Hi , I need some help Please . I bought an 89 XT 600 with the top end off and needing to be rebuilt.

I just put new Yamaha .50 piston and rings in it and new timing chain , new valve seals, also lapped the valves into the seats. put it on the bench put diesel and it did not leak though the valve seats . we put the engine together ,, cam lobes all pointing down , piston up top dead center and the marks on the cam sprocket and fly wheel lined up. adjusted the valves to maximum clearence specs . I also cleaned the carbs , put a 130 main jet in and turn out the mixtures screw to 3 full turns . I even put on brand new intake manifolds/boots on it and siliconed the rear air box boots around the seal where it meets the airbox. I used propane to see if there is a leak somewhere , never made a difference in the way it ran.

it kick starts fairly easy , seems to idle but it with pop back through the carb , the plug is white when I pull it out to check it. the engine heats up really fast .

we couldn't do a air leak down test or compression test because my buddys fitting didn't fit where the plug went , his fitting was to big . but starts easy and the deisel didn't leak through the vavles while on the bench . he did have a fitting to just put air in the cylinder though , he put 45 lbs going by the commpressor guage and we did get some air through both intake valves and 1 exhaust valve .

Can someone point me in the right direction , am I having carb problems or head problems ,, I'd hate to pull that head back off , but if it has too , then it has too.

Thanks Randy

Did you forget to fill the oil?!?!?!

First things first!

Make sure the oil is circulating nicely!
just turn the bike on and immediately go to the oil blew screw on the top of the oil filter casing and remove it very carefully because if the oil is circulating as it should you will get an oil shower!

(it happened to me a couple of weeks back lol)


Vando

Adjusted valves again. Have a look at timing chain

I took off the valve adjustment caps on the rocker cover ,, there was plenty of oil up there ,So I'm assuming the oil is circulating, the valve clearence is still where I adjusted them too.

Think maybe the timing chain is off a tooth ?

I'd first check the carburettor. Why did you install a 130 main jet? The orginal one incorrect? How do know? According my info most LH side mainjets are 135 or larger on the XT.

Check:
- Float level
- Synchronisation of second stage - should not open at the same moment as the first stage, but only after 5 - 6 mm lift of slide valve first stage
- Needle positions first and second stages
- Remove the little filter on top of the float valve seat
- If this is an older bike, the mixture (idle) screw might need another turn out - but wait till you have the rest sorted

I don't think you have a head problem.

Auke

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Auke
http://aukemarieke.blogspot.com

2003 model xt600 has 130 primary mainjet (left carb), and 120 secondary jet. ( right carb) And they are jetted fat from factory.

I have another set of carbs off an 86 xt 600 parts bike that I picked up . I put them on it ,,,,it ran the same as with the original 89 ones,

Both sets of carbs had 125 primary main jet in them main carb , thats why I went up to a 130 , I do have a 135 I could install .

I took the little filter screen out already , the other set of carbs didn't have one.

The needles are fixed in the secondary carb , so I didn't mess with the needle in the primary one.

I didnt touch either set of carbs butterfly adjustment for the secondary carb,, since both set of carbs made the bike run the same way , thats why I was wondering if it has a head issue.

I'm puzzled.. air mixture screw is 3 turns out already .

Thanks for the feedback and guidence , I really need the help .. I'd hate to send it to the dealer to get straightend out , it'd cost me a fortune .

Thanks Randy

Take your air filter out and make sure all passages are clean and try again. The air box has a tuning effect much like the exhaust has and any blockages / dirty air filters or corroded gauze can have this sort of impact. Especially around the midrange upwards.

Today , I turned the mixture screw out another turn , so now it's 4 full turns out , still doing the same thing.

I cleaned the air filter and air box before I did the carbs , now I have a single small air filter , it goes over the metal cage,, but I believe theres supposed to be another one that goes over the smaller one and cage , making it a 2 stage filter set up.

I looked it up online for oem parts and it shows 2 filters ,, Man would that be nice if it's only running the way it because of the filter set up ..

It does it also though with the choke full on .

Thanks

My money is still on air starvation. The carb wont work right if there is an intake imbalance. You may want to check that the silicon you put on the back rubbers hasn't blocked any of the small air entry ports at the back of the carbs. For future reference, use grease and not silicon.

As I understand we are talking here about a problem with idle running. This means that the airfilter (in / out / 1 or 2) is irrelevant: the flow is so low that there will be hardly any resistance with whatever setup.

So, if it's the carb, we have to look at mixture preparation for the idle circuit.
Lean running:
- Low float level, you did not say you checked that
- Low fuel flow, although a long shot: same as for air filter
- Air leaks
- Synchronisation. I have seen these carbs 'adjusted' so that the 2nd carb is slightly open @ idle - there will not be enough air flow to make petrol flow from 2nd stage jet, but there will be additional air into cilinder, leaning out the mix
- Blocked idle jet or passages
- Air leak in the coaster system?
- The needle in the first stage does have a slight influence on idle running - check again the setting. (Remark: needle second stage fixed? Not on European bikes, and I cannot think of a reason why they do that on USA bikes)
- Why not turn the idle mixture screw out another few turns - just see what happens. Improvement -> we are too lean. Worse -> we are too rich

I would vote for lean running, but in the same way the carb should be checked at idle for too rich running.

The best way to troubleshoot a carb is by bringing it back factory settings, and then to start changing - one thing at the time.

__________________
Auke
http://aukemarieke.blogspot.com

The silicone is only on the boot section That meets the air box ,, I have only the tightening clamps on where the boots go over the carbs .

I also ran the bike with no silicone on the boots back there and it was doing the same giving me a lean condition , thats why I put the silicone back there to eliminate that area from an air leak , I had already replaced the intake manifolds before this also.


I'm willing to try anything though. I hate trouble shooting.

Thanks Randy

I'm going to have to take the carbs off , I never did check the float level . How do I adjust that to make it richer ? I know there is plenty fuel flowing into the carb .

I'll have to check for the sync adjustment too . set it at 5mm .

I took a propane torch ( not lit of course ) and let it flow all over the carb ,, if there was an air leak at the carb it would have sucked in the propane and made it run different. it didn't at all , So I think I can eliminate an air leak .

Here in the U.S. all the mfgs, have thier bikes running lean right from the factory , due to the federal EPA standards for emmisions.. that might be why theres no adjustment on the secondary needle , I didn't even look at the primary needle adjustment since I seen the secondary.

I do have the spare set of carbs off the 86 parts bike , that I did try on this bike and it ran the same . I could take that apart and Inspect and reclean it , adjust the sync on it , try to start fresh with that one.

Thanks Randy

Well, let's not assume the lean condition. What I meant is to adjust the float to the factory setting.
From the net I found the following settings for the carb (European 43F):
Teikei Y27PV/43F00
main jets: L/R 130/125
Needle Left: 5C37 / 4th notch from top (=blunt end. Are there really no notches on the needles? see picture here: [url=http://www.xt600.de/xt_werkstatt/_special/-special-vergaser/sek_duesennadel_assy.htm]www.xt600.de Sekund

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Auke
http://aukemarieke.blogspot.com

Can't get this working .
Continuation:
Right needle: 4A71 / 4th notch from top
Idle jet: 46
Float height: 25 - 27 mm. Adjust: float bowl off, carb upside down, measure distance between bowl mating face and top of float. Adjust by bending copper tap on float needle. 25 mm = richer, 27 = leaner. Keep it in that range for now.
idle speed: 1300 +- 50 rpm
Mixture screw: 2,5 out basis, although experience learns that older bikes need more turns: 4, 5 ,6 is not uncommon
Synchronisation: 5 mm, although there was a later bulletin from Yamaha, requiring 6 mm

Possible issue: it might be that there should be washers between needles and slides. Is everything there as it should?

Possible issue: loose electrical contact in the ignition, that plays up with vibration. All connections clean and tight?

Good luck

__________________
Auke
http://aukemarieke.blogspot.com