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

I recently was having issues with my 1984 XT600 (LC) dying at highway speeds. If I let off the throttle and tried to cruise at 55mph it would sputter and die. After a weekend of troubleshooting I found out my XT600 had a black screw in valve under the tank. OK, so California models suck. Literally, the clogged "roll over valve" was causing a hardcore vacuum in the tank and making gas and air evacuate the carb bowl and travel backwards up the fuel line. This "roll over valve" is listed as #26 on this diagram:
1984 Yamaha XT600 (CA) XT600LC Parts, 1984 Yamaha XT600 (CA) XT600LC OEM Parts - BikeBandit.com

The previous owner just removed the canister and plugged a long piece of fuel line from the broken roll over valve to a nipple on the carb just above the fuel line nipple. I just removed the roll over valve and it will just act like a vented tank now I'll eventually try to put a one way valve on there like they sell for MX bikes to let air in but no gas fumes out. in the winter when I store it I will WD40 the empty tank or fill it with gas and add stabil to prevent rust from condensation.

The scoot will run with that nipple on the carb plugged or unplugged. It just makes a sucking noise like "ffuff fuff ffuff" as you go down the road. This leads me to believe that dirt could get sucked into my carb bowl... so I'm going to cap it off. pretty sure thats a safe bet as the parts fiche doesn't even show the nipple on the carb.

So if you have stumbling issues at highway speeds make sure its not due to crappy California emissions gear that is faulty/improperly removed. I made sure this fix was repeatable and sound advice. I put the parts back on and the fuel line to connect them and it caused stumbling EVERY TIME. Take it off and it stopped acting up EVERY TIME. Also make sure you're not lean due to your airbox snorkel coming off under your seat as I'm sure that was not helping the troubleshooting process.

Just thought I'd share since I was sooooooo pissed off at it this weekend and there wasn't a ton of California Emissions stuff linked to sputtering out at speeds. And I know the roll over valve was bad because air could not be sucked or blown through it and if tapped on a hard surface debris would come out of it.

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Perpetually fixing an XT600 as old as I am...