midrange hit

okay so i have a 2006 Yamaha yz450f and first things first this thing is amazing. now, i have a full fmf titanium factory 4.1 exhaust with the megabomb header, jd jet kit with the thick o ring, iridium plug and the twin air proflow kit. the jetting specs are as follows:


Pj: 48

Needle is the red needle from the kit on #5 clip

Fuel screw: about 1.25 out

Question is, i want the midrange to be more snappy it seems to be sluggish when around half throttle i feel like it should pull harder then it does. The top end is amazing and the bottom is alright too i wouldn't mind some more response when the throttle is snapped open though when rpms are lower and like from no throttle to a quick snap such as if you tried to hop over a log or something. i live in central Md so the altitude is not that high.

Any thoughts are really appreciated. Thanks Again

Move the clip to position 3 fropm the top/flat and retest. You make no mention of a bog, just the sensation of low on power mid throttle.

okay thank you i will try that this weekend. you dont think that will lean it out too much do you?

Your bike jetting looks rich to begin with. Typical pilot on that YZ is a 42, clip position os #3

yeah i wanted to start out rich and see what happened i was running a 168 main and felt the the plug was too white. thank you for the advice

You cannot read plugs with todays pump fuels. Een then, you must run/chop and pull the plugg immediately, very hard to do on a modern bike. That and a new plug must be used every time. You want to do it scientifically, use a wideband on a uncline timed set distance run.

Start out rich and see what happened and then make the changes gradually.

okay so i raised the needle clip to the forth position from the top and left everything else the same and i had alot of bog when throttle was opened quickly the midrange did feel a little better but i would rather have the softer hit midrange and not have as much bog. just a side note so far i am not impressed with the jd jet kit. maybe i just need to fine tune it some more. do you think that if i bring it to the third clip the bog would go away or get worse? also, if i go up to the third clip do you think that i should change anything else? i jave alot of different size jets laying around

...and there in lies your problem. You do not set the needle to deal with a bog, you set it for steady state, undler load running. You adjust the A to deal with a bog. The problem is not the jet kit, it is the installer. Again, I explained it should be on the third clip, not the fourth or the fifth.

First, did you check/set the AP timing EXACTLY per the manual? Did you confirm you have a good squirt? Did you do the oring mod or put a stiffer AP spring in? What size leak jet are you running?

okay ill try the third clip tomorrow and i will set the ap per manual and see what happens im not sure how its set up yet all i know for sure it that when i put the jet kit in and had the carb off i adjusted the screw so that there was no play in the linkage and i do have the thick o ring on the arm too.

You do not just arbitrairaly turn the timing screw. There is a very specific method to follow in the book. It is 99% accurate. Some need slight tweaking after that is done by riding small adjustment, riding.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now