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1978 YZ250E Set up and Tuning

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I recently purchased a rebuilt '78 YZ250 for Vintage/Vet motocross racing. If there are any other owners out there I would like to discuss riding, jetting and suspension tuning experiences. Thx!IMG_1872.JPGIMG_1619.JPG

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Wow that bike looks great! My uncle actively races his '74 YZ250A and Im sure he's upgraded the rear suspension. I had my '85 YZ's rear suspension re-valved with a more modern set up from race tech. Im not sure if your ignition is different than the '74s but I know he's upgraded his to a modern ignition because of all the problem he was having. 

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That suspension has been worked on for sure. It has quite a bit more travel than stock that year.My first YZ 125-E had very little travel compared to your bike.Good job.

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Haha so coincidently I talked to my uncle today and turns out he owned a '78 250 when they came out. He said the only problem he ever had with it was it would detonate like crazy when going up long hard hills. He said he called up Don Jones and told him about the pinging and he told him to bring him the head. Don did some work on the head - apparently lower the compression a tiny bit in the process - and my uncle never had a problem with detonation again.  I guess the ignition on those were different by then and better than the previous generation. 

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Thx for the inputs. This model does have a modern electronic CDI type ignition. Perhaps the earlier models had the old style with points? I think I recall having points on my early '70's Hondas.
From what I was told, it simply has rebuilt stock suspension components. I've had the forks apart and have begun tuning with different fluids. When I got it, the forks were impossibly stiff, for me. They had very thick oil in them. I've started my tuning with a lightweight 5wt fork oil. The manual says the forks use 14 psi. I started by cutting that in half down to 7-8 psi. Definitely, not enough damping. I've since tried 10 psi and 12 psi and like them better....of course they are nothing like modern forks. I have not set the sag. The fork springs are stiff and have a very long (~2 in) spacer thats difficult to compress the springs and get the fork caps on. The most unusual thing about the forks is the rake angle. It's 30.5 degrees! You can see that in the pics. There are no damping adjusters on the forks.
I have not had the shock apart. I did discuss it with the PO. He said he just rebuilt a stock shock. I started my tuning with the damping adjuster in the middle and have since gone out (lessened damping) a couple clicks, twice. There are not independent compression and rebound adjusters.
This is one of my first 2-strokes, so I'm learning about how they run, jet, feel and sound. This air-cooled bike really sounds neat relative to my water-cooled '83 CR250. You can definitely hear the big fins ringing and the stock silencer doesn't do much. I'll keep my ears open for the detonation. I will get some more experienced riders opinions when I get it out to the track in a couple weeks. From what I have read, stock compression ratio is 7.3:1.
The PO said the engine was not broken in when I bought it. I took it easy for the first few hours. I've been running 91 octane gas with Maxima SuperM at the specified 20:1 premix ratio. The bike seems to be jetted pretty rich in stock form and I am at 2,500 -3,000 feet, so I have been slowly leaning out the main jet, the needle, and the pilot jet. It's pretty close now, still a bit rich and I am thinking about changing to 32:1 for the final tuning.

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Here's a spec sheet from the April 1978 issue of Motorcyclist magazine. Dyno says it makes 31 hp at rear wheel, but doesn't reach half power til 5,000+ rpm! Coming off modern 4-strokes, that takes some getting used to.

Bike cost $1,568 new in 1978.

IMG_1874.JPG

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26 minutes ago, Sofiedog said:

Here's a spec sheet from the April 1978 issue of Motorcyclist magazine. Dyno says it makes 31 hp at rear wheel , but doesn't reach half power til 5,000+ rpm! Coming off modern 4-strokes, that takes some getting used to.

Bike cost $1,568 new in 1978.

IMG_1874.JPG

Hey thats only $5,800 in todays money. Well I know my uncle put a modern FMF Factory Fatty on his 250A. He says it would also fit right on his 2007 250. So maybe thats something you'd want to look into?  Im sure that would help with the power band, compared to a '78 pipe. 

Thats a cool observation about the sound difference of an air cooled bike.

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Interesting point on price...let's say retail for a new 2016 YZ250 is something like $7,500? What justifies the $1,700 increase in price? Well, the '78 os a very simple bike...for starters, no water pump, hoses, radiators, or shrouds. Second, no front and rear hydraulic calipers, discs, or front/rear hydraulic controls, just shoes drums and cables. Third, forks are simpler without internal cartridges and compression and rebound adjusters. Shock is larger, but less complex. There are no progressive linkage components. Last, the engine is simple, just a reed valve and carburetor.
So, the 2016 YZ is more expensive in real dollars, but it seems like a good value relative to the 1978 when you look at all the added features.

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Well its not exactly an apples to apples comparison since they're separated by 40 years and available technology was completely different... and we don't know R&D costs, or parts costs, or demands, or units sold, etc. But you definitely get waaaaaaaay more motorcycle in 2017!  I was just curious how much a new YZ cost in 78 - in todays dollars. Might be able to argue that things just cost more money now. OH man this is getting off topic. Either way I think this 78 is a cool bike and I love the colors!

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That's an awesome bike man. I have grown to love those old Yamaha air cooled two strokes when I aquired my own recently. So much fun. Mine ain't as pretty as yours, but for $200 I ain't complaining. ;) Mine has a supertrapp style muffler as well. My '78 yz400:IMG_20161124_173952594.jpg

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13 hours ago, Sofiedog said:

Interesting point on price...let's say retail for a new 2016 YZ250 is something like $7,500? What justifies the $1,700 increase in price? Well, the '78 os a very simple bike...for starters, no water pump, hoses, radiators, or shrouds. Second, no front and rear hydraulic calipers, discs, or front/rear hydraulic controls, just shoes drums and cables. Third, forks are simpler without internal cartridges and compression and rebound adjusters. Shock is larger, but less complex. There are no progressive linkage components. Last, the engine is simple, just a reed valve and carburetor.
So, the 2016 YZ is more expensive in real dollars, but it seems like a good value relative to the 1978 when you look at all the added features.

I did that comparison a while back with my first new race bike, a 1981 YZ125. It cost $1650 - $4600 in today's $. That's Canadian $ - converting back to $US gets $3450.00!!

Yes, the bikes back then were simpler, but they also changed a lot from year to year. Today's 125 and 250 have gone over 10 years without significant change. 

PS That's a really nice looking '78. Enjoy.

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I've been reading the April 1978 Motorcyclist review of the YZ250E. They seemed to like the engine, gearbox and handling. Main complaint was the weight being heavier than the competitors. It does feel heavy when you ride it.
There was also an interview with Keith McCarthy, Bob Hannah's mechanic. He described the changes he made to a stock YZ250E to prep Hannah's bike for the Seattle Kingdome Supercross.
They got rid of the fork preload spacer.
They changed the fork damping by filling the original 1.2 mm damper rod bleed hole and redrilled to 0.08 mm and filled with Bel-Ray LT200 shock oil (weight).
They used nylon pressure tubing in place of the front brake cable jacket.
Bars were replaced.
Monoshock pre-load set to 305 mm. Stock is 300 mm. Damping was set 4 clicks stiffer than stock.
Mikuni Pilot jet size was reduced to a #50. The stock #380 main was used.
Stock porting was used with porting to only match cylinder and liner and match transfer ports to center cases.
Shift lever was replaced with a longer XT500 lever.
A Bassett silencer was used.IMG_1875.JPG

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I love reading stuff like that. Old magazines have so many articles on the old bikes. Helps us see what they looked like new and how they did back in the day.

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I love reading stuff like that. Old magazines have so many articles on the old bikes. Helps us see what they looked like new and how they did back in the day.

Me too. I love motorcycles and motorcycle technology. I really enjoy reading about how the technology changed over the years...good ideas and bad ideas. Yamaha really jumped out ahead with the long travel monoshock concept in 1976, but had some production implementation issues...that's why I got the 2nd gen 1978.
The '78 got a new engine with a couple more hp, more durable piston and ring design, larger reed and carb, and a 6 speed gearbox. The forks are longer to achieve more slider overlap and the shock was revised to increase travel and reduce temps. The chrome-moly frame is lighter and it got the aluminum swingarm. So, although a '76 would be a great bike to own, I thought the '78 would be more fun to ride.
By 1978, the CRs, RMs, and KXs were lighter and were able to achieve as long rear travel by laying the shocks down (moving the top shock mount forward). By 1981, Honda released their Pro-Link suspension, (progressive link) and Yamaha was placed in a catch-up position to produce a progressive link.

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Sofiedog: a good source of info on the bikes from the 70's would be Bob Blose. If you want to start setting up the suspension, that's who would be your best bet...

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Here's a copy of the nice 3 page ad for the YZ series...IMG_1877.JPGIMG_1876.JPG
Looks like the 400 didn't get the nice heavy steel kickstand!

That's about the only issue I have with the bike. Everything else is great. Just no kickstand.

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I can understand wanting a kickstand for trail riding. Looks like the mounting tab is there on the frame on the 400. But, for the track, I may it off.
I was thinking the other day about trying to take some weight off my bike. There are not many opportunities...remove kick stand, aluminum silencer, aluminum handlebars,...couple pounds, maybe..

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My 400 actually seems lighter to me than my '83 xr200r. I've tried picking up both and the YZ is easier to man handle around. Maybe I'm crazy, most would think the 200 would be lighter, the again it is a 4 stroke.

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