40 hp yammy running bad

[woodenskiff]

need help with motor

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hello im new here but thought your advice could help me out bought a 85 40 lx 2 stroke for 500 bucks from a guy who did a full rebuild replaced 2 of the 3 carbs and then winterized it then sold it to me a year later. the problem is that when its at no wake speed it seems to shake a lil more then exspected and when i give it full throttle sometimes it reacts and runs as it should and other times it just boggs down for 30 seconds and then will start to go as it should. i am gonna change the plugs and i noticed some varnish in the carbs so i was also gonna clean them up. just wanted to get some insight from some guys that have more exspirance then me in the yamaha outboard world........... i also put 3 times the right amount of marine stabill in the fuel tank by accident to (brother put it in then i put a double dose in to clean it out) and was running the lowest octaine gass avail at the station not sure if that wouold make a diff but thought it might did a i also did a compression test and the numbers were 110 in two and 112 in the other


posted a thread earler and wasent getting a response so i thought id try again

[CatCam]

Yes, change the plugs!!

Stabil, even with 3 times the amount won't hurt anything.....trust me I use it all the time, forgot many times I put it in at the house and added another dose when I got down to the fishing camp....I alway put a little extra in for good meaasure so I'm always over dosed!

Okay - back to the problem - yes I'm pretty sure with the motor sitting up that long you probably got gunky carbs.....You can pull them pretty easy to do drop the bowls.....you will have a low speed jet and and a high speed jet. When I cleaned mine, I removed the jets and used a strand of copper wire to run through the jets then I sprayed with some carb cleaner. You want to use a soft metal as a "Pipe cleaner" you don't want to scratch up the jet orifice.

Also - Make sure you check you fuel system, i.e. tank vent, primer bulb, lines, etc. IF you are using gas with ethanol, keep an eye on older fuel lines....it doesn't like the ethanol. Find non-ethanol gas if you can.

Try this and post back.....if problem persists we will try more drastic measures......

[woodenskiff]

thanks for the reply a couple of quastions tho my first is should the tank vent be open or closed during operating i tighten it all the way closed ? do you know the settings for the adjusting screws ? the fuel line that i am running now is old should i get a new one ? another thing that dosent have to deal with the carbs but is still a prob is when i shift into reverse it makes a grinding sound untill i go all the way on the shifter then goes into gear can any adjustment be made to fix this / thanks alot

[CatCam]

Vent should be open when running your motor, I generally close the vent while trailering, I don't want gasoline sloshing around in the boat while I'm on the road.....maybe this is your problem!!

Don't mess with any of the adjustment screws until you run it again with the vent open!

If your fuel lines look old I'd replace them....

If you look above the lower unit you should see a rod with a barrel nut, this is the linkage adjustment....I think they both have left hand threads, that is your adjustment...

BTW - back in the day I had a 1986 Yamaha 40HP -- damn thing was bullet proof! We pulled trawl nets all day long with that puppy - Sold it to a Vietnames fisher in 1999....he ran it until Katrina took care of the boat it was on! I don't know how many thousands of hours was on that thing!

[woodenskiff]

thanks alot

i was wondering what the diff is with the vent closed or open ? what would that do? it sucks being 85 miles away from my boat i just wanna open it and see if that did the trick. when i adjust the gearing what way would i wanna turn the barrel and will i do this while its running and in gear or off and start it periodicaly to check the adjustment? thanks for all your help man its been great just cant wait to get down there and get it fixed and catch some flounder

[CatCam]

The new tanks are self venting, the old ones with the knurled screw on the cap are manually set. If you leave it closed the fuel pump has pull against a vacuum in the tank, so leave it open when running.

Ummmm Flounder sound real good!!! I grilled up some redfish for Mother's day!

Keep us informed if this did the trick.

Take Care,
CatCam

[woodenskiff]

well just ran the motor with the vent open and took it out it worked for a lil while then starting giving me problems again where to start now ? and how do i do the gear adjustments found the nut on lower unit but wasent sure what to do

[rodbolt17]

the only adjustment on the gear shift is the cable.
make sure when in N the post lines up with the mark on the slide.
always shift quickly and firmly int any gear.
sounds like its time for a carb job and a fuel pump.
do them together.

[woodenskiff]

what is the barrel nut for on the lower end it goes into reverse but only after hearing some grinding will take apart carbs and clean has a new fuel pump on it already

[99yam40]

The barrel nut is the means you disconnect the shift linkage so the lower unit can be dropped on the older motors