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Avgas jetting

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Ok, 08 crf450r, new bottom end (stock), new piston and rings (je 13.5:1), new head and valves(stock)

Situation: since weather warmed up, 80+, bike has 15.7 hrs on it. Fmf mega bomb header, and I run straight avgas. Bike wont start with choke, must twist throttle once and use hot start then usually fires right up. Fuel screw (after pre race practice 1) will not affect idle if turned all the way in and 2) will not affect idle as you turn it out (will make it somewhat sputter if turned in while warming up). Now, im meticulous with maintenance, change oil every 3 hours, air filter service regularly (take subframe off airbox and scrub it all, allows my hands to really feel filter install). Notice a bit of smoke when opening throttle a bit while warming up, smells like raw fuel not oil but isnt black. Think I need a leaner pilot jet. Between the megabomb and powercore + avgas, thinking im rich on pilot circuit and it didnt show up when it was 40 degrees and below because of air temp. Any thoughts?

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I used to race with a mixture of 50/50 race gas/avgas but I have read and heard of people having valve trouble running pure avgas in their bikes. If you're running about right on your jetting at 40 degrees you would be a bit lean at hotter temps since colder air is more dense than warmer air. I think I got that right anyway. Your air screw is making no difference?

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I used to race with a mixture of 50/50 race gas/avgas but I have read and heard of people having valve trouble running pure avgas in their bikes. If you're running about right on your jetting at 40 degrees you would be a bit lean at hotter temps since colder air is more dense than warmer air. I think I got that right anyway. Your air screw is making no difference?

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I used to race with a mixture of 50/50 race gas/avgas but I have read and heard of people having valve trouble running pure avgas in their bikes. If you're running about right on your jetting at 40 degrees you would be a bit lean at hotter temps since colder air is more dense than warmer air. I think I got that right anyway. Your air screw is making no difference?

FUEL screw is not making a difference

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That's a tough one but if it won't start with the choke on that tells me that it is something in your pilot circuit and at this wee hour of the morning I think you need a richer pilot jet for warmer temps, or do I have it backwards. Let me think on it a bit.

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Why does this matter? Every VP race gas is leaded also?

no sir they make unleaded race fuels.

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I'm not sure what VP is but race gas has no lead.

race gas comes in leaded and unleaded. Lead is the best octane booster and also a great valve cushion. Today I checked valve lash, perfect. Today I checked plug, perfect but replaced for just no reason. Drained fuel, put 93 pump junk in, well seems fine now. Will practice tomorrow and fiddle. Cant believe the avgas in this machine requires a smaller pilot but not main or needle change....still sorting this out.

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Maybe in a 1950's era Lycoming or Continental engine but not for high revving modern dirt bikes.

pretty sure it still holds true.

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Formula One race cars stopped using leaded fuel in 1993 and NASCAR started using unleaded in 2008. The only reason you can still get 100LL avgas is because so much of general aviation is still flying with 1950's & 60's engine technology, and lead prevents their valves from sticking. Lead in fuel is bad and has no place in modern engines.

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Ok well i guess i stand corrected

 

Let me rephrase my last post.

 

Every VP race fuel i have ever seen says leaded. I am admittedly no expert. I don't typical run the stuff as I'm just a vet amateur at best and ride a stock bike

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Well like I said in an earlier post I used to mix avgas and race gas until I started doing a little research. The main reason that nascar banned it was because so many guys on the pit crews were getting sick from lead poisoning.

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Maybe in a 1950's era Lycoming or Continental engine but not for high revving modern dirt bikes.

Don't know what you are talking about, but at a glance, VP C12, 111, and 113 have lead additive. Been running straight AVGAS 100 octane for awhile without any problems or jetting changes.

Edited by willbilly

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Do your research then we'll talk

Still dont know what you are talking about. VP Race Gas contains lead.  I was merely stating that I had no problems using avgas.  Maybe you should do some research, but I am done talking to you.

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