Remember to rejet whenever you install a performance exhaust!

Thanks for the input, I’m going back to a stock air cleaner box and filter. Will this flow plenty of air? 

The stock airbox is okay for stock power levels. It will choke up to a greater and greater extent going beyond that.

If I had an RT2 and I was looking for some more thrust I would look at an earlier piston port jug. The reed valved 360's need larger reeds and there is very little room to work within the casting. The 74 360 got a little better, you can stuff a reasonably sized block in those with a lot of grinding. I don't think the same can be done with the early bikes that used four petal reeds.

I would go with an RT1-B jug, widen the exhaust port to 68% of the bore diameter, match the transfer port heights and square off the transfer port windows for maximum area. On the intake side I would go for a 34mm carb and port the intake to match it. The original cylinder head design on these is a mess, they usually require welding and machining to get a proper squish band with the right chamber volume.

A proper pipe really lights things up, though it is difficult to fit a long enough chamber on there to make really good low-mid. In a way the later 360/400 is better here since the pipe can be routed through the chassis. On the early bikes there isn't a great place to route a fat midsection. Underneath fits but the path is too short.

I'd probably do the engine stuff and see how it runs with the stock exhaust. That might be enough to satisfy.

Probably really hard to get hold of nowadays, but maybe see if there are any GYT (Genuine Yamaha Tuning?) parts out there. Enduronut and/or DEET might have some of the super rare stuff.

Thanks for the input, probably get this rig back on the road and see how it performs.

For those outside the US, "MX" below means "motocross", not "monoshock".

I think it was Enduronut that schooled us years ago on the GYT parts...  Technically all are "GYT" because they are Yamaha designs...  but in the early days before there were official MX models they sold special "GYT" kits and parts to convert an Enduro into an MX bike.

Then at some point...  probably no later than 69-70 for most models... you would just buy the MX parts to convert an Enduro to a competition machine.

I believe there was a brief timeframe where you could buy either a "GYT" kit OR production "MX" parts to convert an Enduro...  they were not exactly the same parts.  

Pretty sure by the days of the RT2 it was simply RT2MX parts you would buy to hop up your RT2 Enduro. 

"Pretty sure by the days of the RT2 it was simply RT2MX parts you would buy to hop up your RT2 Enduro."

Thanks Mark.

I just had in the back of my mind the extra exhaust mount bracket on the RT2 that was only needed for a GYT exhaust. Or maybe this was just a carry over from the earlier 250 (DT) models, pre MX, that the RT shared the frame with? 

All the Yamaha factory parts are technically "Genuine Yamaha Tuning"...  I was just mentioning that in the early days, starting in the mid 1960's, Yamaha marketed a "Get kit" (GYT kit).... 

Later when the standalone MX bikes were sold you'd just buy the MX model parts for an Enduro...  so you might use a RT2MX pipe on an RT2...  not something that was called a "GYT kit" pipe?   (Though the earlier "GYT kit" pipe would probably work just fine on an RT2.. both the GYT and RT2MX pipe might need a mounting bracket to use on an RT2, I don't know)

My point was just that for the later models like the RT2 you might want to look for RT2MX parts and not GYT kit parts?