1998 40Hp 2 stroke won't run

[Sushiholic]

after returning from a two week vacation, it would not start.
once the fuel enrichment valve was turned to middle position, "manual" it starts, but smokes and runs rough. After a bit, if no throttle is applied it sputters out. if the valve is turned to "automatic" or "off" it sputters out immediately.
it will run underway, but rough and only to about 6 mph. prior it did 25 mph.
its on a small 15 foot center console.
inline fuel filter was changed, and plugs also replaced. also tried switching out the fuel line and bulb.
any suggestions ? all local shops are backed up for many weeks. I can swing a wrench, so do I start by replacing the fuel enrichment valve/assembly or do I clean out (or rebuild) the carbs ? could it be the fuel pump ?

[99yam40]

I would pull carbs and clean them up.
If you find water trash in bowls the clean flush tank,pump and lines before reinstalling carbs,
Make sure to follow the link and sync procedure in service manual after reinstalling the cleaned carbs (every time)

[TownsendsFJR1300]

+1 ^^^.

Make sure you literally pull the two jets out. Just don't spray them and say their clean. Visably look thru them and if you see plenty of daylight, your good to go.

You'll likely find a fair amount of brown varnish in the bottom of the float bowls and in the middle of your jets (which is the issue) and its not un-common.

Once you get it runni ng correctly, yamaha sells a product called "Ringfree" which works extremly well at cleaning the fuel system. Unless you drain the carbs and the fuel is going to sit for a month or more, put in some sort of fuel stabilizer or you get to do a "do over" in a month..

[Sushiholic]

carbs cleaned, now it starts but wont idle

I cleaned the carbs. The top two had gunk, grit and water in the bowl. The 3rd was DRY. the needle operated by the float was stuck in the seat. Had to yank it out with pliers. I bought a new need and seat, and cleaned the carb as well. Upon assembly the engine now starts, probably better than it has while I have had it. but once the rpms drop down, it wont idle, it just dies. The one thing i did not touch on the carbs is the "adjustment" screw on top with the spring.

[99yam40]

Did you follow the link and sync procedure in service manual like I told you you need to do?

It is to make sure all 3 carbs are in the exact same position when opening and closing. Also measure the timing to make sure it is in spec after motor warms up.

Some times it may take an heated sonic bath cleaning to clean the carbs good enough.
Make sure the red lever on the enrichment system is in normal position

You might want to do compression test to see if you hurt the one cylinder that was running without any fuel and oil

[TownsendsFJR1300]

If the sync and link is correct and doesn't help, I would carefully turn in each air screw (one carb at a time) and document the # turns for each.

Then, pull each out, try some carb cleaner thru that opening should crap be in there. Re-install each screw and adjust back to original.

I don't think I've ever seen a needle valve that needed pulling with a pliers, damn! You may want to confirm, by pulling the drain plug on the carb(s), that you're getting fuel to each bowl.

If one screw is way out of adjustment more than the others, please post back. Someone here will know what the setting should be.

I may have mis-read/mis-understood your post (#4), I think your referring to the idle adjustment screw?


Don't know your model # but here's a link to your possible carb, part#7 or 26? #7 is the physical butterfly/ idle stop screw. #26 is the screw I referred to above re documenting the adjustment of it.

http://www.boats.net/parts/search/Ya...TOR/parts.html

[Sushiholic]

I am going through that now. And yes there is fuel in each bowl now. It runs as good as it ever has, just wont idle at all. made it to 24 mph in seconds.

Yes it was the #26 screw I was talking about.

[rodbolt17]

if you did not pull apart the enrichment pump or the fuel pump or carefully clean the lines, you most likely re-introduced debris into your once clean carbs.
its all part of cleaning the carbs.

[Sushiholic]

cleaned carbs 3rd time. Link and Sync (as best i could per manual)

it starts. once idle drops it puts out a chirp (lean sneeze?) and stalls

advice appreciated

[TownsendsFJR1300]

Were you abe to clean the enrichment pump as posted above?

Also, did you get the idle jets OUT of the carbs for cleaning and can see thru them?

A quick drain of the carbs, catching fuel in a tuna fish can (checking for debris) wouldn't hurt either. A squeeze of the primer bulb to flush again, wouldn't hurt with the drain plugs out.

[Sushiholic]

cleaned fuel pump...nothing. Turns out that was fine. One clogged idle jet. the side holes made it seem like it was blowing air. now you can see through it. guess what ! Idles like a CHARM, and runs great. Thank you ALL. what a great bunch of guys.

[robert graham]

Now you got it runnin' right, add a fuel/water separator (Walmart/Attwood unit $28), use Stabil all the time, learn to drain carbs for any lengthy motor lay-ups of a few weeks or months....pretty well eliminate carb problems....

[TownsendsFJR1300]

Excellent!!

As posted above, nowadays, with the crappy fuel, use a stabilizer (I don't care for Stabil, some bad experiances with it) and a fuel system cleaner, at least occassionally. The Yamaha stuff isn't cheap, but it really does go far at 1 oz per 10 gallons..

I've seen/fixed the exact same issue, 3 times last week, two mowers, one HD, CAT pressure cleaner, ALL THE SAME, varnished up carbs/jets. My mower is 15 years old, the carb has NEVER been off it/cleaned/bowl removed for maintainance, etc.. Runs like a top. Ringfree and "Gas Shok", also very good products, IME..

Well worth the investment IMO...

Have fun!