2004 wr450 with bad backfiring issues

Alright I will play around with the jetting some more this evening, Is there anything else besides the carburetor I could look at that could cause backfiring and bogging. Valves maybe?

Well, if it had reeds... :busted:

Valves issues usually result in hard starting which you don't seem to have. Great idea to check them anyway. Shim any into spec and check them again in an hour of riding or so if you've never shimmed them before, then every 10 hours. Give me a :thumbsup: for not mentioning this earlier; I focused on the question and not the bigger picture. :smirk:

Alright I tried searching but couldn't find anything, what is the proper way to count grooves on the jet needle for adjusting the clip? Do you count from the top down or the bottom up.

Top down starting with the first groove.

Update, I got the carb off and thoroughly cleaned it. I reinstalled the carb and now the bike will start and idle fine but when I ride it still backfires a lot on deceleration and seems to bog and surge really bad past 1/2 throttle. I set my jets according to the chart in the 3rd post on this thread www.thumpertalk.com/forum/showthread.php?t=411240 for 4 to 8 thousand feet and 75 to 90 degrees but test drove it at 3,500 feet and 45 degrees, would this difference cause these issues? Also, I have installed a yz throttle stop and have opened the air box for the doctor d pipe but had forgotten to cut the gray wire before I test drove it, could this have cause my problems?

Thanks for any input.

So, you set it up as per that thread:

Elevation 0 to 4,000. feet

75 to 90 degrees: 165 main, JD Red #5, 45 Pilot, 2.0 turns, 65 starter jet, #50 leak jet

But if you notice...in that same thread:

Elevation 0 to 4,000. feet

30 to 45 degrees: 172 main, JD Blue #5, 48 Pilot, 2.0 turns, 75 starter jet, #0 leak jet

This is what your actually riding at right now, and that is a significant jetting change

Don't worry about the 500ft difference...worry about the temps, and jet accordingly. I think your only issue is ...your jetted too lean.

Run this (assuming your tempature is still in the 45 degree range....), and report back:

Elevation 4,000 to 8,000 feet:

30 to 45 degrees: 170 main, JD Blue #4, 48 Pilot, 1.75 turns

I don't think you have a "problem", you just need to get the jetting dialed in.

While I'm certainly NOT going to say Indy's jetting chart is not accurate, or a good starting point, I am a firm believer in following the instructions that came with your JD kit to the letter for a starting point....can't remember what the settings are for your conditions off the top of my head though. Like I said in my earlier post, the $$ you spent for those 2 needles, and a few main jets, etc did NOT pay for the hardware, it went to pay for the R&D that went into making those jetting instructions....:thumbsup:

Alright I pulled the carb and re jetted again to these settings

4 to 8 thousand feet, 60 to 75 degrees: 168 main, JD Blue #3 or JD Red #5, 48 Pilot, 1.5 turns, 70 starter jet, #40 leak jet

Once again I test drove it at 3,000 feet and it was dark again so the temp had dropped to 50 or 55, this time the bike ran better with no bog. The backfire didn't seem quite as bad but was still there, I could see blue jets of flame coming out my muffler every time it backfired. Should I expect this bike a 2004 wr450f to pop and backfire more than my 98wr400 did?

I wonder if an air leak at the header could be the culprit? What is the preferred product for sealing the exhaust at the header, I can't see anything on header currently.

Your first issue was the pilot was clogged- wont idle, needs choke, back fires and runs like shit- old gas etc.

Would have been much easier to clean the hell out of the carb, get it running and then evaluate the jetting.

With a running base line much easier to make only small changes to jetting (if even needed) befofe changing everything all at once.

I wonder if an air leak at the header could be the culprit? What is the preferred product for sealing the exhaust at the header, I can't see anything on header currently.

Did the previous owner install the new exhaust system himself? Did he replace both gaskets as well. If not, I would replace with new exhaust gaskets. I know some riders put a little bit of High-Temp Sealant on the gasket sealing the tailpipe to the header, but it will eventually burn off anyways. New gaskets are a better option in my opinion, if you think you may have an exhaust leak.

You COULD have a small air leak, you would have to take exhaust off and inspect. In my case, I had a small leak between header and mid-pipe, and I could see the soot from where it was blowing through the seam.

I still think your on the right track, and it's simply a matter of dialing it in, and your getting real close

some bikes are very fussy, and they really react to temp/humidity changes.

You have a after market exhaust which generally = go a bit richer. You tested it at the cold end of the range as well. But you also saw improvements (bog is gone), which means...your going in the right direction.

Does it only backfire when you let off the gas?

Your actually testing by riding, with bike FULLY warmed up, and not just on the stand?

Did you use JD Blue #3 or JD Red #5, you do not say which?

The Blue #3 is a bit richer on the bottom end the the red #5.

The jetting will never be static, unless your temperature, humidity, and altitude are.

The jetting you have right now, may be perfect for summer.

You also need to use the fuel screw to fine tune. I adjust mine pretty much every day, and sometime 2 or 3 times a day as weather/temps change.

If your only issue right now is the backfiring, and it is only on deceleration, or when getting off the gas when riding, and if your at red #5 - *I* would go to blue #3, and if you still have some backfiring, try adjusting with the fuel screw.

By the way, JD has awesome customer service, I had several phone calls and emails with them as I made changes to my bike....give them a call...they stand behind their product, and they WANT your bike to run good using it.

You also need to remember that if you get your bike dialed in PERFECT right now, it probably won't be perfect for the summer in a few months...lol

Your actually testing by riding, with bike FULLY warmed up, and not just on the stand?

Definately don't rely how it responds after changes with the bike on the stand. When I was making my jetting changes a few months ago, I made that mistake. It was backfiring and popping on decel alot. Once I got if off the stand and rode it around, it responded so much better, almost no decel pop. Why is this? I'm assuming it needs to be tested under load, to get the most accurate results?

Definately don't rely how it responds after changes with the bike on the stand. When I was making my jetting changes a few months ago, I made that mistake. It was backfiring and popping on decel alot. Once I got if off the stand and rode it around, it responded so much better, almost no decel pop. Why is this? I'm assuming it needs to be tested under load, to get the most accurate results?

It defiantly needs to be warmed up fully, but when the bike is not moving, with no air flow through the rads, the operating temp will not remain constant at all...it will go from to cold, to too hot in way to fast of a time.

These bikes do not like being run without moving

since I have NO desire to be re-jetting every week to accommodate changing conditions, I simply aim to jet for the best compromise to accommodate the majority of my riding season, and use the fuel screw to accommodate the changing conditions as much as it can. In the late fall, by rights, I do need to actually go up a needle clip, and up on the pilot, as the fuel screw simply can't accommodate such sever changes between summer and fall up here in Canada.

Unless you REALLY enjoy fiddling in your carb, and you MUST have the absolute BEST performance without question, it's all about finding the sweet spot to get you through your season, and compromises. Might be a bit rich in middle of summer, and it might be a bit lean in early spring/late fall, but thats good enough for me!

Sorry, I forgot to mention it's on the blue needle #3 and the bike was warmed up and tested on a paved road not on a stand. I did play with the msr fuel screw I installed and I have it set at 2 turns out. It backfires whenever I let off the gas and a few times when I was kicking it over. My 98 wr400 popped and backfired occasionally but not like this one, it defiantly seems more noticeable. Should I expect the 2004 to backfire more than my 98 did? I am going to take a closer look at the pipe for an exhaust gasket.

Thanks for all the input hopefully I get the bike inspected for a license plate and registered today.:thumbsup:

Is 2 turns out on the fuelscrew just rich of the "lean peak" at a fast idle? Or did you just set it there? (trying to make sense of this)

Your 450 should run just like your 400 if it's jetted correctly.

If getting it running right is getting to be too much take it to a shop. People will ride a bike that runs like shit forever and spend way more time and money screwing with it all the time when they have no idea what is going on. A local independent dirtbike shop will probably jet it in an hour or so and you'll be MUCH happier in the end.

These are not new motors and there are TONS of tried and true settings that most shops have seen so it should be fairly painless.

Just saying....no offense meant.

I started with the fuel screw one turn out, but the bike would only idle for 5 or 6 seconds before dying. So as I turned the screw out it would idle longer before dying until it wouldn't die at 2 turns out, and thats where I left it. I think I have an exhaust leak because I looked and I cannot see any sign of a gasket where the engine meets the header, Should I try to get a gasket from an exhaust shop or try to order one from Yamaha? As for paying a shop to work on my bike, maybe that is an approach for some people. But I am too poor to pay anyone to work on my bike, and in the past I have paid to get things fixed or tuned only to have them returned in worse condition. Also I am going to be riding anywhere from 2,000 to 10,000 feet this summer and want to get good at adjusting the jets and carburetor. Plus when you break down on the trail 60 miles from the truck the experience you have from working on your bike really comes in handy.

Understood. You're probably lean still on the fuelscrew.

Get the factory gasket for between the head and the header. It looks like a copper ring and you'll need to pull the header off the engine to see it. Not sure if "I looked" meant that you pulled the header off to check. Chances are that you won't be able to see it if you look from the side. If the midpipe leaks, just rub a little red RTV in the seam.

There's a process for setting the fuelscrew.

From where you are (at 2T open):

set the bike at a high idle (1800 RPM or so).

Open the fuelscrew some more.

If the RPMs go up, keep opening the fuelscrew until the RPMs peak and then drop.

You want the fuelscrew set just where the RPMs start to drop. That's the rich-side of the lean peak.

Now. count the turns that you have the fuelscrew open. If you're more than 2 1/2 turns open, the pilot jet is too small. Go up 1/2 size.

However, if you turn the fuelscrew open and the RPMs drop, then go the other way ("in") and find the lean peak, then set the fuelscrew just to the rich side of it and count the turns open again. If you're less than 1T open, the pilot jet is too rich (which probably isn't an issue here). But if it is, then go down 1 size and try again.

When the pilot jet is sized properly for the atmospheric conditions, the fuelscrew will be set between 1T and 2 1/2T open.

I appreciate that you just want to use 1 set of jets for a riding season, but that's not always possible.

Thanks for that info on setting the fuel screw I will follow your procedure when I get the chance, I really don't mind changing the jetting , here in Utah I will be riding so many different elevations and temperature ranges I figure I just need to get good at it. It took me 40 minutes to pull the carburetor, change jets, and reinstall. I Hope I can get my time down to 20 or 30 minutes. I will also pull the header to check for the copper gasket, if its not here I will order one.

Thanks again for all the suggestions.

No need to pull the carb. Just loosen the 3mm screws on the intake boots and twist the carb so the float bowl points to the left side. Saves 18 of those 20 minutes...

"I appreciate that you just want to use 1 set of jets for a riding season, but that's not always possible."

That was me....:thumbsup:

"I appreciate that you just want to use 1 set of jets for a riding season, but that's not always possible."

That was me....:thumbsup:

Oh yeah, haha! :smirk:

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