Taming a YZ 400

[FenryHonda]

I realize this should be posted in vintage, but there's not much traffic there.

I am just getting back into motocross (post vin) after a many year lay off. I have never raced an open class two stroke, and my ride is a '77 YZ 400 with Boyesen reeds, a DG national pipe, and DG Type II silencer. I'm still working the jetting out, and getting close. It will bog a bit down low, and then hit hard.

I would like to tame the hit a bit so the front wheel will not climb so abruptly. I'm a big guy, and even when I am on the tank the wheel will loft, even in 5th gear.

 

[BEEF706]

Good luck Fenry, I had a '78 in '78-80 and as I racall that's the way they ran, took to the first race after just break-in miles, got on the gas hard in 5th on the backstrait and looped it out. I weighed about 225 at the time and was the most surprised guy on the planet (I bought it because my 250 couldn't pull me well). If I recall even with the stock pipe and silencer, that thing was a brutal accelerator, jet it clean and feather the clutch. :aj:

 

[FenryHonda]

Thanks for the reply, I'll just have to get used to it.

 

[Dewster]

I had a 1980 PE400. Same thing, any bit of throttle in any gear would yank you like theres no tomorrow. This bike was stock and still too powerful. I weighed 150lbs at the time... way too much bike for me. The one thing I did do that helped a bit was to put a slightly worn tire on the back. Just be careful when gasing it in the turns, tends to slip out from under you.

 

[maicomotoman]

I have PVL ignitions on my bikes and it seems to make the power much smoother. Especially the '73 Elsinore, which was a light switch with the original ignition:eek: They are expensive, but probably the best thing(besides suspension) that you can do to these old bikes. Maybe a smaller carb would emphasize the low end of the powerband? Good luck!

 

[maicomotoman]

Oh yea, rich jetting can make 'em hit hard too...

 

[FenryHonda]

I would like a PVL also, but I need that for my '74 MX 250 first.

As far as jetting, it has the stock pilot, the needle is in the 2nd from top notch, and a 360 main jet.

I realize an open class bike hits hard, but like I said, I'm just getting back into this. It is very easy to pull 5th gear wheelies. In the lower gears it just comes up so fast.

Back when I raced motocross before, I would feather/fan the clutch exiting corners, so I should just start doing that again. I have been riding 4 strokes mostly lately, and will have to readjust my riding style.

Would running a thicker base gasket help any?

 

[BEEF706]

Base gasket oughta help some, maybe see about a spacer of some kind at the ehauhst pot/pipe juncture? Wish I'd thought of that back in the day.