
bp316 said:
When I picked up the boat (brand new) in 2005 it easily reached 50mph but still had a slow plane time. This summer it was barely able to reach 40mph, the time to plane is painfully long.
Other info: I can maintain around 30-32mph at 4000rpm. I seem to max out at 5200rpm

Engine serial: (I don't know 100% what I have, but I do have correct serials straight from dealer) 0W065927 Model number 4M4103LTS = 5.0L ALPHA MPI 3" RISERS, Manufacture Date: 09/27/2004.


Thanks in advance!
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Need to ask, are you going by boat speedometer only? Maybe it's off due to being partially clogged up now. Do you by chance have a gps to confirm.

Also you may want to check fuel pressure just to confirm, it should read between 38-43 psi on average, the regulator specification on your gen 2 cool fuel system is 43 psi.


kj-GB said:
The Mercruiser main dealer mechanic is having problems sorting, its ticking over at 525-560 rev he says should be at 600 then he checked the fuel pressure found it went up to 90psi (which he had never seen before) he said should be around 32-38psi.

took the regulator of at the cooler 3 and found a ring of paint had come off the housing and was stuck across the regulator he removed that and it performed better the revs came up but the pressure was still gradually building up to around 50-55psi so he thinks the regulator part below is faulty.
Click to expand...
On the newer engines like yours Mercruiser has lowered the rpm down to 540 rpm even though the manual still says 600 rpm. Have your guy call merc to confirm.

The fuel pressure should read between 41-45 psi on average, the regulator specification on your gen 3 is 42 psi.

For paint inside the fuel module, you'll want to read this, http://clubsearay.com/showthread.php/51399-*Gen-3-Cool-Fuel-Module-Issue*/page5?highlight=paint+gen

kj-GB said:
Guys thanks for the info, now I have to decide which regulator to change the one on the cooler 3 or the one on the fuel rail, as they are both joined by a rubber tube,
Click to expand...
The regulator on the fuel rail is a dummy and does nothing on marine engines.
 
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