Another one for the pros on 1992 40 MSHQ Yamaha

[Douglasdzaster]

Motor has been doing good for a while now. I thought I had bad water leaks until I learned all was normal. I still have a lot to learn from this project motor.
Like I said it’s been running good and I’ve been enjoying trips to the lake. I was flushing the motor at idle here at home and after warm up all of a sudden the rpms drop. I checked temperature right away and it was 138. Then I grabbed the primer bulb but it was rock hard. After about a minute the rpms came back up to normal. I ran it again the next idling and after a while the rpms went down again and this time it died. Started back up with one pull but I stopped running it and started checking things. Here’s what I’ve done.
Checked compression 105 , 110 , 105 . Checked plugs and they looked good and all the same. Next I ran the motor and pulled the plug wires one at the time. All three changed the idle the same. I started at the portable fuel tank removed fuel , checked for water and trash found none. Tank is clean so is pick up. I’ve made sure all connections and clamps where good while inspecting the fuel line. Did not pull the fuel water separator because it only has about 10 hours on it (let me know if I should anyway). Fuel filter under the cowling was clean again no water.
Tomorrow I’m doing a spark test for color and length of spark. If that checks out I figure I’ll pull the carburetors.
Question: If a needle is sticking closed now and then would it cause rpms to drop or would it start missing?
This outboard has turned out to be a whole new animal for me. It’s my first and I’ve been enjoying learning while working on it thanks to everyone that’s helped me along.
I really appreciate any advice or ideas what to check on next. Thanks

[Keithbaja]

I would ck the fuel for water. In Cali I sea water issues almost daily and that's on 10% ETH. 4 or 5 YRs ago mercury marine sent out a TSB to cali. Dealers stating that in this market the gas has and can go bad in 15 days Yikes !! Besides "Phase seperation" it chews up fuel systems. Its so bad they can't sell it small plane airport's. Wish U luck

[Douglasdzaster]

I would ck the fuel for water. In Cali I sea water issues almost daily and that's on 10% ETH. 4 or 5 YRs ago mercury marine sent out a TSB to cali. Dealers stating that in this market the gas has and can go bad in 15 days Yikes !! Besides "Phase seperation" it chews up fuel systems. Its so bad they can't sell it small plane airport's. Wish U luck

Thanks for the reply. I checked the entire system and even though I didn’t find any water I replaced the fuel anyway. I keep fresh none ethanol in it. I know it’s possible to still get a bad batch. I buy it from a place that sells the most in my area in order to get the freshest possible. Even then I still feel like I don’t know for sure what I’m getting. I treat it like ethanol and use an additive and keep it fresh.

[Keithbaja]

A sticky needle valve shut or open can/will do a lot of crazy sh-t. I'd try tapping carbs fuel intake area with screwdriver handle. Also ck for vacuum leaks. I assume this is two stroke. If so a reed valve can also do what your described. A cracked, chipped or loose reed has a habit of back spitting back thru intake and carb sometimes. Good luck

[Douglasdzaster]

A sticky needle valve shut or open can/will do a lot of crazy sh-t. I'd try tapping carbs fuel intake area with screwdriver handle. Also ck for vacuum leaks. I assume this is two stroke. If so a reed valve can also do what your described. A cracked, chipped or loose reed has a habit of back spitting back thru intake and carb sometimes. Good luck

Thanks for the information I’m pulling the carburetors to inspect and clean everything. I’ll check those reed valves as well.

[Douglasdzaster]

Thank you everyone for the feedback. I have a question. When the carburetors where rebuilt a few months ago. Everything was replaced. #1 and #3 have a 115 main jet. The #2 ( middle carburetor) had a 120 which is no longer available so I put in a 125 jet. Could this cause idle problems or other issues?

[99yam40]

no that would not affect idling
looks like they listed the 120 or the 125 for the center carb main jet so it should be just fine

[Douglasdzaster]

UPDATE: I pulled the carburetors today. Everything was clean and no water in them. I gave them a good going through anyway.
When I removed the seats the o rings on all three were torn up. Had to use a pick to get two of them out. I replaced all of this with new about three months ago. New seats,o rings, jets, everything. I remember the seats not wanting to go all the way to the carburetors body’s so I probably messed up the o rings then. Put new o rings on today and the seats went on down like they were supposed to. After tightening each one I pulled them back out to check the o rings this time and they looked good. I wonder if I had the wrong size in the kit the first time around. Also after putting the lower carb back together when I tested the needle by blowing through it and it sealed , turn the carb over and blew through it again and the needle was stuck closed. I tried several times before replacing that needle and it worked properly after that.
So I fixed a couple of things today. Checking the reeds. Reinstalling the carburetors and do a link and sync tomorrow and see how she runs.
Thanks you everyone for your ideas and sharing your knowledge. I’m very grateful. Hopefully I’m up and running again.

[Keithbaja]

Good on you for the blowing and turn upside down test. Soooo simple and tried and true test. I've been finding swollen floats a lot lately. Sticking to the insides due to this BS fuel. (ETH). Look for chafing and with your testing it will show up.