Yamaha 9.9 wont start/running

[BigSpartan]

Ive got a '97 yamaha 9.9 for my jon boat but ive been having trouble with it not starting or keeping it running. I had it out the other day and it took a while to get it to start and after a few pulls it backfired. Im guessing it backfired from the carburetor. After another couple pulls it started up . It has trouble idling whether warm or cold also .I have to keep the throttle open some to keep it running.

I took it out for a ride to see if it would stay running and it stalled a couple times. on my way back in i also noticed the primer bulb for the fuel line wasnt holding pressure . (i had to keep pumping it until it got hard)

Does anyone have an idea on what this could be? Ive been told a few different things that could be wrong with it but im not exactly sure. Anybody have any tips or troubleshooting ideas i could try?

[99yam40]

My guess since no one but you knows what motor you have is clean the carb and replace the fuel pump,
set to spec in service manual

[panasonic]

Please post the exact model and serial number located on the identity tag on the transom bracket.

[BigSpartan]

Unfortunately i dont have the boat with me right now so this is the best ive got . Its from when i bought the boat and motor.

[99yam40]

seems it is a 4 stroke,
not sure how the starting enrichment system works on it, but I guess since it still has problems after it is warmed up I would still recommend cleaning the carbs

[boscoe99]

It is a 1996 F9.9MSHU four stroke model.

A primer ball is normally not hard when the motor is running. But it should not collapse or flatten in any way.

If the primer ball is continually pumped so as to keep the motor running I would inspect/replace the fuel pump. More than likely the pump has never been serviced.

If the fuel pump is known to be working normally I would dismantle and clean the carburetor. Making sure that everything is clean and free of debris. More than likely the carburetor has never been cleaned.

[boscoe99]

seems it is a 4 stroke,
not sure how the starting enrichment system works on it, but I guess since it still has problems after it is warmed up I would still recommend cleaning the carbs

Primestart.

[BigSpartan]

I guess i shouldve been more specific .When i bought the motor i was told it was a 1997 ..looks like i have some reseach to do. The bulb doesnt necessarily go flat it just goes alittle softer then it would be when i first start the motor .Would a dirty carb make it back fire as well?

[panasonic]

I would take all the advice given so far. Rebuild or replace fuel pump, clean the carb, replace the fuel filter,. I would also pull the spark plugs and have a look at those as well. All maintenance items and if they have not been done....then any or all of then can be causing you trouble.

Then again the previous owners may have kept the engine well, but we can't tell from here.
You say it runs, so there can't be too much wrong with it. They are very good little engines. Let us know your progress.

[TownsendsFJR1300]

Parts 8 especially and #9 (low speed jet) will clog up: https://www.boats.net/catalog/yamaha...shv/carburetor.

All jets need to be removed and cleaned. #9 usually has orifices that go side-ways and are no larger than a needle and easily missed, pay close attention.
*#9 jet should be made of brass and will very likely NOT want to come out. Use penetrating oil, some heat and grind down the correct sized screw driver to remove the jet.


As posted above, service the fuel pump.

[BigSpartan]

I appreciate the help. I will get to working on all that stuff today .Hopefully i can get it done and itll run correctly.

[panasonic]

Very simple little carb on that. Carb and fuel pump are wide open to remove and reinstall. Good luck

[BigSpartan]

I figured out what my problem was. Changed the spark plugs and it ran grean .No problems after that .I am looking into changing the fuel pump and getting the carbs cleaned as preventative. But so far it just need some new spark plugs .