High comp piston, now running very hot quick

[CodyRosa]

Hi, I've heard that higher compression pistons make a motor get hotter.. but how much quicker? How fast do these machines get hot? I haven't rode mine in a month so I don't quite remember. I drove mine (10.25:1 hi comp piston) 1/2 mile going maybe 25mph and when I parked it, it just slowly died down (from getting hot im guessing). I touched the fins and they're way to hot to touch..

I don't remember this machine getting this hot this quick but I could be wrong.. just could someone refresh my memory please?

Thanks

[dougspcs]

Did you do any rejetting after the piston install? Make sure your carb is jetted properly and your cylinder temp isn't too high..a white tip on your plug will tell the tail there. Lean = too hot!!

You sure wouldn't want to burn a hole in the top of your new piston and spoil all that hard work..

But that aside if everything looks normal there, ride on.

[fallguy666]

If its jetted properly it shouldn't get a whole lot hotter than stock.it will be hotter but not that much.lmo

[Poco Loco]

Also race gas helps keep it cooler. You need more octane to match the bumped up compression. If you running lean it will run very hot.

[dougspcs]

I agree with Poco Loco..raising the octane may be all it needs also.

Perhaps just a simple jump to Super pump gas..race gas is tres expensive and in some areas hard to come by.

What machine we talking about here anyway Cody??

[CodyRosa]

Well doug this is my auto x. 200M top end. I'm running premium right now. I'll check my plug again. Last night when I check it was black. I did turn the screw but forgot to check the plug so maybe its running a tad lean now. I was told I didn't need to rejet for a high comp piston BUT I did change the exhaust from the stock 200M to a 200x header/muffler.

[CodyRosa]

176873 Ok i took the plug out and this is what i got. I can wipe the black off like nothing so i'm guessing lean?

[dougspcs]

You'd probably best to try a fresh plug to get a clean reading..

But yeah it does kinda look that way.

[fallguy666]

Yeah ,you need to try a brand new plug and see what color it is after you run the snot out of it

[Poco Loco]

You wont get an accurate reading on the plug unless you do the test correctly.

If you want to check your main jet setting you need to be running on the main at shutdown. Example...Get on a long road or hill. Go through the gears and top out at full throttle.

While at full throttle Kill the ignition and let off the throttle at the same time. Pull in the clutch coast to a stop and pull the plug and examine it. This method give you a true and accurate main reading. Plug color can change in a short period of riding.

So many riders never get a true accurate reading of the plug because they go for a ride and then cruse back to camp or the garage on their pilot jet.

Give it a try and see the results and jet accordingly to the color of the plug.

[CodyRosa]

I'd love to do an accurate reading haha but I wanna break it in first. I wanna wait before I go full throttle. When I get the chance I will do that though. That plug actually is new, well 10min on it =D

[yaegerb]

No, you don't need race gas with 10.25:1. 93 at most is sufficient and you can still get away with 87. Your plug color indicates a lean condition. You need to rejet your main to a 112 or maybe even a 115 and work down from there.

[Poco Loco]

I'd love to do an accurate reading haha but I wanna break it in first. I wanna wait before I go full throttle. When I get the chance I will do that though. That plug actually is new, well 10min on it =D Full throttle for a short period will not damage your motor. Ive never had any issues during a plug check with a fresh motor. And as far as fuel, if you mix 110 octane with premium 50/50 it will put you rite around 100 octane. Thats a good mixture for a high comp. motor. And it keeps it afforadable too. Avaition gas is good too and sometimes easier to get.

[CodyRosa]

Ok,and what kinds of places carry 110 octane? I never heard of anybody selling it.

[Poco Loco]

Well in minnesota ,I cant tell ya that. Here in cali. you trip over it every time you turn around. Go to a local airport and get av gas. Google it.VP Gas sales outlets. Ask local racers. Or run 87 like someone else said and listen to your motor ping. Figure it out.

[yaegerb]

hmmmm, built a few motors in my day, all were on the honda 200cc platform and all of them were performers. Doubt the motor will ping on 87, but if you are worried about it spend the extra money on 93 or unload your wallet on race gas which is totally unnecessary for 10.25:1. Avgas, don't recommend it, but don't take my word for it. Here's a good article on octane.
http://www.klemmvintage.com/gasolines.htm

[CodyRosa]

Oh Yaegerb I just run 91 or 93 whatever premium is. Another question while were at it.. this machine seems very slow. Although I'm not on it, its not fast maybe 30, 35 tops it feels. I'm running stock gearing 11, 40.. so maybe I should throw my 13 tooth up front? It sounds like its doing its job lol just not moving anywhere that fast.. at least not as quick as it was before.

[gootheboy]

10.25 is a pretty mild piston. 93 should run fine but sounds like your running pretty lean. what cam, exaust and carb set up do you have?

[CodyRosa]

I'm running 91 at the moment. no 93 around me =( I was running a tad lean when I wrote this post but its running great now. Its quicker now then it was when I did the post. I have yet to try it with 55's and 13, 40 gearing. I'm going to try that tomorrow and see if its fast.
Stock cam(=( i know i know.. i need an aftermarket cam or xr200) 200x header/muffler and carb is stock 200M. 95 main I believe. I have the air screw turned in half a turn from stock and it runs great.