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RMZ 450 backfiring... pop baam!

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Hi there... glad to see we have an expert on hand!

I have just bought a new RMZ450 - 2 weeks old and everything has been great...until !!!!!!! I put Leaded 100 octane race gas in there last weekend.

Prior to that I was 50/50 mixing Avgas (98 or 99 octane) plus 96 octane unleaded. The jetting is stock for New Zealand and I ride sea level to 400 feet usually.

What I noticed was during downhills only , the bike started to backfire ?! Nothing else had changed but the fuel so I have to assume that was the culprit... but why? What does leaded fuel do to the jetting/combustion to cause that? :applause:

I would have thought leaded higher ocatne would be great for the engine?

Any comments gladly accepted.

Cheers :eek:

John

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the fuel richened the pilot circuit.this combined with a possible pipe leak will cuase big explosions in the exhuast.

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Thanks Burned! So I can either lean the air screw or change back to my regular fuel right?

I'll check the exhaust too.... thanks again.

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Also different fuels have different properties, The race gas might be 'thinner' maning more octane can get through the jets, but certainly race fuels and higher octaned fuel has different properties. I don't exactly understand it myself.

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