07 WR450f Burning Oil

[dhi002]

I went for a 20 mile (woods/street) ride the other day. The bike ran beautiful in the woods, but experienced some hesitation at about 55 mph on the street. Along the way i stopped to rest. I happend to check the oil after 10 minutes of sitting and noticed there was no oil showing on the dip stick. I had been pushing out some blueish/white smoke. I realize i probably need to have the engine rebuilt (bore, pistons, rings, valves ect.) If i am burning that much oil shouldnt the bike be running poorly in all riding situations ? Any comments is much appreciated.

[Sknight]

Mine's using oil but still running great. It's not using as fast as yours but I figured out that it is putting out blue smoke if you watch at the right time.

Odds are your valves are fine they just need to be leak checked.

[travertt]

You may have waited too long to check the oil (10 minutes) and thereby allowed too much of it to drain back into the engine and therefore show a low reading on the dipstick.

Try starting the bike...get it completely warmed up and shut it off. Wait about 30 to 60 seconds and then check the oil. This is in line with the manual's instructions. You may find things are not as bad as they seem

[dhi002]

Thanks for the replies guys. I actually went for a ride today.....strictly woods. I went about about 7 miles and i blew blueish smoke when i started and when i gave it a lot of gas. The bike ran great, but did mis-fire a few times when i let off on the gas. I stopped twice and let the bike rest for 5 minutes before checking the oil and it was right at the full line on the dipstick. Kinda confused by this since the muffler end is wet of oil and i did blow a good amount of smoke. Gonna keep a close look at this each time i ride. Was hoping to get through the summer until my mechanic buddy can help me with the rebuild.

[tribalbc]

Could be as simple as a leaky valve seal especially if you get the most smoke at startup.

[dhi002]

Went for a ride a few days ago and i looked like a smog machine. Im not gonna fool around anymore and risk seizing the entire engine. I just ordered a big bore cylinder kit today. Gonna re-do top end including valves/seals which should solve this blue smoke situation. I will revert with what i find when i tear the bike down.

[dhi002]

Okay, so last week my mechanic buddy and i rebuilt the top end. New big bore cylinder and piston, new valve seals etc. She starts right up and the bike idles and runs fine except now we are getting a mid range bog in every gear and some back firing when you let off on the throttle. Any ideas what this could be ??

[Sknight]

Did y'all rejet it to match the extra displacement? You're moving more air but the same amount of fuel. I imagine you'll need to go up a couple of jets.

[dhi002]

Did y'all rejet it to match the extra displacement? You're moving more air but the same amount of fuel. I imagine you'll need to go up a couple of jets.

Did not as we didnt think that 3mm would need a rejetting. how is it that i am moving more air ?

[Sknight]

Think of it this way, originally you had a gallon bucket, you now have a larger bucket, 7% larger to be reasonably close. That bucket is going to take more air to fill up every time the piston goes down. Before if you poured a quart of water in it took up 25% of the room in your bucket but now that quart takes up 23.35% of the volume. By that reasoning (Which may be wrong, but remember this isn't to be taken as gospel for exact numbers.) you're running 1.65% leaner. The carb throat will allow more air volume due to increased vacuum from the higher swept volume of the cylinder, but the jets restrict the fuel flow despite higher airflow. A bit more will flow but not nearly enough.

Jump up about two jet sizes, I bet you'll love it.

[dhi002]

Think of it this way, originally you had a gallon bucket, you now have a larger bucket, 7% larger to be reasonably close. That bucket is going to take more air to fill up every time the piston goes down. Before if you poured a quart of water in it took up 25% of the room in your bucket but now that quart takes up 23.35% of the volume. By that reasoning (Which may be wrong, but remember this isn't to be taken as gospel for exact numbers.) you're running 1.65% leaner. The carb throat will allow more air volume due to increased vacuum from the higher swept volume of the cylinder, but the jets restrict the fuel flow despite higher airflow. A bit more will flow but not nearly enough.

Jump up about two jet sizes, I bet you'll love it.

Thanks. I havent had a chance to do anything, but what your saying is that the bigger bore is pulling more air and that the bike is running too lean ? Are you referring to the "Main" jet when you say "jump up two jet sizes"? Right now the main jet is 170. What do you recommend? sorry, i am new to this and most of the information i do know is from research. Any advice is much appreciated.

[Sknight]

No worries. Tuning is something many try and few (Including myself.) get correct all of the time. I can make a muscle car scream but I'm still wrapping my head around the finer aspects of these.

You're on the right track, the engine is drawing more air now but your jets are restricting fuel flow. Since you have a 170 main see if you can get a 172 or a 174, fortunately you also have the needle height to adjust also, for now you can lower the clip on the needle to richen it up some.

Air is a compressible medium, fuel isn't. A carb of specific size will allow more air (Carburetors are rated at a specific vacuum number, max air flow or CFM at 28" of vacuum.) if a larger signal is given but fuel being a liquid is only going to flow X amount through that hole now matter what is happening. You're now sucking in 480cc's of air instead of 450cc but flowing the same fuel as when it was 450. You just need to match the fuel rate to your air rate.

Sounds simple doesn't it? It actually is, once you get it it'll be like falling off a stump.

[KennyMc]

Noting the backfire on decel, I would also suggest you go up a size in the Pilot jet.?

[barbwire44]

The popping on decel does sound like a lean pilot jet, but to go up on the main or richen the needle after a big bore kit is usually the opposite of what happens when you go to a big bore, A big bore will pull harder across the jets and require a smaller jet.....kind of the same reason you will see a 250f will have larger jets in it than a 450f.

[Sknight]

So you're moving more air but need less fuel? Does the 250 have the same CFM carb for a real apples to apples comparison?

Going leaner with more airflow goes against everything I've ever done but OK.

[CanadianWR450]

Your moving more air, but at a higher velocity. The higher velocity "pull's" more fuel through the jets and orifices.

This is a bad comparison, but think of it this way:

You have a hose with a fixed orifice, and it will allow 1 GPM through it at 10 PSI.

If you jump the pressure to 15 psi. your going to be moving a lot more then 1GPM through that same orifice. Higher RPM also = velocity, so the effect seems to be more on the top end (My own personal findings anyway).

I needed to go richer on the bottom (fuel screw handled it, but it could probably even use 1 size up on pilot), and down on the main one size when I went to a big bore.

[Sknight]

I would have to say that you were jetted rich before the big bore. I said initially that more fuel would flow because of the increased air flow and higher vacuum signal.

That increased air demand is every where. Why do you need to go richer on the bottom, but leaner on the main? Because the main was too big to start with and increased demand made it worse.

Lets agree to disagree, the OP needs to rejet, that we all agree on.

[dhi002]

I spoke to someone at JD and they said when you go bigger in the bore that the needle regulates the mid range and needs to be adjusted lower. The main jet regulates the top end. Does this sound right or did i mis-understand them ?

[Sknight]

You're correct, once the carb is open a certain amount the needle is just hanging there for the most part and the main jet is doing all the work. Let's one system cover a wider range.

When you say lower, do you mean lower the clip or lower the needle height? If it was lower the clip then it raises the needle height. If it was lower the needle then you put the clip in a higher position on the needle which lets the needle hang lower.

[dhi002]

You're correct, once the carb is open a certain amount the needle is just hanging there for the most part and the main jet is doing all the work. Let's one system cover a wider range.

When you say lower, do you mean lower the clip or lower the needle height? If it was lower the clip then it raises the needle height. If it was lower the needle then you put the clip in a higher position on the needle which lets the needle hang lower.

I believe its "Lower the needle height". Hopefully i will get to it this weekend and will revert with outcome.

thanks for all that have commented.