XR4 backfirin'

[xr400xr50r]

'97 XR4 backfirin'

Hi Guys........me again. This message is also listed on another board.

Well, I had my first real trail ride over the weekend. Over 30 miles of trails and had only one (1) real complaint...early in the day doing some 1st and 2nd gear riding (mostly 2nd gear) the bike would back fire at low rpm as though it were "loading up". It only did this one or two times and when I ran it through the gears at a higher rpm it didn't happen again for the rest of the day.
That and the supposedly "typical" near-stall when you "blip" the throttle at idle.
Here's a little background. I just did an oil/filter change before the ride (1.9qt MOBLIL 1 MX4T fully synthetic motorcycle oil)and the oil level on the bike's dipstick (not the owner) is about an inch from the bottom of the stick (the 1st quarter of the dipstick range?? Is this normal??) The level before the oil change was at the upper limit.
I am wondering if my slow jet (#60) is too rich? Do these bikes "load up"? Also, I was running 87 octane as that's all I had at home (man, that was probably a bad idea). I haven't replaced anything in the carb yet (everyone says to the the dual taper needle) and I am really as "low-buck" as possible.
Well, if anyone has any tips feel free to share.
Thanks in advance
John

 

[snaggleXR4]

Hey,
I'm in Florida, sea level, and I have an aftermarket airfilter, snorkel removed and XR's Only Competition exhaust. My jetting, recommended by XR's Only for my specific setup is 160 main/60 pilot. Assuming your bike is all stock, with the snorkel and stock exhaust with the baffle still installed, you will be on the rich side. The '96's and '97's came with 162/62 jets stock, the '98+ bikes have 142/52 jets stock. The '98+ bikes are jetted better with the stock setup, but will be very lean if you make any airbox/exhaust mods. The '96 and 97 bikes were way too rich stock, better with snorkel removed and baffle removed, but still very rich.

If your bike is still stock, and you plan to keep it that way, aim closer to the 98+ jetting of 142/52. My bike will still try to stall at idle if I blip the throttle REALLY fast, but under no circumstances have I experienced it even in really slow riding conditions. I think leaning the pilot does help the off idle stumble, but does not totally cure it. I bet one step leaner than the #60 would do the trick, but you might need to go a couple steps, just remember, richer is better. In addition, I would try to adjust the pilot screw to see if you could lean out the mixture a tad. It probably won't be enough by itself, but it's worth a try.

Good luck, keep me/us informed of your progress. Keep on thumpin'!

 

[snaggleXR4]

Hey,
I almost forgot. When you change the oil, put in about 1.5 qt's at first. Let it sit for a while. With the bike up straight on a stand or something, unscrew the crankcase oil check bolt on the right side under the oil hoses coming out the side. Oil should just be level with the hole, just dribbling out. Then, put in the other .4 quarts. Start up the bike and let it idle and get warm for a few minutes, or ride a short distance. With the bike still level, check the oil, you should be near the full marks of the dipstick.

It's scary beacause with the oil in the tranny and in the frame, sometimes it looks like there is not enough. It is really important to get the bike hot, and check the oil while the bike is level. Kinda screwy that way, but that is the trick. Good luck.

 

[xr400xr50r]

Snag,
I ran the bike again tonight (I rode the bike at VERY low speed for 5 minutes), brought it back to the garage, leaned against a wall to make it level, shut the bike OFF and checked the oil again. I got the same result as the 1st time I checked it after the oil change...an inch up from the bottom of the dipstick.
It doesn't (and didn't) burn any oil and as it sits in my basement it isn't leakin' any......this has me perplexed, can their be any "air lock" or anything silly happenin' here? The oil change seems a simple concept, but I have figured a way to screw up just about anything.
I may drop to a 58 or 55 slow jet...I will do some more reading.
Thanks Snag for the replies. This board is a great source of info.

btw, not listed in any earlier post, I am running with the snorkel out and a stock exhaust for a '97

John

 

[snaggleXR4]

Hey,
Hmmm. Very strange. But again, I must say I've experienced the problem before. Check your crankcase oil check bolt, make sure there is oil in your tranny. Not that it will help in this particular situation, but per the Honda Service manual, the dipstick should just sit on the threads, do not screw it in to check the oil level.

Again, if you have oil in your tranny, and you know you put in almost 2 quarts, you should be good to go. Keep checking it though, maybe after a longer ride it will show a more accurate amount.

On your jetting. A good friend of mine has a 97 XR400. He has stock 162/62 jets, no snorkel and has removed his baffle from the stock pipe. His bike runs kinda blubbery and floods pretty easily if he kills it, but otherwise runs ok. So, if you have your exhaust baffle in you will still need to be a bit leaner as mentioned before.

 

[xr400xr50r]

Snag,
Thanks again...I did notice that perhaps the oil level is a little higher than when checked IMMEDIATELY after the oil change. I will keep checking to see if the level comes up any.
I am pretty sure the exhaust baffle is still in (I ain't tore it apart yet)....my service manual doesn't show much about the exhaust system; just a picture of the pipes and the muffler. I guess they don't want you to remove the baffle. If I choose to do so, is it as simple as removing the the bolts that hold the tip on and pulling out some kinda baffle??
Also, I read in some other posts that sometimes backfiring when letting off of the gas meant that it was TOO LEAN? I don't know, I think that I am going to get an A16A needle and leave the jetting alone. I think the bike is pretty awesome (compared to the '80 Honda XL500S and the '72 Yam CT1 175 that I had been beating around on).
As far as starting the bike, mine is a one or two-kicker (after 5-6 half kicks with full choke, full throttle, compression released and then one bump past TDC). This is the way the previous owner showed me how to do it and I have it down to an art.......I can start this bike with my left foot wearing flip-flops (or shower shoes). I love it!!
Thanks again Snag

 

[snaggleXR4]

Hey,
On your 97, the baffle will come out. Remove the screws and pull like crazy. It will be stuck pretty darn good but it will come out. Keep in mind it will be very loud. I don't recommend even trying unless you plan to put in a Vortip or another aftermarket baffle.

Yes, I did think about the backfire because of being lean. That is true. However, you said it backfired while putting around in 2nd gear. To me that means your pilot. With a #60 pilot and your baffle in, you can't be anywhere near lean. You never did mention your main jet. Maybe you are lean there, but if it is stock, then it is a 162, and that's not lean either. Maybe, as you mentioned, you oiled your airfilter too much and for that short time, you were way too rich. If you don't get backfires again, maybe that was it.

Check out bajadesigns.com. They have a XR400 section, and they have the dual tapered needle, and even a different slide that they will trade in for a discount. Good luck, and enjoy your bike.