Yamaha 90 2 stroke. Did I blow it?

[Jonb1032]

2006 90 horse 2 stroke 900 hours. . A few months ago got a old boat. I start it once a week every week for a 5 minute idle. Finally got to take it out (my maiden voyage). A quick run to just get wet. Mostly no wake zone and a short faster run. The temp alarm went off, I put it in neutral for a few minutes. Alarm went off I slowly headed back to dock. It seemed to run ok but won’t idle now. The idle starts around 900 and slowly drops until it stalls. It seems to be ok when I’m gear and I give it some gas. Pulled plugs to see and they look they all look the same. Maybe dirty carbs? What would the symptoms be of a overheated and damaged motor?

[99yam40]

Bad compression is one

[Jonb1032]

Would bad compression cause it to start and idle normal for a
few seconds and then slowly lower rpm’s and then stall?

[Jonb1032]

Also would any standard engine compression test kit work on Yamaha.

[99yam40]

Would bad compression cause it to start and idle normal for a
few seconds and then slowly lower rpm’s and then stall?

probably not, sounds more like a fuel issue, but it is always good to check compression on all cylinders when a problem shows up due to overheating.
you need to find out why it overheated also.

[Jonb1032]

Thank you I will check compression. Unfortunately the previous owner kept boat docked in salt water for several years. He did flush with fresh water but sat in water most of its life so I assume water passages aren’t the cleanest. He mentioned occasionally the temp alarm would come on. I hoping the overheating alarm was only a coincidence and maybe when I ran at higher speeds fuel issues arose.

[Keithbaja]

Start with a new water pump and salt away
then clean the fuel system and Refresh.

[brian3006]

Change the thermostat, then if it still overheats, see if you can get a temp reading on each cylinder head at the time (IR Thermomoter) see if one is a lot hotter than the others. If so, then I would start looking into water passages being clogged around that one. When you take the cover off to change the thermostat you will also get an idea of what the water passages look like.

If there is a lot of salt buildup, might be worth flushing it out with rydlime. Look it up on youtube. pretty simple process and I have hears good results from it.

[Keithbaja]

Thermostat tip. Tap, Tap, Tap. you can tap up, down, sideways and in. Start to turn out and then back in. Take your time DON'T break the bolt.. Way undersized IMO. Reinstall with grease

[Keithbaja]

OOPS, Forgot the aerokroil. Magic sauce
pb blaster, liquid wrench and others don't compare. That's called by many as kyoil.

[robert graham]

Start with a new water pump and salt away
then clean the fuel system and Refresh.

My 2nd on this….your motor is most likely fine but just in need of some maintenance…..the thermostat and Pressure control valve are dead easy to remove/ clean/ inspect/ replace if needed….Also the water pump is an easy job to replace….if you can’t do these then find a mechanic who will….it shouldn’t cost too much $$$$

[Jonb1032]

I did a compression check today, all 3 cylinders show 125 psi. So I have that going for me. I also changed water fuel filter, gas filter on the engine itself and new bulb with hoses, needed it anyways. All 3 plugs after running look the exact same. It fires right up runs good 1000 rpm or so for about a minute then drops to 800 then to 600 then stalls. I’m going to try to clean the carbs next and yes I imagine the water passages are rough so flushing is also on list. Just tying to get the idle fixed first. I feel better all cylinders read same pressure. Hoping for carb issue.

[99yam40]

sounds like it is running out of fuel.
have you checked the fuel pump for holes and all the connections to see if they could be sucking air on the suction side of the pump?
tank pick up screen also

[Jonb1032]

I greatly appreciate your assistance here, quick refresh on history. Previous owner used boat approx 4 days a week. Kept up on normal maintenance, however it was kept in salt water at dock for many years. I received it 4 months ago, couldn’t take it out until now. But I did start it every week let idle for 5 minutes or so. No problems at all. Finally took it out ran fine until a overheat alarm, I let idle for few minutes alarm went off I proceeded back to dock at slower speed. There when going to neutral and idle at dock it dropped rpms and stalled. I restarted ran for a minute then stalled. Took it home proceeded to flush but continued to stall.
I can throttle up it seems rev up but when I return to idle it stalls. It does seem odd though when in gear and reving up a little. It doesn’t like to hold any rpm’s it does seem different. But I have limited experience with this boat.

I will check fuel pump. I could try to run on a external tank hence bypassing the boats tank. If cleaning the carbs is a
new rebuild kit needed or can a disassemble and
clean all jets and holes be almost as good? Again thank you.

[Keithbaja]

I've done them at the dock, beach, boat ramp, yady, yady, yady. A carb kit is priceless when something goes astray. And why take the time and not do it RIGHT with new parts ???? BTW float level is VERY critical !! As a general rule invert the main body and adjust float parallel to the body with no down pressure on float. Turn back upside and you should be able to blow thru intake.
turn upside down and u shouldn't be albe to blow thru. Highbilly style, but it works, always ck for fuel leaks for a few minutes. If your mixture at idle is adjusted correctly if u still get a lean sneez, Readjustment on float level slightly to a bit higher level. Carbs are not for the common guy to mess with. And alot so called pros don't get them correct. Good luck..