I have a local track near me called Zoar Valley MX Park. Once a year they host an incredible event, and they've recently added 2 $$$$$$$$$$$ classes. One is a 125GP and the other is a 250GP. Rules are pretty simple, air-cooled, drum brakes, bike had to be equipped from the factory with them, you can't back-date any bikes. The hype leading up to this event gets pretty huge, as the rider entry list makes it look like it's going to be a killer race....
But sadly, it never materializes. Most of the heavy hitters break their bikes either in practice, or early in the race, leading to some uneventful races.
My question is.....what can be done to ensure some longevity? I have the bike already and it's 100% apart. Are they setting their ring gap too tight? Too much compression? Can the fins be modified to improve the cooling?
as others commented in Youtube, the 1981 4V3 did come standard with Gold rims. Also 43 mm forks with DLS (at least later in model year) and trans was changed to 5 speed instead of 6 like 1980. If that bike is a former racer it could be a bitsa with parts from both 80 & 81. They are a blast to ride/race but had some issues like the OEM ignition failures- which was already upgraded on yours.
Upon further examination the bike is a hodge podge of assorted parts. The frame is legit 1981, as is the engine. The wheels are DID wheels date stamped late 78, so likely off of a 1979 YZ. I'll be on the lookout for a YZ 465 parts bike lol. I can't identify what forks it actually came with. They are held on at the bottom of the right leg by 4 bolts like a CR, or much later year YZ's. I've looked at all sorts of partzilla diagrams for late 70's and early 80's YZ's with no luck at all. They are going in the trash bin anyways. I'm guessing they are from a DT or an IT. They are 38mm forks. I didn't pay anything for this bike, I traded another bike for it that I got in a package deal. I'm not really out anything. My budget for this build will be around $6500 give or take. I think I can build a screamer for that!
glad you're sorting out what actually belongs on that model stock from factory as that's a good baseline to work up from. 1 thing I forgot to mention was that 1981 also came with the boost bottle, which I couldn't see in your video. Your intake manifold would have a special spigot on top where the hose to boost bottle connects. Most people didn't have the patience (or skill?) to properly jet and tune with the boost bottle system on there and removed them and used the 1980 intake manifold instead. The forks look similar to Yamahas of the era and I've used IT forks before as well and they have that 4 bolt clamp axle holder on them. The front brake cable holder on Left fork lower looks like Yamaha to me too. I've had 3 of these and also 2 YZ465 & 1 YZ490 over the years- 2 of which were in similar condition requiring a lot of parts that were hard to find. My 1st 1 was around 1989 and we had almost no aftermarket parts available and mostly relied on Cycle Salvage yards for spares & replacements. Have fun!
The intake boot has been replaced at some point as it has no outlet for the bottle. My 490 has the setup on it. I can still get new intakes with the outlet on them, and I'm sure I can find the "bottle" as I believe they are the same from model to model. The hose should be easy to get as well. This is a fun little project for me, as it's a bit different from restorations. I have almost a year to make this bike happen, but ideally I want it done sometime around spring, that way we can test it and address any issues. I already got my order in from VMX. Going with the international color scheme with gold wheels, white plastics, red decals.
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I was well into VMX by early 2000s and started with old 1st gen MONOshocks I grew up with. Then the competitiveness and class hopping bug got me. More experienced vet guys said always try to get last eligible year of any class you want to race in. I found a smoking deal on 1981 250h by accident on CL a couple miles from me for $150.00. I did mechanical refurb and cosmetics and added DG exhaust system, reeds, gently cleaned up ports, etc. It was a blast to ride & race! Light in the front end and quick off the gate. Really had to concentrate riding it. I was in my 40s and good shape then so the mistakes and crashes were easier to recover from 😅
Got another 1 in trade that was running from a guy in our VMX club for an extra 1985 RZ350 I had hanging around. That 250H became the racer and I parked the previous racer to await a full restoration at a later date. 81 YZs were getting too much for me and crashes weren't as easy to recover from into my 50s, injuries and surgeries piled up and somehow, I got shorter along the way 😑 Stumbled onto the 1979 YZ250F that fit me better and had 6 speed so grabbed a few of those and still have my ex racer. Then class change again when Marty Tripes Vintage Revenge 100cc exploded. Stayed with 100/125cc racing until it faded away and I relocated and primarily just trail ride these days. Good Times!
I'm currently on the hunt for some parts lol. I need 43mm forks, triples, front and rear wheels, and possible a swingarm. Ideally I'd like to find a YZ 465 roller, as it would have everything I need. I did find a 1984 YZ 250 for cheap, that will have everything I need, but will have the stupid Z-spoke hubs.I don't want those. I have an 85 YZ 125 sitting here, and it has 43mm forks, but I'd have to fab up a bracket to mount a drum brake to the front. I'm not really pressed for time, as the race is only 351 days away lol. MX Locker is basically useless as everyone tags their crap and I get all sorts of useless items, even when I type in YZ 465 in the search. eBay has had some luck, but guys think their stuff is worth hundreds for a $10 part.
If you have the Swing arm off at one point.... can you weigh that mother of all Swing Arms ! ( I believe the 250 & 400 are identical )...
81 YZ250 is a great bike. Biggest improvement would be either a vintage fox twin clicker shock or Racetech will make you a brand new modern like shock for it. I built my own version of the fox shock but the rebound circuit on the shock is just an orifice setup and not as nice as what Fox and Racetech can provided.
If you are really going to make a bracket for a disk brake fork might as well find a cartridge fork to use. There are a few places that make brackets for the Honda 43mm forks that come on XRs and 86-88 CRs. IF you want to stay Yamaha then you want the 88 YZ forks. All the 81+ YZ465/490 bikes had 43mm forks and rubber mounted triple clamps that really opened up the riding position of the bike over other YZ clamps. If your in the market for 88 YZ forks I have a nice set of built forks, sprung for 180lbs MX, GVs, rebound pistons, and recent bushings that I've been meaning to move. I might even have a DSP drum and front wheel kicking around as I had a 79 400 and 81 465 that I raced for a few years before moving on to my 86 250
The rest of the bike is solid and parts are relatively easy to get.
Funny story is that I traded an 88 YZ 250 for the 81 lol. The 88 was a hot mess though. I think I'm going to go with a dedicated drum brake fork setup as I don't want to ruffle any feathers at the race. Some guys can really scrutinize the rules and cry foul when you start to back date stuff. We had an XR 200 class, and a guy brought a new CRF 230 and put drums on it. The XR's are allowed to be bored out to 240, so technically he was within the rules, but some guys were not happy to be racing against a bike built in 2023, that has nearly zero hours on the chassis.
I honestly don't know how crazy the suspension needs to be, the track is very tame. It's a legit 70's track. Running it backwards, there's only 1 jump on it. GNCC guys usually haul ass on it.
It's very light. I'll try to get it weighed this weekend, when I'm out there. It's honestly about the same weight as a traditional linkage type swingarm from a newer bike.
It's 10.8lbs with the bushings still installed and the shock bolt attached.
I'm not having much luck sourcing a pipe/silencer for the bike. VMX sells a DG kit but I really want the PFR stuff. I called AMS Racing as they have them on their website but he said they aren't in stock and the owner of PFR moved his shop, and hasn't gotten back up to speed as of yet. I just want the big ticket items here early in the build. I can get oddball stuff as the build gets closer to the finish.
try this shop. showing pictures of them like they carry them, not sure if in stock..
1980 - 1981 Yamaha YZ 250 | Pro-Form Racing Pipes (PFR) - AMS Racing
That's the place I called. They don't have them in stock.
DOH! totally missed that reading your posts 🙃 IIRC the guy that owned Maicos Only had bought the PFR business and it stayed real busy and always behind on deliveries. He seemed a little prickly to deal with. In our 100cc Vintage Series he chose "4Q" as his number 😆
On last 2 of my 3 YZ250H bikes over time I used DG full exhaust systems and never had a performance problem with them. Never did more than seat of the pants testing vs stock though. My stockers were beat up and DG was quickest and cheapest way for me to solve that to complete my racers.
Have you looked on eBay and considered used for non-DG alternatives? Out of USA maybe? Just thinking out loud here...
I'm on eBay all day looking lol. There are stock pipes that pop up here and there. I already have the stock pipe but it has a few dents and a small split in it. Plus guys want $250+ for a stock pipe, that you can't really see up close. I don't know of any other companies that make vintage pipes for YZ's other than DG. I've used PFR stuff before and the fit/finish/sound is excellent! The DG stuff looks nostalgic, but I remember them not being very good. They are more or less a replacement if your stock stuff is trashed. I can find DG stuff for $705 at VMX. I will use that option as a last resort. Here's my 480 I did last year with PFR pipes.
Rich at Dynoport will make a custom exhaust if you want him too or at least he use to do it. Not sure of the cost but he'll also setup for what ever power spread you want.
I know your in Upstate NY but I'm not sure how far he is from you as he'll most likely want the bike.
Give him a call
(315) 253-9631
I've always found the DG stuff hard to jet, both the YZ400 and YZ465 I had ran better on stock pipes than the DG that came with them. The 400 DG split at the seam.
I reached out on facebook, and a guy there got a hold of the guy from PFR. We are in contact now, and he's doing a pipe next week! I'm beyond excited!
I remember a dyno test from the 80's between pipes. I don't remember the magazine, maybe Dirt Rider? The DG pipe made less power than the stock pipe. They did their best to defend it, as they never really trashed a company in any mag, This was right around when Pro Circuit started to really take off. After that DG fell off the face of the earth. I don't believe that was a coincidence. It seemed like a bike would hit the market, and suddenly the very next week, DG would have a pipe for it. I understand the basics of how a 2-stroke pipe works, and there's a shit ton of math/physics involved regarding chamber volume, exhaust port timing, pulse wave speed, etc etc. It's not something you can just throw together. It seemed to me that DG would just bang out a pipe ASAP, and people would gobble them up. But once some serious competitors hit the market, with the performance to back it up, people took notice.
I also remember reading a Yamaha wrench report (remember those?) from 1984, where they were talking about modifying the YZ 250. They suggested cutting the pipe in half, and removing 1mm of material (something like that, just a sliver) and then re-welding it back together. Obviously this was done to slightly decrease the volume, which effects the power output.
I looked into DynoPort, it seems like he focuses on snowmobiles. I do remember seeing his pipes on bikes at my local track back in the late 90's though.
1mm should not make a significant difference to volume or tuned length.
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