2006 Yamaha 90AETO idle problems

[Ishvania]

Hello everyone from autumnal ( correctly said ? ) finland.

I have a little problem with my Yamaha. Its 90AETO like topic says. Prime start and 171 hours on it. First when it came to me it was stored sideways maybe a couple of weeks if that makes a difference. Now the motor is on its place. Problem is that it idles roughly ~800 rpm, poppes and stalls. It stays running with 1200 rpm but still idles roughly. Immediately when you but the gear on the idle drops to 600rpm and works fine. Also with WOT it runs great. But when it drops to idle it starts to run roughly and stalls. Idle jets ? Fuel pump is new.

Maybe primestart ? In cold starts ~40F it raises the rpm to 11-1200 revs but drops to normal idle after 5-20 seconds ? Primestar "valve" not workind or bad diaphragm ? First it idles fine but after dropping the rpm to normal ~800 it begins to run roughly at stalls. Too much fuel ?

[TownsendsFJR1300]

Sounds like the Primestart is working normally. It should raise the idle cold and lower as it warms up..

Even thou the engine has low hours, it does sound like the idle jets are clogged... Those orifices are smaller than the mains and easier to clog..

I'd clean the carbs, especially the idle jets/circuit and go from there..

[Ishvania]

But why the Prime Start works only max 20 seconds. Some people are saying that it should warm up the engine at least one - two minutes if the weather is cold ? Maybe the needle valve does not work like it should ? Where does the Prime Start feed the gasoline from its pump? Is there own "jet" for it ? Just wondering because the engine starts like a dream in cold weather and works fine before the Prime Start drops of.

I red somewhere that someone had exactly the same problems that i have and the reason was Prime Start fuel pumps bad diaphragm and the engine got too much "raw" fuel ? --> Engine starts like it should, it idles with higher rpm for a while with Prime Start. Then the rpm comes down quite fast, the engine starts to cough, idle roughly and then stalls.

[ausnoelm]

No use trying to convince yourself of a fault, do some very basic trouble shooting first, then, you will find the carbs need a clean, not a spray or some "stuff" added to the fuel.

[Ishvania]

No use trying to convince yourself of a fault, do some very basic trouble shooting first, then, you will find the carbs need a clean, not a spray or some "stuff" added to the fuel.

We have had couple of Yamahas in the family, none of them have had there carbs cleaned ever. This would be the first one, so thats why the carb clean isnt the first thing me to do. One of them was -88 70BETO. We had it almost 20 years and we did nothing to it. Once we changed the impeller, spark plugs few times and thats all. New gear oils every year and rich oil/gasoline mixture in it before winter. No single problem ever with that engine, same thing with other 80-90s Yamahas .

One thing could be perhaps smaller idle jets in these newer 2-strokes ?.

[ausnoelm]

OK, please yourself.

[pstephens46]

No use trying to convince yourself of a fault, do some very basic trouble shooting first, then, you will find the carbs need a clean, not a spray or some "stuff" added to the fuel.

171 hours on a 13 year old motor is not much use.
Easy to imagine jets being somewhat clogged. My guess is the motor runs good as long as primestart is supplying extra fuel for startup. Then it struggles after primestart closes.

edit - I quoted the wrong post...anyhow

[99yam40]

the cough to me sounds like a lean sneeze.
chase that down the best you can
yes there is a jet/seat that the needle sets down into.

taking the carb and Primestart apart to inspect it all is a good idea.

also does you motor change idle timing also for cold starts and the use ta temp switch to signal when the motor is warmed up to change the timing back to normal?
easy to use a timing light to watch timing

sounds like this motor is new to you so you have no idea how well it was taken care of ,what kind of fuel was used, how long it sat between runs.etc.
the fuel bowls are vented so fuel will evaporate and leave a residue that will plug things up.
a plugged up pilot jet/passage will cause problems at idle also

[Ishvania]

Thanks for the ideas. Today i checked the Prime Start pump diagram and it was like new. Put it back together. Also measured the Primestart "waxvalve" and it was ok. Didnt have enough time to do more.

But...because the motor runs perfectly at sea when the gear is on from idle ( 600rpm ) all the way up to 5500rpm no matter how long you drive im starting to be pretty sure that next thing to do is order new parts for the carburetors and rebuild them. Must be the idle jets because only problem is rough idle at low revs and stalling at 800rpm when gear is "neutral".

[Ishvania]

Hello again !

I took the carbs of yesterday. I disassembled them to pieces and then cleaned them with carb cleaner and pressured air. Lowest carb had some dirt inside. I didnt replace anything because everything was like new inside, float needles, gaskets etc. Put them back together and adjusted the idle mixture screws. Next 15 minutes and the engine was ready to rock. The engine started, prime start worked again only about 20 secs and the revs came down. Idle was still little rough but it didnt stall anymore so i stopped the engine myself after for a while. I screwed the idle mixture screws in and checked that even the springs was exatly in same position in each carb. This time i tightened screws also with little more power. Then i opened them 1 1/4 turns and now every screw is exactly in the same position. I fired up the engine and the result is here------------> https://bawuka.kuvat.fi/Mb/VID_20191017_122930.mp4.

Maybe a little fine tuning later but pretty happy for the result.

First carb clean for me. Pretty easy job, little use of common sense and everyone can dot it by themselves.

[panasonic]

Nice clean looking engine. Glad you sorted it out.

[TownsendsFJR1300]

Sounds like a rock solid idle now... Glad it's up and running good again..

[robert graham]

If the motor is going to sit unused for several months or longer try draining each carb with the brass hex drain bolt on each float chamber....it's an easy 5 minute job that could save future plugged jet issues in the future....it also allows for removal of any water or debris from that critical float chamber...

[99yam40]

That 90 3 cylinder should have a link and sync procedure that needs to be followed each time the carbs are put back on.
It makes sure all carb throttle plates are opening and closing exactly the same..
the mounting studs and hole have a little slop, so this needs to be done each and every time the carbs a put back on


service manual will have it in there

[Ishvania]

Hello, i did the link and sync procedure just like the service manual said.

Winter is coming so the engine is going to to sit unused at least 5-6 months. Im going to spray some extra oil to engine through throttle bodies and drain the carbs after that.