A few engine questions, plz read

[2000yfm350x]

Hey there guys and gals, got a 2001 warrior and am new to the yfm 350 engine, did a valve adjustment the other day and noticed there are dual springs in my head, are theses stock? Never rode one before other than mine so idk how they run, when I first got it it seemed to pull slot harder up high and longer than I assumed it would, not sure if it has a cam in it or not, but I been chasing issues with it, need to buy a new carb, when I first got it you couldn't rev it up and dump the clutch or it would pull the tires about a foot in the air and die out then come back, rebuilt carb with a kit I got with the quad and fixed that issue, then a new issue soon popped it's ugly head, now it doesn't wanna rev above 5-6000rpm, based off how it sounds and reading the rev to 8-8500, acts like valves are floating, this is all before the valve adjustment, when I was in there doing the adjustment the other day I also noticed the the timing chain tensioner is maxed out and chain is sloppy as hell, did the valve adjustment and checked chain due to noise that developed, haven't rode since the adjustment but the chain is soo sloppy the the cam is off one tooth clockwise and when you try to move it one tooth back counter clockwise it is off a tooth the other way, so I'm sure that and the junk carb are my issues but my question is really about the springs in the head, just giving a detailed back ground on the bike since Ive had it. Also while I'm in here, I've done a lot of searching and can't find much on CWR engines for these bikes, Greg seems to have a strong and successful career at ATV engine building so no doubts just wanna know peoples story's on how there's have ran, kinda anxious to get to that point lol thanks guys and gals!!! Mine also has a decompression lever on the head so gotta call Yamaha and see if my engine belongs to my bike and it's just a head swap or what. Thanks again

 

[Ed G.]

From my past experience, higher revving engines 7500rpm+ tend to use duel valve springs. Not to be to general in my response but cam timing is definitely important along with proper air fuel mixture. Cam timing would cause a loss of power or backfire/pop in most cases but fuel can cause misfire if too rich and feel like a rev limiter. If you have a loose chain start with that.

 

[2000yfm350x]

Thanks for the response, carb has issues and is gonna get replaced with a bigger fcr unit for future upgrades and a chain and guides is in the mail. Bike has other issues but just wanna get it reliable this year so next winter all hell can brake loose!! Carb has a port off accelerator pump that is full of green corrosion I can't get out, soaked it for a couple days and nothing. So it can go in the trash can soon. The rpm I do have is good enough for trial riding so I'm happy ain't no need racing right now my Budds 450r that is now 510cc would kill me lol

 

[2000yfm350x]

Valve adjustment fixed my rpm issue, even quieted the engine down soon much that I would never think the chain was on its last leg, time to finish taking the plastic off and send them out for paint. Have new chain installed and ready to ride soon

 

[lbjamm]

Sounds like you're on the right track. I installed a FCR37 on mine and in the process of tuning now. Those early heads had the decompression lever. Mainly because of the pull start. Later models were strictly electric start.

 

[2000yfm350x]

I've been watching used edelbrock units online, quite a few of them on eBay, off other bikes but anything can be made to work. If noticed been looking into a fcr can't remember the size tho, 38 or 39 I think. Bike is pretty easy to work on, haven't found anything I don't like about it other than the blown rear shock looking at used banshee units to fix that. Engine I'm assuming is original, says 1yu or something with 00 in it and the bike is a 2000 so idk. Still gotta call Yamaha and check on that but it does have the wrong head/valve cover on it.