YFZ easy fix?

[PolarisRider]

Alright guys heres the story. I ride a 300ex that is on ebay right now that I am selling. My buddy has a YFZ450 that he would let go for about 2500. The guy before him put some insane compression pistion and a big hotcam into it. It has a complete aftermarket exhaust and was supposedly jetted properly. The thing is, it runs like complete crap. When he first starts it up it'll run for about 30 seconds strong as hell and then backfire like crazy and shut off every now and then. I think it the extreme compression of the piston that is doing this. I belive the compression is like 14.5:1 which in my mind is crazy becuase anything past about 12:1 on my little 300 is pushing detonation, haha.

My question is that if I buy this and put a stock cam, exhaust and piston back into it, will it be alright. Thats the only thing i can think the porblem to be.

Opinions?

[TheNewn]

Sounds like it might be running too lean and over heating?

That's a pretty good price for the YFZ, but if you have to do too much work to it, bills could add up right quick. Might be able to just swap out pistons to something with lower compression. And be sure that the jetting is correct.

What is the rest of the bike like?

[yfzrider310]

Did he run race gas....110 octane. That might be the problem.

[PolarisRider]

Originally posted by yfzrider310
Did he run race gas....110 octane. That might be the problem.

Not all the time, but right now it is currently running 114 octane.

[PolarisRider]

Originally posted by TheNewn
Sounds like it might be running too lean and over heating?

That's a pretty good price for the YFZ, but if you have to do too much work to it, bills could add up right quick. Might be able to just swap out pistons to something with lower compression. And be sure that the jetting is correct.

What is the rest of the bike like?


Thats what I was thinking. Im probably going to get it, put the right jet in it, and sell the exhaust and cam to pay for a new stock piston and cam. I will put the stock exhaust back on.

Should that hotcam mess anything up?

Oh and for as the condition of the bike, it looks amazing.

[IMSROLL450R]

The problem with the bike isnt the compression, its either the fuel, jetting, or valves being out of adjustment. I have ran a 14:1 for a long time with no problems until my valves got a little slack in them. I would jump all over that bike for that price, get the valves shimmed for free if you have a manual, buy some race fuel, and ride the crap out of it. Sounds like the guy that has it doesnt know what he has.

[PolarisRider]

Haha. No he doesnt know what he has.

The thing rips like hell when it runs good.

[PolarisRider]

Here is the only picture i got of it. It has some hgih end full exhuast on it right now.

[TheNewn]

Looks nice from the picture, if you don't feel like paying for racing fuel after you get it. I imagine you could always put a stock piston in it and keep the hot cams/exhaust.

The valve thing never crossed my mind, definitely worth checking.

[Honda5]

it's not the compression I run15:1 on one of my 450r with 110oct. I would drop the compression to stock and keep the cam then check the valves and jetting and you'll have a great quad.

[06YFZ450SE]

Thats a nice looking YFZ. Before I would take stuff off the quad . I would check the jetting and values first. You might change the jetting and check the values and it might run like a bat out of hell..Sounds to me its running to lean..

[PolarisRider]

Originally posted by 06YFZ450SE
Thats a nice looking YFZ. Before I would take stuff off the quad . I would check the jetting and values first. You might change the jetting and check the values and it might run like a bat out of hell..Sounds to me its running to lean..

I do think it is lean. I still am converting everything back to stock and just running premium. A stock 450 is still a BIG step up from a 300 I rode for 3 years anyways.

[06YFZ450SE]

Originally posted by PolarisRider
I do think it is lean. I still am converting everything back to stock and just running premium. A stock 450 is still a BIG step up from a 300 I rode for 3 years anyways.

Ya Its a big step up. I went from a 99 350 Warrior to a 06 YFZ450..

[#17YFZRACER]

if you get it please take off the 6-pack rack. trust me on this one;)

[PolarisRider]

Haha, is there a story behind that?

[420yfz]

i had a yfz that would only fire up for a short amount of time, spit sputter backfire run like crap, ended up being the stator.

it was also high comp with cams, only trouble i ever had with valves is starting, never lost power, just would not go with the electric start or kicker, had to be bump started.