Shake, Rattle, and Backfire!?


7 replies to this topic
  • siscokid7

Posted September 27, 2008 - 06:05 PM

#1

For you guys that didnt know i was trying to get an 08 yz450 or an 07. first the deal on the 08 fell through. Then the 07. Well god was with me and I got my 08 for a really good deal. But anyway on my first ride I noticed the bike has some quirks to it. I had some problems when I had a Yfz450 quad so I hope it's nothing major. So does anyone know why this thing backfires on decel? I mean It is constant! My quad used to do the same thing but it was improperly jetted for the exhaust i was running. Could this be that bad from the factory? Also the bike seems to run really lean. Anyone else have this problem? And I noticed a loud rattling coming from the engine near the back. Is this normal? All the nuts are tight and its not the exhaust. Last thing, the front end does not feel really confidence inspiring. Im about 220 lbs and the forks seem stiff and yet soft at other times. Any suggestions?

  • Slinkyman16

Posted September 27, 2008 - 06:30 PM

#2

first.. dump the front tire..
2... yamis come jeted lean as hell from the factory.
3.. the sound is normal.. search engine noise here.. yamaha made a reliable motor but didnt think much about engine noise
4.. get a respring. or revalve.. ur about 40 pounds over the reccomended weight for the bike.. so handling will be effy. also suspension needs to be broken in as well.. give it a good 2 hours and then start messin with the clickers.
also.. note that the yzs to most have a front end push.. theirs a few things u can do.. easiest is adjust ur sag and drop ur forks to the line..
then their comes diffrent offset triple clamps.. most like the 24mm others like 22mm offsets.

but i also believe that u just need some seat time so everything will come into place soon enough

hope this helps..

  • siscokid7

Posted September 27, 2008 - 10:00 PM

#3

Thanks for the info. I heard about the push but didnt know what to expect. Also the front tire is definitely going. You are the umpteenth person to tell me that. I still cant believe the engine is that noisy. I took it out and let a friend do some blow-by's then compared it to his quad(yfz450) and the bike is way more noisier. I know the quad engine is in a milder state of tune but it is a big difference. Thank you for pointing out that I'm overweight:cry: But seriously I also think I need more seat time. Its hard going back and forth from a quad to bike. Especially on the same trail!! My breaking points are all over the place. I almost forgot I was on the bike today and didnt slow down in time for a sharp right hander. On the quad i'd drift in 3rd. On the bike I'm sliding in 2nd. Oh well. That stock muffler is crap! I better get a pipe soon so I can hear the exhaust over the engine racket!:lame:

  • Slinkyman16

Posted September 28, 2008 - 01:08 AM

#4

Thanks for the info. I heard about the push but didnt know what to expect. Also the front tire is definitely going. You are the umpteenth person to tell me that. I still cant believe the engine is that noisy. I took it out and let a friend do some blow-by's then compared it to his quad(yfz450) and the bike is way more noisier. I know the quad engine is in a milder state of tune but it is a big difference. Thank you for pointing out that I'm overweight:cry: But seriously I also think I need more seat time. Its hard going back and forth from a quad to bike. Especially on the same trail!! My breaking points are all over the place. I almost forgot I was on the bike today and didnt slow down in time for a sharp right hander. On the quad i'd drift in 3rd. On the bike I'm sliding in 2nd. Oh well. That stock muffler is crap! I better get a pipe soon so I can hear the exhaust over the engine racket!:lame:


yeah.. these motors are built to last.. not built to be quite.. add a alum skid plate and then u will really hear some noise. and i didnt know u were overweight.. people are all built diffrent.. just saying for that weight ur over the reccomended weight for the springs and u should either respring or revalve..

seat time will be the bigget improvement.. get used to bike for a good week.. ride it then start making changes to the things u think u need or want.. it wont take much to get this bike perfect..

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  • grayracer513

Posted September 28, 2008 - 08:34 AM

#5

So does anyone know why this thing backfires on decel? I mean It is constant! Also the bike seems to run really lean. Anyone else have this problem?

First, try a fuel screw adjustment. Then, check the user jetting DB for the '08 (linked from here: http://www.thumperta...ad.php?t=694921 )

Decel backfire is generally always either a lean idle mixture or an air leak in the exhaust. However, notice that most of the posters in the '08 jetting thread have NOT increased the pilot jet size.

And I noticed a loud rattling coming from the engine near the back. Is this normal? All the nuts are tight and its not the exhaust.

If this occurs at low RPM under a load, it's probably chain slap, and just normal.

Last thing, the front end does not feel really confidence inspiring. Im about 220 lbs and the forks seem stiff and yet soft at other times. Any suggestions?

Here's how you fix that:

> At 220#, you need to go up to the next heavier spring rates so the suspension will work correctly.

> The tire MAY be a problem, it may not. The 742FA works very well, but in a limited range of soils. Change it if necessary.

> Move forward. Way forward.

> Change the handlebars. The stockers are too low, too straight, and too far back. I know everyone has their personal tastes in bars, but trust me on this. If you are bigger than 5'10", go buy a set of Windham bends. This will also help you move forward more comfortably, and make the bike feel less cramped when standing.

> Set your rear sag at around 95-98mm, and pull your forks up in the clamps 5-10mm

The difference will be immediately apparent.

  • siscokid7

Posted September 29, 2008 - 11:43 AM

#6

yeah.. these motors are built to last.. not built to be quite.. add a alum skid plate and then u will really hear some noise. and i didnt know u were overweight.. people are all built diffrent.. just saying for that weight ur over the reccomended weight for the springs and u should either respring or revalve..

seat time will be the bigget improvement.. get used to bike for a good week.. ride it then start making changes to the things u think u need or want.. it wont take much to get this bike perfect..


I was kidding. At least I dont think im overweight.:lame: Joking. I dont know what front tire to get. I put a 756 on my sons bike and it is a night and day difference. I went riding in the mud yesterday. The whole trail was about 6 to 10 inches in some places and I really began to notice alot of vibration transmitted through the bars. I got arm pump in my thottle hand after about an hour which is rare. I always get it clutch side after 15 minutes so no big deal. Does the bar bend affect this? Also you guys running gnccand enduros have a new fan. I fought with my bike the whole time just barely holding on, and you guys make it look easy!! Any woods riders have any tips for tight trails? Only about 2 feet wide at most parts and 3.5 at the widest.

  • siscokid7

Posted September 29, 2008 - 11:52 AM

#7

First, try a fuel screw adjustment. Then, check the user jetting DB for the '08 (linked from here: http://www.thumperta...ad.php?t=694921 )

Decel backfire is generally always either a lean idle mixture or an air leak in the exhaust. However, notice that most of the posters in the '08 jetting thread have NOT increased the pilot jet size.

If this occurs at low RPM under a load, it's probably chain slap, and just normal.

Here's how you fix that:

> At 220#, you need to go up to the next heavier spring rates so the suspension will work correctly.

> The tire MAY be a problem, it may not. The 742FA works very well, but in a limited range of soils. Change it if necessary.

> Move forward. Way forward.

> Change the handlebars. The stockers are too low, too straight, and too far back. I know everyone has their personal tastes in bars, but trust me on this. If you are bigger than 5'10", go buy a set of Windham bends. This will also help you move forward more comfortably, and make the bike feel less cramped when standing.

> Set your rear sag at around 95-98mm, and pull your forks up in the clamps 5-10mm

The difference will be immediately apparent.


I called pro circuit about the fork springs and they will have someone call me back. He said at my weight being a novice rider the heavier springs may be to stiff for me to reap the benefits. I have to play around with the settings I guess. Is the windham bend like Kevin Windham? Im 6ft so the bars are a little cramped to me. I am a little ticked that as soon as i got the new bike 2 days later Im spending money, but I guess you gotta do it right or not at all.
The sag is measured with 2 people right? And the 95-98mm is with me on the bike?

  • grayracer513

Posted September 29, 2008 - 12:37 PM

#8

With all due respect to whoever you talked with at PC, others disagree. You should be using .48 front springs, and a 5.7 rear. The stock rates are .47 kg/mm and 5.5 kg/mm, so they are pretty close, but when springs are too light for the rider, the compression damping has to be increased to carry part of the load the springs should be handling. When the compression damping does too much of the low speed compressive energy absorption, it has to be set so high that it becomes too stiff at higher speeds, when it should be doing the bulk of the work. Everyone I have installed springs for to compensate for their heavier than designed weight has universally said they felt the improvement in overall suspension performance very early.

One other thing to consider is that the bike is new, and it may just take a while to loosen up.

As to setting the sag, we find these items in Common Threads:

http://www.tootechra...ension_tips.htm

http://www.tootechra...pension Tip.htm

Setting supension:

http://motoman393.th...suspension.html

And, yes, the bar bend is named for Kevin Windham.





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