Jetting Q? No Jetting Answered..... funny story

[Beuy65]

Firstly thank you for all of the information contributed on this site. I am new to 4 strokes after decades of riding 2 strokers - what a learning curve.

So my story, 08 WR 450 decorked, AIS removed, grey wire and GYTR full system - bought 2nd hand one owner with a receipt from the bike shop for re-jetting! Just says "comp jetting installed". She runs great but backfires like a basted on decel - so bad that after I repacked the silencer it poped out rivits so I have been trawling through all of the posts attempting to gain some insight on the issue. After discovering how hard accessing the Carby is on these models, swearing etc etc thinking why did I buy a 4 Stroke (only out of frustration as I do love it). I have now had the carb in and out a number of times but things just weren't adding up.

Current jetting is

Pilot 50 (I'll come back to this)

Leak 45

Needle 3#

Air/fuel 2 turns (adjusting never really makes any difference)

Main 175

So I have sealed all exhaust joints, set and reset, air/fuel, needle, check main jetting, compared this to info in this site. Pilot seems to be in line for my location/mods/temp etc but all roads lead to this issue being to lean on pilot?

So I visit the local dealer and have a good chat, all agree lean pilot so go richer - great guys at the shop give me 55, 58 and 60 pilot and tell me to bring back the ones I don't need once it all sorted. thanks guys!

So out comes the carb again (can get it done in and out in an hour now) and .....mmmm hang on these Jett's are exactly the same but the whole in the 50 is sooooo big - a least 30% bigger than the 60.....wtf? Speak to the guys at the shop again, definitely the right part. Oh well let's put in the 58 and see...thinking I am going to have to pull this thing out again (mumbling 4 stroke profanity).

To my surprise she runs great, no back fire and idols way better, air/fuel adjustment even works now WOW! Quick ride up the street and I am for the first time in weeks smiling from ear to ear.

So it seems the bloke that owned it previously paid $500 at a shop to have "comp jetting" installed and they drilled out the pilot to some ridiculous size so it was that rich it was just pooring fuel through into the exhaust on decel and she was lighting her up. Unbelievable.......

Now that the saga is over I can laugh about it but....aarrrr how frustrating

[SteveThe Snakes]

Only one other minor thing. You don't have to remove the carb for main jet or pilot jet.

[Beuy65]

On alloy frame models? Do you just remove the rear shock and use a right angle screwdriver? As you cannot rotate carb due to the frame stopping it.

[SteveThe Snakes]

No just remove the float bowl nut then use the right angle screwdriver.

[flyandride]

You can change the jets on that bike without removing the carb.  For the main jet, get a 6 mm jet wrench, bike shops have them or get on ebay.  

Or make it easier on yourself.  Get you wife, girlfriend whatever, just a female with small hands to do it.  Much easier

[SteveThe Snakes]

You can change the jets on that bike without removing the carb. For the main jet, get a 6 mm jet wrench, bike shops have them or get on ebay.

Or make it easier on yourself. Get you wife, girlfriend whatever, just a female with small hands to do it. Much easier

How come I never thought about that wife girlfriend wrench deal ?

[RMK800]

So what pilot size did you end up with? Anything over 48 to 50 would also be too rich. Most at sea level run around a 48 and at high elevation a 45.

[Beuy65]

58 is the current pilot - 45 is standard in OZ.

[beairmo]

58 is the current pilot - 45 is standard in OZ.

My 09 with similar mods needs a big pilot also. And I can change either the main or pilot in 5 minutes. I lay the bike on it side, loosen the carb to rotate it about 10 degrees, then unscrew the bowl nut. Laying it on the side makes it easier to install the new jet without having to do i blind.

[RMK800]

My 09 with similar mods needs a big pilot also. And I can change either the main or pilot in 5 minutes. I lay the bike on it side, loosen the carb to rotate it about 10 degrees, then unscrew the bowl nut. Laying it on the side makes it easier to install the new jet without having to do i blind.

I like that idea of laying it on its side. I have tried to do it blind and have been frustrated and have given up. I can get into the carb in 15m by raising the subframe and removing the shock. Im going to try that next time, see if I can save myself 30 minutes.

[SteveThe Snakes]

Use a tool like this http://www.harborfreight.com/8-piece-right-angle-screwdriver-92630.html then get a longer screw driver bit that fits the pilot jet. You can use a small piece of tubing to start the pilot in. Nut drivers are also available that fit the main jet.

 

No need to rotate the carb or pull the sub frame. By the way getting the sub frame up is easy. Putting the air cleaner boot back on the carb can be a major bitch as in no fun.

[RMK800]

I like that idea. I guess I've been lucky, usually the first or second attempt and the carb air boot goes right on, but I can see how people can get hung up on it. Once the pilot it set, then really it's just changing the main jet and I like your tips for that.

[Beuy65]

Thanks for the tips guys! Had a further play yesterday out at the track and this made for much easier and quicker changes. 58 was good but but slight cough under even power around 1/4 throttle so changed to 60 and she is running sweet.....she went good before but now it's all in tune WOW these bikes have some grunt!