1986 Yamaha 90 hp 2 stroke ETLJ problem with engine sputtering when I reach 3,000 RPM

Blue Man

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My motor has about 80 hours on it. It is new to me but seems to have a problem I'm having a hard time sorting out. Almost every time I hit 3,000 RPM it starts to sputter and shake...almost like it has a fuel issue. Sometimes I can slowly nudge it past the issue and it will get to 5,000 RPM but eventually the sputtering finally comes back and I try again.

I've replaced all the fuel lines, fuel filter, fuel pump, spark plugs, and rebuilt the carbs but still having the same issue.

Any suggestions?
 

robert graham

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I run a 1999 C90 and if mine did that I'd run the motor at the 3000 RPM/sputtering range for a few minutes then immediately turn the motor off and remove/check spark plugs for any indications like rich or lean mixture or other possible causes.....spark plugs can tell you something about the running condition of the motor.
 

Blue Man

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Great suggestion Robert, thank you for taking the time to post that. I'll take a look at that tomorrow.
 

gm280

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One other thought. When you rebuilt the carb(s), did you make certain the floats were good and set properly at the correct positions. Because even if everything else is new (fuel lines ,filter. pump) if the fuel bowl levels are too low, it will start starving for fuel and run lean. Also did you remove the main jets and make certain those passages were clean and clear as well? Because right around that RPM, the carb(s) could be going from a strong idle mid supply to the main jet passages to provide fuel... JMHO!
 

Blue Man

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Thanks for the reply GM280. I'll have to check with my engine-savvy buddy who helped me do the work to see what he says. (And by helped me do the work, I mean to say, did it while I tried to be helpful). That said, sometimes, if I increase the throttle really slowly I can get it past 3000 RPM and get the motor running great for a good run around 10 minutes or so. That is what seems strange to me. If it was starving for fuel, how could it ever get to 5000 RPM? My friend's brother suggested we check the amps at the coils when it is running badly and make sure we're getting full electrical power.
 

Blue Man

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My buddy also said it seems more like hitting a rev limiter because it doesn?t always cough or sputter and it?s not always at the same RPM
 

Blue Man

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Does anyone know if this motor has some kind of rev limiter that could possibly be broken?
 

99yam40

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that would not kick in until close to 6k.
Check compression, spark, timing , and fuel pressure.
Monitor spark and timing along with fuel pressure while problem occurs
Leaking fuel pump can flood #3 cylinder and keep it from firing properly

Still may have trash in carbs from lines and fuel pump when you put the clean carbs on and flushed stuff into carbs
 

Blue Man

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Well I haven't been able to check the fuel pressure or timing yet, but I did find one thing that was suspect...the battery connections were all extremely loose. I put it in a trash can and ran the RPM up to 6000 without a problem so I'm hoping that was why we had so much coughing and sputtering sometimes at around 3000 RPM and not others maybe as the engine would shake it had better connections at some times and not others and that is why it worked sporadically. I don't think I'll know for sure if this was the primary source of the problem until I test it under load.

However, I pulled the plugs and they seemed pretty wet, and the motor was running really rich. It smelled strongly of gas after about 6 minutes and our eyes were watering. I will post these details as a separate thread. Thanks everyone for the suggestions/assistance.
 

Blue Man

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No Title

Well I thought I had this sorted out with the battery cable connection problem, but I took the boat out last Saturday and I'm still having the same issues. Works great for 5 or 10 minutes, has problems for 5 or 10 minutes. Repeating over and over.

GM280: I was reviewing about what you said about the floats and I was thinking if there were an issue with them being too heavy or positioned incorrectly, wouldn't the problem be constant? (I'm not pretending to be an expert, it just seems that way to me and I thought I'd run it by you).

Robert Graham: I wasn't able to pull the spark plugs right when the problem occurred, but I did pull them and they're brand new, but aren't looking good (see pic). It does seem to be running rich as I mentioned in the other thread.

99yam40: I’m not sure how to monitor the fuel pressure. I did squeeze the bulb when the issues were occurring and although it wasn’t totally full, it was definitely not soft and empty. Squeezing the bulb didn’t seem to have any effect on the problem by the way.

Next plan going forward
I think the next thing we're going to check is the timing. I'd also like to check the gas tank vent to make sure it is working but I have no way to access it without cutting through the fiberglass deck. I guess I'll try to test a fuel tank vent problem by running the motor with the gas cap off. The fuel tank vent thought is based on this post my buddy found:

"In the water, start the motor and run it at idle for a few seconds. Shut it off, remove the line that feeds the carbs from the fuel pump. Then I like to use a jar with a length of fuel line. Start engine and watch the jar fill up. Should fill somewhat quickly. If it starts off great then peters out, there is either a restriction in one of the filters or lines or the fuel tank vent is plugged. Occasionally a fuel pump will die (not common with Yamaha). If it flows good until the carbs run dry, then it's probably a carburetor."

I'm also going to pull off the water separator which has only been on for about 3 or 4 engine hours to see how it looks.

Thanks everyone for the suggestions and if you have any further thoughts, I really appreciate the feedback!
 

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Blue Man

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I am really frustrated with this problem. I just rebuilt the carbs...the first time I just cleaned everything and re-used all the same parts. This time I replaced everything with a carb kit. I'm still having the sputtering problem when I get it to 2800 RPM. I can't really check the engine timing though because I can't get it to 4500 RPM where the manual says it needs to be to test the timing.

If you have any suggestions, I'd love to hear them. I can't really afford to take it to the shop but I'm not sure what else to try at this point.

Thanks,

John
 

99yam40

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As I said before compression , spark, and timing can be tested.
You need to test them to rule them out.
The ignition system has testing procedures in the manual so you can test voltages into and out of CDI even while problem is there to see if spark is the problem
If nothing is found wrong with them them you are left with a fuel to air ratio problem.
Too much or too little fuel will not let a cylinder fire and burn the fuel properly
Fuel pressure and vacuum can be tested, look here to find some good reading on all sorts of things http://forums.iboats.com/forum/engin...-questions-faq
It is a possibility you have an air leak into the fuel system and you motor is running out of fuel

Fuel pump leaking into #3 crankcase will affect only #3.
There are seals at the top and bottom of crank and seals between the cylinders on the crank. lets hope they are not a problem.
I am fairly sure that your 3 cylinder 90 has recirculation check valves on the block/ crankcase like my C40. I found 3 of the 4 bad but it did not have a problem like your motor.

Test what you can to make sure and move on to other things

I had a problem with high speed miss on my 3rd hand C40 when I 1st got it.
Ran well if I took the cowling and silencer off and ran into the wind only.
Took me close to a year to finally figure out someone had drilled out the main jets
Replaced them and it is good to go now.
All you can do is test everything properly and eliminate what you can
 
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Blue Man

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Thanks 99Yam40. I've exceeded my skill set and tools for testing these, so I'm going to take the boat to the local yamaha dealer and I'll be handing them a printout of your comments.Thanks for the suggestions.
 

robert graham

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Thanks 99Yam40. I've exceeded my skill set and tools for testing these, so I'm going to take the boat to the local yamaha dealer and I'll be handing them a printout of your comments.Thanks for the suggestions.
Well, you do seem to have a curious problem and since I run a C90 2 stroke similar to yours I'll be real interested to hear from you regarding the final diagnosis....hope your Yamaha dealer has a good mechanic who can troubleshoot this for you....Good Luck!
 

Blue Man

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OK, I finally figured out the problem. The computer that controls the over-rev on the motor must have a problem. We removed the over-rev wire and it runs like a champ now! Thanks everyone for your help!
 

Blue Man

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I don't remember the color and I won't have access to the boat for a while, but the wire connects in the bottom left wire connection port on the computer where there is a label that reads over-rev".
 
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