Yfz Cam Mod

[motorhead]

Was thinking of doing the hot cams on the yfz but it seems that there might be some bottem end loss, I mainly trail ride so I dont want to sacrifise bottem end but yet it would be nice pulling hills in the coal pits. Im wondering if I should just retard the exhaust cam for now,this is a freebie that everyone seems to be doing.
Just looking for opinions on performance on trail riding before and after these mods
Heres a nice link on the timing mod for those who are unfamiliar with it http://www.yfzcentral.com/cammod.htm

[rpyfz450]

I retarded the exhaust cam and the motor screams. There seems to be some arguments this doesn't reduce low-rpm power, it just adds high-rpm power making the motor seem like it has less low end.

I would like to put the exhaust cam back in it's factory position some time soon just for comparison.

[motorhead]

Thats what I wanted to hear.Thanks RP. Hope to do it this week. How did it effect the jetting? I gotta check the valve clearance while Im in there.I hope they dont need adjustment,kind of a crappy set-up with the selectable shims in there.too bad they didnt use a threaded style adjuster.

[rpyfz450]

<div class='quotetop'>QUOTE (motorhead @ Apr 3 2006, 08:17 PM) <{POST_SNAPBACK}></div>

How did it effect the jetting? I gotta check the valve clearance while Im in there.I hope they dont need adjustment,kind of a crappy set-up with the selectable shims in there.too bad they didnt use a threaded style adjuster.[/b]

I don't remember the jet change, but I'm pretty sure it needed one. If I had to guess, it might want one size bigger on the main. If you'e going to be running it wide open, do a high speed chop and check the plug. My ATV responds pretty clearly to jet changes and I change jets using the seat-of-the-pants method these days. BTW- I'm assuming you have an aftermarket exhaust system and run with the air box open. If not, you should consider it.

Are there engine designes out there that have threaded adjusters without rocker arms? I've never seen that on a motorcycle. All SOHC motorcycles have tappet adjusters as far as I know

[motorhead]

yea,gytr filter with no lid,stock exhaust with just the silencer removed,I heard from others that the stock exhaust flows fairly well so I havent upgraded yet.
It must be a space issue to not use threaded adjusters.plus the rocker and follower is just more moving parts to rob horse power and eventually break. Im just spoiled working on cars,almost everything is hydraulic valve lash or adjustable without having to buy selectable shims.

[rpyfz450]

<div class='quotetop'>QUOTE (motorhead @ Apr 4 2006, 06:52 AM) <{POST_SNAPBACK}></div>

no lid,stock exhaust with just the silencer removed,I heard from others that the stock exhaust flows fairly well so I havent upgraded yet.[/b]

Yeah, the "no lid" part is the most important one. I had mine set up for a quite a while like that (SA removed).

Only of you had another YFZ to compare it to would you notice the amount of low rpm power that's missing. The ATV will have lots of power up top, but there'll be a deficiency when it comes to "rolling on the throttle". If your not on MX courses, you may not see the need for this. You'll probably never notice it if you ride not-so-tight-trails and mining/fire roads where you have the luxury of downshifting for more power whenever you want.

There were two specific obstacles, one at Mt Pleasant, and another at Rausch Creek, that I couldn't clear with the stock exhaust. After the LRD Pro+4 pipe installation the former obstacles became mere speed bumps.

[motorhead]

Where did you get your exhaust and how much did you pay? $500.00 seems like the running price. I did find this on ebay $438 and $14.50 shipping. http://cgi.ebay.com/ebaymotors/LRD-PRO-4-C...1QQcmdZViewItem

[rpyfz450]

<div class='quotetop'>QUOTE (rpyfz450 @ Apr 2 2006, 11:47 PM) <{POST_SNAPBACK}></div>

I would like to put the exhaust cam back in it's factory position some time soon just for comparison.[/b]

I rode this weekend with the exhaust cam in the stock factory position and the ATV was down on power. I'm changing it back before next weekend.

I recieved an email from one of the aftermarket camshaft manufacturers. His opinion was the YFZ exhaust camshaft is installed in by the factory in the slow position just to make it easier to ride. The retarded position is what the engine was really designed for.

[motorhead]

I will take your word for it,Im happy with the way it runs in the retarded pos.I did the exhaust and the cam mod at the same time and the performance improved all the way across the spectrum.even the throttle responce seems better.
Have you had to adjust your valves at all? Mine are all at the high end of the spec.I probably wont bother even checking it again until the winter.

[rpyfz450]

<div class='quotetop'>QUOTE (motorhead @ May 24 2006, 06:41 AM) <{POST_SNAPBACK}></div>

I will take your word for it,Im happy with the way it runs in the retarded pos.I did the exhaust and the cam mod at the same time and the performance improved all the way across the spectrum.even the throttle responce seems better.
Have you had to adjust your valves at all? Mine are all at the high end of the spec.I probably wont bother even checking it again until the winter.[/b]

I just changed back to the camshaft position last night.

Yes, one of the intake valves measured 0.01mm too tight after 5 months (December 2003). Since then, all five valve clearances have measured within specification up to a couple months ago.