07 450 Backfire

My bike probably has 10 or so hours and now is making a loud POP on decel and when starting when cold or warm. I adjusted the fuel/idle combo at the track and could not get it to really go away. I also sprayed some carb cleaner up in the pilot without removing the pilot to clean it out but no improvement.

Any suggestions as it really is annoying and sounds horrendous.:lol:

Its your jetting.

What jets are you running? Whatever they are you're most likely lean. I just rode my '06 450 today for the first time and it's doing the same so I put in a 48 pilot jet and 170 main and that should take care of the problem. I'll know more tomorrow but that seems to be the optimal jetting for sea level.

My bike probably has 10 or so hours and now is making a loud POP on decel and when starting when cold or warm. I adjusted the fuel/idle combo at the track and could not get it to really go away. I also sprayed some carb cleaner up in the pilot without removing the pilot to clean it out but no improvement.

Any suggestions as it really is annoying and sounds horrendous.:lol:

The 48/170 is a good combo. Stock needle and clip position. I was running this today at SCMX and the setting was good. Just needed a little bit of fine tuning on the fuel screw. Bike was starting on a half first kick. Really impressed.

That 48/170 combo seems to be the hot setup for these yamaha 's.

During the winter with a 45 pilot jet the Yamaha will pop like crazy. You will also notice a power increase when you put a 48 pilot jet in along with the bike not popping anymore.

Great info, I am going to roll with the 48/170 combo and see. I rode at Cal City MX yesterday in the hi desert and today will roll locally at Piru. www.pirumx.com

I just started to do this over the past week as the temps have been cooler.

I have an 06 with the 48 / 170 combo, fmf powerbomb and 4.1 can. It still pops a little on decel with the fuel screw out 2 turns. I'm at 600ft above sea level. My 03 also poped a little with the aftermarket exhaust on it. Never seems to go away all together. I do notice a big difference between 1 and 2 turns out on the fuel screw.

I forgot to add that I did the trick of using an o-ring on the actuator arm for the accelerator pump. The response is a bit snappier and I never encountered any stalls or hesitations with this, regardless of how rapidly I worked the throttle.

Btw, the original recommended size is too small, (in my opinion) and tends to stretch too much, slowing the response process - certainly too much when rev climbs are really short. Thick mud may require something different.

I did not want to wire it so I simply went with a beefier ring.

Lastly, I also noticed that on this carb, verses some of the other FCRs that I have worked on, that some of the AP screw settings will cause the follower to lift from the cam, in which the gap causes a delay in the spray. I would say that it may be best to go with a setting that at least zeros this gap. Doing so will also not produce too much or too long of a spray.

And I’m still running the standard leak jet so perhaps there is some potential there as well.

Does the boyseen quick shot do what the AP mod essentialy does? I had one on my CRF250 and it made improvements on quick acceleration.

I need to eliminate the pop and run the 48/170 setup but dont want to run into another issue with a bog on the low end.

Does the boyseen quick shot do what the AP mod essentialy does? I had one on my CRF250 and it made improvements on quick acceleration.

I need to eliminate the pop and run the 48/170 setup but dont want to run into another issue with a bog on the low end.

The word on the street is that with proper tuning the bike can perform just as well if not better than just bolting on a quick shot.

There really doesn't seem to be any limitations within the stock design, it's just a matter of getting things fine tuned with the various jets.

On the older carbs it's a different story.

Dave is right about the older carbs. They didn't have a leak jet which creates a huge problem as far as tuning the AP squirt. Without a leak jet the squirt is much too long and the volume of fuel is way too much. Tuning the leak jet, AP timing and inmproving squirt response via an o-ring or wiring is the best way to overcome the bogs and hesitations. The AP covers are a gimmick. They may do something on one bike and hinder the next. This is why Honda came out with a revised AP linkage setup on the 07's that actually pushes the AP linkage instead of relying on slow reacting spring pressure.

Another Vote for the 170/48

Well, the 48/170 combo let me down tonight.

Things got a little warm in California today and the bike was not on par with what it was over the colder weekend. Just about had the fuel screw completely shut.

Temps were about 68F.

I never bothered with another pilot since I only had an hour or so to get some laps in.

FWIW

I've had good luck with 45/165 in my '06.

I've had good luck with 45/165 in my '06.

This is what I ended up with also. Tried the 48/170 and it was too rich.

Run a 48 pilot in the summer and bump it up to a 50 in the winter.

I've had good luck with 45/165 in my '06.

Yea...this is beginning to make sense.

I'm surprised that Pro Circuit went with such a big combo.

Thanks for the heads up!

I've had good luck with 45/165 in my '06.

So I trired the 45/165 at the track the other day - about 300' above sea level, 50-60F and it's much better than the 48/170 combo. Much easier and smoother out of the corners.

Thanks for the heads up!

Hey guys, what is the stock main jet in your 06? I've got and 07 and mine has a 160. Going to a 170 seems like a huge jump. I wonder if the needle setting could be a little lean instead? Winter weather here is keeping me from trying your settings. I did go with the 148 pilot and that helped with the pause when twisting the throttle quickly. By the way, I learned from Zip-Ty racing that the bike should be in gear when testing throttle response because of the neutral sensor, which alters the timing some when not in gear. I don't know why it has to though. Forgot to ask.

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