2007 yz450f vp fuel to 93 octane

I just bought my 07' yz450 about 3 weeks ago. The guy I bought it from said he has always run VP racing fuel on the stock jetting, bike had a 3 gallon IMS tank full of fuel when I got it. Anyway first ride it ran great with very little popping on decel and started pretty well too. Went out yesterday and filled up the bike with 93 octane pump gas and now it is popping very bad on decel. I tried adjusting the air screw and it helped a little bit along with turning up the idle a bit too but still popping pretty bad. As I said the only thing that has changed is the fuel, can it have this big of affect on the jetting? Power wise the bike ran strong and didn't feel any different than when running the VP. I reviewed the jetting threads and everyone seems to start with fattening up the pilot, I just need to find out what pilot is in it which should be stock.

I just need to find out what pilot is in it which should be stock.
Then you should review the jetting thread. :smirk:

http://www.thumpertalk.com/forum/showthread.php?p=6980892#post6980892

As you can see, it's a 45 stock. That should be big enough, and your popping problem could be the result of either an air leak in the exhaust or of the pilot jet having a varnish deposit in the orifice, reducing the effective size of the jet.

Have any modifications been done to the motor?

Then you should review the jetting thread. :smirk:

http://www.thumpertalk.com/forum/showthread.php?p=6980892#post6980892

As you can see, it's a 45 stock. That should be big enough, and your popping problem could be the result of either an air leak in the exhaust or of the pilot jet having a varnish deposit in the orifice, reducing the effective size of the jet.

:smirk: I guess I should have said verify that the jetting in it is truly stock, which would be the 45 pilot. So changing from the high octane race fuel (112 octane I think) down to the 93 octane pump gas wouldn't change much? Like I said it didn't pop much at all with VP fuel, temps were about the same. Starting isn't too bad but it always takes about 3 kicks to get it started. I did check the pipe connections and they seem fine and tight. I guess varnish is a possibility but it ran fine a week ago now it is popping.

Rider X this bike is completely stock, no motor mods what so ever.

Gray are these numbers incorrect? I got them from the jetting forum and they all say stock but don't match the stock you list for the 07'.

geshields

TT Bronze Member Join Date: Dec 2008

Location: Texas

Posts: 186

Model: 2007 YZ450F

Edit Revision Date:

Main Jet: 165(Stock)

Pilot Jet: 45(Stock)

Starter Jet: Stock

Leak Jet (if any): Stock

Fuel screw/Setting: 1 1/2 turn out

Needle/Position: Stock

Filter: Twin Air

Pipe/muffler: DR. D Stainless w/spark arrestor installed

Altitude Range: 100-300ft

Temp Range: 60-85F

Humidity Range: 70-95%

Comments: O-Ring mod done to Accelerator Pump. No Bog. Runs perfect and keeps on pulling...

The only thing that doesn't match there is the main jet. YZ450's were delivered new with three main jets, and some dealers would change from the installed jet to one of the others while assembling the bike. It's not at all out of the question that they changed the factory installed jet midyear after the manual was published, either.

The only thing that doesn't match there is the main jet. YZ450's were delivered new with three main jets, and some dealers would change from the installed jet to one of the others while assembling the bike. It's not at all out of the question that they changed the factory installed jet midyear after the manual was published, either.

Ok I'll need to open it up and check it what's in there. If you think it is just varnish what is the best why to remove it from a jet?

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