1999 yamaha 9.9hp 4-stroke outboard hard starting, won't idle

This motor is a model T9.9elhx electric start, 4 stroke. I have removed and cleaned the carb, installed a carb kit and a new diaphragm assy(as it was leaking). The motor will now start when I place my hand over the air intake but will not run if I remove my hand, sometimes it back fires through the carb. It absolutely will not run at idle at all. I have checked the starter set(I am told this is an auto choke??) by connecting it to the starting battery and it moves. I am still not convinced this thing is OK since it will only start and run if my hand is held over the air intake. The fuel is new 89 octane with marine stabil and enzymes in it. Put in a new set of NGK CR6HS sparkplugs, still have problem and I'm just baffled with what is the trouble with this motor??? Any help/advice is appreciated(please don't suggest I buy a Johnson although that may be a solution).

The carburetor jets and passage ways are very small and it is easy to overlook them in a carburetor cleaning.-----------I think you need to revisit cleaning of the carburetor.--------------And you can not buy a new Johnson.

I can appreciate the suggestion however I have taken it apart twice already and have cleaned it as thoroughly as I know how, also put a new repair kit in it. What function does this starter assy have exactly, I am wondering if that could be my problem? Spark and compression are fine by the way. However we will also pull it off and clean it again. Any other Ideas on this one?

I am having the same problem with my 1995 9.9 yamaha. I could start it if I covered the 90% of the air intake and it ran well as long as it was covered. I took the automatic choke off and covered the hole it inserts into in the carb. It runs great in this position as well. I tried replacing the auto choke but it did not fix the problem. I don't know where the wires come from that control the auto choke but am afraid that may be the next step. I have not taken off the carb as it was just cleaned last year when I bought the motor. I too would like to know what the next step is.

A thorough cleaning of the carburetor is needed.-------------------------IT IS VERY EASY TO MISS THE SMALL HOLES AND PASSAGEWAYS.--------------I carry a small piece of electrical wire in my wallet to show that a single strand is all that will go in the jet.----------Always run carburetors dry when you are not using the motor for a while.------------------------I bought 2 --------9.9 Hondas last year because they would not idle and the owner could not find a shop that knew how to clean a carburetor.------------------Cleaned both carburetors ( no money spent ) and both run OK now.

Thanks. I think we'll do that next. It's what my mechanic suggested as well.

Hi racerone,
Thanks for the encouragement, I am not giving up on this engine, it has run like a dream up until now; I would buy a new carb if wasn't so expensive (over $300). So do you think it will do any good to soak it in a cleaner solvent for a while? If so can you suggest a type of solvent that will do the job? I like the advice about running the gas out of the carb, that has to help. I am also using enzymes and stabil in all my gas. Can you believe it the current administration wants to increase the content of ethanol in gas to over 15% or more if they get their way. What the hell are we boaters going to do then, go back to rowing????? Guess we can use our outboards for anchors????

Bob W

I use a " kleenflow " product for problem carburetors.---------------You have to be careful soaking a carburetor as any plastic / rubber parts will suffer.---------------Take the time to study all the carburetor parts and determine how / where the gas flows.------You have checked for a strong spark on both cylinders and done a compression test ??-------I am convinced that you need to look for something in the fuel system !---------I know someone locally that has issues with hard starting on their Yamaha , essentially a new motor that never gets used ( sailboat ) and I think they refuse to listen to good advise.---It never starts the way it should.

many people over look the idle jet there is a rubber / plastic plug that needs to be pulled out then underneath that there is a idle / slow jet size 48 and gunk's up really fast due to the ethanol used our gas today its a dealer only part or if u can find a mechanic that does small engines he probably has the tools and no how to clean this jet after jet is cleaned or replaced you can put it back in and it should run fine


JP Small Engine Repair
Pasadena, MD 21122

Thanks R Cox.
I have the same problem on my 9.9MSHY. Cleaned the carb several times now and Yea I did overlok a white plastic plug tha appeared to just block a ?? with no apparrent pupose. I also purchase a new starter asembly. I love this carb except for that idiotic peace of crap.( i like a real choke that at least you can understand and work with when jets get cllogged). Tomorrow I pull of the caprb and check that out. I have a good feeling that he mystery is solved. Thanks again Robert Cox from JP small engine repair.
I have hope again.
Rick
The Barefot Captain LLC

Again thanks R Cox of JP small engine repair.
I feel stupid havin over looked that plastic cap hiding the idler jet inside. Sure enough it was clogged and a short clening later my engine was runnuing. still not perfect but it's getting there . Sme good carb cleaner in the gas (wal mart carries ne with toulene and acetone that I belive is a Sea Foam type cleaner for $3.50) and she runs great atbut still stops qat idle un less she's hot. Tinking it must be that stupid starte assembly needing adjustment . If you have any more words of wisdom I am all ears.

Hope this machine works and you can also post some image regarding the experiment.