1984 Husky 500xc with 390 motor restoration.

I am restoring (sort of) a 1984 500xc, and plan to go vintage racing with my son this spring. I am missing the cylinder and head for my 500, but have a near complete 390CR motor from a 1979CR. I am missing the head and pipe, but have the head coming from ebay. My cylinder is original bore, but it was cpseized, so it gets a new piston and overbore. am using the 390 motor as the 500 will be too much for my son, who is a novice at motocross, but in his teens, was a competitive BMX racer who was a strong intermediate. We rode mostly offroad in the mountains when he was a kid. I raced MX before I had him.

My first question is: do the 390 motors need any type of head mod to run on modern fuels? If they do, I’d rather do it now while it’s apart, then have to redo a bunch of stuff a second time.

Second question: Is there and recommended porting changes while it is apart? I never owned a 390, other than one given to me as a basket case that I rebuilt and sold in the late 90s. I read great things about them.

I will be making a custom cone pipe for the bike. I have a software package to design a pipe. I need to get the piston first, and measure the port timing to do this though.

Pics soon. I need to figure out the best way to post pics here and will upload shortly. I will be racing one of three bikes, a 1983 Husky 510TX, a low hour original in unrestored condition, a 1982 KTM504, or a 1982 Honda 500 with a 1985 husky frame.

Pretty cool! I have an 86 510 I'm working on. So you like the big bore four bangers? Lots of work on a tight MX course but !Holeshots!

Vintage racing is great for open four strokes. Long straights, sweeping turns, no huge jumps. I rode four strokes most of my life, except a couple husky 500s and a Honda 250. Husky knew what they were doing when it comes to natural terrain motocross. Supercross, not so much. My 83 510 is my favorite bike ever.

Most of the Northeast VMX tracks are tight with a lot of turns. Unadilla is the exception.

Cylinder head arrived today. I found some porting specs for the 390, and will get to grinding this weekend. I will measure out the port timing, and get the pipe cone dimensions calculated.