Hey, Just thought I would share my experiences with y'all. I had the yz450 cam installed on my 450, and experienced extremely hard COLD starting. Hot start was fine. The power gain was great, once you got it running.
I have since had the stock cam put back into it, and the thing fires right up cold and hot. So then, I decided to keep the original cam in, and just retard the timing. The thing has a harder time starting cold, then when the original timing is in the bike, but it still starts ok.
We have checked the compression levels through out these changes and with the original I had 120lbs of compression. That is really good, as the manual calls for atleast 75lbs. When you put the yz450 cam in, it drops down to a mear 20lbs of compression. With the cam-mod (stock cam retarded one tooth) I got 70 lbs of compression.
So, I guess my question is, is I thought more compression gave you better power. With these cam mods its actually giving you way way less, and I think causing hard cold starting. You can definately feel the difference when you ride between the stock cam, and the new timing of the yz cam or the retarded stock cam. The bike is a lot faster in the mid and upper range, BUT with less compression?????
I am stumpted, and I dont know what to do. One thing is for sure, my bike does not like the yz450 cam at all. upon trying to start it cold, it backfires horribly, and takes a good 100 turnovers to finally lite. Once lit, the thing runs like a dream, and the jetting is absolutely perfect, according to the spark plug, and the great performance that I have.
Anybody that could help me out on this delema I would sure appreciate it!!

 

Here is the help you need. You put the cam from the wrong engine in your quad. The cam is not for your engine. Stick with what came in the quad. If you want to change cams put a YZF engine in your quad otherwise stick with what came in it. Leave the exhaust timing, as is, for power on the bottom and mid or move one tooth for power on top end. That's all there is to it.

 

That pressure sounds real low. Not sure how the auto de-compressor is set-up. Were you able to disable it to test compression? You may not have seen much power because the de-compressor may have blead it off. Also, did you have the carb open to allow full air flow into the cylinder?

Has anyone disabled the de-compressor with the cam mod? If so, does this solve the cold starting issue?

 

Boom - Were your valve clearances in spec with the YZ cam??? how about with the cam-mod??

Ive had the cam-mod since I bought my YFZ in september with no problems

 

Hey, thanks for the replies. I am just about at wits end with this whole cam thing.

ridnwarrior: The yfz motor and yz motor are almsot identical. THe only differences are, longer stroke, different cdi, and a little higher compression. I know of several people that have put a yz cam in there quad, and had know problem. The reason people go that route, is to actually aleviate the hard cold starting problem, cause on the yz cam, the decomp pin stays in the right place. With the "cam-mod" (retarding it a tooth), your actually putting the decomp pin the wrong place, which does cause "harder" starting then stock. THough, in my experience, the yz cam was even harder!!!! The cam-mod takes a few extra role overs, but it atleast starts!

DuneMe: Yeah, that pressure is WAY too low, and I am suprised the bike actually ran well with the yz cam in it. I really don't know about the decomp set-up, and how that all works. I'll have to check with my mechanic to see how he was reading the compression levels. That does bring up a good point, wonder if the decomp is stuck open or something?? Although, I dont think it is, cause when the original cam is installed, on stock timing, I am getting 120lbs of compression! Dont know, I'll find out for ya, and get back to you!

schwendi: THe valve clearance was in spec by the book for a yfz. I have never heard of anyone changing there valve clearance with the yz cam, as the lift and dur are the same on both cams. The only difference is suppose to be where the decomp pin is. The decomp pin is exactly where its suppose to be on the yz cam, when installed on the yfz. Its when you do the "cam-mod" and retard it a tooth, when you have the decomp pin in the wrong place, by one tooth.
I have not changed any valve clearances though, and they are to spec with the service manual for a 04yfz450. Thats great that you have not had a problems with your cam mod. I just had the "cam mod" done to my quad, and I still have the power gain up on the mid and upper ranges, like I did with the yz450f cam. The only negative I have seein thus far with the cam mod, is it does take a little longer to start cold, then when its set to factory timing. But, its worth it. Atleast it starts now, in a reasonable amount of turnovers.

So, I am going to run the quad with the cam mod at this point. Im just really wondering why the quad is only running at 70lbs of compression, vs. the stock 120lbs I was getting with the factory timing. I dont understand how this can be, when I feel such a better power when running with the cam mod, but with less compression. Fricken WEIRD!!!
Thanks again for the replies. I WILL figure this out someday!

 

[quote]
Originally posted by: 135boom
Hey, thanks for the replies. I am just about at wits end with this whole cam thing.

With the "cam-mod" (retarding it a tooth), your actually putting the decomp pin the wrong place, which does cause "harder" starting then stock. THough, in my experience, the yz cam was even harder!!!! The cam-mod takes a few extra role overs, but it atleast starts!





Wrong, sorry boom that you are in a pickle and I wish I could help, but please don't say the cam mod makes it hard to start as this is crap. My bike is normal as all of the other bikes I know are the same as mine.
I accept you have a problem somewhere and I'm sorry I can not help.

Geoff.

 

The motors are actually very different in the lower end (beefed up tranny gears, crank, rod and pins). It is true the cylinder head and valvetrain are identical with the exception of the exhaust cam.

I would not be surprised of someone installing a YZ cam into a YFZ needed to adjust their valve clearance ... or even another YFZ cam. They are all manufactured to the same specs .... but have small irregularities and you are moving the cam a few degrees off its original base circle when doing the cam mod. That is why everyone has different tappet shims installed in their machines although they all run the same cams .... I have around 170's in my exhaust side and another guy I know had 140's .... that is only a .30 mm difference and would not be noticeable to the eye ..... but would cause major problems.

get the service manual and do the work yourself .... its the ONLY way you will know 100% that its done right

 

Wrong, sorry boom that you are in a pickle and I wish I could help, but please don't say the cam mod makes it hard to start as this is crap. My bike is normal as all of the other bikes I know are the same as mine.
I accept you have a problem somewhere and I'm sorry I can not help.

Geoff.[/quote]


"wrong" How am I wrong. I wasnt speeking for every yfz out there. Clearly I have a problem, or my bike is somehow different than many others, that doesnt make me wrong!! And how is that "crap" Thats nice that your bike is normal, and so are many others, but MANY OTHERS are having harder starting issues with there cam mod, or yz cam too! Thanks for accepting that I have a problem, realize that for some reason, people are having different results with messing with the exhaust cam. Maybe it does has have something to do with what "shwendi" is talking about?
I wasnt trying to speak for every yfz out there though, and I wasnt trying to say that the cam mod is flawed, I was just trying to find someone that knew a little something about the different compression levels that you get when doing upgrades to the exhaust cam. Dont tell me I am wrong. I DO have a problem, and I am not the only one that has experienced this.

 

check those clearances ... more than likely they are too tight keeping the exhaust valves open when they should be closed.

this is also a good way to burn your exhaust valves [img]i/expressions/face-icon-small-wink.gif[/img]

 

Thanks man. I will do that, and see what I find. I am starting to think, after talkin to a few other folks that that cam was not in there right, and that it may have been advanced one tooth. The yz450 cam has different cam markings then the yfz cam, and I think that yamaha may have screwed up. We'll see, thanks again for the reply. ~135boom