397cc Air-cooled, 2-stroke, single
|Bore / Stroke||85mm x 70 mm|
|Compression ratio||7.59 : 1|
|Fuel System||Mikuni VM36SC|
|Spark Plug||NGK B8EV '76 , '77-78 , '79|
|Final Drive||Chain: 520x105 |
|Frame||Tubular steel double cradle|
|Front Tire||3.00-21 '76 , '77-78 , '79 |
|Rear Tire||4.50-18 '76-79 |
|Recommended Tire Pressure||Front: 13 psi
Rear: 15 psi
|Seat Height||910 mm|
|Weight||103 kg (wet)|
|Oil Capacity|| change: 1.1L
rebuild: 1.25 L
|Recommended Oil||Yamalube 10W-40|
|Manuals||1978 YZ400E Service Manual
1979 Yamaha YZ400F Service Manual
Take a 1975 MX400, paint it Yellow and add the spedo air forks and you end up with the 1976 YZ400C (I only saw 1, I swear it felt like an MX400).
- SERIAL # 510-100101 - 102838
A great leap forward in frame, engine and suspension design, the 1977 YZ400 was only lacking in it's ability to track corners because of the round tubular swing arm that caused too much flex. The monoshock was now encased inside the Monocoque frame that ran under the gas tank.
- SERIAL # 1W4-000101 - 006720
Expanding on a good thing, the 1978 YZ400 became stable with the box section aluminum swing arm and longer travel (at both ends). The bike was a bit heavy (tipping the scales around 240 lbs.) but long gone was the cracks in the frames, common with the previous (non-Monocoque) designs. The rake was also a bit long which made the 1977-1978 YZ400s better at cross-country than in motocross.
- SERIAL # 2K8-000101 - 007406
All good things must come to an end (which very much describes the 1979 YZ400). The rake was decreased to improve the handling in motocross but the 396cc engine was a step backwards (in this editor's opinion). This engine was only used on this bike and the 1980 IT425. Previous engines used the over-square 85x70 (397cc) design (even the SC500 used the same crank 95x70). This engine was 82x75 and never used again.
- SERIAL # 2X5-000101 - N/A