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Need race fuel/octane recommendation for my slightly modded xr100

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85 xr100. Been 10 years or so since my last post and forgot what fuel to run. My mods-

powroll 9mm stroker crank. Wisco 120 piston. Mega cycle cam. Aftermarket valves can’t remember which ones. Flat slide carb which runs better then my oversized round carb. Cdi conversion. Bbr pipe. K/n air filter. Will upgrade rev box at some point. Port n polished. Other then that she’s stock.  Thanks for any help 

525CA300-3946-47DE-BF34-AF47E2E7661B.jpeg

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That’s a killer XR! If you’re running pretty high compression, then I would suggest some good VP fuel.

And what flat slide are you running?

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12 minutes ago, CRFrider007 said:

That’s a killer XR! If you’re running pretty high compression, then I would suggest some good VP fuel.

And what flat slide are you running?

Got the flat slide from xr100.com. Used to live down the road from them. I can’t remember which carb been so long 

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1 hour ago, CRFrider007 said:

Nice man I bet your XR is pretty quick!

Yea it’s like a mini 450f. Can’t keep front tire on ground. But I’m geared low. Can’t wind out the stroker motor

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2 hours ago, CRFrider007 said:

Yeah I bet she’s a ripper. What’s the total displacement on it??

I believe it’s a 150 now with 14.2:1 compression. Very hard to kick. Have a 200r kickstarter on it. Supposed to push start only but I still kick it. 

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6 hours ago, CRFrider007 said:

Wow that’s insane. No decomp??

No. I’ve already striped the kick start shaft once before. Kick starter put holes in a lot of my shoes. I just find tdc and go past it a hair then kick. 

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23 hours ago, rasta said:

85 xr100. Been 10 years or so since my last post and forgot what fuel to run. My mods-

powroll 9mm stroker crank. Wisco 120 piston. Mega cycle cam. Aftermarket valves can’t remember which ones. Flat slide carb which runs better then my oversized round carb. Cdi conversion. Bbr pipe. K/n air filter. Will upgrade rev box at some point. Port n polished. Other then that she’s stock.  Thanks for any help 

525CA300-3946-47DE-BF34-AF47E2E7661B.jpeg

Compression 14:1 I would start with 100 Octane and listen for any pre-detonation, if there is any go to 110.  This also depends on Elevation that you are riding as you go up in elevation your Octane needs will drop.  So at sea level you may need 110 at 4200 feet+ you may only need 100.

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47 minutes ago, Dodging_roost said:

Compression 14:1 I would start with 100 Octane and listen for any pre-detonation, if there is any go to 110.  This also depends on Elevation that you are riding as you go up in elevation your Octane needs will drop.  So at sea level you may need 110 at 4200 feet+ you may only need 100.

I am at sea level. Was thinking of mixing 110 and premium but I will try the straight 110. I can here it rattling on pump gas under heavy load

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Damn man, I thought at first I was looking a a really trick dirt squirt........

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1 hour ago, adrew said:

Damn man, I thought at first I was looking a a really trick dirt squirt........

I know. I throw of a lot of people with that tank decal. Wish I had a superrat 

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Posted (edited)

Straight VPc-12 is what I use to run in my DR170 Powrolll motor. Was a fun bike.

IMG_0617.JPG

Edited by pedec

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Should be fine on 100 octane. Check your local municipal airport, most will sell you 100low lead for about $5 per gallon. Yes I know it’s not race gas but we run it all the time except on race day when we want the extra punch of u4.4. Don’t believe what the haters say. It’s good gas and won’t hurt your engine. If it was bad airplanes would fall down. No it doesn’t make optimum power but neither does race gas if you miss the jetting by one size.

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We don't use it all the time, we've blown up 2 engines so we're more careful now.

 

 

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