yfz cam mod backfiring

**super90** · 10-03-2008, 01:38 AM

Today I finally got around to doing the cam mod on my stock 04 yfz engine, I know for a fact I did it right by retarding the exhaust cam 1 tooth clockwise, but whenever I give it gas it will backfire and shoot flames out the pipe. What jetting should I be aiming for? I would have to go up on the pilot jet correct?

**hondawasaki** · 10-03-2008, 03:23 AM

I can't remember changing my pilot, but I changed the main and needle to the stock yz450 specs. Mine is also an 04, but I did the wr crank, R+D accel pump, and air screw at the same time, so it may not be the same animal. I can look to see my exact jetting when I get home. of course I am at 4700 ft too.

**super90** · 10-03-2008, 05:10 AM

Sorry I meant the main, I dont know why i was thinking pilot. Im around 5000 ft so it shouldnt be much different altitude wise. I have a hmf slipone + a k&n filter, what needle clip position did you use? Im going to play with the clip and fuel screw today before I buy more jets since it was already rejetted for the pipe. But holy ^&#* this thing runs good! Seems like im hitting the rev limiter before I can shift!

**Jason Hall** · 10-03-2008, 06:28 AM

I just did the cam mod on a 04 along with a 06 crank and new piston. The one I did still had the stock pipe. I knocked out the baffle and bumped the main up to a 180. I had to run the needle all the way rich, alng with the 180 main. These Yamaha's with the cam mod are friggin RIPPERS man I'm VERY Impressed with the quick reving 2 stoke feeling power. The 04 I did had a 158 main stock, I first put a 170 In and It was alot better. I bumped up to a 175 and It got even better, but with the 180 It seemed to be the best. I was flabergasted that this thing would pull a 180 main. I found that the bike still has a slight stumble If you just romp the throttle real quick. This 04 had a 50 leak jet. I will be Installing a 45 leak and that should fix the stumble. I hope this helps you out some.

**super90** · 10-03-2008, 04:19 PM

Thanks for the tips, I went out today and bought a 170 main and it actually runs a ton better. Also I adjust the needle clip to the 6th notch. I set it back to stock for now because it was getting hard to tune and started cutting out later in the day out on the trail. Im guessing it was just a simple intake leak, but I was overthinking it. Only thing I dont like is how hard it is to get to the carb, is there any easier way to do this? I have to completely take off the tank, side pannels, air box + intake. somewhat of a pain in the ass

**SWIGIN** · 10-03-2008, 05:31 PM

Originally Posted by super90

Sorry I meant the main, I dont know why i was thinking pilot. Im around 5000 ft so it shouldnt be much different altitude wise. I have a hmf slipone + a k&n filter, what needle clip position did you use? Im going to play with the clip and fuel screw today before I buy more jets since it was already rejetted for the pipe. But holy ^&#* this thing runs good! Seems like im hitting the rev limiter before I can shift!

just wondering..........where in PA are you at 5000 feet?

i swore up in the potter/camerin county area it was like 2000 ft in the mountains...i used to have an altimiter and it showed the lancaster area at like 500 feet.

sorry, way off topic....just wondering

**brapp** · 10-03-2008, 06:17 PM

yeah we range from 1700 up to liek 2400 her ein bradofrd and sullivan counties .

**Jason Hall** · 10-04-2008, 08:27 AM

Yes the carb Is a nightmare It was the only complaint I had when working on the quad. I think It's overall an awesome bike. I left the plastic right off until I got the carb straight. If It got better with the 170 I would say you need to go bigger.

**trizilla** · 10-04-2008, 08:39 AM

highest spot in potter county is around 2500 ft.

**super90** · 10-04-2008, 01:08 PM

Ok so now I know I dont know anything about altitudes

Highest spot is mt davis at 3,213 ft. Well Im going to buy some more jets and play with it tonight. Oh and about the cutting out, I heard something about a sensor inside the throttle that could be dirty or broke? Is that a possibility?

**super90** · 10-05-2008, 01:28 AM

Wow this is turning into a nightmare!

Last night I had to make a gasket for the cam chain tensioner, dont exactly remember what I did but today I went out and the battery seemed dead. So I charged it up fully and it wouldnt crank over at all even with a wrench manually turning the flywheel, it would turn to a point and just stop. I pulled the tensioner and it turned over freely again, and of course the cam jumped a few teeth. So I ripped that off, retimed it to the stock configuration, adjusted the tensioner and it fired up just fine and ran just like before. So I recharged the battery and started to look over the motor and now the head gasket is leaking either coolant or oil, im guessing it overheated somehow before I found the intake leak and blew it out. Im not sure why the motor wouldnt turn over though before and thats what scares me. It was either hitting a valve or the cam chain was binded up in the bottom case.

**Jason Hall** · 10-05-2008, 11:45 AM

Maybe it was liquid bound from coolant. Are you preloading the timimg tensioner before putting It In? I know you can't even jump one tooth on the exhaust cam without loosening the Intake cam, so that makes me wonder about the tensioner & the timimg chain being stretched.

**super90** · 10-05-2008, 12:56 PM

Yes, I am pre loading the tensioner before putting it in. But last night we were trying to figure it out and I had a 17mm socket in the crank case and the tensioner was out, and my friend hit the starter button. Im assuming that caused the chain to skip. I checked the timing right after that and it was way off. What is this liquid bound you speak of? Oh and the cam chain is not really stretched at all, I just put it in this past summer.

**KASEY** · 10-05-2008, 04:34 PM

this is the exact reason i have left my 450 alone,,, when you have to drive 200 miles to ride i do not want problems,,, besides i have not talked to anyone yet who has convinced me 100% that i need to do it either,,,,,,

**Jason Hall** · 10-05-2008, 04:56 PM

If your friend hit the start button with the tensioner out, you probly bent the steel chain guild down under the stator cover. That Is most likely the reason It would only turn so far each way. The chain was bunching up on that steel guild.

Normaly all this would not happen, Jetting Is the only thing that really needs to be changed. With the cam mod the yfz Is basically the same top end as the YZ, so I don't see to many reliablilty problems. Other than the cranks take a dump In the early yfz's, because of oiling Issue's.

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yfz cam mod backfiring