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#4201404 - 11/30/09 05:55 PM Outboard Power Loss, Why?
obsessedwithbass Offline
Outdoorsman

Registered: 06/29/07
Posts: 26
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.

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#4201758 - 11/30/09 07:30 PM Re: Outboard Power Loss, Why? [Re: obsessedwithbass]
joho5 Offline
Extreme Angler

Registered: 07/03/08
Posts: 2419
Loc: Abbott, TX
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?

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#4202501 - 11/30/09 11:27 PM Re: Outboard Power Loss, Why? [Re: joho5]
OldFrog Offline
TFF Guru

Registered: 02/16/06
Posts: 46232
Loc: Probably not where you think
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..)
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#4202535 - 11/30/09 11:47 PM Re: Outboard Power Loss, Why? [Re: OldFrog]
obsessedwithbass Offline
Outdoorsman

Registered: 06/29/07
Posts: 26
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.

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#4202943 - 12/01/09 08:30 AM Re: Outboard Power Loss, Why? [Re: obsessedwithbass]
Mike Halfmann the boatmann Offline
TFF Team Angler

Registered: 11/08/05
Posts: 4061
Loc: San Marcos, Texas
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.
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#4204660 - 12/01/09 04:40 PM Re: Outboard Power Loss, Why? [Re: Mike Halfmann the boatmann]
Michael Bristow Offline
TFF Guru

Registered: 05/30/03
Posts: 12269
Loc: Denton, Tx, USA
Compression check first...

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


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#4204761 - 12/01/09 04:57 PM Re: Outboard Power Loss, Why? [Re: Michael Bristow]
obsessedwithbass Offline
Outdoorsman

Registered: 06/29/07
Posts: 26
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!

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#4206578 - 12/02/09 09:14 AM Re: Outboard Power Loss, Why? [Re: obsessedwithbass]
Fish Hauler's Guide Service Offline
TFF Team Angler

Registered: 02/04/08
Posts: 3953
Loc: Waco
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.
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#4206860 - 12/02/09 10:18 AM Re: Outboard Power Loss, Why? [Re: Fish Hauler's Guide Service]
joho5 Offline
Extreme Angler

Registered: 07/03/08
Posts: 2419
Loc: Abbott, TX
about $300 of that is labor...thats why I do all my own work.

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#4208749 - 12/02/09 06:34 PM Re: Outboard Power Loss, Why? [Re: joho5]
Josh315 Offline
Outdoorsman

Registered: 12/12/08
Posts: 76
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.
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#4210282 - 12/03/09 08:38 AM Re: Outboard Power Loss, Why? [Re: Josh315]
gary purdy Offline
TFF Celebrity

Registered: 05/24/03
Posts: 8674
Loc: Littlefield Tx & Lake A. H. US...
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
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#4212309 - 12/03/09 06:10 PM Re: Outboard Power Loss, Why? [Re: gary purdy]
JohnnyRazorhead Offline
Outdoorsman

Registered: 11/16/09
Posts: 25
Loc: Fort Scott, KS
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.

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#4212339 - 12/03/09 06:25 PM Re: Outboard Power Loss, Why? [Re: JohnnyRazorhead]
Josh315 Offline
Outdoorsman

Registered: 12/12/08
Posts: 76
I think its the ethynol killing my pumps too.
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#4225879 - 12/07/09 04:09 PM Re: Outboard Power Loss, Why? [Re: Josh315]
obsessedwithbass Offline
Outdoorsman

Registered: 06/29/07
Posts: 26
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!!

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#4227595 - 12/08/09 02:01 AM Re: Outboard Power Loss, Why? [Re: obsessedwithbass]
H20 Dawg Offline
Pro Angler

Registered: 03/06/09
Posts: 991
Loc: Kansas
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.
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#4227769 - 12/08/09 07:21 AM Re: Outboard Power Loss, Why? [Re: H20 Dawg]
gary purdy Offline
TFF Celebrity

Registered: 05/24/03
Posts: 8674
Loc: Littlefield Tx & Lake A. H. US...
Then your getting too much fuel to #3 via the carb or the manual fuel pump diaphram. You also are getting too much oil or not enough fuel because the plugs should`nt be getting carboned up that quick. Still hav`nt seen where you changed the manual fuel pump diaphrams.
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#4233444 - 12/09/09 03:19 PM Re: Outboard Power Loss, Why? [Re: gary purdy]
obsessedwithbass Offline
Outdoorsman

Registered: 06/29/07
Posts: 26
Okay, rains finally stopped. Checked both fuel pump diaphragms and they are both fine. They both look newish to me. I think the previous owner had them changed 2 years ago before I bought it along with all the fuel lines under the cowl because they all look new to me. Changed primer bulb and external fuel lines. When I described that the newly installed plugs had carbon on them it was after I ran the motor while fishing for 2 days and probably went through 25 gallons of fuel. That's why all 5 of the plugs firing had some carbon on them except of course the one in broblem cylinder 3. They weren't dirty like a well used plug, but one could tell they had been used. Anyway, while I had the fuel pumps out, I squeezed the primer bulb enought to check if fuel would leak out of the fule pump pulse holes and nothing did. So, I took her out to the lake this morning and she's still weak. I think there's a gremlin living in cylinder 3 of my motor!

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#4234023 - 12/09/09 05:43 PM Re: Outboard Power Loss, Why? [Re: Mike Halfmann the boatmann]
OldFrog Offline
TFF Guru

Registered: 02/16/06
Posts: 46232
Loc: Probably not where you think
Originally Posted By: Mike Halfmann the boatmann
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.


Did you do this?
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#4234289 - 12/09/09 07:00 PM Re: Outboard Power Loss, Why? [Re: OldFrog]
obsessedwithbass Offline
Outdoorsman

Registered: 06/29/07
Posts: 26
I didn't ohm the coils but I forgot to mention in my first post that I switched them around so each cylinder got a different coil, but cylinder 3 still has no combustion. I'm so frustrated, it hurts! Maybe I'm not holding my mouth correctly shocked

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#4235569 - 12/10/09 01:03 AM Re: Outboard Power Loss, Why? [Re: obsessedwithbass]
OldFrog Offline
TFF Guru

Registered: 02/16/06
Posts: 46232
Loc: Probably not where you think
Any water droplets on that plug, by chance?
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#4235903 - 12/10/09 07:22 AM Re: Outboard Power Loss, Why? [Re: OldFrog]
gary purdy Offline
TFF Celebrity

Registered: 05/24/03
Posts: 8674
Loc: Littlefield Tx & Lake A. H. US...
Did have a 1991 150 Yamy several years ago that after a lot of testing to try and find a running problem that #6 cylinder would drop intermittently. Another customers Yamy was in for service and after asking him for permission, I tryed his ICU on the problem motor and that fixed it. Only other thing I see from reading is that you hav`nt removed and inspected that carb. Good Luck
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#4236514 - 12/10/09 10:20 AM Re: Outboard Power Loss, Why? [Re: gary purdy]
Performance Outboards Offline
Pro Angler

Registered: 11/15/09
Posts: 770
Loc: Metro areas- Hou, TX
Hey give me a phone call today and let me see if I can help over the phone. 2813129856.
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Call & Arrange your powerhead re-build today! I can work with trade-ins & I'll give you more for your core! Need a boat mechanic to come to you? I'm a Mobile Marine Tech. also. Call & schedule today! 281-312-9856

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#4237496 - 12/10/09 02:30 PM Re: Outboard Power Loss, Why? [Re: Performance Outboards]
obsessedwithbass Offline
Outdoorsman

Registered: 06/29/07
Posts: 26
No water droplets, oldfrog, good idea though. Okay, the only thing now that seems obvious that I haven't looked at closely, without taking my motor appart, is the inside of the carb for mechanical failure. Cary and Gary might have the right idea. I might be getting too much fuel when I open up the throttle since idle and high rpms get their fuel from separate delivery systems. I might be getting okay fuel on idle but floods when I open the throttle. I'll take it off and look at it. I'll keep you guys posted on what I find.

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#4266733 - 12/18/09 02:44 PM Re: Outboard Power Loss, Why? [Re: obsessedwithbass]
obsessedwithbass Offline
Outdoorsman

Registered: 06/29/07
Posts: 26
Okay, found the problem. Cary was right about the cylinder flooding. Fixed it and now it runs like it used to!! What caused the flooding was maybe a manufacturing defect. The center of the brace that the float hinges on was set about 1 to 1.5 millimeters further backwards compared to the other one. That in itself didn't cause the problem. The carb bowl gasket has an extra useless quarter or half inch squares behind each side of the float hinge brace that just sticks out into the bowl (don't know if float hinge brace is what the actual term for it is). Maybe the extra piece is to hold the gasket piece for the high speed jet at the right position for assembly but it seems a bit too much since it partially caused the problem. Anyway those extra pieces, when it finally curls a little from soaking in gas combined with the more rearward setting of the foat hinge, was hitting the float enough so it couldn't float high enough to close the valve and gas was just flowing freely into the bowl. SO i cut enough of that peace so it wasn't in the way and tadah, it worked. Now the float closes the valve when enough gas is in the bowl. Thanks for all the suggestions! My boat runs like it should. I love this forum! It really gets you to some good people! Merry Christmas everyone!

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#4268490 - 12/18/09 11:52 PM Re: Outboard Power Loss, Why? [Re: obsessedwithbass]
OldFrog Offline
TFF Guru

Registered: 02/16/06
Posts: 46232
Loc: Probably not where you think
Glad you got her fixed !
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#4385996 - 01/20/10 10:18 AM Re: Outboard Power Loss, Why? [Re: OldFrog]
eyc0r (Corey C) Offline
Pro Angler

Registered: 09/27/09
Posts: 603
Loc: Tomball, TX
It seems like I have this same exact problem...

Cary and I will be talking soon! smile
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#4500007 - 02/16/10 02:45 PM Re: Outboard Power Loss, Why? [Re: eyc0r (Corey C)]
eyc0r (Corey C) Offline
Pro Angler

Registered: 09/27/09
Posts: 603
Loc: Tomball, TX
After it was all said and done, Cary got me moving and moving quickly!

If you have a boat problem in the (Northern) Houston area, make sure you call Cary at 281 312 9856. You won't be sorry.
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