xr200r cranking pressure allowable overages

[mrmikkelsen]

So, I am somewhat experienced with these two valve Honda motors, but not in the area in which I am playing around now so I could use to technical input.

Situation: I am building a 150cc motor mating a 1982 xr125s lower end with an atc185 top end to run in ahrma's pv 125cc two stroke class. So far I have cut down the cylinder to match the short stroke. Recut the piston dome to match the deck height of the littler piston, including recutting the outer circumference of the pop-op portion of the 10.5:1 Wiseco piston. Installed Kibblewhite valves and heavy duty spring. Installed a Web Cam mid-range cam. Confirmed clearance for head/valves and piston dome. In comparing the atc head with the xl125 head, it appears that the atc head may either have been milled, or came stock less extra material on the sealing surface. My guess is that it has been milled.

SO, I kick it over and it builds 225 psi of cranking pressure. Stock 200r specs call for 200psi. I expect to be over stock, but I have no idea what this motor can tollerate. Am I in the ball park for a moderately modified motor at 225? Or is this thing really pretty mild still? Or is it crazy high on cranking pressure and going to lead to an early death?

Thanks for any input you have!!!

Jon

[Lead Head]

I don't *think* it should be an issue, but you'll definitely want to be on the listen for detonation.

If you still have the ATC cam, you may want to switch to an XR200 (or better) cam. It should lower the static compression a little bit.

[mrmikkelsen]

Thanks for the reply Lead Head. Yep, I do have a Web Cam mid-range cam in there, maybe could have popped for more of a high strung cam, but I am old and would like some measure of low rev power to assist when I let it fall off the bubble.

225, if it is okay with race gas, or better yet 50/50 race/pump I'll happy as a clam.

Anybody else out there got a second experienced opinion? The more more merrier.

Thanks again!

Jon

[beezer]

I run mine on pump gas. I have a 10.5 piston and a Webcam.

No pinging from mine.

[Chuck.]

I'm running 11:1 on pump premium without problems but I limit total advance to 29 degrees,which you can do if you use the XR185/200 CDI ignition system. My motor is a 218 with a Powroll Torque cam which closes the inlet valve 4 degrees sooner than the XR200 cam. Here is some cam data that I collected that may help in picking a cam:

Inlet closing ABDC:

Powroll Torque measured 42

Powroll Track 43

Powroll P714 measured 52

XR200R measured 46

TLR200 measured 32

ATC200X per Megacycle 37

ATC185C per Megacycle 36

Megacycle 143-00 46

Megacycle 143-20 59