07 yz450f coughing/popping

I'm having a problem.... its at the whole power band. from inital throttle to WOT and cruising at any speed it coughs, and then backfires when i let of throttle. it was there since the day i got the bike new but a little worse now except for the popping which is way worse.

07 yz450f

I'm at 2000 - 3000 ft. around 55-65 degrees here now. I first installed a twin air air filter. no change. installed 160 main (165 stock) and needle at same position from dynojet as per their instructions of having aftermarket exhaust. a little worse. i just put on my yoshimura rs-2 slip on. no change. Fuel screw just makes it pop a LOT more at about 1 turn. 2 turns out, same running condition just less popping. I'm thinking main is rich but it seems to be popping a little more than it should. it also seems like those coughs or bogs i'm experiencing is from a pop during accel. so i dunno rich or lean? main jet? needle position? I just bought a #48 pilot jet (have a 45 stock) after reading on this issue a lot but now i'm not sure that will do anything for me. it gets pretty hot here in the summer months so i'm thinking it'll be a bit rich around that time

its the biggest jet in the f'ing kit. what a waste...im so pissed. what if i raise the needle? will that help a little with the main being small til i get a new main? 170 seems to be the magic number for people on the jetting spec post. and after taking it for another quick ride before i start playin with the carb, i noticed its not that bad coughing from about 2/3 to WOT. i was thinking i was too rich! eep.

another thought. what about going back to stock 165 jet with dynojet needle? or stock needle even? I dont understand why their biggest jet in the kit, rated for aftermarket exhaust below 3000ft would be smaller than the main, specially if yammies are lean from factory. I hate dynojet lol

165/168 will probably turn out to be what you end up with. Use the OEM needle.

The needle modifies the fuel delivery from the main at ~3/4 throttle down to ~1/8. Raising it won't make up for a small main jet.

When looking at the jetting DB, focus on the '07's; they jet out a little different than '06's, and to be frank, 170 is too rich in most cases

one more Q. whats the oem needle? NFLR?

so sorry i was completely wrong! theres a 165 main in the dyno jet kit for higher altitudes and the stock is 160. sweet! Ima put the dyno 165 and see what happens with the dynojet needle. sound like a good plan?

you da man man!

ok so all my hopes have gone out the window. put in the 165 main and 48 pilot and lots more power it seems and less popping but still that damned coughing sputtering which seems to hit harder cuz of the power i guess. so its obviously not my main or pilot? its only when i apply throttle. leak jet? accel pump timing? i only let my bike warm up for 5 minutes though so could that be a problem? im gonna wait to hear from you guys before i touch another tool...

5 minutes? that should be plenty of time i think unless its really cold there

what position is the circlip of the needle in? (how many from the top)

4th position like stock. no real bog either its just sputtering. and after a thorough warm up and adjusting the fuel screw more, it seems to occur 90% of the time at a constant steady throttle. if i start in first and slowly turn the throttle til max rpms theres a fair amount then from 2nd to wide open in 4th theres barely any as long as you keep the throttle rolling up through the gears. if you stay at a steady half throttle, quarter throttle, max throttle in any gear it sputters/coughs.

try unplugging the TPS and see if that improves it at all

I'm having a problem.... its at the whole power band. from inital throttle to WOT and cruising at any speed it coughs, and then backfires when i let of throttle. it was there since the day i got the bike new but a little worse now except for the popping which is way worse.

07 yz450f

I'm at 2000 - 3000 ft. around 55-65 degrees here now. I first installed a twin air air filter. no change. installed 160 main (165 stock) and needle at same position from dynojet as per their instructions of having aftermarket exhaust. a little worse. i just put on my yoshimura rs-2 slip on. no change. Fuel screw just makes it pop a LOT more at about 1 turn. 2 turns out, same running condition just less popping. I'm thinking main is rich but it seems to be popping a little more than it should. it also seems like those coughs or bogs i'm experiencing is from a pop during accel. so i dunno rich or lean? main jet? needle position? I just bought a #48 pilot jet (have a 45 stock) after reading on this issue a lot but now i'm not sure that will do anything for me. it gets pretty hot here in the summer months so i'm thinking it'll be a bit rich around that time

I normally don't like to give out my jetting primarily because i'm no jetting guru, and second there is just too many possible variables between 2 riders even with the same bike, but here is my experiences with my '07 (completely stock) within the same ambient temps as you. Fattening up your pilot might help :

http://www.thumpertalk.com/forum/showthread.php?t=498012&highlight=jetting

Keep in mind as well, from my experiences with the YZF's you're overly jetted rich, your top end acceleration will be slow and lagging but consistant, when you're lean your engine will rev real quick, and hesitate and pop. The "tone" of the engine when accelerating helps me out a lot when diagnosing ill jetting.

Edited by Polar_Bus

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