Flat Mid Range

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firsthere
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Flat Mid Range

Post by firsthere »

Hoping to get some advice a on flat mid range issue. Fresh topend, PC 2 pipe, AB lid removed CEL needle 3rd, 152M, 38P the rest stock. Elev 4000'

I finally cleaned up the bottom end and the very top RPM hits pretty hard, its just waiting thru the mid for things to happen. There is a slight surge when transitioning from the pilot to the needle though the bottom end is near perfect. I have been playing with the needle jet as of late and hesitate to go any richer as the CEL is a thinner needle as it is. After reading posts of other brands, some talk of advancing timing and others changing power valve springs. Possibly the air box lid is an issue. Kinda at a loss at the moment.
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bufftester
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Re: Flat Mid Range

Post by bufftester »

Mid range is going to primarily be the needle taper, which means having a bunch of different needles which isn't the cheapest way to go, but if you're looking for max performance there it is. An AS or RB modded unit might be a good upgrade option as well, but you're still going to need to tune them.
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rungrandpa
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Re: Flat Mid Range

Post by rungrandpa »

I stayed with stock timing. Air box lid removal didn't make a difference for mid-range for me.
I ended up with a handful of needles and spent some time experimenting. I ran a CEL for awhile.
I settled on 40P 152M and BGP (same as 1173 2.735) needle.
Not perfect but pretty good.
firsthere
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Re: Flat Mid Range

Post by firsthere »

I'll continue experimenting and do have a 1173 needle from previous KDX. The Air box is now taped with 2'' open in back. I may try opposite to the front of the box. Next would be try the old fmf turbine core , and or new stock reeds.
firsthere
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Re: Flat Mid Range

Post by firsthere »

As it turn out I only had the 1175 needle so I experimented with the CEL by lowering the clip to the 4th notch (which was counter intuitive to my thinking). This picked up the lower middle range significantly though still a bit flat in the upper range of the needle zone. I may try the lowest notch to see it that helps. I have never set a needle in lowest position before but assume it means It needs a richer, thinner taper. Would that be a BGP (same as 1173) ?

I also thinking possibly the main jet maybe affecting the upper part of the range also, maybe I'll try moving up to a 155 is first.

It's Funny how certain elevations and temperatures (probably moisture also) affected the power output. 4000', +-35f, shady mountain side it ran best in where currently setup. I could almost live with that but obviously its not always going to be the same conditions.
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rungrandpa
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Re: Flat Mid Range

Post by rungrandpa »

35 degrees and runs good means to me the bike is running rich at warmer temps.
1173 is BGP. BGP is leaner than CEL. CEK would be the next step richer, but running your CEL in the bottom notch is no big deal to try.
I run a 40 pilot. 38 bogged for me.
Jets are us --https://jetsrus.com/a_jets_by_carbureto ... 27-48.html
firsthere
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Re: Flat Mid Range

Post by firsthere »

Dropped the clip to the bottom, it runs even better! I knew the power was there, somewhere in the jetting. Still a little faint upper mid. I'll try going up to a 155 main. I had to open the airbox to a 2" opening across the entire back as the 2x2 stifled the topend completely. I'm still not ready to abandon the restricted airbox lid idea though. I remember my 89 and 90 had issues (never resolved) when the lid was removed.
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rungrandpa
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Re: Flat Mid Range

Post by rungrandpa »

I'm interested in your MPG if you get a chance to measure. When I jetted for max performance my MPG suffered enough for me to notice.
I was riding pretty fast, though, chasing my son around the desert.
firsthere
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Re: Flat Mid Range

Post by firsthere »

I would be glad to share that, prior to, it was getting about 30+ MPG on 70/30 logging road/trail. It maybe this spring though as winter is moving in. I know what you mean chasing the kid around the desert, riding with my son causes way more wide open throttle than I'm comfortable with. Luckily, I know the routes up here in Oregon so he has to follow.

After trying the 155 main, bottom clip on the CEL it was a little too rich. Sputtering and almost fouling plugs. I then raised the clip to the 4th notch and it seems that is where it will be for my winter setting. May still try the 1173 later on though.
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Re: Flat Mid Range

Post by firsthere »

I decided to have a look at the KIPS after it started running erratic following a couple of wide open session. The valve is occasionally sticking open and seems reluctant to move off the closed position which maybe affecting the midrange also. Has anyone dealt with this situation? My first thought is the copper coat spray on the head gasket may have gummed up the drum piviots on the head. As mentioned the cylinder was replated and clean along with the KIPS components. I also installed new seals on the cross shafts.
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Re: Flat Mid Range

Post by KDXGarage »

Check the bores of the subvalves, since you got it replated. Sticking was the cause of poor running for one guy I remember specifically.
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firsthere
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Re: Flat Mid Range

Post by firsthere »

Yes, I remember seeing overspray in all the PV bores prior to assembly. I greased the pipe side gears and cycled several hundred times and it seems much better. we'll see how it runs once hot, then pull the cylinder if the stiction pesists.
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