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Outboard Power Loss, Why? #4201404 11/30/09 11:55 PM
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obsessedwithbass Offline OP
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Hello, I have a '91 Yamaha ProV 150 on a Ranger 351V. I've had this boat for about 2 years and have been happy. The hole shot to planing used to take about 3 to 6 seconds depending on extra weight (fuel, passengers).

After about a month ago, after a day of fishing, I was headed back to the ramp when I noticed my boat lose power during the hole shot right before planing. I went back to idle and tried to get up on plane again and again but this time it took about 40 seconds to get up on plane even full tilt down, like the RPM gets stuck at around 3500 and the boat nosed up about 35 to 40 degrees. Once on plane though I noticed I lost 10mph of top end speed and I can only get 4900 RPM WOT. It idles fine like always though.

So, I've checked spark on all 6 cylinders and they all jump a spark tester perfectly. Checked with a timing light and timing is good and advances normally. Replaced Spark plugs with proper gap. Fired it up with only one cylinder at a time and it fires up for all 6. Drained all carbs and nothing but clean fuel came out and the see throught fuel filter is perfeclty clean. Fuel is brand new. I looked into each carb with the boat on the trailer in the water at the ramp and when throttled up, high speed jets are all spraying the same amount of fuel. It doesn't sit around since I fish long and hard about every weekend so it always empties and gets filled with new fuel. Compression on all Cylinders is same as when I bought it, around 90psi. Checked Carb/throttle linkages and they're all normal. Prop spins effortlessly in neutral. I use only Yamalube 2-M and always keep oil tank no less than 2/3 empty. Help me, I'm Stumped! Can anyone think of anything else that I need to check. Thanks for all the helpful replies.

Re: Outboard Power Loss, Why? [Re: obsessedwithbass] #4201758 12/01/09 01:30 AM
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joho5 Offline
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could be a minor air problem...mine was doing close to the same thing and the restriction was in the primer bulb. Check all your hose fittings and connections, then if you havent changed your primer bulb in a while, I would do that for routine maintenance and then also to see if it fixes the problem.

compression good on all cylinders?

Re: Outboard Power Loss, Why? [Re: joho5] #4202501 12/01/09 05:27 AM
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Yup, I'd look at the fuel line first, too. If it's 2 years old, go ahead and replace the whole line, bulb, etc. It's cheap insurance anyway.

Drain the lower unit oil and pay attention to it as it drains, too. Look for anything unusual.

When I first started reading your post , the first thing I thought of was that it wasnt trimmed down all the way at the hole shot. But since it got on plane, and still wouldnt rev...that's not it.

Pull a plug and look at it. Tell us what you see. Any water droplets on it ? ( head gasket) Is it fuel fouled? ( power pack or coil maybe..)


Now, Donald...please pick John Bolton for your running mate.
Re: Outboard Power Loss, Why? [Re: OldFrog] #4202535 12/01/09 05:47 AM
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obsessedwithbass Offline OP
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Thanks for replying joho5 and Oldfrog. I'll change the fuel line and primer bulb since it helps to keep it new anyways. Compression in all cylinders is as it was when I bought the boat, around 90psi all around, and it ran great until this thing happened and it lost power. I change lower unit lube every 4 months just to be over careful and it's been normal. Prop spins effortlessly in neutral and idling around without opening the throttle is normal. Spark plugs look normal, no water just fuel/oil mixture and some carbon deposit. I've replaced spark plugs to no avail. I've checked timing and ignition coil spark and all are normal. I've even started the engine with a slight push on the throttle and just one spark plug wire on at a time and it runs with just one cylinder at a time. Head gasket is dry all around. I hope the fuel line and bulb replacement does the trick. I'll let y'all know if it works or not. Thanks again guys.

Re: Outboard Power Loss, Why? [Re: obsessedwithbass] #4202943 12/01/09 02:30 PM
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Mike Halfmann the boatmann Offline
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I would be looking at ignition coils. You need to OHM each one, cold and hot, and run an inductive timeing light on each sparkplug wire while running. I'll bet the farm, you have one not firing at a higher rpm.


mike halfmann
Re: Outboard Power Loss, Why? [Re: Mike Halfmann the boatmann] #4204660 12/01/09 10:40 PM
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PGR Mike Offline
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Compression check first...

Check the hub of your prop and make sure it isn't slipping.



Re: Outboard Power Loss, Why? [Re: PGR Mike] #4204761 12/01/09 10:57 PM
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obsessedwithbass Offline OP
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I've checked the compression and they are all around 90psi which was what it was when I checked them before I bought it 2 years ago. And with the motor dead, I put it in forward and the prop is locked in with the shaft and in neutral it spins freely. Normally I top off at 5600 RPM going about 59 to 60 mph on GPS Now when it can't get on plane, it's at about 3800 rpm and when it planes out I top off at 4800 RPM at 49 mph. I'm stumped!

Re: Outboard Power Loss, Why? [Re: obsessedwithbass] #4206578 12/02/09 03:14 PM
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James Tucker Offline
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OK, I ran into the same issue with a 90hp Yamaha.
The problem is either a pinhole in the fuel pump diaphram or ignition coil.
That is what my local boat mechanic told me. He suggested to get the carbs rebuilt while it was all apart anyways. Was gonna cost around $400 total to get it fixed.

Re: Outboard Power Loss, Why? [Re: James Tucker] #4206860 12/02/09 04:18 PM
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joho5 Offline
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about $300 of that is labor...thats why I do all my own work.

Re: Outboard Power Loss, Why? [Re: joho5] #4208749 12/03/09 12:34 AM
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I have the same year pro v150 and am still having a similar problem. It didn't want to plane out and when it did it would run about 10-15mph slower than it did before and wouldn't rev out. I replaced the fuel pumps first and it instantly helped out for a little while. It started doing the same thing again so rebuilt the carbs totally and it ran perfect. After a couple months went by it started acting up again when I am at full throttle it revs all the way out for a few min and then starts to lose rpm every 5-10 seconds like its starving for fuel. I have noticed though when I pump the primer ball when it starts loosing rpm's it runs strong. I replaced all my fuel lines,primer bulb,fuelfilters and it is still doing the same thing I personally think the fuel pumps are not keeping up and need to be replaced again and they are not that old at all. I would strongly suggest doing a carb job if it hasn't been done in a while and replacing the pumps. You can get a complete kit for that year motor for about 150.00 and it comes with all the seals,gaskets and new floats and pins. The pumps are about 90.00 for both.

Re: Outboard Power Loss, Why? [Re: Josh315] #4210282 12/03/09 02:38 PM
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You can replace the fuel pump diaphrams for about 10.00. I have changed so many that I have gotten to where I can change the diaphrams without removing the pump. I have also just in the last few months besides the fuel hose problems, started seeing problems with the anti-syphon valves sticking and problems with plastic fuel selector valves. I wonder what else ethynol is going to do? Had a 1995 200XRI Merc last week that the fuel supply hose from the vapor seperator to the electric pump was swelled up like twice its normall size. HUMM


The world will not be destroyed by those who do evil, but by those who watch them without doing anything. Remember what He has done and remember that He is not done yet!-- GOD IS GOOD
Re: Outboard Power Loss, Why? [Re: gary purdy] #4212309 12/04/09 12:10 AM
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Make sure your tank is ventilated properly. It may have a partial restriction over time not allowing as much air to enter the tank as fuel leaving the tank. When this happens it will typically idle fine, take off okay then quickly lose rpms to equalize air inflow with fuel outflow. If it is completely blocked it will run then die. After a few minutes it will start and do the same over again. Just a thought.

Re: Outboard Power Loss, Why? [Re: JohnnyRazorhead] #4212339 12/04/09 12:25 AM
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Josh315 Offline
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I think its the ethynol killing my pumps too.

Re: Outboard Power Loss, Why? [Re: Josh315] #4225879 12/07/09 10:09 PM
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obsessedwithbass Offline OP
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Ok. Changed the fuel line and bulb and re-checked filters and all are working fine and clean. Tested the motor and still weak. Checked all new spark plugs and the one in cylinder 3 is squeaky clean, no carbon, just fuel with slight blue tint. Cleaned carbon from all plugs and arranged them in different order and re-tested motor and cylinder 3 is still has no caron, just fuel/oil mixture so it's getting fuel. Moved coils around and cylinder 3 is still not combusting so it's not the coils. Tested with timing light and spark tester again and cylinder 3 had right timing and consistent spark. SOOOO, if I have good compression, fuel and air, spark, and timing, WHY ISN'T IT COMBUSTING!!!! I'm going bald pulling my hair out! Please help me, somebody!!

Re: Outboard Power Loss, Why? [Re: obsessedwithbass] #4227595 12/08/09 08:01 AM
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I had a similar problem with low power (not getting on plane and low RPM's) ended up being the clamp that holds my throttle cable to the side of my hotfoot. I'd punch it all the way to the floor but the outer sheath had moved so the cable wasn't pulling the linkage on the motor all the way. But you said #3 was not burning. Sometimes you get spark but not under a load. Switch #3 plug wire with another one and see if the #3 carbons up then. If it does, then it would be the plug wire.


Originally Posted By: JCBfromTHF
Water Dogs rock!!!!!

The water is always clearer, on the other side of the lake. ><>
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