Vintage Dirt Bike Q & A

It took me about 6 years to finally get this thing finished. Still got a few things I need to do, but it runs and goes and stops. After I got the timing set and some gas in it, it fired right up. Runs really smooth, throttle response is awesome. I replaced the stock ignition with a PVL, other than that and the Mikuni, motor is stock with a 70.5mm Wiseco piston. I replaced all the bearings and seals, had Mr. Crankshaft rebuild the crank, and just cleaned everything up. I plan on cross country racing this with AHRMA, so I had Race Tech rebuild the forks for me. I'd like to get some custom shocks for it eventually, but I'll stick with the Progressives for now.

Got a XR500 plastic tank on it's way, this one is pretty beat up. I'm not real sure how the plastic one will line up mounting wise, but I've seen another MR250 with the same tank, so it'll work one way or another. I need to cut the steering stop off and make a new one. The old one is bent up pretty bad on one side so the bars hit the tank when you go from lock to lock. I also have a new seat cover coming in.

I'm going to try and take it out tomorrow and run it around some and see how close the jetting is. I took it up and down the street a few times and it felt decent, but I haven't been on a 2 stroke in so long that I really don't know what I'm listening for as far as tuning goes. It seemed kinda rich just past half throttle, so I may lower the needle one notch and see if it changes. I'm running the VM36 Mikuni on recommendation from Mitchie. Mostly it seems about right, but I never did ask what elevation he's at. I also stole his universal FMF silencer idea, it sounds sweet! I'm hoping if it seems to be running right, I'll take it to the Spring Trail Ride at Loretta Lynn's ranch this weekend. It's a really good trail for old bikes, nothing too severe. I can already tell it's going to be fun to ride though. I can't even remember what it was like to ride it's been so long since it was running last. And I already love the smell of a fresh motor after the first startup, but with the 2 stroke mixed with 110 race gas, even better.

That is Sweet!

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(2) 1968 DT1 1970 RT1M,1970 DT1C 1971 RT1B Enduro 1974 MT250 1974 DT250A (2) 1975 DT400B 1974 DT100,1978 DT175
1975 CR250M1 1979 CR250R 1979 Kawasaki KZ400H1 Jesus is Lord!!

Took it out for the first yesterday and I found out two things...

1. Must have at least blue locktite on EVERYTHING.
2. NEED SOFTER SPRINGS FOR THE SHOCKS.

I'm pretty sure I forgot to put locktite on a few bolts, but there were a few on it that are no longer there that I'm almost positive I did. Wondering if the forged piston is making the vibrations more severe because I don't remember it being that much of a bone shaker.

I will say this, the thing has got some great power. Pulled hills like a champ and I rarely opened it up that much because the rear end would kick the crap out of me on every bump. But that low end grunt was very nice even without the old flywheel. This PVL seems to be the business.

Now, I gotta look for some rear brake parts because the brake stay bolt to the swingarm fell out and the plate rotated and kinda tore up the arm and cable end. Had to roll down some fairly steep hills with just front brake and engine braking. On a positive note, the front brake works great! The rear did too, until it didn't.

Great job!

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'74 CR250M

Thanks!

Took it out for another ride last weekend and did about 25 miles or so on a 3-4 mile loop. One of the guys I was riding with builds some very nice CanAms and Ossas and had a sweet PE175 there that day. He races with AHRMA as well and knows a good deal about suspension, so I picked his brain a little. One guy thought I had Progressives for a lay down shock bike(like a PE does). But the fella with the CanAm and PE told me it may just be the wrong length as well as springs being too stiff. It was beating me to death!

My thought was partially that and possibly the way they are mounted. When I was trying to get the eye into the frame mount, they were REALLY hard to get in there. I sanded down the rubber on both sides of the shock eye to give it a little more room, but it was still a pain to get in there. I was thinking maybe the shocks are binding somewhat. But the wrong length shock is making me wonder as I'm pretty sure these are at least 1" longer than stock.

I'm torn on what to do. I was planning on eventually getting a set of Works for it since I'm going to be racing it, but I don't want to spend the money right now as I won't be racing it until probably the end of July. I'm worried that softer springs on these shocks won't help it enough.