CC, that second sweet spot...again

[bradf]

CC, lemme give you the details first on the RB on my 220:
42 pilot, 152 main, CEK 3rd. AS shipped 7/8.
Ron shipped with a 40, but I have been riding in 38-45 temps and put the 42 in. Three times now I have started the second sweet spot search @ 2 1/2 and felt (heard) what I think is significant pinging on decel. At this point 3rd gear roll on at slow speeds had a bog. Adjusting in by 1/16ths I have consistently arrived at 1 3/4 to 2 turns out. At this point there is no decel pinging sound and the 3rd gear roll on (including 3rd gear starts!) is smooth. I think I remember Wibby saying he had set his to 1 1/2 and had great results. My questions to you is this:
Have you heard pinging when the AS is too far out?
Is the seat of the pants smooth 3rd gear roll on the point that we are to achieve? If so I have found it.
Is the bog (hesitation) during roll-on the tell-tale sign of lean?
What is the air speed velocity of an unladened swallow?
Thanks CC.

[skipro3]

bradf:
I wonder if you are at the "second sweet spot" at 1 3/4-2 turns out and that the first sweet spot is at 3/4-1 turn out on your bike? Have you tried an air screw setting of less than 1 3/4-2 turns? I have the Air Stryker RB modded carb and was trying to find the 2nd sweet spot on mine this weekend with about the same results. I didn't try a richer A/S setting because I didn't think of it until right as I read your post here.
I am running a 38 Pilot and my A/S setting is at 1 turn out so maybe I don't have the first sweet spot with that lean of a pilot.
I'm not trying to hyjack your post, just curious on any attempts you may have done to go richer on the A/S setting from stock.

Also you asked if the third gear rollon is what the point of the exercise is. To my best knowledge the A/S adjustment is to set the point of low engine speed / one eighth throttle response. The test is done in 2nd gear at a slow, almost walk pace with throttle off. Wick the throttle to 1/8 and hang on. The bike should instantly respond on the first sweet spot. Choppng the trottle and wicking to 1/8 repeatedly will feel like riding a bucking bronc, the bike will be leaping and snapping with each twist. Hold the throttle at 1/8, and the front wheel should easily loft with no bar pulling or sitting way back on the saddle. You will know you are NOT on the sweet spot when there is any bog, hesitation or need for engine rpms to build before the hit ocurrs.
Thanks!

[cicone]

[quote="bradf"]
What is the air speed velocity of an unladened swallow?

African or European?

[bradf]

Ski, my first AS "high RPM" normal spot is about 7/8 out. This is just a modified PWK, not an Airstriker. I think that Ron had it set up for an outside air temp of lets say 60 degrees which would mean the 20 degree colder I am riding in needs richer. I definitely LOVE the way the engine responds at this second sweet spot. It is everything CC said it would be. Tomorrow I put on my DF III's. Next mod will be the EFM auto clutch. Cicone: Well, I uh, I dunno...WAAAAAAAAAAAAhhhhhhhhhh

[canyncarvr]

CC, lemme give you the details first on the RB on my 220:
42 pilot, 152 main, CEK 3rd. AS shipped 7/8.
Ron shipped with a 40, but I have been riding in 38-45 temps and put the 42 in. Three times now I have started the second sweet spot search @ 2 1/2 and felt (heard) what I think is significant pinging on decel. At this point 3rd gear roll on at slow speeds had a bog. Adjusting in by 1/16ths I have consistently arrived at 1 3/4 to 2 turns out. At this point there is no decel pinging sound and the 3rd gear roll on (including 3rd gear starts!) is smooth. I think I remember Wibby saying he had set his to 1 1/2 and had great results. My questions to you is this:
Have you heard pinging when the AS is too far out?
Is the seat of the pants smooth 3rd gear roll on the point that we are to achieve? If so I have found it.
Is the bog (hesitation) during roll-on the tell-tale sign of lean?
What is the air speed velocity of an unladened swallow?
Thanks CC.

First off (the disclaimer): I don't know of anyone that has experimented with and found this #2 spot on a 220. Jim Crenca is the only other rider (whose name I recall for sure..there was one other rider) I know of that has looked for and found it..and he has a 200. Most others that have at least considered the idea have gone along the path of, 'I set the airscrew to 2 1/2 and it didn't work, so I put it back.' That is not at all conclusive.

I have not found any pinging present with adjustment of the airscrew alone. There is pinging in my bike, but it isn't goverened/related/affected by the airscrew. Mine (pinging) is a result of the porting from frp and I have yet to get rid of it with any jetting combo. I CAN get rid of it with Trick114, but then the bottom-end response of the bike takes a huge and unacceptable ding. **edit** Toluene @ 5% takes care of it..both detonation (gone) and bottom end (wunderbar!)! **edit**

I question that what you're hearing is 'pinging' on decel. I understand the process...say a hard most-of-the-throttle run generates a good deal of heat, the pipe starts 'working', then you cut the gas ending up with a lot of heat and not much fuel. Still...is it a 'pinging' as you would hear,say, in a car that is running too low octane fuel? The 'marbles in a coffee can' sound?

Even at 38-45º I think you should give the 40 a try. Did you change to a 42 for a reason other than it being cooler? As ski says, it's reponse that's the issue with the pilot/air screw. Changing it 'just because' it's cooler isn't necessarily correct if you aren't changing it from a known correct condition. Unless you are having problems with very high idling (as in a runaway sort of thing) on a choke cold start, your pilot jet is not too small.

Your 1/16 changes are on either side of the 2 1/2 spot? Not just down, right?

As far as the 3rd gear roll-on part....on my 200 there is a definite change in 3rd gear pull when the air screw is set to the (approximate) 2.5 out. It is much harder pulling in 3rd and there is much less tendency for the front end to jump up when I'm on uphills in lower gears. It will come up if I want it to (jump a rut, a root or air it out over some acceleration whoops), but it's a much more controlled and controllable process than it is with the airscrew down in the 1+/- (call that 'normal') range.

Generally a bog or poor response when tuning the air screw/pilot circuit for 'low engine speed / one eighth throttle response' is a lean condition.

But...I get excellent throttle response in the above noted throttle area in BOTH #1 and #2 air screw positions. I am not sacrificing 1/8 throttle response for a better 3rd gear 'roll-on' pull.

That was true before the porting work and Ron's head modification. I don't know that was true on my modified owm PWK. I don't recall discovering this #2 thing before I put my air striker on. Jim C. has a modified oem PWK and found it to be true on his bike.

If you're game, I'd suggest trying all of this with the 40 pilot..and the CEK on clip 4. Again...that's where my 200 would be with the CEK this time of year and I do understand that you have a 220. While I a do understand that the 200/220 don't respond the same to every setting/mod/jetting-sequence I certainly don't know which mods can be equally applied to both bikes.

****
I want to hear how you like the DF3! ..or not

[bradf]

CC, I just installed my new DFIII. I also changed the pilot back to the 40 as suggested. It's too cold to ride but I'll let you know how everything works when I can ride.

[canyncarvr]

Hhhmmmm...too cold to ride....

Am I talking to Wibby under another name? ;)

It's purty, ain't it?

I was reading a write-up on 1 dir racing last week (say 'wonder racing'). They made some obvious pokes at MotoTassinari, saying, (paraphrase) 'There should be no airfoils, air-formers, guides or anything else restricting air flow in a well designed reed cage.'

Keeping air 'smooth' is always an advantage. Dumping it from a nice round hole (carb) into a rectangular thing with lots'a sharp edges all over the place don't make no sense to me. But..you know what? They din't ask me what I thought! ;)

The DF3 is pretty smooth, though. Much moreso than the II is!

[bradf]

CC, you are right. The pinging is actually popping. Pinging would occur during throttle on. It is normal to go somewhat lean on decel as the the vacuum is quite high at that time. Has anyone else heard this decel popping? I think I am overly concerned about nothing (fear of lean). That popping sound is what chased me away from the 2 1/2 turns out and got me to adjust to 1 3/4 out. I compensated by richening the pilot to eliminate the momentary lean. I am satisfied that the pilot, main and needle are spot on. Plug and seat of the pants are very happy (sounds like I am in San Quentin doesn't it). I am going to do this all over again beins the DFIII is in. I will let all yall know what the outcome is.

[Indawoods]

Decel popping is backpressure release. Thumpers do it all the time because of the valves, I would check to make sure your pipe has a good seal to the cylinder (o-rings), check your compression and check your seal on the reeds (are they closing all the way back down) w/DFIII no worries. It shouldn't pop.

[BJH]

[ Mine (pinging) is a result of the porting from frp and I have yet to get rid of it with any jetting combo. I CAN get rid of it with Trick114, but then the bottom-end response of the bike takes a huge and unacceptable ding.

CC, Just a thought, but have you tried using double base gaskets to increase the squish band area to see if that will get rid of your pinging? If that works you may want to ask Ron to "flat top" your piston so you can avoid the possibility of an air leak from the double base gaskets.

From my readings on two-stroke engine theory...The pipe effectively supercharges the intake to the cylinder from the previous exhaust pulse. Therefore allthough your "static" compression (the volume of the cylinder from BDC to TDC) ratio may be correct. The "dynamic" compression ratio (the actual air / fuel charge volume from BDC to TDC) has been improved greatly from an very efficient pipe, the head mod, and the easier breathing from the porting.
Am I all wet on this or do you believe it has merit?
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DIGITAL VAPORIZER

[canyncarvr]

Double base gaskets will have no effect on the squish band. It will have an effect on combustion pressures/compression #s and ratio for sure. The head has been modified by Ron. That was done after I put together the frp ported topend in an attempt to rectify the problem. It helped, but didn't completely get rid of it.

The supercharging effect of a 2-smoke is indeed part of what makes it run so well. Certainly static measured pressures have nothing to do with what's going on when the scavenge/ram effects of the engine are going on 'real time'. An improved-breathing engine will effectively increase dynamic compression and certainly may make them too high. That's what happened in my case, anyway.

A BTW...I didn't have the cylinder ported because I was looking for more power particularly. The plating on the cylinder was damaged and it needed to be bored/replated to fix it. No better time to have the thing ground on some. If I knew then what I know now, I wouldn't have done it. The oem cylinder worked just fine as it was. Like skipro said, I could probably get the thing exchanged for an oem cylinder from frp but I haven't bothered bothering with that. Too much bother!

[BJH]

[quote="canyncarvr"]Double base gaskets will have no effect on the squish band. It will have an effect on combustion pressures/compression #s and ratio for sure. quote]

Ok so in theory using double base gaskets or flat topping the piston could reduce your compression and stop the pinging?
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Marijuana News

[canyncarvr]

That is true. A double base gasket will reduce static (and dynamic) compression figures. 'Flat topping' (I guess that means removing some metal) will reduce the same in the same way.

It would tend to reduce any pinging there was due to excessive pressures.

But....

It also changes the timing of the whole thing. The transfer ports, the exhaust port, the intake port...all of them are raised. Doesn't seem like any kind of good plan to me. Raising the exhaust port is something that is generally good for higher rpm ops (thus things like KIPS and servo controlled power valves on RZ motors). Decreasing compression will lessen bottom end response. I don't know what the effect is of raising the other two..intake and transfer ports..is.

If I had to reduce compression I'd have Ron change the head. That would keep all the 'valve' timing (port stuff) the same. As it is the pinging is minimal and not really a problem. It might be of note if I was concerned about my bike being a sand machine..but..hey! That's why-the-hell I bought a BANSHEE fer crin' out loud! ;)

The only time I have to worry about my pinging problem in the woods is when I'm trying to dust/keep up (either/or depending on how he's doing that particular day) with my CRF250-X riding buddy! I can't keep up with him in the woods (couldn't if he was riding a skateboard..he's good!) and the only time we're WOT kickin' some serious butt is when we're on the way back from the Foots Creek Deli (some fish-n-chips and a beer...a cheap 22 oz'er) headed back up to Irongate. None of which means anything to you I'm sure...but when you come out here for a 'tour', keep that in mind! ;) BTW, a KX500 rider on a 'tour' with us said, 'I couldn't ride a 200 like that!' Well...that's how I choose to remember what he said, anyway. ;) If YOU know diffrent...don't disabuse me of my own particular fantasy, OK?

I'm no kdx magician. I enjoy my bike as it is..even with the frp induced dribbling (I'll get that goo taken care of eventually!! Really!!!) and some detonation from time to time. The bottom end of the thing is perfect. I remember when I changed from a -30 to a -35 everytime I changed from open to woods riding. Don't do that no moh. My 2-hunny has all the cajones it needs for any tight woods situation..even with a rev profile pipe.

OK...guess most of the above is an apple martini induced rant. A lot of those of late............ Call me disillusioned or some such.............

So...sue me!

[m0rie]

OK...guess most of the above is an apple martini induced rant.

Ah, listen up folks...its not just a rant. Its an apple martini induced rant!

-Maurice

[Indawoods]

Double Head gasket would be cheaper and faster to try.... ifn' you were going to try. I almost did it on my now ex-infamous KTM 250 EXC.

[BJH]

Just needling you for learning purposes CC. It seems everytime I bug you enough to say something I learn a little
I'm not really very fast myself and I'm surely not a wrench expert. That's one of the reasons I'm in here. Plus it's a good past time while I drink beer.
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Mexico city hotel

[canyncarvr]

.....:(....another drunken kdxer...

[canyncarvr]

Double base gaskets will have no effect on the squish band.

This needs some clarification. The 'squish band' as defined by machined clearance in the head is what I was referring to. Obviously the installed height of the cylinder won't have anything to do with whatever clearance/angle/etc is in the head.

But...the piston crown does make up the bottom of that configuration when things are squished.

My comment was to be taken rather specifically in regard to head shape and base gaskets. Squish band adjustments are generally made to the head..not the piston. It could easily be argued that, considering the piston is part of what makes the shape, that what I said was wrong. OK. I'll give you that. Certainly I wasn't clear on the (teensy) point I was trying to make.

....how muddy is that??

http://www.muller.net/mullermachine/docs/squish1.html

When you folks know better...you'd better call me on this crap!

[skipro3]

BTW, a KX500 rider on a 'tour' with us said, 'I couldn't ride a 200 like that!' Well...that's how I choose to remember what he said, anyway. ;) If YOU know diffrent...don't disabuse me of my own particular fantasy, OK?

You remember right. I was with you guys that day and was dogging it back up as I was digesting my fish-n-chips. Mainly because I didn't want to drive all the way back home when I crashed. And at the speeds you guys were riding, I would have. I have a dreadful fear of head-ons on fire roads.

Double Head gasket would be cheaper and faster to try.... ifn' you were going to try. I almost did it on my now ex-infamous KTM 250 EXC.

I've done this to "tame" bikes that were too much for my abilities at the time but it was way back, like a 74 Bultaco or 78 Husky. Not a wimpy 250!

Just needling you for learning purposes CC. It seems everytime I bug you enough to say something I learn a little
I'm not really very fast myself and I'm surely not a wrench expert. That's one of the reasons I'm in here. Plus it's a good past time while I drink beer.

AMEN, that's me to a tee!

[canyncarvr]

A btw...I didn't mean to infer that I am fast. One ride with Marty (the CRFX'er) would prove that idea false no matter who was chasing him.

Wrench? I done that to my knees (both of 'em!) more than a few times. That's why I wear my Asterisk Cells all the time!!

ACLs? Who needs 'em!!