78-79 YZ250's...

EastFlorida
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EastFlorida
Edited Date/Time 6/26/2019 4:23am
Looks like I'm picking up a mix of YZ's next weekend. 78 and 79, so I need to know where to get parts, plastics, etc. These bikes will be my first resto/race bikes...

Shock/fork mods, engine parts, etc... Any upgrade suggestions?

Thanks for any help you can provide.
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450exc115
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450exc115 6/20/2015 7:01pm
6/20/2015 7:01pm
Lots of oem available for both bikes. EBay, speed and sport, nw cycles have a bunch of parts.

Forks are the same between the two years. Racetech emulators and springs go a long way to get them close to modern. The shock technology is dated but there are a few tuners that can get them working well. You can spend a lot (piston kit and springs) and really make them work or just change the oil and seal head to get them functional. Focus on suspension as the motors were pretty good. If you need more power any of the vintage porting guys can make them rip.

I have a 79 YZ400 and really love the bike. It's a lot of fun to race and not far off my modern 450 in overall performance. I'm only slightly slower and that is mostly due to braking. Smile
Shawbridge Husky 6/21/2015 6:07am
6/21/2015 6:07am
I'm doing one, I'll get back to you tonight with the details. They don't mix that easily.
project racer 6/21/2015 6:52am
6/21/2015 6:52am
Engines interchange between the two years, but there is a lot of difference between the two models , on everything else. Even though they look close to the same.

Frames are different, shocks are different, swing arms, air boxes, pipes, seats, tank, side panels. The forks appear the same, but I believe the F had a bit longer stanchion tubes, over the E.

E had a peaky type power spread, kind of like a big 125. The F had much better low-mid range, and still had good top.

I wore this one out from late 78 to 1980. Rode it on stock suspension, cause I did not know any better. One of my favorite bikes ever.

450exc115
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450exc115 6/21/2015 7:04am
6/21/2015 7:04am
Shawbridge is right, 79 had major changes to the chassis but the motors have interchangeable parts. Forks and wheels swap, topends swap etc. Personally the 79 is the better of the two but the 78 is a good bike.

The Shop

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project racer 6/21/2015 7:09am
6/21/2015 7:09am
Does not take much to go from the internal rotor ignition to a '85-'88 YZ 80 external flywheel set up. Taper is the same. I ran this '87 YZ80 system on my 79 YZ250 Champion short tracker. 14 ounces of weight added to the flywheel. Great tractability and what seemed liked an increase in the rev limits of the 250 ignition by at least a couple of thousand rpm.

It would twist tight. Only concern was main bearing life and crank end durability with the added weight hanging off the end of the crank. Could have been bad if that flywheel got out from under the cover at 8-9000 rpm, but never had a problem.

Never lost a crank, and only one main bearing failure in 5 years of racing the Champion with that ignition.
It would run with the mid 90's water coolers on short tracks up to 3/8 mile.

Stock "F" porting, Falicon crank, 39mm Keihin D slide carb, jemco pipe, and the 80 ignition. Nothing real trick,but it was a great running engine.

The red and blue bike.





Shawbridge Husky 6/21/2015 2:09pm
6/21/2015 2:09pm
Good tips PJ, I'm going to buy that Keihin car you recommended.
If I recall it was stock jetted for a '91 KX 250 right ?
EastFlorida
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EastFlorida 6/21/2015 2:25pm
6/21/2015 2:25pm
Thanks guys! I hope to pick them up this week - 8 hr drive round trip. I'll post before, during and after pics. I hope to tap into the wealth of experience on here helping me out.

Shaun
EastFlorida
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EastFlorida 6/21/2015 2:33pm
6/21/2015 2:33pm Edited Date/Time 6/21/2015 2:35pm
I was thinking to build one for Hare Scrambles and the other for MX. Should I build the 78 for HS and the 79 for MX since it is the "better" of the two?

For HS, I need more torque and softer suspension...
Shawbridge Husky 6/21/2015 3:38pm
6/21/2015 3:38pm
In stock form the E model suspension will be better for motocross.
They took a step backwards in '79 with the F model, it needs work.
Personally I like the F better, just based on looks and the fact I had the 125F as a kid.
coolhand
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coolhand 6/21/2015 4:02pm
6/21/2015 4:02pm
I have a 79 if your interested...
EastFlorida
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EastFlorida 6/21/2015 4:47pm
6/21/2015 4:47pm
Anyone have a link to download a Yamaha Service Manual for a 78 & 79 YZ250?
450exc115
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450exc115 6/21/2015 5:41pm
6/21/2015 5:41pm
I run my 79 yz400 in the woods. Great spread of power. The 250 is the same way. The 78 gas more hit and isn't as good a turner in the woods.
Brett Campbell 4/26/2019 8:16am
4/26/2019 8:16am
project racer wrote:
Does not take much to go from the internal rotor ignition to a '85-'88 YZ 80 external flywheel set up. Taper is the same. I ran...
Does not take much to go from the internal rotor ignition to a '85-'88 YZ 80 external flywheel set up. Taper is the same. I ran this '87 YZ80 system on my 79 YZ250 Champion short tracker. 14 ounces of weight added to the flywheel. Great tractability and what seemed liked an increase in the rev limits of the 250 ignition by at least a couple of thousand rpm.

It would twist tight. Only concern was main bearing life and crank end durability with the added weight hanging off the end of the crank. Could have been bad if that flywheel got out from under the cover at 8-9000 rpm, but never had a problem.

Never lost a crank, and only one main bearing failure in 5 years of racing the Champion with that ignition.
It would run with the mid 90's water coolers on short tracks up to 3/8 mile.

Stock "F" porting, Falicon crank, 39mm Keihin D slide carb, jemco pipe, and the 80 ignition. Nothing real trick,but it was a great running engine.

The red and blue bike.





Any chance you still have a factory manual for the 79 YZ250 lying around.

Thanks
Sofiedog
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Sofiedog 4/26/2019 10:08am
4/26/2019 10:08am
the '78 YZ250E has a peaky but fun power band in stock trim...I'm running the stock Mikuni carb with stock pipe and silencer....stock forks and shock...a trip back to 1978.

5
Brett Campbell 4/26/2019 10:47am
4/26/2019 10:47am
The powerband on my 79 YZ250 is a little peaky also. I did read that Yamaha lowered the ports in 79 to try and smooth it out, but it still comes on suddenly at about 3000-3500 RPM.
1
project racer 4/26/2019 12:34pm
4/26/2019 12:34pm
Brett Campbell wrote:
Any chance you still have a factory manual for the 79 YZ250 lying around.

Thanks
No manual. I had five of those engines E-F, they would fall together for me after so many hours spent with them.
wfoyz250
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wfoyz250 4/27/2019 4:35pm
4/27/2019 4:35pm
Rode a '79 250 back in day, darn good bike. Got back into MX in '09, bought a '79 to ride VMX. It was a low hour stocker when I began modding it over the years. Now with 43mm forks, DLS front brakes, racetech suspension, rear shock dual spring, reservoir. No engine mods.......it has loads of power. Even the vintage "squid kids" ride it and are impressed.
3

Pit Row

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Brett Campbell 6/10/2019 6:03am
6/10/2019 6:03am
I completed the rebuild of my 79 YZ250 engine this weekend. It is running great. After the break-in, I checked the compression and it is at 200 psi. I made a custom head gasket out of .016 thick copper. The stock head gasket is .043 thick. That brought the squish down a bit.
bmb
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bmb 6/23/2019 4:13pm
6/23/2019 4:13pm
I just finished my 79 project. I haven't even rode it yet.
5
wfoyz250
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wfoyz250 6/24/2019 4:54am
6/24/2019 4:54am Edited Date/Time 6/24/2019 4:56am
BMB.......fine looking machine. i see you used the later model fenders. I did the same. If you plan to ride/race the bike, pull those forks up in the triples, about 3". It will corner MUCH better and not handle like a "chopper". Sitting on the bike,
the rake angle will be even more noticeable. The 38mm forks on those bikes are extremely longer than the 43's I adapted on my bike.
1
ohiomotoxer
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ohiomotoxer 6/25/2019 1:57am
6/25/2019 1:57am Edited Date/Time 6/25/2019 2:03am
BITD

Engine: RPM out of Toledo.
Rear shock: Fox Air
Forks; Trick Kit
Muffler: Answer
Air Filter: Phase II
Hannah shorty levers.
Gunner Gasser throttle
Preston Petty front fender

Jofa
Scott Boots
no gloves
Bell hat
Hallman visor
Carrera goggles
American Competition (Fremont Ohio) AC= always cookin'

Flicking the camera guy "I'm in first place.....priceless...


3
bmb
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bmb 6/26/2019 4:23am
6/26/2019 4:23am
wfoyz250 wrote:
BMB.......fine looking machine. i see you used the later model fenders. I did the same. If you plan to ride/race the bike, pull those forks up...
BMB.......fine looking machine. i see you used the later model fenders. I did the same. If you plan to ride/race the bike, pull those forks up in the triples, about 3". It will corner MUCH better and not handle like a "chopper". Sitting on the bike,
the rake angle will be even more noticeable. The 38mm forks on those bikes are extremely longer than the 43's I adapted on my bike.
Thanks. I will follow that tip. Any advice is appreciated. I grew up in a Suzuki dealership. The vintage Yamaha stuff is all new to me.

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