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99 yz400f not idling

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I have a 99 yz400f that I can not get to idle properly. It starts easy and some what idles with the choke pulled out, but as soon as I turn the choke off it hesitates and dies. Any one have any ideas what it could be? I've messed with the carb jets a little. Tried couple different main jets 175 and 200 bit still nothing. I've put in a new needle and seat as well as a pilot jet 45. I ride at about 6000-10000 feet above sea level. Cleaned the carb 2-3 times to be sure it wasn't that. I had and exhaust air leak but got that all fixed up. I just want to go ride! Anyone help me out? Have any suggestions?

Thanks

JB

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17 year old carb may not be able to sustain an idle due to all the wear points being way past useable service.

Ream the passage above the pilot jet with solvent and fine wire, as there is a tight bend.  The most common reason for pilot issues.

Replace the needle jet (not the jet needle) as it will be completely worn out by now. Same with the slide plate seal and gasket.

There is also a main body seal the seals the two halfs of the carb body. They eventually go bad, but don't try and replace it until you know you can get the gasket.  JD Jetting...

165 main is what you should be running, and they have nothing to do with idle......

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I have the 165 in right now didn't mean to put 175. So you are saying my issue is I might still have a clogged passage in the carb. I replaced all jets and seat and some gaskets and o rings. I haven't tried the slide plate seal and gasket because I don't know how to do that. My carb was all beat up from previous owner which I should have checked out before I bought.

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17 year old carb may not be able to sustain an idle due to all the wear points being way past useable service.
Ream the passage above the pilot jet with solvent and fine wire, as there is a tight bend.  The most common reason for pilot issues.
Replace the needle jet (not the jet needle) as it will be completely worn out by now. Same with the slide plate seal and gasket.
There is also a main body seal the seals the two halfs of the carb body. They eventually go bad, but don't try and replace it until you know you can get the gasket.  JD Jetting...
165 main is what you should be running, and they have nothing to do with idle......

Well not broke or anything just super dirty and gunk all over in it. almost gone acc pump diaphragm. Bad gas ect..
I have the carb off and plan on giving it one more really good clean. If that doesn't help have any other suggestions or do you think it's a wore out carb?

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I already explained what to do mechanically

I would soak the carb for a few days in simple green or pine sol.

Do not use ANY automotive solvents on this carb, or you will melt the internal seal

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I would start out with a full breakdown and very through cleaning. You'd be amazed at the amount of crap that comes out of a 17 year old carb!

Make sure you've got seals in all the right places and the pilot screw is set to stock setting.

 

I have a 98 400f and had very similar issues awhile back, turns out there was some gunk stuck in the pilot jet. (which is directly responsible for idle.) Once that was cleaned out, it runs like a champ now!

Don't both with the main jet when dealing with idle issues, main jet is only in play when dealing with 3/4 or more throttle.

 

From there I'd move on to the plug, make sure you're running the correct plug (CR8E) and that it's not all fouled up with soot. If it is, replace it.

 

And lastly, check the TPS (throttle position sensor) that shouldn't prevent it from running, but if it's feeding the ECU a bunch of bogus numbers, it will cause the spark timing to move around unusually and lead to whacky behavior. (testing info for TPS is located in owners manual)

If you're not sure, just unplug it, it will run on a static map.

Edited by Michael Cahill

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I would start out with a full breakdown and very through cleaning. You'd be amazed at the amount of crap that comes out of a 17 year old carb!
Make sure you've got seals in all the right places and the pilot screw is set to stock setting.
 
I have a 98 400f and had very similar issues awhile back, turns out there was some gunk stuck in the pilot jet. (which is directly responsible for idle.) Once that was cleaned out, it runs like a champ now!
Don't both with the main jet when dealing with idle issues, main jet is only in play when dealing with 3/4 or more throttle.
 
From there I'd move on to the plug, make sure you're running the correct plug (CR8E) and that it's not all fouled up with soot. If it is, replace it.
 
And lastly, check the TPS (throttle position sensor) that shouldn't prevent it from running, but if it's feeding the ECU a bunch of bogus numbers, it will cause the spark timing to move around unusually and lead to whacky behavior. (testing info for TPS is located in owners manual)
If you're not sure, just unplug it, it will run on a static map.

In the process of a good clean. Have extra plugs (CR8E). I tried unplugging the TPS and it does act better but still does when choke is turned off. Hopefully this good clean will do the trick!

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Also! Make sure you've got the pilot screw set at the stock setting. (1.5 turns out from lightly seated) If that's not right, it will never idle right.

And I'm sure you've checked already, but make sure you've got fresh gas, it'll run like crap on gas that starting to go bad.

And if that still doesn't work, I'd look into either re-jetting with stock jets, or go with a JD Jetting kit. Possible that the previous owner had a weird one in there that's throwing things off, but more than likely it's just clogged!

 

With the behavior you've described, I'd be willing to bet you've got a clog somewhere in the pilot circuit, which is responsible for delivering fuel at or under 1/4 throttle.

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Thank you guys for your help it is much appreciated. I will be putting carb back on, cleaned the whole carb and used all new jets. I used a wire tool to poke through the pilot ports I didn't do that before just air. I feel like I poked through some gunk and got it all cleaned up! I will find out soon!

Now that I have the carb back together I think the jet needle is set one notch down from middle. Should I leave it and try or should I put it back to the middle?

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