Is "lean down low" a problem?

[farmerj]

I kinda like the way a 2-stroke runs when it's almost out of gas - so smooth & crisp - but I realize that you can't jet it that way, or you'll be too lean and damage the engine.

Is that true "down low" - say at 1/4 throttle or less? Or is it only at higher rpms that being too lean creates damage?

Asked another way, will you damage an engine if you're too lean at low throttle openings (but "correct" up top)?

Jeff

 

[Jakobi]

Its a tough one to call. I wouldn't reccomend going too lean as you may get pinging and cause damage under load. In saying that I jet my bikes on the lean side on the bottom end because I like clean crisp running and find the 4 stroking annoying. Its taken me quite a bit of testing to get the right diameter needle to give clean response without losing too much torque too. At around 1/4 throttle you are really getting into the clip position too and the half clip differences can make a big difference fine tuning it all.

 

[BryanMcc]

Its a tough one to call. I wouldn't reccomend going too lean as you may get pinging and cause damage under load. In saying that I jet my bikes on the lean side on the bottom end because I like clean crisp running and find the 4 stroking annoying. Its taken me quite a bit of testing to get the right diameter needle to give clean response without losing too much torque too. At around 1/4 throttle you are really getting into the clip position too and the half clip differences can make a big difference fine tuning it all.

when you say four stoking what does that sound like?

 

[Jakobi]

Firing every other stroke. Blub blub blub. Open the throttle more and you get the brrrr.. back it off.. blub blub blub... Wick it wide open.. BRAAAP!.. or if its too lean when you wick it it'll goo Buuuhhhhhhh WAAAAAAHHH!!

Dig those sounds

You will expect some light burbling when the engine isn't under load or it will be far too lean when under load and lack balls.

 

[nato]

I like to run mine a touch rich down low so listen to this and its what Jake means by blub blub blub hahaha.



Its clean and crisp everywhere except the pilot and i like that.


http://www.youtube.com/watch?v=o-PwnLrO4MI

 

[Jakobi]

Yep! Thats fine with a bit of blub blub. I'm like nato. Not overly rich on the bottom. Its gotta blub at light throttle but notice how quickly it cleans up if he rolls it on or puts load on it.

http://www.youtube.com/watch?v=5Juxzlo9DVc&feature=relmfu

In this one you can hear at slow speeds and light throttle mine burbles a bit too. Once you turn the throttle it cleans up quick.

 

[GMP]

The bikes make best torque off the bottom and acheive max engine life a little rich, plus you then have a buffer if conditions change to load the engine heavy (steep hills, deep sand, etc). Its important to test under load, up and down the road is not a good test. Too lean can seem really nice on the stand or under light load, really snappy off the throttle, but get it on the side of a mountain and all that snap is gone and you have flat power.

Don't get hung up on tan plugs and dry silencers. If you want that get a four stroke.

 

[Jakobi]

The bikes make best torque off the bottom and acheive max engine life a little rich, plus you then have a buffer if conditions change to load the engine heavy (steep hills, deep sand, etc). Its important to test under load, up and down the road is not a good test. Too lean can seem really nice on the stand or under light load, really snappy off the throttle, but get it on the side of a mountain and all that snap is gone and you have flat power.

Don't get hung up on tan plugs and dry silencers. If you want that get a four stroke.

Nothing more true than this. I have been there and done that myself. There is no joy in making your 300 run like a 125. The same principles apply with the gearing (regarding engine load). As the gears go higher so does the load so ideally you want to test your engine for response on an incline in 3rd gear or higher.

This is the weakness in carb design that it can't adjust for engine loads or environmental variables and where EFI shines brightly. The benefits are that if you manage to get a blocked jet on the trail the carb is much easier to deal with.

 

[farmerj]

Its clean and crisp everywhere except the pilot and i like that.

It's great to know that it's possible to like the "off-idle blubbering," that has always driven me "nuts"! I suppose I just need to spend more time twisting that thing on the right side of the handlebars - but invariably, we come off the fireroads and into singletrack, and it seems like I spend a lot of time playing around at low throttle openings...up then down again...

Those are great responses, thank you.

If you want that get a four stroke.

I just might (kidding) - but that doesn't work, either. All of the 4-S I've ridden lately "sign-off" abruptly at stall speed, and I dislike that more.

I believe what you're saying, GMP. I just got some larger diameter needles, so I'll see if I can bring the blubbering down a little bit and be careful about going too far.

Jeff

 

[Jakobi]

If you have a play with a few different needle diameters and pilots you'll soon feel the effect that they individually have on the bottom end and what it feels like when the torque signs off.

Everyone speaks about using the pilot to determine response up to 1/4 throttle, and it does effect that range, but it is in conjunction with the slide and needle diameter. I have had the best success by using the pilot to set the idle up and just off idle. The needle diameter then has a more pronounced effect at small throttle openings ie 1/8th throttle.

For example I can use a 35 N3CH#3 178 and the bike will hang idle and be hard to start, lack torque, and still burble up at part throttle. Moving to a 38 N3CH#3 178 the bike will now idle, run torquey, but still burble a bit more than I like. 40 N3CW#3 178 and the bike only has a very slight burble at part throttle light loads. Torques, grunts, idles, perrfect. Moving to a 42 N3CJ#3 178 and the bike runs well but lacks a bit of the punch and grunt off idle. Occassional hanging idle comes back when riding goat trail in the lower rev range. 45 N3CJ#3 178 rips again, but now supplys too much fuel to idle as well and start as easy. Bit of excess burble but clears up immediately. Above 1/4 throttle they all run the same, and thats for my 250. For the 300 the 42 and the J diameter worked better and it actually liked a leaner needle position too. All with AS2 carb and #7 slide.

It really is all trial and error though and finding out what works best for you, your style, your conditions and bike, and where you draw the line at 'good enough'.

 

[BryanMcc]

I guess the noise I had I question happens both when I get off the gas like coming down a hill no clutch it fires intermittently, is that what you would call four stroking? Also it kind of blubbers at very low load with low throttle openings. Sound like a rich pilot? went from a 42 to 40, not much change. Wondering if it could be my needle. JD red in middle clip. Takes throttle instantly and runs clean, so I hesitate to go leaner on needle.

 

[GMP]

Sounds normal to me, I'd run with it for now. Two strokes will always stutter or "4stroke" under no or low loads when jetted correct for normal loads. That was my point before, don't get hung up on this as a parameter for jetting. Basically you want the bike to have good response and torque UNDER LOAD, without loading up in the woods. Forget about everything else. With a lean dia Suzuli needle I can make my bike respond off idle like it has no flywheel under no load, but it sucks on the tough trail here. So I'll go one step more and say if its crisp and clean with no load its too lean. I guess if you ride all flat easy trails thats fine but I suspect you don't.

Find a steep hill or some sand to challenge the motor, that will tell the true story.

 

[Jakobi]

I guess the noise I had I question happens both when I get off the gas like coming down a hill no clutch it fires intermittently, is that what you would call four stroking? Also it kind of blubbers at very low load with low throttle openings. Sound like a rich pilot? went from a 42 to 40, not much change. Wondering if it could be my needle. JD red in middle clip. Takes throttle instantly and runs clean, so I hesitate to go leaner on needle.

A well jetted bike will fire occassionally on decelleration. Its normal. I found going richer will make it do it more often and make it more of a surge or tangish sound. This is different to 4 stroking though. 4 stroking is the stuttering or blubbering and as Glen has said, cannot be avoided under low/no load without falling too lean under a load. I do my jetting tests through some tight single with decent hills. Walking pace and use 2nd gear to make sure it can grunt from a stand still and still pull well. I then follow up with some 3rd and 4th gear up hill runs. Also my previous post was in relation to needle diameters which are only effective on the straight section of the needle. Up to 1/8th throttle only. Moving a full clip position to influence this throttle range is a crude approach which will no doubt result in the bike feeling flat and lean somewhere else in the rev range. JD offers 2 different diameters only. Red and blue.

Also in my videos if I'm not on the throttle its usually closed. Coasting at part throttle at a constant speed and no load on the engine it will burble away as much as any other.

 

[farmerj]

All very helpful.

Jeff

 

[firffighter]

Hey Jeff,

Thought I'd throw in my .02.

I messed with jetting a lot with the '03 EC250 and decided that living with a blubbery down low was just the way it was going to have to be. The feeling was that going down to a lower pilot would result in too lean and cause problems.

My brother who also owns an EC250 decided to try a 38 pilot last year. He was hooked! It really tranformed the bike into a singletrack killer. Rather than tha blubbering down low, it is now crisp and delivers smooth power right from the get go. This allows you to truly run a gear or 2 higher and still get snap when needed.

He ran it all year and checked his clearances this past winter. All in perfect shape with no evidence of things being too lean.

I changed my jetting this year to a 170 main and 38 pilot and absolutely love it. No blubbering, no hestiation. Just smooth crisp delivery throughout.

Others in the NW have run similar jetting as well.

Happy Harvest!