YZ 490 J or K expansion chamber design wanted

[Zakk]

i'm interested to build an expansion chamber for my YZ490 engine as i don't have an original exhaust and i didn't want a DG one. anyway has anyone got any drawings or designs used back in the day on the YZ490 J or K model?
thanks

[jimg1au]

i have a yz490 pipe in the shed if you are in sydney you could come and have a look.i think it is a side port one.
jim

[Mick D]

Hi Zakk, I see you are new amongst us, Welcome If you are after someone to make it for you? Depending on where you live. If And if you don't mind getting in a Que for a while?

Try Geoff Morris at Broadford Vic (forum-GMC) or if in Newcastle region(forum- lozza). I say local because I imagine they would need your bike as a routing model.

If you are looking to make it yourself, try downloading the free chamber design link from here IAN WILLIAMS TUNNING

[Zakk]

hi Jimg1au, i'm in Adelaide so i wouldn't be able to look at your pipe, but if it is a side port and you are selling it then let me know.

Mick, thanks for the welcome. i was going to make the exhaust myself as i'm a welder and have made road race 2 stroke chambers before. i'm a bit wary about those 2stroke exhaust programs, i think you really need a proven design or its sort of hit and miss. i've got a couple of old 2stroke design books but they're sort of dated now, they don't cover the 'fatty' type pipe designs used in the last 20 years.

[Zakk]

I have a new GMC system  coming for my YZ 490. I am in Adelaide , if you like to have a look at it .

thanks for the offer. is the pipe to suit the early sideport J or K engine? i wouldn't mind comparing the dimentions to my stock YZ250H pipe.

[holeshot buddy]

j and k are different j is the same as 465h

[Zakk]

i thought the mounting points of the YZ490J and YZ490K might be different due to the differences in rear shock positions, but DG list their IT465J and IT490K pipe as the same, also i think they list their YZ465H and YZ490J/K as the same one... it does get a bit confusing as the IT's were a year behind the YZ's until 1983.

either way i was going to make the pipe to fit my YZ490 engine in my IT250J, so it's a expansion chamber design i was after, although if someone does have a standard YZ465H or a YZ490J or a YZ490K pipe they want to sell then let me know, i could always modify any mounting points to suit if needed.