KDXRIDER.NET

OLHILLBILLY wrote:

Mr. Wibbens wrote:

Tedh98 wrote:

If you wind out the engine to 9K rpm and then cut the throttle but don't pull in the clutch, the engine is spinning at 9K but only has enough fuel entering the engine to sustain idle, which shouldn't be enough to properly lubricate.

But when you pull in the clutch, the rpm's drop and the rpm's then better match the fuel entering the engine.

At least that is how I look at it.

Thats a little more extreme than typical engine braking dontcha think?

Anytime the throttle is closed and the engine is turning above idle RPM, there is "insufficient" (that's probably the word I should have used instead of "no") fuel/oil coming into the motor to lubricate the bottom end at that rate of motion. There is enough residual oil on the bearings to last for a period of time. How long that period of time is, is what your comfortable with.
Kinda like the 60:1 mix folks, if your comfortable with it, hey.. it's yours.

+1

Engine braking on a 4-stroke is good for the motor, there is more oil splash from the crankcase to the underside of the piston than when revving.

2-stroke if the throttle is closed you only have the oil/fuel mix you would have at idle going around the engine at 8000 odd rpm. You decide.

well if you are stoopid enuf to run it at 8k you probably should not even be riding the phukin thing

lol. True enough.

Point is, on a 4 stroke, you can hammer down through the gears to slow up after a straight for the upcoming curve. The 4 banger doesn't care of slamming it into second gets it to 8k. The 2 stroke MIGHT care, or it might not. I don't care to find out, so I always clutch on downhills or heavy braking.

I never much cared for the engine braking on a 4 stroke anyway. I'd rather coast when I let off the gas, and brake when I hit the brakes. Just feels more natural to me.

Remember the oil injection pumps on the older 2 strokes? It varied amount of oil pumped in not only by throttle position, but also by engine RPM. I suppose there was a reason for that.

Engine braking is pretty important to me and how I ride. We've got long steep downhills here where you won't have to touch the throttle for 20 minutes or more. It's the number one reason I have doubts about getting an autoclutch. If you are just relying on your brakes, it just does not work very well and it takes a lot more out of you

Takes 3 seconds to activate the clutch... I don't think that's a reason to NOT get a REVLOC Dynaring autoclutch.

Try that with the alternative....

I'd have to see it to believe it. As hard as it is to get the E series clutch cable set to just the right point where it works without dragging or slipping, I'm thinking a little more than 3 secs

I would like to see one, hopefully I'll get to try Road Rash's out

basically, do it, the oil sits in the crank plenty long enough but will wear away from the piston surface pretty quick, you should be fine in 90% of riding, just dont go down the side of a mountain in 1st gear at 30mph

plus use decent 2-stroke and perhaps even activ8 friction reducer and a tiny bit of mechanical sympathy (my arse... just thrash it and rebuild it.)

The pilot jet flows fuel even when the slide is at it's idle stop. If anything as engine speed increases, and the slide stays there, more fuel will flow (get 'pulled' in)creating a rich condition. Ever ride a great running bike down a huge hill, and have it blubber when coming out of the bottom?

On the other side of the RPM spectrum...If this didn't happen any full throttle run, then let off gas, would seize motors instantly. It is also a hurdle to duplicate this with fuel injection (only a 2T issue).

fuzzy wrote:The pilot jet flows fuel even when the slide is at it's idle stop. If anything as engine speed increases, and the slide stays there, more fuel will flow (get 'pulled' in)creating a rich condition. Ever ride a great running bike down a huge hill, and have it blubber when coming out of the bottom?

On the other side of the RPM spectrum...If this didn't happen any full throttle run, then let off gas, would seize motors instantly. It is also a hurdle to duplicate this with fuel injection (only a 2T issue).

It could only "pull in" so much fuel. Still the fact is that it could be running too lean in the right situation. And as far as the full throttle run, then let off gas, would seize motors instantly. That would not be the case due to the residual lube on the bearings. If you need to prove this point in your way, tie your bike to the back of a truck and start it, put it in second gear and leave the throttle closed. Pull the bike down the road at about 30 mph for a while and let us know the results. Again, this is common practice for some, but there could be a potential for damage.

fuzzy wrote:The pilot jet flows fuel even when the slide is at it's idle stop. If anything as engine speed increases, and the slide stays there, more fuel will flow (get 'pulled' in)creating a rich condition. Ever ride a great running bike down a huge hill, and have it blubber when coming out of the bottom?

On the other side of the RPM spectrum...If this didn't happen any full throttle run, then let off gas, would seize motors instantly. It is also a hurdle to duplicate this with fuel injection (only a 2T issue).

+1

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fuzzy wrote:The pilot jet flows fuel even when the slide is at it's idle stop. If anything as engine speed increases, and the slide stays there, more fuel will flow (get 'pulled' in)creating a rich condition. Ever ride a great running bike down a huge hill, and have it blubber when coming out of the bottom?

On the other side of the RPM spectrum...If this didn't happen any full throttle run, then let off gas, would seize motors instantly. It is also a hurdle to duplicate this with fuel injection (only a 2T issue).

+1[/quote]

So.... with the throttle slide down the pilot can flow the same amount of fuel as the MJ does at WFO?

BS.


re: Ever ride a great running bike down a huge hill, and have it blubber when coming out of the bottom? Wink


No, not really. Few months ago though I followed my buddy on his "great running" 200 exc down a really really long downhill fireroad at high speeds. I kept my bike clutched and gave a little throttle once in a while, he kept it in gear and off the throttle. Engine braking into the curves, in effect. The bike sputtered and died out when he gave it gas at the bottom all right. We never did get it started back up. Had to cut the riding weekend short. I don't think it was a rich condition though.... We're rebuilding his bottom end this week. Destroyed big end bearing, and associated carnage.

OOPS


I think if you're a big fan of engine braking, you should prolly be riding a 4 stroke. At least until we see wet sump 2 strokes. What's the big deal? Pull the clutch in and use the damn brake. That's what brakes are for.

Indeed....I will certainly say there is a point where you're going to start running out of pilot fuel for the RPM, but most engine braking scenarios are safe, and like I said sometimes you'll actually load up. I'd say hitting 'overrev' RPM with the throttle closed for huge distances is of course too far.. Was just making a point that in most cases you're getting more fuel than one would think. How much fuel do you think you're getting in there when you just burp the throttle w/ the clutch in? If you're on the lean-edge with the pilot you could actually starve the engine here (just like a "lean-roll seizure"). I do avoid engine braking when I can, but there are cases where you will boil the **** out of your brakes if you don't use the engine....Then you ONLY have your engine. I'll paraphrase Juliend, and chalk it up as 'be smart about it'

I have read this entire thread, and I would be lieing if I said that I never used engine braking on my KDX (or any other two stroke), but I would also be lieing if I said that I thought it was fine to do it at very high RPM, and for extended periods of time. I usually ride using a combination of regular braking, engine braking, downshifts, throttle blips, and clutch work to try to save my engine from extreme engine braking exposure.
It just feels like the right thing to do.

If you have enough time to think about all this ****, you really need to find better trails

some good argument on both sides, I do use engine braking a lot before entering corners using both braking + downshifting.
The questions is, has anyone seen or experienced an engine seized in REGULAR use? (no pulling the bike in 2nd gear behind the truck for 1000 miles )

The only one i've SEEN was my buddies KTM. He wasn't dogging it, just a really long downhill wide open road, cruising down in top gear about 45/50mph. Trashed the lower rod bearing. Funny thing, I know his bike is pig rich on the jetting.

So it's my estimation, small amounts are fine. Extended periods of engine decel are bad.

juliend wrote: So it's my estimation, small amounts are fine. Extended periods of engine decel are bad.

+1

juliend wrote:The only one i've SEEN was my buddies KTM. He wasn't dogging it, just a really long downhill wide open road, cruising down in top gear about 45/50mph. Trashed the lower rod bearing. Funny thing, I know his bike is pig rich on the jetting.

So it's my estimation, small amounts are fine. Extended periods of engine decel are bad.

+1