Need some expertise on Motor (please read)

[bad01300ex]

ok i posted this over at YFZCentral as well, trying to get as many opinions as possilbe.

ok this will be a long post but need to figure my motor problems out.

Got my yfz last may, bought it used (an 04) for 4500, the guy i boutght it from had an FMF titanium slipon and he said he jetted it for it. He also said that he had been riding it and it started smoking so he replaced the top end. Well i figured it was fine so i bought it anyway. From the day i brought it home it was backfiring and i figured thats just what they do then i read into it and realzied it ment it was lean. well i kept riding it and and i started to have some battery problems, of coures i figured it was the headlight deal. In the mean time i put on a k&n filter which made the backfiring worse. I started riding it at the track and noticed a clickin/rattling noise while riding and thought it was my chain and didnt think much about it.

Well i figured out the noise was happening when i wasnt rolling so it was coming from my motor after asking around at the track a few people seemed to think it was my bottom end. well me and my friend tore into it and checked the compression which was 30 so now we new somethin was up. we checked the valve clearenses and the intake valves were stuck open, the when we got to the cylinder the walls were scarred up and one side had a groove around the top.

so i orderd valve spacers, cylinder and new toppend and figured this would take care of things. I also got a HMF slipon which came with a 170 main and 48 pilot. well after weeks of waiting for parts i finally got everything on, jets in (which by the way the previus jets were 162 and 42) turned the fuel screw out 2.5 turns.

well tonight me and my friend go to break in the new topend and what do you know the noise is still there and it still backfires like a mother f+++!!!! but it runs extrememly well

we think the noise may be the timing chain rattling? could this be? the noise comes at lower RPMs but not low enough at idleing or higher revs, so it doesnt seem to be bearings bc that would be consistant.

So, with all of that said, is the backfiring caused by poor jetting? 170, 48, 2.5 turns, HMF slipon, open airbox with k and n filter.

AND, would any of you keep riding with the noise? could it be the timing chain rattling? or what else could it be?

also figured out the reason it wouldnt start off of the battery is bc of low compression, i always had to roll it off, but it starts imidiatly now.

I know this is alot to read but im at a loss of what to do (and money) i just need some opinions i know some of you guys know alot bout these motors

Thanks for any comments/opinions you might post

[jshtex]

From what I understand it is impossible to get an accurate compression number unless you disable the decompression mechanism. It is designed to bleed compression at very low rpms, such as cranking it over.

My opinion is that the YFZ motor is more noisey than others I have owned, but if you are worried about it I would take it to someone with some experience with that bike.

As for the jetting, every bike is different. Ours runs fine on a 168 mj. My advice would be to buy an assortment of jets and start playing with it. My son can change ours in a couple of minutes now so it isn't too bit a deal.

[muff]

heres a couple things that might get you started, well that come to mind right away

1. check to make sure the chain chain tensioner is working. the chain is never loose enough where it "rattles".
2. check your intake and carb boot, it sounds like you might have a crack in either which would cause a lean condition


what exactly did you replace in the top end? What was the reason for the valves sticking open? What kind of compression are you getting now? Valve clearances good?

I would not run the motor like that...its only going to create more headaches and problems. Fix it now before you're replacing more stuff than you really have to.

[SRH]

these motors are a lil noisier than a 400ex motor or something too, just how they are....

but if its bad, def like muff said look into it before you really ride it, you dont want a big problem on your hands

[Ride1Rob]

What they said and... You didn't mention needle position. Although your jets may be good, you may not be dumping enough gas through your carb b/c of your needle position. That can cause your bike to run to lean/too rich as well. I'm in Florida and I have 168 main, 48 pilot, 4th clip on NCVQ needle w/ 2 1/2 turns out. I set up a friend of mines w/ the spare jets that I had 165 main, stock pilot on 3rd clip, 2 1/2 turns out and his bike runs as good as mine. I have an Alba pipe and he has a GYTR.

As far as the rattling goes... That bike shouldn't make rattling noises. Do you have a skid plate underneath? Sometimes mine vibrates and rattles b/c the bolts become untight.

[bad01300ex]

ok, for the jetting, the needle is on the 3rd clip from the bottom, and 2.5 turns out on the screw with 170m and 48p, checked my plug today and it was black, so im rich right? well tomorrow im goin to get an assortment of jets and play around with it.

For the motor, the things we replaced were the ring/piston (just to be safe, didnt really HAVE to) the actual cylinder because it had a groove around one side of the top, got the right valve spacers and the clearence is good now, and the chain tensioner does work, but my friend who put it together said it seem kinda loose, so this rattling is beyond me or anyone who listens to it. the strange thing is it only makes the noise at certain RPMs, but it is coming from the motor, ive checked all other bolts ect.

The problem is i dont have any more money now, and i cant sell it like this so im stuck with it.

How much does sparks or other motor builders charge to rebuild the motor??

Im thinkin i might could borrow the money and do it now rather than blow the motor and have to buy even more stuff.

So my options are ride it, or go in debt and get it built:(

[Ride1Rob]

If your friend says that the cam chain is loose, somethings not right there. When the tensioner tightens you shouldn't be able to move, tug, or pull that thing even a little bit. If so, that's more than like your problem w/ the noise.

[zeppelin]

see if the bolts holding the heat sheild on are loose, mine would always do that and make a horrible buzzing/rattling noise

[brian250racer]

How loose was the wrist pin in the connecting rod? The YZ motor in my hybrid developed a little play in it, and it rattled a bit right up until the point where the connecting rod broke...:(

if the cam tensioner is good. check the timing chain. make sure it is not stretched and kinking up. as for a motor builder, i will go through your whole motor for cheap as long as you pay shipping. i have opened up a shop in my house and can take care of you for cheap. thanks let me know