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fuel system help 1990 xt 600 fuel system help 1990 xt 600
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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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Photo by Andy Miller, UK,
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  #16  
Old 7 Aug 2013
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My experience is you dont need new plugs. Actually the new plugs can be harder to "read" becasue they're so new, and take a while to take color.
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  #17  
Old 7 Aug 2013
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I have found out that on 2 strokes, new plugs yield a more consistent result.
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  #18  
Old 7 Aug 2013
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Bogging and hesitation which clears is a clue to an over-rich mixture at that part of the throttle opening...

I'd lean up the pilot circuit a little.. Worth a try.

How's your float heigh too ?? Quick blips can drain the bowl if the flat valve isn't keeping up with demand.

Remember, with carb tuning, do one thing at a time... Pain in the ass I know but it's the best way to fine tune your settings..
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  #19  
Old 11 Aug 2013
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The bike runs great she pulls hard in all gears and cruising on the highway at 50,60,even 70. At 35 she has a hesitation. I am noticing at idle when I give throttle she will stall. I just want to she if she is loading up and seeing what comes out of exhaust . I do notice now that when the choke is out and start her the idle goes up then I push it in she stalls but starts up. So what I do is start,warm up then drive away put choke in and she don't stall
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  #20  
Old 11 Aug 2013
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Some motors like to be warmed up for 3-4minutes before being able to give throttle without a stumble. It's called Cold-blooded around here. Now once it warms up for a number of minutes, it will then run fine? You should be letting it idle to warm up anyway for several minutes (I start mine and then button up jacket and put helmet /goggles on, then gloves) just to make sure all upper parts of the motor have oil before putting any stress on them, plus it allows the piston and cylinder to expand together and not cold seize.
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  #21  
Old 11 Aug 2013
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I let her warm up she will stall if I don't push the choke in slow cause she reves up a little
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  #22  
Old 11 Aug 2013
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What idle rpm have you set your bike?

Just count how many turns you have on your fuel screw, take one turn in and see what happens.
If you can't fix your issue like that it's either your floats set too high OR the float pin isn't fully closing probably because of some very little dirt. (remove the float pin seat and clean it off!!)

And one more thing.. on the carbs, there it is a FUEL adjuster, NOT air adjuster!
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  #23  
Old 12 Aug 2013
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Thanks for your help . I put new jets stock, o rings, needle valve for float but did not check height , also feul mixture, and screen inside carb also coasting enricher set too, along with intake and oring too. I will try adjusting fuel mixture in and take it from there will keep in touch,
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  #24  
Old 12 Aug 2013
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Quote:
Originally Posted by jjrider View Post
Some motors like to be warmed up for 3-4minutes before being able to give throttle without a stumble. It's called Cold-blooded around here. Now once it warms up for a number of minutes, it will then run fine? You should be letting it idle to warm up anyway for several minutes (I start mine and then button up jacket and put helmet /goggles on, then gloves) just to make sure all upper parts of the motor have oil before putting any stress on them, plus it allows the piston and cylinder to expand together and not cold seize.
No, its called lean jetting

The topend have oil and oilpressure in a couple of seconds. There sno need to warm up a bike for several minutes. A car doesn't need it, a bike doesnt need it either.

Its fine to start the bike before you put on your gloves, helmet and such, and enjoy the sound
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  #25  
Old 12 Aug 2013
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If you have to wait several minutes before the all parts of the engine have oil it would be dead along time ago...
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  #26  
Old 12 Aug 2013
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It's not the oil temperature you have to worry about.. I agree with JJrider. It's about the engine being a the correct temperature to burn the fuel/air mixture.


I always warm up my carbed bikes. If you kill the choke too soon it will just stall when you pull away.

Honda Dominators, XR650L's and most of the big CV carbed singles are TERRIBLE for this.

Chokes circuits are often terribly set up from the factory too.


Oil temparature IS important too. You're oil isn't at the correct viscosity or evenly distributed and at the right pressure until it's warm.

Maybe this is me just thinking a bit old school....
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  #27  
Old 12 Aug 2013
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You aint getting the oiltemp up much by idling 2minutes, theres not much flow compared to when the bike is driven. Also, it warms up very "uneven" when left idling, instead of driving.

But I guess theese bikes are tough, and one way or the other, they will last a lifetime.
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  #28  
Old 13 Aug 2013
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We get dozens of motors seized around here from people just starting them up and taking off(colder temps usually).The piston ends up expanding too quickly and =thunk! I think it takes more than a few seconds for everything to get oiled from a cold start. No not minutes but more than a few seconds. I guess this is why I will always buy my toys new if I can at all help it. Remember 80% of wear is at startup, hit the gas right away and that number goes up to 95%. To each his own I guess.

And my KTM is jetted rich(black plug) and it needs choke for several minutes till the head is nice and warm or it stumbles badly, will die if the choke is shut off, it is cold blooded, not lean. You need to ask, Why is a choke needed for all carbureted engines?
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  #29  
Old 13 Aug 2013
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Choke is needed for carb engines and fuel injector engines has the same but its a fuel injector that provides more petrol at cold stage. All engines needs more petrol at the cold stage due to the temp mixture of petrol/air, thats the ignition point of this mixture that changes. You never do anything wrong to the engine idle it for a while before doing high rpm, but there is no damage to the engine riding it normal to heat up compare to just standing on idle. If you dont get enough oil in the engine when riding your bike its something totally wrong with the pump or oil.
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  #30  
Old 13 Aug 2013
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You need choke because when cold the gas/air-mixture doesnt vaporize as good.

And you can easely have a lean idle-curcuit, and be rich everywhere else, so when you do a plugtest, its shows up rich. You need to test the plug at every carb-"curcuit". My xt600e needed a bigger idlejet, but a smaller mainjet when I fitted a new exhaust-system.

My bike is ridden daily, including winter. The record being -18 degrees C. I guess it should be dead long time ago. Gave it a new piston and camchain after 120.000km+ a few months back, just to be sure it would still thump on.

If you want to see how fast oil comes to the topend, just remove a valvecover and start the engine. Do keep a rag close by.

I've heard stories of guys beeing so obsessive with letting the bike warm up by idling, that the gas started to boil in the gastank

Agree to disagree?
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