05 YZ450F questions - new owner

I just bought a nice 05 YZ450F and I've got two questions.

1) Regarding jetting, it runs fine and cranks easy, but it has light backfires when you let off of the throttle. I'm an old 2 stroke guy making the change, so I'm wondering if this is a lean or fat condition (or normal for this bike) and also any recommendations for jetting at about 1000 ft.

2) Regarding oil changes, will I be OK if I drain the oil from the plug on the right rear side of the motor and the drain plug in the front of the frame, or should I be taking more drain bolts off. What about screens, etc. that should be cleaned. I usually change my 2 strokes every 50 miles. How long should I go on this bike and what oils do you recommend.

Thanks everyone for your help. I'll be glad to answer any questions on KTM 2 strokes if needed.


On my '03 450 (I think it's the same) I pull both drain plugs. The one you mention with a 12mm wrench and a small (8mm) drain bolt on the left hand side under the shift lever. I also disconnect and drain the oil return line on the right hand side (rear brake side) this drains the frame filter easier than the drain bolt you mentioned. I did pull the frame drain a couple of times and the filter inside as well but I've never found anything there so I don't pull the frame filter out any more.

Thanks for the info. I saw the little 8mm bolt and it looks like a pain to take out (with the skid plate under it). I'll follow your suggestions.


I've got an 04', so they are pretty much the same.....

1) The backfiring more than likely, is simply due to the Fuel screw needing to be richened up. If you're unfamiliar with the Fuel screw, do a search on it, to get a real understanding about it. But as a general rule, you're weather is probably getting colder down there, and you're getting slightly lean. The Fuel screw is recessed near the front of the Carb, and you either have to use a short stubby screwdriver to get to it, or install an aftermarket adjustable Fuel screw, that you no longer need a screwdriver to adjust it. It is metering the amount of Gas, so you want to turn it OUT to richen the mixture, or turn it IN to lean it out..(I think that's opposite of 2 stroke AIR Screws) Anyway, first try turning her OUT maybe a 1/4 turn, and see if it backfires less. It's normal on these bikes to experience an occasional Slight backfire on deceleration, but you don't want it happening all the time.

I'm going by memory here, but at 1,000 feet, the stock jetting may be fine.

My manual lists a #165 for the main jet, and a #42 pilot jet. Other's will probably chime in with more precise info. I switched to an aftermarket jetting kit known as a J/D kit, that uses special tapered needles. It definately improves crispness....runs about $ 65.

2) Consensus seems to be that you should take out the three bolts for a normal oil change, (the big one up high in the front, and the two near each other near the gear shifter). You really only need to take the 4th one (oil strainer up in the front frame), out when the bike is being broke in, or after you do any big internal engine work..i.e. new piston, cams, etc. I don't race, but I ride both track and trail, and I change oil and filter out every 10 hours, or slightly less. I generally don't run at high RPM, and basically short shift the bike. If I were racing and bouncing off the rev-limiter, than I'd change oil at shorter intervals.

Oil brands raises all kinds of arguments.....I use Yamalube 4R, and I've had no problems. Just don't use any Oil that has "friction Modifiers" in it. This will cause the Clutch to slip, since the tranny and motor share the oil. It's funny, but I can pretty much tell when I'm getting near 8 or 10 hours of time on the oil. The shifting will start to get just a tad bit "notchy"...letting me know she wants new oil. Oh, by the way, get a Scott's Stainless Oil filter. It filters better than stock filter's, and lasts forever....you just use Carb cleaner to spray it out, and re-install. Expensive at $ 65 or so, but it will last forever as long as you don't smash it.. I think o.e.m. filter's run about $ 11 each, so do the math.

Hope this helps...

Oh, almost forgot...

When you take off the Oil filter cover to replace, or clean it.. Just take off all three bolts at the same time, pull the cover, and let the oil pour out.

The Manual has you removing the lowest bolt, and letting, the oil come out through the bolt hole, before removing the other two bolts. This will eventually lead to a stripped bottom bolt hole, because you're letting all the old oil (with little bits of steel, aluminum) pour through a THREADED hole. Over time, these particles fill up the threads, and you get a busted off screw, next time you go to remove it. It's a pain in the keyster to replace, so just take off all three cover screws at once.....enough said.

Light decel backfiring is normal. IMO, if it never does it at all, it's too rich. That said, read:


I change oil in my '03 just about exactly as you outlined:

1) Run the engine for a minute, shut off, and drain the frame at the drain plug. (Tip: (should be obvious) Turn the front wheel to one side and hold the drain pan up close to the plug. You'll see why). Replace the plug.

2) Remove the filter and clean or replace it depending on which filter type you use. Close it back up before continuing. Heed Flintlock's advice about not using the lower bolt to drain the well.

3) Drain the crankcase.

Refill, run for 90-120 seconds, shut down and check the level.

I do not remove the frame screen except for once when I first buy the bike, or if some major damage/work has occurred. I also do not use the oil line as a drain because it isn't a drain plug, and isn't set up to tolerate being used as one as well as the frame drain, and it doesn't drain as easily.

On the subject of oil:


Thanks guys for taking the time to give me some great info on this bike. I really appreciate it.


I also second (or third) not using the oil line for draining because that o-ring WILL wear out, at an inopportune time (i.e. when you don't have access to a replacement) and will leak profusely.

Besides which, the threads in the drain plug are 8mm steel on steel. The threads at the oil line are 6mm in an aluminum case.

Just want to make sure I understand here.

Rather than drain from the right side drain bolt, drain from the filter cover?

Then drain from left side?

I have an 07 but assume this configuration has not changed. I don't have torque wrench adaptor for the right side drain bolt anyway. I would rather not mess with it if I don't have to. Thanks.

You assume wrong. The '06/'07 is completely different, except for the oil filter and its cover. The advice given applies only to '98-'05 YZF's. There is no oil in the frame on the new ones.

Thanks for the reply Grayracer. I will follow the book, if shavings in the threads has been an issue, why didn't they design it to drain from the bottom (vertical threads)?

I think you're slightly confused..... What were talking about on the pre-06' models, is that when taking off the oil filter Cover, the Manual recommends that you remove the lowest bolt (from the cover) and allow the small amount of oil to drain thru this bolt hole. There are three bolts that hold the cover on, if you allow oil to run thru the bolt hole (which is threaded), over a period of a number of oil changes, any debris will flow thru the threaded hole, and lay within the threads of the hole. Than one day, you go to install the bolt, and snap, you just broke off the bolt in the hole from the debris. This has happened a number of times to people.

I think it was Grayracer513, who suggested instead of removing the lowest bolt, and allowing oil to drain from it...you simply loosen all three bolts holding the cover on, and pull the entire cover off in one motion. Now the oil just flows out mainly from the much bigger opening, and doesn't have to flow thru the small bolt hole, thus no more debris clogging the threads, viola! no more broken bolts, stuck in your case.

I think this was just an oversight from Yamaha, not realizing over a period of time that any debris would run thru the bolt holes threads, and accumulate, and f' -up your threads.

hope this clarify's it.

Yup, I am always confused......:lol:

I think I understand the procedure now and the why's, thanks for the clarification. My comment was more related to the right and left side drain bolts (not the filter). The mechanical engineer in me wonders why they don't drain from the bottom of the case (with vertical holes). I'm sure they have a reason. I guess I assumed that there have been issues with filings in these threads as well? Maybe that is where I am confused....

Yeah it doesn't seem to be an issue anywhere else that oil comes out, maybe it's just that the hole is so small, and that the threads are perfectly 90 degrees horizontal, that it's the perfect niche for grit, and metal shavings to sit in. It's not a one time thing, it usually happens after you've done several changes, before it rears it's ugly head. Some guy's will purposely run a tap thru occasionally just to make sure. I think it's like a 6.0x 1mm??

It's a matter of scale. An 8mmx1.25 thread is just more tolerant of chips than a 6mmx1.0. That and the Allen bolt in that hole is fairly soft.

My question to Yamaha engineers will always be, "What were you thinking when you put a drain plug directly behind the frame rail (crankcase drain, '06-7)? Was it just too easy to use where it was on the '03? Are you going to come and help people pull their engines to repair the threads when they wear out?"

If we strip the bolt....more than likely we take it to the dealer? Hmmmmm....design at its best (or worst). I'm gonna buy a torque adapter now for that pesky right side drain bolt.......

Regarding the "popping" when you let off the throttle, have you checked the seal between the header pipe and the muffler? I've found that 4 strokes in general will pop like crazy if there is an air leak there. If the bike runs good, I would check that first before playing with the jetting.

My 04 yz450f started popping on deceleration also, I was told it was running to lean, i had that taken care of but the guy at the shop told me that there was a small leak in my exhaust, first joint joint out of the head, it still pops a little on a hrrd decel but he said it would not hurt it and it was not worth the cost of a new exhaust, i hope thats correct :busted::worthy::ride:

I used to live in North MS. and tweaked the fuel/air mixture screw in the carb. during the winter months because of the temp. and humidity change and it worked just fine. Buy alot of carb cleaner and blow out that bottom bolt hole under the oil filter with the cleaner to flush out any debris when you change the oil. Also, in the summer months be sure to store you bike with the valves closed (in T.D.C.) to keep as much of that nasty Ms humidity out of the engine.

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