Bad Misfire With New Exhaust

[Seabass]

I went and installed the latest and greatest from Big Gun, their "EVO R" pipe, and had a great time until...... going into a big whoop section in forth gear. I let off the throttle to about 1/4 throttle and used the engine breaking to slow me down so I could gauge the size of the whoops. Once I figured they were huge I cracked the throttle and nothing! The bike just died and my family jewels made friends with my stabilizer. This same scenario happened alot this weekend and needless to say jumping into looooooong whoop sections or deep washouts was something I dreaded. When I was running the stock pipe with the baffle removed this never happened. The Big Gun pipe came as a race pipe (too loud) and I put the baffle in to quiet the pipe. Both ways the bike would just quit on me when I backed off the throttle and then cracked it to get the front end off the ground. The bike would eventually re-start after about five seconds of holding the throttle open. I'am also running the Gig Gun header pipe and I'm using the stock needle as the factory set it, a 50 pilot jet and 170 main jet. I've also cut the grey wire, removed the air box snorkel and am running two turns out on the fuel screw mixture. I shall be forever grateful to those that can shed some light on my predicament

[Dan_Lorenze]

Hmmm....

On Sunday I too was dealt with a good portion of Whoops.. I too noticed one hiccup and a sudden loss of throttle but I wrote it off as I was a bit low on gas or I figured the carb hit a "Dry" spot going over a the gnarly whoop section, doesn't sound as bas as yours.. I run a 170 main with great results, my pilot is a tad leaner than your 50, I'm running a 48 with the stock 04 needle. I'm somewhere between 1.5 and 2.0 turns out on the fuel mixture screw. You're new pipe might have different jetting requirements than the stock unit, It can't hurt to see what a 48 and 168 would do to your bike.. Just a thought.. Other than that, how do you like the pipe over the stock pipe???

?

[Seabass]

I like the Big Gun pipe. The race mode is way too loud for my liking, but the baffle insert quieted it down quite a bit. The bike seems to have a bit more bite down low, the front end came up alot easier than I remember. The race set up allows a longer pull on top, but it killed the down low torque. One peculiar thing happened after I started running the quiet baffle, the logo burned off the silencer! This years pipes have a sticker instead of the aluminum logo that was riveted on. I got a really good deal on it, otherwise I woulda gone with Yoshimura or just left the stocker on. (One more episode like this weekend and it probably will)

[xcracer123]

Call Big Gun and ask what jetting they recommend. You are certainly too lean! You will need to richen it up considerably with the free flow exhaust. I would also get the adjustable fuel screw for fine tuning. Hope this helps ya!

[Seabass]

Big Gun sez that no jetting changes are needed, I talked to them when I was installing my pipe. I also am using the ZipTy fuel mixture screw. Some posts I've read after seardching have stated that a condition like mine is caused by too rich a pilot jet/ needle setting. ?

[RADRick]

Big Gun sez that no jetting changes are needed, I talked to them when I was installing my pipe. I also am using the ZipTy fuel mixture screw. Some posts I've read after seardching have stated that a condition like mine is caused by too rich a pilot jet/ needle setting. ?

Sounds to me like you're too rich on the pilot jet. Since you have a baffle installed, I would try going to a 68 pilot and see if you can get the fuel screw down to 1-1/2 to 1-3/4 turns. Also, the FCR carb has a tendency to squirt too much fuel with the stock accelerator pump setting. This is to overcome the factory's lean jetting and prevent off-idle stumble. Try adjusting the AP so that it starts a little later in the throttle opening. The adjuster is under the cover where the bellcrank is.

[Seabass]

Sounds to me like you're too rich on the pilot jet. Since you have a baffle installed, I would try going to a 68 pilot and see if you can get the fuel screw down to 1-1/2 to 1-3/4 turns. Also, the FCR carb has a tendency to squirt too much fuel with the stock accelerator pump setting. This is to overcome the factory's lean jetting and prevent off-idle stumble. Try adjusting the AP so that it starts a little later in the throttle opening. The adjuster is under the cover where the bellcrank is.

Is that pilot number correct (68)? I went with a bigger pilot and installed a 50. The pilot is the jet right in front of the main, correct?

[jasilva]

He meant 48 I'm sure. Yes the pilot is right in front of the main. What have you done to your needle? If your running the stock needle you are definitely too lean there.

Joe

[Seabass]

He meant 48 I'm sure. Yes the pilot is right in front of the main. What have you done to your needle? If your running the stock needle you are definitely too lean there.

Joe

My needle is still in the stock setting as it came from the factory. I've been putting off messing with the needle but I'll give it a go this afternoon after work

[RADRick]

He meant 48 I'm sure. Yes the pilot is right in front of the main. What have you done to your needle? If your running the stock needle you are definitely too lean there.

My bad, 48 is indeed what I meant. You need to concentrate on one aspect of the throttle opening and get the jetting right for that circuit instead of trying to get it all right at once. Each jetting change is responsible for a different throttle position, but there is some overlap that can cause one to affect the other. If you do one thing and it doesn't work, go back to where you started and do something else. Otherwise you have no way to tell if it's a problem with the initial change or a combination of both. I usually start by getting the pilot jetting right. Once that is done, getting the other settings in line is fairly easy.

[jasilva]

Good point Rick, however the stock 05 needle is non adjustable and way to lean on anything except a stock bike. I have my JD blue needle set in the 4th clip position and it is crisp right off idle. Seabass, if you have a 50 pilot and the stock needle it sounds like you may be rich at idle and then way lean when you open the throttle aggressively. Main jet doesn't even come into play until 3/4 throttle so I would change the pilot to a 48 and get the fuel screw set for a good idle and easy starting. Then get an 04 needle in there and start with it in the 3rd clip position from the top. Drop the clip one position and see how it runs, if it is better then go one more and see what you get. I'm betting the 4th position will probably be right except maybe at high altitude. Once you have this part dialed in then you can mess with the main. If the bike burbles and doesn't want to rev clean on top then you may be fat on the main but a 168-170 should be about right.

Joe

[RADRick]

Good point Rick, however the stock 05 needle is non adjustable and way to lean on anything except a stock bike.

Damn! I forgot about that. Everything you said is right on. Once you get the pilot circuit right, everything else should fall into place with a little bit of fiddling.

[charliep]

Damn! I forgot about that. Everything you said is right on. Once you get the pilot circuit right, everything else should fall into place with a little bit of fiddling.

Rick, hahahahahha..........I think he should start with the pilot circuit first, then fiddle.

[Texas4play]

I definitely agree with the 48 pilot idea - 50's too fat. The stock needle (although non-adjustable) is set at a #3 clip position (when compared needle-to-needle with a "normal" one) so it may be ok for now. Also, do yourself a favor and get an adjustable fuel screw (can't forget about the fiddling). But, for now, do your jewels a favor and clean up that pilot circuit first!

[jdd123]

It sounds like the bike leaned out with the pipe. That hesitation off the bottom sounds very similar to the infamous bog on the WR250's. You can try a larger pilot and it will help as long as you do not make the pilot circuit too rich and foul plugs.

The leak jet is what controls the amount of fuel injected when you crack the throttle. Selecting a smaller leak jet will squirt more fuel when you crack the throttle. A larger leak jet will inject less fuel. There is a detailed discussion about the accelerator pump, leak jets, and diaphrams in the 250f FAQ in the 250 forum. I am assuming your new pipe leaned the bike. It would help if we knew what bike you had. The 05's are still restricted even with the baffle removed.

[Seabass]

Thanks everyone for your responses. ? I changed the pilot to a 48 and put it in last night. Riding around the neighborhood it seemed to work, but I don't think I can tell until I put some hard miles on it. The problem was intermittent last time I rode it so I guess I'll just wear my cup when I race this weekend! ?

And I forgot about the needle being non-adjustable for the '05 Wr's. I was gonna take a look at it last night and I'm glad I didn't, I'd probably still be cussin' and trying to figure how to drop the needle with no grooves! ?

Texas4play- I've got the ZipTy fuel screw adjuster

JDD123- My bike is an '05 WR 450

[jdd123]

The only way to adjust the needle is to order an 04 WR needle or a YZ 450 05 needle. (I'd bet they are the same part number).

My WR, according to the manual, as a #50 leak jet stock. This is the number I had to go with on my old 03 WR250 as it bogged off idle. They put like a #90 in which made it way too lean. I also found that the bog would reappear as the air temperatures got colder (below 50 degrees F). So far, on my 05 WR the bog hasn't shown itself. But, I have a stock pilot and at my altitude, it is like a richer (48) piolt.