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Old 06-04-2014, 08:49 PM
laker taker2 laker taker2 is offline
 
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Default 2 stroke Outboard motor issue

First off thanks to anyone that reads this and attempts to offer advice.
I have 1995 75hp mercury 3 cyl, 75 hp 2 stroke. I installed new spark plugs, a new impeller kit and it's streaming water full blast, new fuel filter, new fuel line and primer bulb. The easy cheap obvious stuff to rule possibles as per symptoms below.
decent 2 stroke outboard mechanics are to find. So I fear if take it in here they will start it in a tank or put the muffs on and tell me it runs fine. Here is your bill.

I took it out on the lake tonight with the easy change stuff all new to rule possibilities. It starts and idles fine. But when I open it up it stumbles upto 2900 rpm and stays there.
I then let off and slowly eased in to the throttle and it took off like normal to max rpm. I ran up and down the lake for 15 mins at mid to full throttle. I turned it off waited a few mins then Started it and cranked it wide open, it got to full throttle again but stumbled 2 times briefly like it was starved for fuel but still went full throttle. Turned it off and then it did the 2900 rpm Max thing again. I decided a cold beer at home was better. If you were me without a decent mechanic nearby not going to rape me where would you start? It's an intermittent issue....... Hard I know.
I can only imagine if I take it in they change one part. I go the lake and same issue, come back and repeat ....... Am I crazy???
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  #2  
Old 06-04-2014, 09:03 PM
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Mulestalker Mulestalker is offline
 
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-Next time out,have a buddy pump the priming bulb at the same time as giving it full throttle,could be an air leak.
-Also could be plugged pilot jets, mains,pull carbs and make sure all orifices are clear and clean.
-old fuel..
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  #3  
Old 06-04-2014, 09:14 PM
rena0040 rena0040 is offline
 
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My guess is carb needs to be cleaned and redone. This is from my own experience of dealing with an old evinrude 2 stroke of my own.
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Old 06-04-2014, 09:21 PM
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Lund rebel Lund rebel is offline
 
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Seems to be sticky float not sure on the design of the carb tho,

Any smoke or other symptoms when this is happening, how old is the fuel in the boat?
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  #5  
Old 06-04-2014, 09:28 PM
laker taker2 laker taker2 is offline
 
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I had 25 litres of fuel from last year with stabilizer and added a full tank of new premium gas last week. The weird part is it feels like something limits it at 2900 rpm when it happens. When it doesn't it goes full speed like normal. If it was fuel or electric issues it should be the same all time wouldn't it???
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  #6  
Old 06-04-2014, 09:34 PM
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RavYak RavYak is offline
 
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There are only 4 things a motor needs to run.

Compression, air, fuel and spark.

You obviously have spark(although possibly isn't running on all cylinders) and probably don't have an issue with air. You can buy a compression tester at Canadian Tire for $30 and will hopefully be able to rule that out as well. Then you know it is just an issue with fuel, either you are losing fuel pressure from the tank or need to take the carb apart and clean it/tune it.
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Old 06-04-2014, 09:36 PM
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RavYak RavYak is offline
 
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Quote:
Originally Posted by laker taker2 View Post
I had 25 litres of fuel from last year with stabilizer and added a full tank of new premium gas last week. The weird part is it feels like something limits it at 2900 rpm when it happens. When it doesn't it goes full speed like normal. If it was fuel or electric issues it should be the same all time wouldn't it???
Hard to know without trying it. Only thing I can think of that could do something like that is if there is something broken/blocking the linkage. That shouldn't make it run rough though, just would max out at a low rpm and stay there.

Edit: When you put it away did you make sure to run the stabilized fuel through the motor for a bit or did you just add stabilizer to the tank? If you only added it to the tank then your carb is probably gummed up.
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Old 06-04-2014, 09:50 PM
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jungleboy jungleboy is offline
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I would be looking at CDI unit , That could cause intermittent spark on one cylinder which would explain the poor rpm at times. also weak fuel pump , it may be just not getting good fuel pressure consistently
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Old 06-05-2014, 07:02 AM
silver silver is offline
 
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I have an engine similar to yours and it has had a problem not that different than yours. When I have a problem with a seasonal engine, the first thing I look at is the fuel. I like to give it a good dose of a carb cleaner, my go to at this point is a product called Sea Foam. I would mix in a good shot of Sea Foam with about a gallon of gas and feed that to your engine, let it run for a few minutes. Every day or so, start it and run it for a minute. Keep this up for a week or so.

If you have a cooty in your fuel system, this may clean it out. Mix some more Sea Foam in to your next tank of fuel and take it for a run. This may work or it may not, doesn't cost much to try.

Regular gas has ethanol in it, it deteriorates over time. My plan at this point is to run premium gas in all my small engines, rototiller, chainsaw, lawnmower, and boat. It will be a bit more work and planning but I think it will be worth it.

Good luck
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Old 06-05-2014, 07:13 AM
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jungleboy jungleboy is offline
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Quote:
Originally Posted by silver View Post
I have an engine similar to yours and it has had a problem not that different than yours. When I have a problem with a seasonal engine, the first thing I look at is the fuel. I like to give it a good dose of a carb cleaner, my go to at this point is a product called Sea Foam. I would mix in a good shot of Sea Foam with about a gallon of gas and feed that to your engine, let it run for a few minutes. Every day or so, start it and run it for a minute. Keep this up for a week or so.

If you have a cooty in your fuel system, this may clean it out. Mix some more Sea Foam in to your next tank of fuel and take it for a run. This may work or it may not, doesn't cost much to try.

Regular gas has ethanol in it, it deteriorates over time. My plan at this point is to run premium gas in all my small engines, rototiller, chainsaw, lawnmower, and boat. It will be a bit more work and planning but I think it will be worth it.

Good luck
Yes Sea foam is a good product and has helped me too. As for gas deteriorating .. so true. I took apart the carb on my Champion generator as it would not start after sitting for the winter and it was incredibly bad. I have taken apart carbs on 60 yr old outboards that were cleaner than that. It was completely gummed up and the float bowl full of goo from fuel that had solidified. Today's gas is crap . You could have a partially gummed up carb from bad fuel and it won't clear itself on its own . So many possiblities but this may be the best and easiest thing to check first
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  #11  
Old 06-05-2014, 07:20 AM
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The Reel Deal The Reel Deal is offline
 
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I have the same issue with a johnson 5o ob.
I took it to BL for 2hours and spent $350, still does it.

I believe it to be an electrical issue since my symptoms are intermittent and all cylinders are running poor when it happens.
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  #12  
Old 06-05-2014, 07:33 AM
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jim summit jim summit is offline
 
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Confirm you have good gas supply and then go further. If the engine idles, it has decent compression, low compression engines are hard starting and don't idle well.

Dig into the carbs first, clean and synchronize. If it will idle and run up to max rpm, then it does sound like the mid range is a fuel issue.

I do occasionally run into one that has a faulty CDI or stator and it can cause the engine to miss fire at various rpm as well.

If you own an ohmeter, compare each coil to the next, then check the low and high rpm coils on the stator. Remove Blue and Blue/white wires from cdi and check for 5800-7000 Ohms. Remove Red and Red/white wire and check for 135-165 Ohms.
The Cdi can not be check with an Ohmmeter, and the trigger is rarely an issue.
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  #13  
Old 06-05-2014, 07:43 AM
kevinhits kevinhits is offline
 
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My 2 stroke was doing the same thing. it was one of the ignition coils
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  #14  
Old 06-05-2014, 07:49 AM
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lilsundance lilsundance is offline
 
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not sure if this engine is oil injected or mixed with the fuel. If injected, check the oil tank is full. If its mixed fuel/gas then the carbs probably need cleaning or its a coil issue. Never had the pleasure of working on anything bigger than a 25hp. lol
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  #15  
Old 06-05-2014, 10:44 AM
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YeeHaw YeeHaw is offline
 
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Quote:
Originally Posted by mulestalker View Post
-next time out,have a buddy pump the priming bulb at the same time as giving it full throttle,could be an air leak.
-also could be plugged pilot jets, mains,pull carbs and make sure all orifices are clear and clean.
-old fuel..
yip!!!
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  #16  
Old 06-05-2014, 04:34 PM
laker taker2 laker taker2 is offline
 
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Will try fresh fuel and clean out the carbs. I do use sea foam on occasion, and always use Amsoil quick shot.
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  #17  
Old 06-05-2014, 07:54 PM
Traps Traps is offline
 
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A very similar thing happened to mine last year, may not be the same thing but after buying a new bulb I tracked the culprit to being a faulty check valve (anti siphon valve) right off the tank, every boat tank has or should one.
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  #18  
Old 06-07-2014, 02:46 AM
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Kokanee9 Kokanee9 is offline
 
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Not sure if you experienced these problems before or after you did the work on it.

If they only started after working on it this year, check that the fuel line is installed in the right direction and also some fuel filters are designed to flow in one direction also.
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  #19  
Old 06-07-2014, 12:39 PM
Reeltime Reeltime is offline
 
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I agree with Silver on using Premium on small engines that do not run all the time. My new Stihl chainsaw dealer said Premium only.

I store my engine with Merc Storage spray and Merc stablizer in the tank to run through the carbs till dry as I fog the storage spray and never had any new season start up problems.

As a thought, my 50 Merc was running a bit like that and I recalled from owning a 35 Merc that there was a need to have the fuel tank - vented. I accomplished this by opening the vent screw on top of the cap. Once vented I had no problem.
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