Yamaha 2stroke 115 idle issues

[Lesiot]

Hey all. Im new here, basicly ran into the site while searching for an answer to my question.<br /><br />Basicly. my parents purchased a semi-v sled with a 2 stroke 115 yamaha back in the late 80's. I utterly love the boat and recently had it given to be due to the lack of use it was getting (it sat for 4 or 5 years with little to no use or maint.) Flushed the oil resevour and the main tank, reoiled it. Pulled the plugs and oil'd the cyls then spun the engine by hand, no grinding or any metallic noises (I'm basing this off of my knowledge of chevy small blocks). Replaced the fuel filter/water separator and put new plugs in (matching plugs for the sticker on the engine - its not at this location or id tell you the numbers). Well, after a little priming and choking it fired and ran. Smoked a little but sence I primed the cyls with oil first that was no surprise. No water at first, shut her off and cleared the **** line and got waterflow back. Everything was good except once it was running it sounded ALOT like it was backfiring. My guess is the carb is partially tarnished or the heads carbonized (again knowledge from chevys). Would there be any fuel additives for 2 stroke auto-mixing (oil/gas) engines to help with that? Also what else would you recommend replacing. The engine seemed to run fine at higher rpms and smooth out so it seems mostly an idle issue. ON the right side (the passanger side) i did see what looked like a little "clear" plastic filter of sorts inside the engine, was wondering what that was. And also as for an air filter, would it be located in the airdam (proper terminology?) on the carb? Last of all. Where would I find a true manual for this? Preferable online as Im HARD on paper books!<br /><br />EDIT: Oh and with the backfiring, it would act like it momentarally wanted to stall, complete with rpm drop. Probibly once every 5 or 6 seconds.<br /><br />Thanks for the info! Really appreciated.

 

[rodbolt]

Re: Yamaha 2stroke 115 idle issues

hello<br /> first off forget everything ya know about chebbies.<br /> if you treat this like a chebby you will have a handful of melted parts and a much thinner wallet.<br /> check with your local library.<br /> test the compression.<br /> if it is good and within about 10 psi bank to bank then replace the fuel pump,clean or replace all fuel lines,remove and thoughougly clean both carbs. do not attempt to use an additive or a spray while running. odds are you will smoke a piston long before the carbs get clean, after sitting so long it will need the pressure valve grommet changed new t-stats and a new pump kit. a 5.7 chebby in a car will tolerate all sorts of wore out and mis-adjusted stuff and still go get groceries. a 115 yammi 2-stroke wont. it will die,the cooling system must be 100% or it will get hot, the fuel system must be 100% or it will cause a lean air/fuel ratio which will melt pistons. the oil system must be 100% or it will fail and rod bearings and pistons suffer yet again. always remember everything that goes past the pistons must lubricate it. never use premixed fuel over about 3 months old, try not to use gas over 6 months old. it tends to leave deposits on the piston skirts.<br /> give this poor old motor a chance and it may live to a ripe old age.<br /> however before I sank a ton of money into it I would carefully inspect the shifter shaft.<br /> they had a tendancy to rust away in salt.<br /> good luck keep posting buy the clymer or seloc and read all about how a 2 cycle works.

 

[Lesiot]

Re: Yamaha 2stroke 115 idle issues

Fortinuately this motors only seen salt two or three times. Mostly running the lower Columbia river so salts not much of a problem. I'll run to the local library tomorrow and see if I can find any books on it. Im also considering trying to go half and half (with my 'rents who admit they will still use it intermittantly if I keep it running) about a new 135 4 stroke yammi. But thanks for the info! Its really appreciated. I'll hafto put apic up of the boat hooked to the back of my 1968 Impala. Only vehicle I have with enough umph to move the boat. And from what i've seen, i'll be around here quite a bit.