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1989 (87 Carb) Yamaha Warrior Carb Mid-Throttle Sputter


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When I get to mid throttle (slide is 1/2 way up) the engine sputters. All other ranges are fine. It all started back when my gas cap was not tight and all the gas evaporated. Sputter problem has remained since then.

If I fully clean the carb, install it, it runs good, but the next day, the sputter returns. When it is cold, no sputter, but returns as engine warms. When the peocock valve is turned off, the sputter stops, then it runs out of gas (that tells me the sputter is caused by running to rich, right?).

Things I've done but problem returns.

-disassembled carb (about 10 times) and cleaned all jets, passages, rechecked float level

-ran without air filter

-changed to smaller jets (main and pilot)

-moved needle valve to next leaner position

-set float level too hight and too low

-cleaned peacock and inline filter

-ran with gas cap loose

-checked spark plug--black with a little bit of white

My only idea now is that the plastic around the needle jet has deteriorated causing it to run rich. I don't have a smaller needle jet, but adjusting the needle position didn't do anything.

Ideas? Thoughts?



Edited by jcole1325
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Is there any smoke when the engine is sputtering? Does the problem still occur when accellerating hard, or does it only do it at even mid throttle, while keeping speed steady? Have you inspected the diaphragms in the carb? Accelerator pump? If all the fuel evaporated from your tank, there is a possibility that some residue has built up in the tank. Did you clean the tank out? You might want to check the vavle lash too.

Also, the carbs are different from '87 to '89, one of the differences is the needle set, you might try ordering a needle set from an '89. I honestly don't know what the big difference could be, the jets are otherwise the same, but I guess the needle design could have been changed to match a slighly different timing curve as the CDI boxes are also different between the years.

Edited by DirtDemon
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Thanks. Good questions.

No smoke when it sputters.

Yes, I completely cleaned the tank (soap and water) and peacock valve, including both screen inlets inside the tank.

If I hold on the spot, it sputters. If I throttle up fast, it’s a flat spot. If I throttle up hard, you can't tell, maybe a slight miss.

Diaphragms? Are you talking about the coasting diaphram? I took it apart and cleaned it.

The accelerator pump spray nosel is clear (it shoots directly into the carb, is that the correct direction?)

The carb kit was for an ’89 (because I didn’t know it had an ’87 carb at the time I bought it).

A friend said it may be the air bleed hole going to the needle jet is clogged. Which explains why it is running to rich. I’ll check it tonight, but I’ve sprayed carb cleaner in about every hole, jet, port, crack, cranny, and opening I can find.

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It's the air bleed going to the emulsafier (needle jet/main). I did like you said and cleaned it with a wire, also carb cleaner. The hole is small, but I've never had this problem before. Why it started, I have no idea. Anyway, I've inspected it 6 ways to sunday so I know it is clean. Tonight I'll install and run it. The real test is waiting a few days and running it again.


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Yes and no. It seems that the engine runs fine as long as the bowl is not allowed to fill/overfill. When it fills/overfills (but nothing is going out the overfill tube) the gas level stops air from coming through the air bleed hole efficiently. If I put my finger over the air bleed hole while the engine is running at mid throttle, nothing happens. If I spray carb cleaner, using a long nossle, and shoot it in the air bleed hole (pushing the gas level down) the engine runs fine for about 15 seconds then the sprutting returns. I think the o-ring around the float needle valve seat/jet is leaking and allowing the level to get to high. Why gas is not running out the overflow tube, I don't know.

As far as the float level, I've checked this many times, 11.4 mm to 12.?? mm, and it seems OK. Also, I've adjusted up and down to no effect.

I have re-installed the o-ring and checked it for leaks by blowing into the fuel line and moving the float. Tonight I'll reinstall the carb onto the quad and I'll let you know how it goes.


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No luck. Nothing seems to work. Back to square one.

My friend suggested the cam might be worn causing it not to pull enough air in to the carb. Thoughts? It is an old quad, 1989, I did nothing to the head when I rebuilt the engine.

Is there a way to test or measure the vacumn/pressure created by the engine. I can take the head apart but I'd like to do it with some confidence that is where the problem lies.

Recap: It sputters at mid throttle. If I spray carb cleaner in the air bleed hole, it runs ok for a minute. If I shut the peacock valve off, it runs good just before it runs too low on fuel. So the problem is not enough air is getting pulled into the carb.

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if your carb is overfueling. it should come out the over flow. if you pull your carb out and remove the float, put it into a clear glass of fuel or water. your float should only go down no more than half way. usually it is a quarter of the way down. your book should tell you where it rides. you could be starting to fill your floats with fuel. if you run a longer hose into a container and slightly drain fuel while running, you are manually controling the float level. see if the quad sputters at mid throttle then. if it does not sputter then it is a fuel supply issue. but before you do anything do the wide open throttle test. Run atv at wide open throttle and shut it off. keep holding the throttle open until you stop. remove the plug and check it. this will tell you if you are rich or lean.

Your Friendly Neighbourhood Mechanic :)

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I'm not saying that you don't have a carb issue, but I would definately have the head done if you rebuilt the bottom end. As old as it is, the cam is probably a bit worn and the valves are probably not seating properly anymore. I would also be willing to bet that the guides and seals are worn too. Check out this link, I found this site a while ago, they have some good prices on machine work for Warriors. They can work your head over and install a new Hotcam and set the valve lash for you. All you will need to do is slap it on when you get it back. They will even supply you with the new gaskets you will need.

Yamaha Warrior performance kit.

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