1980 XT 250 project

So for a few years I’ve been collecting Yamaha Xt250 bits and pieces to eventually put a bike together. Being used to two strokes, it was very foreign to work on the valve train and such and some tools were bought and/or modified to help.

At swap meet, I came across a bottom end for a 1982 TT250, and that allowed me enough parts to put a motor together. So I put this motor together and then I came across an old XT that looked like it’d been submerged or left out in the weather for years (matching numbers :D .) The swing arm and bolt were fused together, so with some interesting angles dad and I cut them out with many cuts with the cutting disc. The frame and motor had to be saved and the shock was salvaged although in desperate need of rebuild. So after a lot of cleaning and bolting together I ended up with a rough running bike. Carby issues are still a problem to this day, but I haven’t spent much time on it of late due to school and other things. I’ve read that the mikuni carby on the single cam XT’s are hardest of all the VM series to tune. Before I give up and buy another carby or a kit to put through I plan to put what I have through every technique known by me or google.

So I had a really nice exhaust that I bought from a guy at a swap meet and it bolted straight up and was nice. He sold me some timing bits and pieces and most of it got used in the motor build because it was in good condition (he said it was a low km bike he wrecked out.) But the old muffler that was on the bike was full of rust. I tapped around with a screw driver and it was like swiss cheese, not to mention half of it including the pea shooter was missing. So I cut it as close to the muffler as I could, as everything between the back of the muffler and the head was just surface rust on the outside and thick carbon on the inside bar the heat guard plate thing, the bolts were seized up and took fair influence just to strip the heads off the threads, but then it is an old exhaust. I managed to save all the guards from the muffler and pipe so they’ll be put aside or put on the good muffler.

Anyway, so with my cut off pipe, I thought I’d make up a pipe to run from the cut to a muffler that will come later. Using cardboard templates and 3D models, I made my design. I used a door from a laundry sink (8mm mild steel sheet), cut out each piece, beat it using a piece of water pipe as a dolly after wire brushing the inner surface (just in case), spot welded each end and then ran weld up the seam. I then cut my angles, chucked some spot welds on and test fitted. After doing more seam welds at each joint, I realised that maybe I need more practise with the welder. I was using gasless on the mig which seemed to spatter a lot.  So I gave the seams a good go with the grinder, and they’re still mega lumpy but they’ll get there eventually hopefully.

 Got the shape I wanted! It's no weak pipe either, nice and light too. Well, lighter than I expected. It's probably a smaller wall thickness than desired but not a bad first time!

 Recycling will save the planet ;) . Dad cut up an old laundry sink and I saved the door. Didn't know at the time that I'd actually use it :P

Test fitment! Just a couple tacks on each joint to get the shape. Thin material though, kept blowing holes with the welder

 You can see here, I've got an 83 twin cam XT seat cable tied on. Bounces around at speed which is spooky haha. It's also seen a hard life. It was also a swap meet item, being swapped for a valiant ap5 manual.

 This was a template I didn't use, as I took this photo after I made the 3D template. Gives the general idea though

 3D template puzzle pieces!

 There's a pipe missing here. The one second from the left was a failed test piece, and the far right was a trial piece. Old cut off muffler in the background

 Here's what's left of the old pipe. Just gave each shield mount a bit of a grind as they were seized up and horrible. You can see the bolt/s missing from the clutch cover, just haven't cut them to size yet :/
You can also see where the kickstarter contacts the rear brake lever. I have yet to fix that too. Seems the lever has too much movement in it's shaft for some reason, although it shouldn't, it has a split pin and washer on the other side from memory.

See the lovely ding in the tank? Makes me sad but it's not a priority right now. It got a new front tyre (Dunlop D606 I'm pretty sure) not long after this photo. It also got a fuel filter cos the tank is full of rust -.- slowly cleaning it out after each ride. Dad reckons there's a plastic surface coating thing you just chuck in, shake it up, pour it out and let it sit that'd be nice.

Plans are:

4 bolt flange for existing pipe so I can just bolt on anything I make

Try different things with the carby

New rear tyre

Get fenders, a seat and a tank that doesn’t have rust

More work on the front forks as they’re rooted

Pull it all down, do some lovely rust removal and paint the frame

Wheel bearings (They’re fine for now though)

Brakes! Got nothing up front and either off or lock on the rear

Replace the cam, I had to buy rockers as the one I had were stuffed, but my cam still has flat spots. It runs fine but I’ve since gotten a spare good one to put in

Get oil gallery restrictor pin for the crank (Yamaha guy in Victoria couldn’t find anything on it… Bit suss)

General clean up and who knows what else

5/7/14
Did some more carby tuning over the past two days. Yesterday, I put boiled up the carby to loosen up the loads of fuel resin that XT's are notorious for and today I set the float and the accelerator pump. Slight improvement, as I'm setting the float by feel over time, because I haven't got clear pipe to suit doing the actual setting check specified in the manual. I forgot to mention that when I rebuilt the motor I didn't have a valve compressor, so the valve stem seals are absolutely non existent. Every time you get some manifold vacuum, it sucks a bunch of engine oil into the motor through the valve stems. It makes me happy to know the head is getting some oil though.

 This is my carby on the stove prior to boiling. Mum luckily let me do it, but the house smelt like wet carb afterwards.

 Pulled the carby down and blew out all the water, and reassembled all the bits that didn't get boiled.

 Carby reinstalled, I read somewhere that apparently you have to take off the air box and swing arm and all this stuff to get the carby out, but I just remove the seat and tank, disconnect the accelerator pump and pull it out. The rubber on the air box side is malleable enough to allow it, but it's a game of tetris. There's only one way to get it out without removing everything around it.

 Bolted on the stock exhaust because I don't fancy blue flame up the leg. ;)

Got it running! Didn't take long, just had to fill the float bowl with the tiny amount of fuel I had available. Had enough for a warm up and quick ride around the house. In this photo you can see burnt motor oil coming out the exhaust, and the motor was still running rough. Had to pump the rear tyre up as it has a slow leak.

So it's coming along very slowly, tomorrow I plan on going back and doing timing again, and some more carb tuning. I really need to pull the head off and do valve stem rubbers, I have a pair from the gasket kit from the rebuild. I have the tool, I'll just need a head gasket to do it. I also have a spare head with a bent valve, but a good cam and good rockers. I might just put that together and do a straight swap.

6/7/14
So today I adjusted timing and cleaned up a spare carby. So now I have that one ready to be bolted on if I need it. A couple small bits are missing so it would require saving bits of another carby to use it.

 My spare carby had a fair whack at some point because the lump inside the mount fowled on the throttle slide. I took everything I could off the slide and ground it down until the slide came out. I noticed previously the throttle jammed on this carby...

 My carb bits that were separate from the carb prior to boiling.

 Carby ready for boiling.

 This is my spare head, The inlet valve in my hand is slightly bent. I like the head because it's so clean.

The rockers in the head are incredibly good considering XTs tend to eat heads... The originals for my bike despite one being broken, were worn concave. These have a lot of meat on them in comparison.

 While I was doing timing I did the cam chain tension. The pin was slightly below flush so I wound it up a bit till it was flush again. Small job for an extended valve train life.

 Here's my pick-up coil on the magneto. I realised before that I'd been setting the gap incorrectly, because in the manual it showed the gap coming from a side on. When I had done this previously, my feeler gauge fowled on the mounts, and lifted the pick-up too high. I went front in this time.

Magneto assembly... There's no trick to getting them on or off, just have the correct tools. Tensioning and cracking the nut is painful, and having a special puller is even hard to use sometimes. Especially when the motor is sitting on a bench half stripped. Sometimes the puller just needs a tap and tighten to pop the magneto off.

So after today, the bike ran a lot better. I think that a lot of my issues came from timing, and I'd been setting the carby to what I thought was right. I knew that even advanced spark wouldn't cause a whole lot of carbon coming out the exhaust. But it runs nicely now, despite being bogged down by oil. It also lacks in the mid throttle range which is carby, I think the accelerator pump. Every time you give it wide open throttle it sucks oil down through the non existent stem seals, so it's really boggy, smokey and looses power. Until you give it wide open throttle again, which is an endless loop. It's really annoying in low speed cornering when the motor won't sit at low revs and it cuts out mid corner. But, vast improvement, it picks up the front wheel when you give it heaps in first which is a good sign... I'm getting close to having some power finally.


13/7/14
So it's been a week since I've done anything with this bike, but I made great progress today. So I continued to play with the float level in the carby today. Because of the bike seeming to lean out at high revs, I lifted the float height up a small amount. It ran rich, still missed and carried on and when I came to a stop the motor stopped and the carby dumped fuel all over the top of the cases.

The spark plug said that it's getting too much fuel, because it had carbon growths on the pickup. It's a bit hard to see in this photo, but the spark plug is not in fact fouled, which is why I thought the motor would miss under high load. Dad suggested changing the ignition coil, but I didn't have a spare. What I did have spare was a voltage rectifier, which is a small alloy box with a single yellow wire attached which is mounted on the frame near the coil. I changed that over, along with some new bolts because the old ones were rusted in and the heads chewed out. I then lowered the float level again. The results were instant, there was no miss fires and power was improved. As well as the plumes of white smoke every time it got any sort of manifold vacuum.

More carby work is needed. Accelerator pump needs adjustment as the motor bogs down in low revs and it's hard to rescue. Dad says it's because the manifold vacuum gets too high. Float level needs to be adjusted aswell because if you don't run the carby down with the fuel tap turned off it dumps fuel despite the float being lowered. The fuel tap leaks down slowly so the sooner the float is reset the better.

After test riding today, the oil running down from the tacho cable drive in the head ended up mostly on the exhaust and due to the heat of extended testing (high speed riding and plenty of sliding), the oil was burning on the exhaust. Needless to say, when clouds of smoke started coming up past the fuel tank I got a bit worried.

Power is a lot better, now small things like oil burning and leaks and squeaks will be chased.

6/8/14

Long time since I last posted, but I've been busy chasing a good ATAR for year 12. During the holidays I did a trip into the wrecker and bought a front brake assembly, a genuine tacho cable which I think is the wrong one (test when I have a bike weekend) and a bash plate. For the front brakes I had to buy the caliper, cable and some second hand shoes. With the bash plate it came out to almost $100, which was a bit rich in my opinion but it's worth it considering lack of brakes. I've been keeping an eye on my oil level, and I'm a bit suss I have a blow by issue as way too much smoke is coming out the exhaust for just valve stem seal. Also the motor is incredibly noisy from the tappets which is a worry for the cam and rockers sake, and considering the tappet clearance being spot on, I think it may be an oil viscosity problem. The bike has been put in the shed until the end of year 12.