Pings and Knocks in 90HP 2 stroke Outboard during trolling speeds

[TSCTSC]

When trolling at about 800-900 RPM at speeds of 2.5mph on my Yammy 2stroke oil injected 90HP, I noticed last weekend that during trolling, there is some pings and knocks when it is running. Basically, it just does not sound smooth. Feels like it is not running well, although it does not stall. Running at higher speeds seems to be OK. I had a bottle of seafoam in 89 octane fuel. The motor was just in for dealer servicing the weekend before and they said that they could not find any problem and they changed the plugs and the gear oil. I do not think they checked the fuel system and cleaned the carburettor. I had asked them about the shock treatment and they did not know anything about them. I even called Yamaha and asked if they knew how to solve my problem and they said that they cannot help me and I should go to the dealer. I do not know if this is just some problem with my fuel delivery or if my engine needs cleaning. It starts fine everytime at the first turn and runs good otherwise. It is just that the rough idle at trolling speeds worry me and I do not want to have a catastrphic problem when I am out in some big water. Can some expert suggest some solutions for me? I am not very good with motors but if someone can teach me or tell me, I could do some simple stuff myself, or if someone can suggest someone whom I can show the motor to. Any help appreciated. Thanks!

[Xplorer]

I dont know if this will clear your problem but i use seafoam also, and i was told to run seafoam thru the system at a ratio of 2oz per gallon instead of the usual 1oz per gallon. This should clean as much gunk out of the system as possible. I troll with my carb'd 90 honda and try to do this for one tankful at the end of the season (in fact just dumped a bottle in the tank last night)

If that doesnt help out you may need the carb's to be taken out and given a really good cleaning. My FIL last week was quoted $180 to have his 90 yammy 4 stroke carb's pulled and cleaned.

[TSCTSC]

Thanks! Does the motor run rough when you run 2oz per gallon of sea foam in it? Or does it run rougher for a while when you a shock treating it with sea foam?

I spoke to my dealer and he said that they did not clean the carbs the last time around. So it sounds and costs like a big deal to clean the carbs. Do you think that it would be worth the money to have the dealer do it or is it something that is actually quite simple that I could do myself? Thanks

[Justfishing]

You might have a buildup of carbon on the pistons. This increases heat and compression leading to pining. Go to bass boat central and find the yahama forum and post the question. Tell us what you find out.

FYI There is a buildup of carbon from the oil used in 2stroke motors. Regular use of seafoam will help keep it clean or use a syn oil.

[Xplorer]

I usually try and get out and run her pretty good for an hour or so at varied rpm's. Lake superior on a nice day allows you to put on a few miles pretty quickly

After doing this i havnt had any issues with rough running with the two bottles of seafoam in my 17 gallon tank.

I believe that the 2 oz per gallon is considered the "shock treatment" with seafoam.

Good luck and let us know how it goes, i dont have the mechanical knowledge to trust myself to take out the 4 carbs and clean them, but after 5 years i havnt had too either (knocking on wood).

I was suprised the dealer recommended the FIL to have his carbs cleaned as the motor was new last July, and he had it in for the 10 hour checkup. Personally i think that he doesnt run it enough and probably left gas in the carb bowls over winter.

[Northlander]

Explorer dont you have a 24 or 27 gal. tank in your Lund?

[Xplorer]

NL,

Nope, only 17. They went to the bigger tank the year after i bought mine (2000). Thats OK tho, with my 90 at optimal cruising speed (@26mph) i am getting 8 mpg so that gives me a cruising range of over 125 miles so I'm not too worried

I do wish that i had the IPS hull tho, my FIL has a 2004 prosport with it and i like it.

If i ever find that money tree on my property i would really like an 18 ft fisherman with a 150 honda and kicker

[TSCTSC]

I checked the plugs on the Yammy and it had on NGK BP8HS-10. I checked the manual and the recommended was NGK B8HS-10 without the P. I called NGK and they said that the P was for projected plugs...ie.for high performance motors when they needed the tip projected way into the chamber. Called Yammy and they said to stick with the recommended plugs. Called my dealer who changed the plugs out for me and they said that the simply replaced exactly what they found in the motor when I brought it in. They claimed that they do not have the time to check which plugs should go into which motor so they always do a one to one replacement. In any case, I felt that they were negligent as my primary complaint in bringing the motor in was to solve the rough idle issue. They said that the plugs could be my problem they would still charge me for them to change the right ones for me. I know it really sounds lousy. But I really could not be bothered to get upset over a few dollars worth of plugs and work. So I went to get a torque wrench and the right set of plugs and changed them out myself. The old plugs looked OK. I did not see any large deposits at the tip of the plugs. I changed them out to the right ones torqueing them to about 5.8Foot Lbs and started running the motor in my garage with a motor flush. I think the knocks were reduced and the motor appeared to be runnning better. It could be psychological. In any case, I realized another thing was that the Yammy actually runs real quiet. I could not hear any adverse sounds at the cylinders. Just a whir...that was all. Most of the noise that the 2 stroke produces came from the propeller where the exhaust exits. Interesting observation for me. So I guess if someone wanted a quiet motor, all he needed to do was to mount some exhaust silencer. Hehe..

Just an account of my experience.

[trollingforeyes]

One other thing to check is your owners manual reguarding fuel requirements. If says 87 octane, stay with the reg fuel. Using high octane in a reg fuel engine, 2 or 4 cycle, will cause a deposit build up in the cylinders. Carbon cleaner (best type from a Johnson/Evenrude dealer at reasonable prices also) will clean the deposits out the motor. Follow the directions on the cleaner to the word. Also make sure you put that can of Seafoam in the last tank of the season. If your motor requires the 87 octane/reg gas you will notice that it will troll smoother with the correct fuel.

Good Fishing!