08 yz450 runs like crap at first


29 replies to this topic
  • 95kawi

Posted December 21, 2011 - 10:03 AM

#21

I found a used 06 muffler for cheap I just want like u said alittle more mid and low end if possible so the 06 pipe will fit with the 08 headpipe?

  • grayracer513

Posted December 21, 2011 - 10:07 AM

#22

No, the '08 header is too large for that. You'd need the complete setup.

  • SilvFx

Posted December 21, 2011 - 12:55 PM

#23

95 Kawi....just sold my '08 YZ450F when I upgraded to a '10 Husaberg FE450. Had the same issue with the stock jetting being lean and difficult to start/rough running until it warmed up. And, I would warm it up real good before riding as people have said above. I also had the advantage of being at high altitude (6K-12K) which in itself alleviates some of the issues with the lean factory jetting.

Even though I suspected the jetting and had bought a JD Jetting kit, I was reluctant to open up the carb in the middle of riding season with some of the stories about how hard it is to get to this carb.

In the meantime, I had purchased a Leo Vince full exhaust system because I wanted some more low end and mid range for trail riding (and this system offers a smaller headpipe -as do the other aftermarket exhausts) and I knew it was a quick swap between weekends. Initially I went the route of a PMB spark arrestor insert ($135) since I was riding in national forests. I later learned that the stock muffler on the '08 YZ450F and the headpipe were less than ideal (lesson learned: always read TT before you start buying accessories). I finally spent the money on the full exhaust system which is what I should have done in the first place. The exhaust system alone improved the starting and cold running as well as the throttle response and low-end without even touching the stock jetting.

Here is a link for a good price on the Leo Vince system I installed. If you purchase you will see the quality of the system is outstanding for the relatively low price. it is stainless so it weighs a bit more than the titanium headpipe but should be more durable. The factory heatshield bolts right onto the Leo Vince headpipe and its about a 15-30 minute install job total.

The price is $366 for a FULL system...which as you will see is a good price for a full system (check out prices of the FMF,Yoshimura and DRD full systems). I ended up buying mine last summer for $337 (no tax, free shipping).

http://store.58cycle...lv pn 3679c.htm

As for the the JD Jetting kit, I finally installed this kit after the exhaust system and wondered why the hell I was so chicken sh*t to install and why I had waited. I followed the instructions to a "T". It wasn't that hard and took about 2 hours with me reading/re-reading the instructions for every step and workly SLOWLY. The follow up install of the JD kit on my boy's WR250F took me about 1 hour since I knew what I was doing.

The results were fantastic and eliminated any trace of a low speed stumble and it became a 1 or 2 kick to start it cold (even with cold temps this fall/winter). It also got me over my fear of how difficult it would be to work on the FCR carb. Wish I had done it sooner. Some people feel its a bit pricey ($72 on TT parts store) for a couple of jets, a pilot jet, couple of o-rings (for accelerator pump), and a couple of tapered needles, but I was happy with the results and the detailed install, tuning, and seasonal adjustment instructions. I also installed the Merge Racing fuel screw ($22 on TT parts store) at the same time. Here are some useful links. Plenty of other retailers sell this stuff, but I provided the links for where I ended up purchasing these items.

http://shop.thumpert...ting_jetkit.htm

http://shop.thumpert...erge_00-019.htm

Enjoy your YZ450F. Even though I am looking forward to the enduro/trail riding/dual sport abilities of the Husaberg FE450, I already miss the incredible burst of power from the YZ450F. I couldnt wipe the smile off my face whenever I rode it after making the exhaust and JD jetting mods. It almost felt like my old '86 CR250 two stroke.

P.S. grayracer513 and William1 are incredible resources here at TT for all Yamaha related questions (and probably for all the other makes).

  • beezer

Posted December 21, 2011 - 01:55 PM

#24

I don't know about a JD kit.

I'd just learn how to adjust the fuel screw.

The YZ carb is easy to work on. The pilot and main jets can be accessed through the float bowl plug. I stole one of the wife's make mirrors and lay that on the cases.

  • grayracer513

Posted December 21, 2011 - 02:17 PM

#25

I don't care for the jet kits, either. I'd rather work with the OEM parts to solve any problems I have. It's not that hard, and by using genuine parts, you have a measurable frame of reference as to what changes were made. With a brand X needle, for example, you have no idea in what specific way it differs from stock.

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  • Gunner354

Posted December 21, 2011 - 03:31 PM

#26

I don't care for the jet kits, either. I'd rather work with the OEM parts to solve any problems I have. It's not that hard, and by using genuine parts, you have a measurable frame of reference as to what changes were made. With a brand X needle, for example, you have no idea in what specific way it differs from stock.

This is one thing that we agree on 100%. I had a conversation with an engine builder from another forum and he stated that he tested the JD needle with an on board air/fuel ratio meter and two identical needles not only read different but he felt the performance difference. A high end measuring tool also
confirmed this.

  • 2grimjim

Posted December 22, 2011 - 02:41 PM

#27

I don't care for the jet kits, either. I'd rather work with the OEM parts to solve any problems I have. It's not that hard, and by using genuine parts, you have a measurable frame of reference as to what changes were made. With a brand X needle, for example, you have no idea in what specific way it differs from stock.


Woohoo! something we can finally agree on!

I have about 40 different part numberd FCR needles, and a dozen different AP diaphrams, not to mention various sizes of Main Air Jets, Pilot Air Jets, Leak Jets, different size float needle seats (for older FCR's), and few boxes of dis-assembled salvage yard FCR's.

I refuse to buy "Jet Kits" for an FCR carb equipped machine. There is absolutely no reason someone can't dial in their FCR carbed machine with OEM parts.

  • 95kawi

Posted December 22, 2011 - 03:54 PM

#28

How could I tell if it needs to be rejected after I put the 06 setup on my bike I looked in the jetting sticky I didn't see any 08/09 with a 06 set up to get a idea

  • 95kawi

Posted December 22, 2011 - 03:58 PM

#29

*jetted

  • 2grimjim

Posted December 22, 2011 - 04:16 PM

#30

A propely jetted bike will start within 3 kicks (hot or cold), idle smoothly @2000-2200 rpm, accelerate smoothly (no sputterign, surging, etc.) with a slow roll of the throttle from idle to rev limiter (in any gear), and at the same time give acceptable throttle response and only a small amount of popping in the exhaust on deceleration. Spark plug insulator should be light brown or straw color. The exhaust header glowing red is not an indication of improper jetting.

But, before you attempt to resolve any problems with jet-changing, you need to make sure the following items are in order;
A) The gas isn't old
:bonk: The valves are in spec.
C) The air filter is clean (and any solvent has evaporated)
D) The carb is clean inside and float level correctly set
E) The engine is mechanically sound (rings, piston, valves and compression ok)





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