Another 1978 YZ 250 question

Jon_Haynes
Profile picture for user Jon_Haynes
Posts
380
Joined
1/24/2011
Location
Clinton, IN, USA
Jon_Haynes
What is the standard go to jetting for a 38mm mikuni on the 78 yz 250.? Does anyone have their old notes handy ? Thanks.
|
BS261
Profile picture for user BS261
Posts
132
Joined
11/4/2015
Location
Rochester, NY, USA
BS261 6/19/2017 2:58am
6/19/2017 2:58am
I'm looking at a Cycle Magazine test of the 78 YZ250, they're saying the first one they tested had a 380 main jet, with the timing set at 2.5 mm BTDC, and a second test bike had a 370 main jet, set at 1.8 mm BTDC and that one dyno tested much better. Hope that helps.
Jon_Haynes
Profile picture for user Jon_Haynes
Posts
380
Joined
1/24/2011
Location
Clinton, IN, USA
Jon_Haynes 6/19/2017 4:57am
6/19/2017 4:57am
Thanks,
Sofiedog
Profile picture for user Sofiedog
Posts
61
Joined
4/18/2017
Location
Tucson, AZ, USA
Sofiedog 6/19/2017 6:31am
6/19/2017 6:31am
I started with the stock #380 main and #60 pilot. Mine has the stock 6F16-3 needle and stock #3.0 slide.
I wound up leaning out the jets for my 2,000 -3,000 ft elevation and for the change from the stock 20:1 pre-mix to the 32:1 that I am running, now.
Right now, I have been trying a #360 main and a #35 pilot with the needle clip in the top position. It may not be completely tweeked in. I just noticed my metal reeds have gaps on the side and I just ordered a new set. Should help make the jetting easier to get dialed in.

The Shop

See All »
Jon_Haynes
Profile picture for user Jon_Haynes
Posts
380
Joined
1/24/2011
Location
Clinton, IN, USA
Jon_Haynes 6/19/2017 1:14pm
6/19/2017 1:14pm
Thanks guys, that helps a lot. I am close but not perfect. it ran like crap when the temp and humidity were really high.

Post a reply to: Another 1978 YZ 250 question