Problem Jetting for LRD full exhaust

[CMR250R]

First off I'm new to this forum and would like to say hello to everyone. I'm having a problem I am trying to fix a YFZ450 for a friend of mine. The bike is a 2005, He has installed a K&N filter, LRD Pro4 series full exhaust, and he is running with the airbox cover on with an outerwear on the K&N. He told me that he jetted the bike to what LRD told him to. The bike had a 175 main in it and the air screw was at 2.5 to 3 turns. He told me that the bike set up like this ran great all winter long. Now it has been hesitating all thruout the powerband. It would like bog twice then it would scream. I changed the main jet a couple times tonight I tried a 165, 160, 155 and basically it didn't help at all yet. The bike is running on race gas( powermist ) and we are located in New Jersey under 3000 feet. Any help you guys could give me would be great. Thanks in advance.

[motomanmike]

ok you played with the main jets now its time to do the tedious process of changing the needle position. I just went through this myself with a new pipe and it gets frustrating but it will pay off. Needle adjustments on the new four strokes do alot more than you think. try raising the needle by placing the c clip lower on it, which will richen your mixture, if that doesn't work go the other way. Find out what works best, the rest will be adjusting your air screw for your final step. run the bike up in gear then back off the throttle and let it slow down while its in gear. If it pops bad its too lean, if it just rumbles slowing down you should be pretty good to go if it pulls ok and doesn't pop while you are on the throttle. I'm running a 180 main jet, with the c clip two notches from the bottom of the needle and about two turns out on the fuel screw. I'm running a full duncan racing fat boy 4 with no air box lid at sea level so you might still be running lean at your elevation.

[RRP]

you didn't mention changing the pilot jet.My setup is,
168 main
45 pilot
2.5 turns on plot jet screw
stock needle clip moved down 1 notch
93 octane
machine runs great no popping or hesitation

[CMR250R]

Thanks for the reply guys. I called LRD the other day and changed the jetting to the 168 main the pilot and the needle were both where they said they should be. After this the bike ran great for a while and then it got hot and started soing the same thing again. I searched more on the forum and it sounds like the stator and the regulator/rectifier may be bad. I've got a hook up at yamaha so I can return the parts if need be. The reason seems that when you take the lights off the bike the stator pumps too much voltage thru and kills the regulator/rectifier and the stator. So thats where I'm at now I really think this will fix the problem. Thanks again for your help. I'll let you know how I make out

[motomanmike]

I personally do not feel that this is your issue however electrical issues are some of the hardest to pinpoint. What would happen if you never ever turned your headlights on? This is why quads are made with voltage regulators because they make more voltage at higher rpms. In addition your jetting changes when your bike reaches optimal running tempurature. This is why you need a "choke" to start you quad in colder temperatures. Most atvs today use an enrichment jet that they call a choke, older quads used an actual flap or plate that would choke off the air to the engine giving it a more fuel to air ratio to acheive the same effect. I have had my lights and all equipment not needed to get rid of the "crap" they come with, lights, switches, safety switches, throttle "tors" system and have not had any issues. I really think you need to try the settings for youself, not saying LRD doesn't know there stuff but i can tell you that if they were there tuning your bike, they would probably try every single jet, in every single needle position but hey if you can return electrical parts after trying them, you better buy that guy lunch.

[daddio]

I've messed with 2 other YFZ's with LRD's pipe. They all started with Arlands recomendations. They both ended up with my set up. LRD likes lot's of fuel. 190 main 47 pilot NCVQ needle on clip #4 down from top and air screw out 2.5 turns. In the winter, I run a 195 main.

[CMR250R]

Well you were right mike. I wasted some time tonight playing bike electrician. I replaced the stator, rotor, and the regulator. The bike ran great for a while then the same problem came back but not as bad as before. We then drained the race gas and refilled it with pump 93 octane. All in all the bike backfires very little on decelleration. but it still hesitates on accelleration. The main jet in the bike now is a 158s? Not sure what the s is for??? The bike starts and idles great I'm really kind of lost now dont know if I shoud try going up or down on the main and the mixture screw is at 1 turn. Its also extremely hard to test this bike because it is so friggin loud and it goes so fast the only place I can really test it is ripping up and down the road. I'm sure the neighbors are loving that. Anyway any help would be greatly appreciated. thanks again.

[korniev]

For LRD try getting at least 178 main jet and 45 small jet.
Also fuel screw must be at least 2 turns out (not more than 3)

[hoser 400ex]

i believe i had a 180-185 in my yfz with lrd. but i also had my lid off the airbox.

[CMR250R]

We finally got it down last night. This bike had an aftermarket air screw and it wasnt bottoming out all the way. it wasn't letting us go to 2 turns out without being so loose it almost fell out, then we took it out and it wouldn't go back in. After cleaning up the threads a little it screwed in and went a lot deeper then before and we were able to set it at 3 turns out. So all in all the bike now has a 160 main, 45 pilot, needle in the 4th clip, airbox lid on, and the screw at 3 turns out. I do believe that when we installed the new stator and rectifier that it also helped because before we did that any jetting change we did seemed to have no affect. We went from a 175 to a 158 and there was no difference before we installed the electrics. Now the bike runs great. Thanks again to all for the info.

[CMR250R]

We finally got it down last night. This bike had an aftermarket air screw and it wasnt bottoming out all the way. it wasn't letting us go to 2 turns out without being so loose it almost fell out, then we took it out and it wouldn't go back in. After cleaning up the threads a little it screwed in and went a lot deeper then before and we were able to set it at 3 turns out. So all in all the bike now has a 160 main, 45 pilot, needle in the 4th clip, airbox lid on, and the screw at 3 turns out. I do believe that when we installed the new stator and rectifier that it also helped because before we did that any jetting change we did seemed to have no affect. We went from a 175 to a 158 and there was no difference before we installed the electrics. Now the bike runs great. Thanks again to all for the info.

[motomanmike]

I'm glad things are looking up. Now if you really want some more power, i would pull that stock suffocator off the top of the airbox and let that baby breathe. You will of course have to rejet AGAIN LOL but if you don't ride in a lot of water it is a definite power increase that you will not regret. Have you done the cam mod yet ??? That helps it rev too :) keep playing, i'm addicted to tuning with this quad.:D