Rebuilding 86 yz490s

[frdmrckr]

Im new to building bikes but not riding them. I needed a bigger dirt bike so i finally got the guts to take out my dads old yz490s. the thing was attacked by mice and the crank bearings are locked up. My problem though is finding a carb. I was wondering what would be a nice replacement for the stock carb

 

[whenfoxforks-ruled]

Crank bearings and rod parts are still available? Vintage Bob

 

[frdmrckr]

Ha ha. yeah. find all that stuff on ebay for a decent price. Amny stores actually carry the bearings still too

 

[frdmrckr]

i guess if a better question is what should the jetting be if i go down to a 38mm carb. the stock is 40 but i can only find new a mikuni with 38. If so just a good spot to start jetting too. im having horrible luck finding info on this

 

[whenfoxforks-ruled]

When I decided to put a 38 mikuni on my CR480 I checked the RM400 and 500 jetting specs. If you look at an online micro fiche it will tell you the oem parts sizes. The 480 pulls clean and hard. Those early keihn carbs were awful!

 

[frdmrckr]

Alright. Thanks for that. Im gonna keep the stock jetting in a 38 and start from there. It is a little larger than what the yz490 used when it used the 38 in older bikes. but mine is also bored .060 over. so hopefully itll be close

 

[ws6transam]

I've got a WR500 with a 1987 YZ490 top-end, and I use the WR500 Mikuni with some slightly altered jetting which seems to run just great. Always starts, and it can putt all day yet rip WOT without seizure or plug fouling. There's a Q-4 needle jet, a #50 idle jet, and a #440 main jet and a 3.5 slide, if I recall correctly. Seems to work great. I saw one on Ebay last week for a reasonable price and it might still be there.

 

[frdmrckr]

I started to find more carbs on ebay too. search terms are everything