Wont start! plz help!

9 replies to this topic
  • sourant75

Posted July 12, 2011 - 06:51 PM


Okay I have a yz450f 2004 and I ran a stock exhaust and stock header pipe with 91 octane gasoline from the pump. I recently bought a pro circuit T4 slip on an kept the stock header and put VP110 race fuel in it. It was waay too lean so i put a bigger jet in it. The bike ran way too hot. Even on the stand it wud puke anti freeze out of the overflow of the radiator and smoke. The plug was still white so I put a bigger jet in it and a new spark plug and now it won't start. I got it to fire once but it wud not idle and it wud POP like crazy then it died. It was only running for literally probly 30-40 seconds and the radiators were already super hot. Plz help I really need to get this figured out before my race on Saturday. Thanks in advance.

  • sourant75

Posted July 12, 2011 - 06:52 PM


I shud add tht it won't start since it was popping.

  • Brokenparts123

Posted July 12, 2011 - 08:02 PM


Go back to stock jetting and regular fuel. Changing your exhaust in no way constitutes changing your fuels like that. Your engine isnt set up to be running such high octane fuel.

  • sourant75

Posted July 12, 2011 - 09:22 PM


I believe you but why the heck do they make it then?! And is it more for bikes with high compression pistons an all that expensive junk?

  • 01cr80

Posted July 12, 2011 - 10:42 PM


I believe you but why the heck do they make it then?! And is it more for bikes with high compression pistons an all that expensive junk?

they make it for bikes that need it, not stock yz450's

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  • intensem1rider

Posted July 13, 2011 - 12:53 AM


There is absolutley no need to be running that fuel on a 450 ridden by someone who isn't an ama pro, switch back to 91 octane.

I am curious though, what jet were you changing? The main or the pilot?

  • sourant75

Posted July 13, 2011 - 08:04 AM


:thumbsup: I guess ill go back to the pump..... I was just trying to give my bike good fuel but oh well, and I was changing the main jet.

  • intensem1rider

Posted July 13, 2011 - 08:13 AM


Yeah, that's why you didn't notice a difference, the main is for wide open throttle. You needed to go richer on the fuel screw, and if that could not be achieved, the next size richer pilot jet then re-tune the fuel screw again.

There should be some info on fuel screw tuning in the jetting section

  • Schpenxel

Posted July 13, 2011 - 10:20 AM


the "good" fuel is more marketing hype than most people realize. just because it's expensive doesn't mean you'll make more power or it will be better for your engine.

use the fuel it was designed for.

  • YZ450Rider

Posted July 22, 2011 - 05:47 AM


Ahhh, I remember a similar issue on my 04 YZ250F. Used to run perfectly. Then it just would not idle right. It would pip and pop and shoot flames out the exhaust. AND it would get hot quickly. Titanium pipe would glow red. !!! I was stumped for about 2 weeks. Valves, Cam Timing, blah blah blah. None were the problem.

Turns out the Pilot Jet inside the carb was actually clogged (thanks to Ethanol Fuel evaporating and leaving the dreaded residue inside.) It was clogged so bad I couldn't even poke through it with my carb jet wire set.

Soooo, I replaced the Pilot Jet with an "unclogged" one. Problem solved.

This was after removing/cleaning the carb like 5 times and I don't know what'all...

You might have "blown" out the carb with air, but check the jets and all passages themselves to make sure they are clear. Take the jet out and look through the hole. If you can't see through it, there's your answer.

This problem almost made me tear my hair out. One small issue that made it run like crap was all it was. After that fix, bike runs perfectly again.

Check all jets for any clogging - especially Pilot Jet. Make sure you can actually see through the jet hole. Don't just assume it is clear because you blew air through it. (I did the same thing and assumed such.)

P.S. DO NOT LEAVE PUMP GAS that has ethanol in it sitting in your carb. When the fuel evaporates it leaves a powdery residue that is notorious for clogging jets and other tiny carb passages. I personally mix 110 race gas with pump gas and problem solved. I have been doing this for years and NO PROBLEM AT ALL. Or you can use StaBil in your fuel. Those of us who don't get to ride all that often have this problem.

P.P.S. "Good" fuel like VP Racing fuel (oh there are only like 70 different formulas of VP Fuel) is not just a marketing gimmick. They make many VP and Sunoco performance fuels that are equal in property to pump gas but much much cleaner and with no crappy ethanol in it. It burns much cleaner than pump gas. Ethanol fuel will clog your carb so fast your head will spin. BEEN THERE! The trick is getting the "correct" performance fuel for your motor and your needs. In my 4-stroke I either run VP MS101 (it is unleaded), or I mix VP 110 with regular gas. Since I have been doing this, my piston, valves and cylinder head stay MUCH cleaner. No crusty buildup at all. And in my 2-stroke, the power valve stays much cleaner and easier to maintain. No gunky buildup at all. That is a better benefit that just horsepower. Proper carb jetting will possibly get you better horsepower. But good fuel gets you cleaner burn and better engine cooling properties. That's worth a heck of a lot later on down the road in maintenance and rebuilds.

My mechanic is amazed at how good my piston, valves and cylinder head looks when we do a rebuild. It is clean as a whistle!

You pay $8,000+ for a new dirtbike but you are going to put the crappiest fuel known to man (pump gas) in your baby? Are you kidding???

It is not just some gimmick. Use the correct formula and you will NEVER go back to regular ol' crappy pump gas. I PROMISE YOU.

Sounds like a sales pitch, and, yes, I am a VP dealer. But I'm also a "client" and I run many different formulas of VP fuel in all of my motors.

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