Adjustments must be done with the carb on and engine running. it is underneath the carb on the engine side of the float bowl. It can be a bit awkward to adjust unless you have a short handled screw driver. (I prefer to use a socket type screwdriver head).

Make adjustments slowly and blip the throttle a few times between adjustments to allow the motor to settle. Keep a record of how many turns you make so you can always return to your starting point. Keep the motor slightly on the rich side when optimum revs are reached by backing out 1/8th turn.

Note: while performing this procedure it is best to also constantly adjust your idle screw to maintain your idle speed at 1000rpm before the next adjustment. A auto multimeter with tacho built in is really useful to give accurate readings because your ears can deceive you.

Just check your sparkplug gap!
If it is out of specified gap it WILL cause an overrich condition!

I it is correct, only then you should adjust your carb!

you got two things to do to that carb right now!
Number 1- Adjust the idle screw to 1300-1400 rpms or it will cause a lag on acceleration!
Number 2- Sparkplug gap!

You've been advised.. if you change the fuel screw before doing those two things you get the risk of the bike running like crap thereafter!

oh yes.. the RPM 1300-1400 rpm is stated in the Workshop Manual!!
Same goes for the sparkplug gap!

That wasn't the question.

First off if you want to check why a bike is running rich, as I said in my first post, first check the float level. Over time the bike will start running richer rather than leaner. Float level increases rather than decreases.
Then check emulsion tubes. The needles tend to wear them oval over time.
Then check carb synchronisation followed by jetting.

Why do I say the bike sounds burbling rich
a) because it is slow on pickup, but once on song sounds fine
b) because on snapping the throttle shut she burbles before dying.

Your low rev theory on "with the inertia of the engine which causes "underpressure" to suck in fuel in" is to do with valve timing. The intake valves close relatively late on the compression stroke at low revs as it relies on the inertial force of the indrawn air to seal the valve preventing blow-back at extreme low revs as when the revs climb the piston will always be moving faster than the drawn air and so maintain a vacuum even into the compression stroke. Valve timing, unless variable, is always going to be a mean best affair. However, variances of the level we are talking about have absolutely no effect on the ability to draw in fuel. You'd never be able to flip, kick or crank start an engine otherwise. How fast do you think your starter motor turns your engine over? However, I will concede the book of words says 1300rpm, though if you did deeper into the rationale I'll think you'll find it has more to do with continuity of motion and balance issues in single cylinder engines more than fuel draw.

Changing the gap in a plug, does not give you a bigger and better spark as the gap increases and has precious little to do with the burn rate of fuel (leaving an enriched state). The true nature of gap size has actually more to do with plug resistance and when the plug arcs. The reason for the larger gap is is simply down to the lower compression ratio in the bike and the cooling properties of the plug to prevent pre-detonation. Increasing the gap increases the voltage required to arc and makes the plug hotter and also more liable to pre-detonation (which could well be why his bike is pinking). In the lesser of two evils a smaller gap is less harmful all round.

I'm not the one who said she was rich, you were.. :confused1:
I just commented on your statement were you said it was rich.
And that rich situation can be caused my an improper sparkplug gap, so check it first before going on to the carb that's it!
Because as I know, and I do know, and probably you do too, properly jetting a carb is not easy!

As far as the sucking in fuel I might have not have expressed myself correctly but the point is, low idle does give a lag when you hit the throttle.
why complicate when he just wants to fix??

I'm not having a go at you Vando, but maybe your heavy use of the exlamation mark doesnt help your cause. Nor does deviating from the OP's direct question. We are here to share knowlege not simply to diagnose and repair. Any advice given is taken onboard and acted on purely at an individuals sole discretion and responsibility after making a judgement of ALL the advice proffered. I am assuming that they can do this as they are adults, no?

However you are still wrong. Running lean or rich has nothing to do with sparkplug gap. That is purely an air/fuel ratio. You can fool yourself by changing the gap into thinking you have solved the problem. For instance by widenning the gap the plug runs hotter and so burns off all residue making the plug look as if the engine has run leaner; and conversely by lessening the gap you make the plug run colder and so collect residue making the bike look rich. In both instance your AF mixture hasn't changed one iota and all you've done is impair the life of your plug and made a marginal change rate to the burn cycle.

Low idle will indeed give you a bit of lag. His lag was all the way up to 3k rpm so I doubt the low revs were relevant. As I said in my previous post, the reason for the relatively high idle rpm is for continuity of motion through 4 strokes. Single piston engines generally dont have the crank mass to maintain enough gyroscopic force when engaging the clutch from standstill and will bog down and stall. Lag from idle on an unloaded engine; even if the idle is too low, should be nothing more than a single revolution or two's hesitation. If the engine burbles until on song while unladen she is simply too rich. (Note I said burble not miss) Also when snapping the throttle closed there will not be a lag below the mean idle speed before the engine settles.

Now testing an engine to give you optimum AF mixture while unladen will almost certainly be too lean while under load, hence why I say back out 1/8th turn rich when making adjustments after going through the standard maintenance checks for float height etc.

But if the bike is cold, it runs richer as it doesnt burn all the fuel, that would also explain the stall, and the hesitation.

Theres to many maybes, and to little input from the troubled owner.

That is true, and you have stated as much already, but as the rider has had the bike for at least a year don't you think the poster would know the difference?

There are many maybe's. I said in my original post the engine sounds as though she MAY be running rich and then proceeded to justify and detail remedial action. You said cold and low revs etc. Together they form a matrix of things to check right? No need to start running off shouting (I believe that is the primary use for excessive exclamation marks) your stated opinion over another posters because soon it starts smelling of one upmanship and self promotion. Every one has an opinion and should be allowed to express it without being railroaded. I could well be wrong in my diagnosis, I have been plenty times before. I have also owned an XT in one form or another since 1978 and rebuild scrapped bikes to showroom condition for a hobby so am not entirely without reasonable credit to provide an opinion, no?

Couldn't agree more

Hello guys, thank you for posting your ideas and theories
Btw the bike was probably cold, I didnt think about that..

Ive been driving a bit now, first time this season and I think everything must be ok. Ok so its not revving like a dirtbike but i dont think its very far from lifting the front wheel when you accelerate from 1st gear and 2nd, and when you think about the riders weight of 136kg that cant be bad. I was turning onto the road the other day and accelerated pretty hard and the back wheel was sliding a tad bit and i started to think that this tihng must have its power onboard after all.. Im now also waiting for a mikuni tm34 from off-the-road.de Should be fun to see, but thatll probably be tha last time i invest any more moeny in my xt.

Nice, please keep us updated on the new carb.

Will do, i just read on a swedish forum that just by changing to this mikuni tm34 a xt600 changed enormously and about like xr650 :S

Ok the carb is fitted now Its a mikuni tm34-b65 from germany pre-jetted for xt600. Response is a ton better and it feels lighter when cruising on the road..more momentum.

Acceleration is good but when i give 85% throttle very fast it surges or bogs for a second. If accelerating not so aggressively though everything seems fine. No surges/bogging when cruising at any rpm..Sincei ts a flatslide with acceleratorpump it may be normal,ive heard that you have to learn how to use the throttle with this type of carb. Or maybe a tiny adjustment on the acceleratorpump is needed.

And with the original carb i never bothered going above 5k rpm because all power was below that..now there almost like a new powerband above 4500+ compared to before.

Sounds like you have some rejetting to do. How did the carb fit, and what did you need to do to make it fit/modify. Was it this one: http://www.off-the-road.de/de/Divers...hschieber.html

Looking forward to hearing more.

Yes thats the one, from offtheroad.de. I specified the bikes current modification, like airfilter and muffler, then apparently they put in the correct jets. A german installation document came with it but it wasnt easy to understand, but it lists what the carb jetting was..blabla main jet pilot jet etc.

Also, a smaller jet was in the kit but I didnt do anything to the carb.

This carb is supposed to fit bolt-on to the xt600.. The only thing is that the left carbs air intake is bigger then the standard carb but theres a plastic converter in the kit. The only trouble was getting the rubber inlets etc onto the carb, because its pretty tight in there. But the original carb wasnt any less tight i think..lets just say, it took me 3.5 hours to get the carb OUT (including pauses and posting on the internet etc )..

Getting the mikuni in was hard..well..i got it in there but thats when the problem started. Getting the carb inbetween the cylinder and airbox is quite easy, the problem is then to get the carb into the rubber..gotta use some force. I had to just push it "through" the rubber inlet..from below.. that made it partly inside the rubber, and then i had to use a screwdriver carefully to just slip the rest of the inlet onto the carb.

It was the first time i tried to take the carb out/in, so maybe this is quite normal. Im not sure getting the original carb back in would have been any easier, but if i have to do it again(id rather not) i would have taken out the rubber inlets first to get some more space in there.

The XT started up like a new motorcycle on the first touch of the starterbutton And ran fine

The only thing now is to try to adjust the acc.pump a bit. Theres external adjustments screws i think for both when the acc pump should start and when it should end..And when you give alot of throttle fast i think whats happening is it gets alot of air and not enough fuel so the acc.pump must be set to end at a higher point..(or maybe opposite, not sure, but anyways it runs good without adjustment too).