Outboard running weird

G

GilBry210

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Joined
Dec 8, 2006
RO Number
24489
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74
I have a 98 Yamaha 90hp 2 stroke, salt water edition. When I first get out on the water the motor will only go up to 2000 rpm in forward, regardless of how much throttle I give it. It will go all the way in neutral and reverse. After about 20 minutes of driving like this it sputters and surges a couple times and then runs like normal. For the rest of the day it will run like normal, even after being turned off for a while. But at the beginning of each day it goes through this process. This all began after I had a prop strike. It jarred the outboard pretty hard. I replaced the prop afterwards.

Here’s what I’ve done so far:

Cleaned the carbs completely
New fuel pump
New filters
New plugs
New Prime Start
New fuel lines and primer bulb
 
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I had a very similar problem with my 98 130hp 2 stroke...sometimes it would run great, other times I couldn't get it over 2000 under load for anything, but it would rev right up in neutral...

After trying all the same things you've done, I gave up and dropped it at a local mechanic. He found a failing check valve somewhere between the tank and the primer pump that was intermittently choking off the fuel.. I wish I had more detail for you, but that was what he told me, and it has been running great since.
 
What Brian is describing sounds like the check valve in the fuel pickup line at the tank. If you have a stand alone gas tank try connecting directly to the engine or primer bulb.
If it's the check valve, some are in the fitting on top of the tank and easily replaced, Others the pickup tube and fitting are one piece which can make it more difficult to replace if your tank access cover isn't directly above the pickup.
 
Worth a look, and not as expensive as some other alternatives. Thanks for sharing
 
Check valve? Are folks speaking of the anti-siphon valve? Same ball and spring action, different purpose. Yes, it's a likely location for clogs. Also check the screen at the bottom of the pickup tube.
 
Update:

Replaced the anti siphon valve at the pickup tube, the old one was bad. Took the boat out and it ran great initially and all day.

Took the boat out again today, same old issue again. Ran bogged down under load for about 20 minutes and then just all of a sudden the rpm’s increased and it ran normally the rest of the day.

I’m out of ideas…
 
I'm sitting here with my admirals baby whaler in the shop at the beach. Last trip down I used it for some night fishing and then later in the morning I was headed to the home dock when I lost power and it idled like it was on one cyl. I did the usual quick checks of fuel lines and connections, shut it down and restarted a few times, with no alarms and no improvement. Called my mechanic and we went over a few things finding nothing so he has the boat. Engine is a eTec 30 with low hours and a new fuel pump. I'm guessing a injector issue. One thing bothers me though after getting back to the dock and shutting down it sat for about 45 min. before I came back and loaded on the trailer. It did not register with me until later that upon restarting and idle onto the trailer I did not noticed the miss. Stupid of me not to see if the problem went away on cool down. If it did I'm thinking defective new fuel pump, overheating issue. I'm just glad I have a place I've dealt with for 40+ years and know they will take extra good care of me. I'll post resolution when I know what it is...
 
It’s not out of the realm of possibility that your new anti siphon valve failed already. New parts are junk, for the most part. Do you have a shut off on the fuel line? Maybe run it for a day or two with no valve, to see if that’s the problem? But only if you can shut off the fuel as soon as you shut down the motor ( and remember to do so!). — at your own risk to bypass this safety feature, of course!

What about the fuel in your tank? A few years ago I had a sailboat, and I could not get the darn motor to run for any length of time. Rebuilt the carb, replaced the fuel lines, anti siphon valve, pickup tube, fuel pump. Whatever I replaced, it would work for a few hours, then die again. Finally I picked up a 6 gallon fuel tank, like the one below. Short hose section and a primer bulb - ran 100% and never had another problem - but it was a sailboat, so six gallons was more than enough for a day of boating. I never did figure up out what the issue was - but after I sold the boat started to think maybe I had bad gas in the tank, or crud in the gas that kept clogging things up.

Sites-WestMarine-Site

West Marine
www.westmarine.com www.westmarine.com
 
I cycled the fuel through a series of filters for bad gas, water, debris, etc… everything was good. Inspection of the tank reveals good clean looking fuel, zero “junk”. What baffles me is how it consistently will run for about 20 minutes initially and then revs up and runs good the rest of the day. Regardless of turning it off for hours and even shutting the batteries off it still runs normally after this initial issue.
 
Is there a flexible hose somewhere under the bonnet between something and anything that could be heating up and collapsing?
 
Did you pull the pick-up tube in the fuel tank to check the screen 'stevenal' mentioned earlier? It's possible the screen may be getting blocked while sitting and the motion of the boat knocks it loose after a while.
 
Bob Ware said:
Did you pull the pick-up tube in the fuel tank to check the screen 'stevenal' mentioned earlier? It's possible the screen may be getting blocked while sitting and the motion of the boat knocks it loose after a while.
Click to expand...
the screen is good. Zero debris in the tank
 
boatbum said:
Is there a flexible hose somewhere under the bonnet between something and anything that could be heating up and collapsing?
Click to expand...
I don’t believe so. It wouldn’t make sense that it would then run better after 20 mins?
 
About the only thing you have not mentioned is your throttle linkage. Have you made sure it is operating fully when the problem is happening? I can not explain why it start working unless there is some kind of gunk that softens after using it awhile and then rehardens after sitting for a day or two. Sounds ridiculous to me, but hey you seem to have checked everything else. Or maybe the linkage slips , but also has a point where it catches and works normally...
 
I don't know anything about Yamahas but my old Johnson had a coil pack for each spark plug. Is it possible that one (or more) of the plugs is not firing until the engine heat up? Generally, it's the opposite, the coil fails when it heats up.
 
Bob Ware said:
I don't know anything about Yamahas but my old Johnson had a coil pack for each spark plug. Is it possible that one (or more) of the plugs is not firing until the engine heat up? Generally, it's the opposite, the coil fails when it heats up.
Click to expand...
After a test today I believe this might be the case. If I removed each plug one at a time the motor almost died other than the one that I believe is going bad. When I disconnected that one it ran the same.

Could the CDI be going bad? Or maybe just a faulty coil pack?
 
Update

I tested the coil packs by plugging them into each different output wire from the CDI. The #2 wire would not create a spark on any of the 3 coil packs with a spark plug tester. They all fired from #1 and #3 coming from the CDI. The #2 wire also had no readout on a continuity test with a multimeter, the other two had a very similar reading.

My guess is that the CDI is failing initially and then starting to send a signal after running for a few minutes.

Any thoughts?
 
Have you checked all your ground wires for clean/solid connections? Another thought, have you checked compression with the motor cold and hot?
This is why I don't like intermittent problems, regardless of the application. :)
 
Mine is fixed. What I thought was a fuel delivery problem turn out to be a overheat issue. Unsure why it did not get a warning alarm. Being it's a small boat and engine I don't have water pressure gauge or temp gauge. No room on the small console for much more than the tach. I may try and fit a water pressure gauge. I did look when the issue happened to make sure it was pumping water, but visual does not tell you everything.
 
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