My experiance with boysen quicksot, stealth fuel mixture screw and jetting


11 replies to this topic
  • runester

Posted May 11, 2007 - 10:26 AM

#1

I used the stealth cover which is the same thing as the boysen, anyway,I also jetted and put in a stealth fuel mix screw when I installed the cover and the bike was TOOOOO rich
to the point it would not start so began the trial and error work to narrow down the cause for the problem and in the end here is what is up with the quick shot (or stealth cover in my case) if your jetting is lean it will fix it , I say this because with the leaner jets in my carb the quickshot was not an issue but when the correct jets went back in the bike would not start then I left the correct jets in and pulled the quickshot and the bike ran perfect ( which is not good I/E your jetting should be correct and should not require an $80 band aid) if your jetting is correct the quickshot will cause your bike to run rich and maybe not even start at all. If you THINK your jetting is O.K. and the quickshot helped YOU then either your jetting is wrong or your mixture screw is wrong . I have been at this for two days now and have been pulling the carb over and over and over and over and playing with jets and screws and the cover to find out why, when I did a jetting, quickshot, fuel mixture screw mod all at once my 07 yz450f would not fire. And now after many many hrs of labor I can tell the quickBOG (burns pun..not mine) IS A WASTE OF MONEY....and I want to add one more thing about the after market fuel mix screws for "on the fly" adjustments... in my case the threading and needle taper were not even close to stock and was a pain the arss to fine tune so be mindful of that when you first install it if you get one that it may be the case for you as well. My bike runs tight now, it is right there when I grab a handful with a 48 pilot, 168 main and the stealth screw at 1/4 turn out.
I hope this helps anyone from having to experiance the 2 days of frustration I just went through...

Rune

  • kxman

Posted May 11, 2007 - 12:46 PM

#2

If you are only running the fuel screw 1/4 turn out try a smaller pilot jet. There is a sticky on the jetting forum about sizing your pilot jet and adjusting the fuel screw.

  • runester

Posted May 11, 2007 - 01:32 PM

#3

Thanks...but it is the taper of the after market screw that has it at a 1/4 turn...the stock screw w/present jetting is good at 2 turns out but thanks!
R

  • kxman

Posted May 11, 2007 - 02:15 PM

#4

Thanks...but it is the taper of the after market screw that has it at a 1/4 turn...the stock screw w/present jetting is good at 2 turns out but thanks!
R

Guess I am a little confused on this and by no means am I argueing but, if you are running the aftermarket fuel screw in your bike why don't you jet for it instead of running the pilot that worked best with the stock fuel screw that you are no longer using?

  • viktobravo

Posted May 11, 2007 - 03:10 PM

#5

Or you could run the Kientech FCR screw, its identical to the stock screw.

  • grayracer513

Posted May 11, 2007 - 03:35 PM

#6

Guess I am a little confused on this and by no means am I argueing but, if you are running the aftermarket fuel screw in your bike why don't you jet for it instead of running the pilot that worked best with the stock fuel screw that you are no longer using?

On the face of it, that seems reasonable, but it may not work out that well. There is a good deal of interdependency and overlap between the different fuel circuits, and if you make the pilot that lean, it may start to have an influence on part throttle performance. I would get a better screw, like a Dr.D, or a Zip-Ty, before I messed with that one any farther.

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  • moto867

Posted May 11, 2007 - 05:11 PM

#7

I don't see what the pump cover has to do with starting. It should only affect things when the throttle is touched. I agree that those things are a waste though. I tried a boyesen on my kx and it ran worse than.

  • motox100

Posted May 11, 2007 - 05:12 PM

#8

Out of curiosity, why did you change so much at once? If it don't run right it makes it kinda tough to know exactly what to change (at least for me). I have an 07' and tried out a few different jets. Mine runs best with basically stock setup, 45 pilot, 162 main, zip-ty fuel screw about 2 turns out. The 48 - 168 combo was too fat in mine.

  • runester

Posted May 11, 2007 - 07:53 PM

#9

"Out of curiosity, why did you change so much at once? If it don't run right it makes it kinda tough to know exactly what to change"

Great question...here is the deal...went to the track last weekend (piru, So Cal)
Anyway bike is NEW went there for the break-in and this is my first four stroke so while getting used to the powerband was a learning curve it was also bogging alot in first-third (didnt actually get up to 4th) to the point of embarrasment, but in alll fairness to myself I only had around 1 hr or so on the track to try to adapt and I was new to the track, anyway, so I started the research and ended up with the following shopping list, 68 main 48 pilot (per burns advise to another So Cal member and based on his dyno run) and the fuel mixture screw was a desicion based on ALOT of opinion in order to have easy access for air mixture...the fuel pump cover was actually a mistake (dont ask) I ordered it when I ordered the mixture screw, I chose that mixture screw because it came up on a general google search with alot of others but was the only one made of steel and seemed more durable in the long run and since it will be fighting gravity and some of these after market screws have been known to become un-seated a fall out I figure it would wear better. So I just got busy the other night (see my ealier posts) and did it all at once HUGE~mistake...before you are too hard on me understand I have been wrenching bikes and cars for 30+ yrs but only two stroke dirt bikes so I really didnt anticipate this carb being so finicky (I honestly didnt even know it had a fuel pump until I ordered the quickshot-like cover) but, yes, it was TOOO much all at once and I paid dearly for that but I can pull that carb out (sub frame, shock and all) in 20 min. so at least I gotgood at that. after alot of trial and error with all the differant little parts
I feel the jetting is dead on right now...I can grab the throttle QUICK from idle and it just barks back then lets out a BEAUTIFUL roar!!!!I LOVE THIS BIKE!!!!!!!!!!!!!
Anyway the fuel screw just has a taper differant from stock but the jetting is perfect as is. I will take grays advice (in that he is becoming sort of god-like to me, honest...I respect any and ALL master mechanics and gray is definately one of those) so I am off to zip-ty for thier screw, Gray, if you read this, will the material they use wear well what with that screw facing south and being adjusted frequently?
I just want to add that I appreciate everyones advice and opinions and the time you took to read and reply!!!
Thanks and have a GREAT WEEKEND everyone and if you are at the competitive edge MX park in hesperia this sunday I will see ya there!
Just be lookin' for the ugly guy on the good lookin white 07 yz450f and that will be me...unless it some other guy on one...then it will be someone else
Kind regards,
Rune

  • grayracer513

Posted May 11, 2007 - 08:20 PM

#10

The fuel screw is not really what one would consider a wearing part, and the force of the spring pushing out on it would provide its own "gravity" in any position.

Which leads to one of the reasons for most of the screws that fall out; low spring tension. Some screws, because of taper variations, compress the spring less than they should. And/or, some also have slightly smaller shaft diameters, which means that under any certain amount of tension, the O-ring applies less friction to the screw. And/or (this is kind of another way of looking at the first problem), the screw my need to be backed out so far in order to mix right that there is too little tension on the spring.

The better aluminum screws work fine. I don't see much reason for them to be steel.

  • runester

Posted May 11, 2007 - 10:59 PM

#11

Thanks gray...
The screw I have from stealth has a soild spring...I bought the spring they sell as a set seperate from the screw itself...the stealth spring has an axtra couple of passes and is very stiff...actually the stock spring seemed a little weak but obviously it does not have to check the amount of weight that the after market screw carries but I would feel better with a little more versatility and given that I only have a quarter turn north on this stealth scew a replacement is definatley in order. Whats your opinion of the zip-ty in house mod? I think I am cool as is but wont know for sure until I get to the track, unfortunately the main track will be closed (a quad race) but they have for more that are open one of which is the "hill track" so I should be able to put her through the paces to really check the jetting but the way everyone raves about the zip-ty mod has peaked my interest...is there drilling involved?
Thats for all your help!
Kind regards,
Rune

  • moto867

Posted May 14, 2007 - 06:00 PM

#12

From what i hear, the heart of the zip-ty mod is an emulsion tube with holes drilled in it like a regular carb,( non fcr). Then they drill and tap the main jet air inlet for an air jet, like a cv carb. This lets air mix in with the fuel on the main jet circuit for better atomization. Check out the factory pro website for more info.





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