1979 YZ 400 parts

Photo of tech data sheet for the 79 400f. As per data sheet stock jetting is : main 420...pilot: 85..needle: q-4...clip position: 6f8-2? Slide cutaway: 4....float level: 18.1+\-1mm.... My bike had a brand new carb on it when I purchased it, Stock needle & jets were swapped over, . I run 75% 91 non ethanol with 25% sunoco leaded 110 mixed 32:1 with amsoil dominator synthetic. I never ran the needle in 2nd clip, started on 3rd clip, good for tighter tracts, maybe woods riding, I have never ridden this bike in the woods. With clip position on #3, it had good throttle response, very little spooge from pipe & silencer. My local MX track is tight with short straights & jumps, not a very good vintage bike track, that jetting worked good there, then I went to Unadilla 2 years ago & the jetting was too lean, much faster & wide open, the bike needed more fuel, so I moved clip to the 4th position, a little blubbery off idle, but runs better mid-top. I think these old air cooled open bikes like to be on the rich side. I guess it depends on what type of riding your doing, but don"t ever think you will get these things jetted 100% spot on throughout the entire range... My bike is for sale if you know anyone interested, I"m a Suzuki guy, so would be willing to work a deal with a certain yr RM 250.

The pipe came on the bike when I bought it, I have the stock pipe but never used it, who knows, it may run better with the stock pipe...my engine is brand new from top to bottom, 2nd overbore, stock porting, new boysen reeds. It has a quick burst of power but signs off early, typical short shift style of power, over revving just produces noise! Sometimes it feels like the clutch is slipping but everything in the clutch was replaced accept the basket which was in good condition...I think the motor comes on so fast it breaks the rear wheel loose easily... maybe try a plug chop test wide open, richer main?