1985 Yamaha 9.9hp 4-stroke carb problem

[KarstRanger]

Problem: I can gently pump the bulb and fill up the carb bowl and unhook the gas line. Then the motor will crank (without using starting fluid) and run for a few minutes on the gas in the bowl, but once I hook up the fuel line (no bulb pumping), it floods out right away -- plugs are wet with gas, fuel drips out of carb.<br /><br />Another test I tried (without motor running) was to pump up the bulb hard with it connected to the motor, then gas comes out all over the carb. Seems like there should be some sort of one-way valve preventing this - is that what a reed does? Or could the little fuel pump be defective - however, it does seem to be pumping?<br /><br />It is a 1985 Yamaha 9.9hp 4-stroke, model FT9.9XK, extra long shaft - was probably used on a sailboat. <br /><br />Initially, this Yammy would only run by squirting starting fluid into the carb when I bought it - but for the price I took my chances being pretty good at lawn mower and other small carbs.<br /><br />I tore down the carb and found evidence of varnish all over. Soaked the metal parts in acetone and brushed and hi-pressure blew out all the tiny passages, ensured the float needle valve and seat are OK, etc. Cleaned out the tiny holes with a thin piece of wire from a wire brush.<br /><br />So now it runs "better", i.e., it appears the float/needle valve portion is working, but how can I figure out the flooding problem? Thanks, KR.

 

[JB]

Re: 1985 Yamaha 9.9hp 4-stroke carb problem

That carb is some engineer's rebellion against convention, Ranger.<br /><br />Had one of those buggers and nothing. . . nothing. . .works like conventional carbs. Sold the manual with it, but you will need one because everything works off of vacuum/temp sensors.<br /><br />My guess is that you have a bad sensor or a leaky vacuum line making it think it needs enriched mixture when fuel pressure is up.

 

[KarstRanger]

Re: 1985 Yamaha 9.9hp 4-stroke carb problem

JB - This thing has temp sensors? I do see little vacuum lines running all over the place. They are making good connections, so I hope are not the problem. I don't see anything that looks like a sensor.

 

[rodbolt]

Re: 1985 Yamaha 9.9hp 4-stroke carb problem

if ya got fuel dripping out ya need to fix the carb. thats why they sell kits.

 

[kerrybraswell]

Re: 1985 Yamaha 9.9hp 4-stroke carb problem

I'm betting that some Bubba that owned the motor before you, tried to rebuild the carb himself and either lost a part or got it back together wrong. I have a 1985 just like yours and it still runs like a top with only a carb cleaning and new plugs every couple of years. Get a carb kit and a manual and rebuild that critter right! Good luck buddy! Kerry

 

[KarstRanger]

Re: 1985 Yamaha 9.9hp 4-stroke carb problem

Thanks for the encouragement, Kerry. While I don't have the service manual, I do have a complete carb parts diagram. I took this carb apart as far as it would go and appears nothing is missing, although maybe "Bubba" put something in backwards and I put it back in the same way. In the carb kit for this one, you only get the needle valve, seat, and a couple of gaskets - and these all check out fine (so I didn't order one). There is a stange diaphram assembly on the top of this carb that I do not understand however. The diaphram inside does not have any holes in it and is still flexible. Also, since the motor runs so well and throttles up and down smoothly when I simply fill the fuel bowl up, I am wondering what should stop the fuel pump from flooding it - could it be a valve in the fuel pump? However I think this is a pretty "dumb" fuel pump, and I think that feedback loop would be handled by something in the carb. For $35, I think I will go ahead and order the service manual to figure all this out. I also need to fix the throttle cable in the tiller handle and some guidance on taking that beast apart would be nicer than "sprong!" as things fly out as I take it apart the wrong way that first time. One question for you - I see a belt that goes from the flywheel to the oil pump. I looks in good shape but have you had to replace yours and how did you know it was time (other than it broke)? Thanks, KR.

 

[kerrybraswell]

Re: 1985 Yamaha 9.9hp 4-stroke carb problem

I assume you are referring to the fuel enrichment circuit (starter plunger) on top of the carb when you mention the strange diaphram on top? Don't mess with it unless everything else fails. It is complicated and requires replacement of all parts instead of repairing them. <br /> I just re-read your original post and notice that you said that the carb floods out when you pump up the bulb. That ain't right!!!!! The float should keep the bowl from flooding when you pump up the bulb. The flooding problem is absolutely in the float. Take the carb apart and check the float again. Either it is out of adjustment and is letting the bowl fill too full or, the needle and seat are bad and letting fuel flow past when the needle is seated or, the float is fuel logged and is no longer floating when the bowl fills. Find out which problem you have and fix that first. I think your motor will run fine after you fix that. You said that the motor runs fine for a few minutes on the fuel in the bowl when you pump the bowl full and then disconnect the fuel line. That is because the float no longer has to do it's job once the line is disconnected. The only job of any float is to prevent the fuel pump or bulb from overfilling the bowl and flooding the engine and yours isn't doing it's job! Order a carb kit including the float, needle, seat, and gaskets. Adjust the float according to the kit directions and when you put the carb back together you will notice that it no longer floods when you pump up the bulb. <br /> I am still on the original belt on my motor and it still looks like new. I will replace it when it shows signs of wear or when it breaks. I do have the service manual for my motor and do refer to it when i take things apart for service (such as the carb).<br /> Let me know how she runs after you replace that float and needle/seat assembly. It's gonna run fine! Later buddy, Kerry

 

[murphyjh]

Re: 1985 Yamaha 9.9hp 4-stroke carb problem

Your float valve is definitely not sealing. It is possible that the metal part of your float has been bent. My Seloc manual says that with the bowl removed and the carb turned upside down, the lower (now upper) surface of the float should be exactly one inch above the upper sealing surface (where the gasket and bowl sit). If it doesn't measure 1", bend it to fix it.<br />Jack Murphy

 

[KarstRanger]

Re: 1985 Yamaha 9.9hp 4-stroke carb problem

Thanks Jack and Kerry - I knew that the float is what controls gas into the bowl in small engine carbs, but this thing with a separate fuel pump and the vacuum lines to the starter plunger, etc. confused me some. I should have tried adjusting the float and I will now. I didn't do anything to the float except pulled the seat to make sure the needle valve and seat were not worn - they look like new. But I will try adjusting the float. I also ordered the service manual anyway as there will be this or other stuff to do. If 4-stroke outboards are anything like 4-stroke dirt bike engines, with decent maintenance, they will last forever. -- Martin Grill (KarstRanger).

 

[kerrybraswell]

Re: 1985 Yamaha 9.9hp 4-stroke carb problem

You are right about them lasting forever. I haven't had to do anything to my 1985 4-stroke 9.9 other than change the plugs and clean out the carb every couple of years. I also make it a habit to change the water pump impeller on all of my outboards every two to three years whether they need it or not and replace the lower unit lube as routine maintenance every year or so. By the way, the specs that Jack Murphy gives are right on the money, however if the float is fuel logged or leaky meaning it is too heavy, then it will sink in the fuel and the proper setting is meaningless. If you adjust it and that doesn't fix the problem, then replace the float, needle/seat, and gaskets and be done with it. I know you will have it running soon! Good luck friend, Kerry

 

[KarstRanger]

Re: 1985 Yamaha 9.9hp 4-stroke carb problem

I ordered the carb kit today from boats.net. I didn't think I needed it, but with yours and Jack's advice, if I am going to pull the carb again to adjust the float, may as well be sure I have a new needle valve/seat. Service manual is on the way, also. I will let you know how it goes. Thanks for the support, Kerry. Best regards, Martin.

 

[KarstRanger]

Re: 1985 Yamaha 9.9hp 4-stroke carb problem

Hey guys - I installed the carb kit yesterday and it runs like a champ. Thanks so much for the advice - you probably saved me at least $150 and lugging that heavy motor up to the local yamaha service dealer.<br /><br />When I compared the old float tang with the new one, the old one was bent - I only measured the new one after installation and it was right on 1 inch. So that was the leaking problem.<br /><br />I wanted to mention that I bought a SELOC yamaha service manual. And, compared against Clymer's that I have for other motors, this SELOC IS THE BEST ! I will always go for them first in the future.<br /><br />SELOC showed me one more jet that I missed cleaning by the way - I thought the plastic cap was just a plug, but there was a dirty jet underneath it, so the manual helped me fix probably another problem with this carb.<br /><br />Next project is mounting this bad boy as an auxiliary/trolling motor on the back of my 19 ft. cuddy cabin. The fun just never stops !!

 

[kerrybraswell]

Re: 1985 Yamaha 9.9hp 4-stroke carb problem

Hey buddy, glad you got her running right! I knew that float had to be the problem. Figured it was either out of adjustment or fuel logged. Those motors run great and are very strong for pushing a heavy load at low speeds. I also use the wonderful Seloc manuals as well as the original factory manuals. Can't have too many good manuals and it is the first thing i buy after a new motor purchase. Take care, Kerry