Well, never thought i would be in this section of the Vintage Enduro's forum? LoL! 4 strokes!  In fact i am not suppose to be buying bikes at all. Bought this nice XT250 plus a matching XT200 a few weeks ago. Both were pretty nice bikes for sure. I went thru the XT250 1st. No matter what i buy or how nice the bike is i always go thru all the maintenance area's of the bike myself. You never know what people do or don't do. I am always glad i do it.
 
I remove the gas tanks, seats and exhaust. I get rid of any gas in the bikes and use it for my riding lawn mower since i used it weekly. This way i can fill the bikes up with non ethanol gas( real gas) from this point on. I remove and completely go thru the carburetors. I remove the fuel petcocks and rebuild them with all new seals. Check the gas tanks for dirt or rust inside. In the case of these 4 strokes, I adjusted the valves, replace the sparkplug, change oil and filter, replaced air filter. 
I removed the monoshock, lubed both the mt bolt and lower swingarm pin.removed air box and clean it.  Adjusted chain, lubed cables and just clean as much area as i can. Check all lights and horn. Check and charge battery or replace.
I always use genuine Yamaha parts and yes it gets expensive real fast. Before you know cost was just about $375.00 in parts just to service this bike. The past owner told me he had his mechanic just go thru the bikes and cleaned the carbs and checked everything out. That always worries me. This bike started kinda hard cold but seam to start and run fine warmed up. Had a very little ticking noise in the top end. Nothing serious.
 
Here is what i found during my service of the bike:
1. Valves were loose by about double on the specs. I don't think they were ever checked by looking at the o-ring seals on the valve covers.
2. Wrong sparkplug in engine.They had a resister plug in the bike because Yamaha doesn't sell the BP7ES anymore. Well Honda does so just buy the right plug from them.
3. Carburetor was a mess! It was clean just not real clean. Missing parts on the choke lever. (very small spring & ball ) gone!  float level off, needle assembly bad, All internal o-rings dry and cracked bad, Air screw out 4 1/2 turns! I replaced all o-rings, gaskets, needle assembly, The little spring & ball (which was available!) and cleaned the carburetor like it should have been. Set all adjustment to spec's. I also replaced all fuel and vent lines with Yamaha OEM parts.
4. Bike had some goofy air cleaner element in it. Dry as a bone. wasn't doing anything. Installed factory new Yamaha fuzzy filter and oiled it.
5. Rebuilt the original fuel petcock, all new seals. It was in good shape and has the filter screen in place. Gas tank super clean. 
6. Charged battery, seems ok.
7. Changed oil and filter even though he said it was just done. Oil was very thick that was in bike. I used Yamalube AP10w-40 4T since they don't make the 20w-40 anymore which was recommended in these bikes back in the 80's.

Then i started doing some research on this model and come to find out there was a service bulletin back in the day for getting more oil to the top end and less to the crankshaft on these 250's from 1980-83 on 3 different models. If the service had been done by Yamaha there would be a center punch mark on the engine serial number - right above it. This one didn't have it. I guess from what i read these bikes if run hard or long periods of time the top end would destroy itself from lack of oil. So after a little more research and watching some youtube and reading the Yamaha service bulletin i went ahead and performed it on this bike. You just take the clutch side cover off, get a 6x20mm steel roll pin and knock it into the crank shaft hole 7mm deep. This restricts how much oil gets to the crankshaft and allows more oil to get to the top end. Luckily this bike wasn't run at highway speeds or long runs. I took a good look at the cam and inside the head area when doing the valve adjustment and it look like new. Anyways it's completed on this bike and i marked the serial number with a punch where people that have done theres told me too, 

Any of you XT owners know about this bulletin?

Now this bike starts super easy. 1st kick cold or warm everytime. No hint of being cold blooded. Runs like a swiss watch. What a difference! I must say these 80's Yamaha 4 stroke enduro's are a blast to ride. This one has plenty of get up and go on the street. Much better ride then the old bikes with almost double suspension travel. Plush with a good seat height still. Love the newer levers, grips and handlebars on these bikes compared to the early 70's 2 strokes. 

Absolutely no vibrations, rattles or strange noises. Very smooth quiet 4 stroke with a broad powerband from idle all the way up.Great throttle response. This bike and the XT200 didn't come with tachometers. I guess you didn't need them? I'm very impressed with these early 80's bikes. You don't see them much and i certainly never rode one. Now that i have i must say it's a big feeling bike for a 250. Has a massive 510x17 rear tire and 21 front. Great suspension and seat, wide handlebars and nice levers and controls. I know when riding the XT200 it's much smaller feeling bike but still peppy for a small 4 stroke. Much lighter feeling. It looks base off the XT125 platform. 

As you can see in the pictures i'm about 1/2 way done with it. Valves adjusted, new sparkplug, new air filter. complete rebuild of carburetor, removed monoshock, cleaned and lubed mounting pins, adjusted chain, new battery. Battery is in a very strange place! sits in a plastic container right in front of swingarm pivot down low. You remove it thru the bottom of the bike. At 1st i thought this is going to be a bear to remove but actually it's easy as can be. Two 6mm bolts. unplug the red wire and out she goes.  

Here is a couple of pictures. two of the finished XT250 and one of the XT200 half way there. 







 



 

Wow that's quite a story & i hate to admit it but i would've just checked the oil & carried on into the sunset they looked 'that good'.
So i've got lots to learn & i must say you're sure doing it how it should be done.
Great patients required to get the desired result.

SKYDANCER , any chance you could post the relevant Service Bulletin , for future members reference .

Swoop56,
I seen it on a XT forum. It's not very legable to post but i typed in Yamaha XT250 bulletin on google and you will gets links to it. All copies i have seen are bad. A guy on youtube actually does the update on the bike and shows the Yamaha bulletin. His name is Jimmytmoto and the video is called Prevent oil failure 80-83 yamaha sr250 xt250 tt250 roll pin mod. That's where i seen it best. 

If i can find a good clean pdf file i will be sure to copy it. 

RT325,

That was my thought when i seen the bikes. I didn't even start them when i went and bought them. The guy wasn't the original owner. He purchased them from the original owner and he is a Honda freak. He has some really nice vintage Honda's and a nice shop and garage. I think he said he knew the people that had these Yamaha's. Once home and i seen how they started especially the XT250) and heard the slight valve noise i knew i had to go thru them being 40 years old. I don't mind it as i like working on bikes being a mechanic for over 40 years. I'm just done doing major work or restoration. 

I finished the XT250 just in time! Tomorrow is the best one day Vintage motorcycle show around at the Gilmore Car Museum in Hickory Corners Michigan. Good weather too. I going to drive on up there and take the XT250 with me. Might enter it into the show or set it in the swap meet area, I do have some old parts to sell. Last time i took a bike up there was 2017 and won 1st place with the 73 Suzuki TS400 i restored. 

Last year i was going to take the 68,70 and 71 DT1's and enter the contest but it rained. So no go. I was sure the 68 would have did well as i have never seen a 68 DT1 at this show. Seen everything else. 

This 83 XT is a good looking bike. Very clean. Only items i painted was the muffler and skid plate. All the rest i left alone. Looks better that way. It still has it's flaws but not much for being over 40 years old. 
She's all loaded up and ready to show. To bad the XT200 wasn't ready. Would have been great to show as a pair. 





 

When we serviced them at work we had a genuine Yamaha pipe that was about as tall as say my hand width. It screwed into the small bung in the top of the oil filter housing & stood vertically. I think the story was, if it rises out the top it's good to go. But I used to fit a clear plastic tube to the top & hold it straight up to equal to the cam so at least I knew it was good to go. To be honest I never found a faulty one. In hind site I think that idea was to blead the air out of the filter housing on filter & oil change but to my mind there gotta be air bubbles going around the whole system so maybe was just to get the filter full & good to go pumping up top. That also reminds me of "might've been TT & XT 500's where they sent an updated oil pump with an extra screw around the face clamping the two halves together, don't think it was 250's. Gotta be careful with the two Orings behind too if the pump has been off. Anyway--now I have you worried--don't worry!!, you have two mint bikes so go and enjoy them. Without reading back sorry I guess you removed & greased the moving parts of the swing arm including where it connects to the monoshock. We had those s/arm bushed wear terribly plus the bolt seize in the back of the motor. Top one would seize in the monoshock too. But on a positive note lol it looks like yours has never seen dirt or wet weather.

RT325,

Nice to know. There is a small bolt in the top of the cylinder & head area that your suppose to loosen when starting the bikes after a oil and filter service. You should see oil come out that hole within a minute of starting the bike which tells you oil is flowing up to the head.Then you tighten the bolt and your good to go. I didn't even know that until i read the service manual? Worked great on the XT250. Oil was there in a few seconds after starting. 

As for the monoshocks, yes the pin in the lower mount and bolt in the upper mount slid right out with my fingers like it was a new bike. I did lube them up. I remember my old IT Yamaha days and stuck pins???

I'd forgotten about the one in the head. Thinking back, the tool for the oil filter housing maybe was my idea too avoid a mess when removing blead screw then oil p#%^s everywhere so come to think I just used an extension from the shop vacuum gauge kit 'don't tell anyone' lol. Think I used that just because it fitted & maybe as a test of how far it would lift, not sure now. Did similar with the top bolt to avoid a mess using something that fitted. That was about 45 years ago haha but things ya remember at times like this. I'll find a pic of a TT250 cam worn out & the bike barely ran. Just inlet lobe. No lack of oil just a bad cam. Only the inlet. Pics up here somewhere maybe by searching but too long ago probably. I'll find it tonight just for a talking point. Had me head scratching as to why it sounded so flat & was gutless but ran perfect & was silent as wear was on the lift not on the back where you set tappets.

Here is a picture of the mod on the crankshaft. You can see the 6x20mm roll pin i installed inside. This restricts to much oil going to crankshaft and not enough oil getting to the head. I was surprized Yamaha messed this up.

2nd picture you can see the small bolt up near the valve cover with the paint worn off the engine that you loosen when starting the engine after a service until oil comes out.

Skydancer the XT250 is one iconic bike, I mean there is a reason Rambo is riding one in 'First Blood' and your workshop is super clean - I am very jealous, maybe if I could keep my desk clean I could keep my work area clean too! There used to be a lovely humped bridge near a place I would regularly visit and this one dude had an XT250 with gold anodised rims and he would always, every time without fail, pull a stonking wheelie as he rode over the bridge - I would get such a kick out of hearing the 'braaap' and then watching his front wheel rise up over the crest of the bridge - thanks for all the service tips.