fuel system help 1990 xt 600
 

I have had this bike for about 6 months now. When I bought it needed new intake gaskets and intake itself they had the wrong ones on there don' t ask.I also took the carbs apart and put new o rings needle valve etc. and cleaned the carb out. Now my problem is when I cruise around at 25 35 she gives a little hesitation but she puuls great and rides great at higher spead and cruises great on the highway. Also she starts great at cold and warm but did noiticed that if she is in idle and I give it a quick hit with the throttle she will stall but will start back up help is needed thanks again

Have you adjusted the fuel screw at the front bottom of the primary carb?

Yes I did which is a pain and burnt fingers too is there a easier way with a tool

Just a short screwdriver....

Which way do you suggest to go in or out thanks

First all the way inn, then 2,5 rounds out.

count the turns you go in! and don't tighten it or you'll break it!!

Often a stutter when giving throttle is the needle circuit. The slide opens up but gas takes a second to catch up. I'd raise the needle one clip after verifying mixture setting. Borderline lean pilot jet will make it worse.

I did purchase new jets and did put everything stock and did turn the screw 2.5 turns out . I will try to adjust needle up one also what should I use to raise the needle thanks.

If your needle has multiple groove you move the clip down one groove, if ther is no grooves like mine I had some thin washers that I put underneath the clip when in the holder. Only needs to be .015"-.025" thick.

Would it be easier to take carb off or can I leave the carb ? Also when cold start she takes time to warm with the choke on only. After warmnup she runs good even when after running and sitting for about 1hr and hot outside I have to choke then ride push choke in goodvto go maybe same problem thanks again

Sounds good. It should need choke to start and warm up for a minute or two. Much more than that it may be a sign of running lean. Did you take the spark plug out? What color was it. To check the needle you may be able to leave the carbs on the bike. Just take the tank off and most bolts should be right there, I used a 90 degree screwdriver for some of mine on the secondary.

maybe I will raise the needle and leave the air mixture alone cause that might richin it up allitle. For the plug drive it then check correct? Thanks

For best results go for a drive and hold the throttle steady at the rpm range you want to check.(18k to2000rpm,then 2500rpm, then 3000,even 3500rpm) Drive for 2,3, even 4 miles/km like that, then quickly pull in the clutch and shut the motor down(before even stopping if possible). Pull the plug and look at the color.

It should be a light grayish or light tan color. If white or real light colored it's lean, dark brown or black= rich. You can do that at several rpms to get a decent idea of what's going on. It is also best to start with a new plug or one that is cleaned. An old tarnished plug may not be as accurate.

This isn't a do-all /end-all way to know just what is going on but it is pretty good for getting close

Actually this is a very GOOD way to check your mixture. It is called a plug chop and your spark plug never lies. Use a fresh plug so you can read the color correctly. Only better way is to use an o2 sensor or EGT (exhaust gas temp) gauge but either is expensive so the old plug chop is your friend. Just buy several new plugs to throughly test thru the ranges.

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.

I have found out that on 2 strokes, new plugs yield a more consistent result.

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..

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

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.

I let her warm up she will stall if I don't push the choke in slow cause she reves up a little

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!

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,

No, its called lean jetting :innocent:

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 :scooter:

If you have to wait several minutes before the all parts of the engine have oil it would be dead along time ago...

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.... :blushing:

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.

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?

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.

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 doh

Agree to disagree? :oops2:

My choke question wasn't asked because I didn't already know , it was to make a point. Isn't much to jetting that I haven't done 25 yrs ago. Now EFI, just dabbled a bit so far.