1986 More Midrange?

pkenney · Post by **pkenney** » 08:56 am Jun 14 2015

Finally got my 86 into the woods yesterday after a long rebuild.
Trails were slimy after an overnight rain so it was hard work for someone who hasn't been in the woods since 93.
The bike ran good at low and high rpms but had a pretty bad flat-spot in the midrange.

I remember reading on here that these bikes aren't known for midrange but also that there are ways to improve it.
Where is the best place to start tuning?
I remember reading ignition timing can change the power delivery as much as carb tuning.
I have stock pipe, DG silencer, Boysens, Unifilter, needle all the way down, stock jetting.

Thanks

kawagumby · Post by **kawagumby** » 11:55 am Jun 14 2015

My bike has no weakness in the mid range.
So you're saying the needle is full lean?

If if has good grunt and good rev out but less mid-rpm power, you will not get better results with timing adjustments, IMO, as the system already provides good timing at both extremes.

Usually low end grunt is associated with more conservative throttle action...quarter, third... top end is often associated with full throttle or close to it....so your pilot, air screw and main jet are probably OK.
if that is the case...the throttle mid-open area may be the culprit.

Try going richer at the needle for a start. Jetting makes a huge difference on relative power, throttle settings and rpms.

pkenney · Post by **pkenney** » 03:14 pm Jun 14 2015

Thanks for the reply and suggestion.
I arrived at that needle setting in my back yard - seemed to work best but couldn't really give it a good test.
Speaking of needles, one of the organ-doner KDXs I bought had a 6DP1 needle instead of the 6FL52 which I believe is stock.
Anyone know anything about this other needle? I have not been able to find anything on that needle.

Jaguar · Post by **Jaguar** » 04:33 pm Jun 14 2015

try a R1174K/2AFKQ needle and advancing the spark a bit.
also an iridium plug with a wider gap helps.
also replacing the stock high voltage coil with a Honda CR coil which puts out more voltage.
also lathing down the head for more compression.

Post by **KDXGarage** » 06:23 pm Jun 14 2015

a Keihin needle in a Mikuni from a 1986???????????????????????

pkenney · Post by **pkenney** » 09:16 pm Jun 14 2015

Is the 6DP1 a Keihin part or the R1174K/2AFKQ?
The 6DP1 is slightly longer than the stocker and has a different taper.
It looks like it would lean out the mixture at partial throttle which is where i was thinking I needed to go.
I might give it a try to see if it works, someone before me was using it.

I already have an Iridium plug and might mess around with the timing if I cant clean up the jetting.

Jaguar · Post by **Jaguar** » 02:54 pm Jun 15 2015

Jason you are so right. sorry for that slip up.
I just now did a quick search for info on your 6FL52 needle and came up with no results. If you want to find a leaner needle then first you need to use a digital caliper and measure its dimensions and then look at this chart:
http://www.jetsrus.com/a_jets_by_carbur ... ikuni.html

pkenney · Post by **pkenney** » 12:42 pm Jun 21 2015

Yay - it's Fathers day and I finally get some time to revisit this.
Happy Fathers day to all the other Dads on here.

I am having a hard time noticing any difference between needle positions (top to bottom) so I'm going to look into the jetting.
Float height looks good too and the timing is aligned right to the mark.
I have a seen recommendation for one size up on both the pilot and main so will contact jetsrus and get an assortment.
I'm starting to wonder if it is a characteristic of this year KDX.
It seems to me like it does not want to be on the needle at all, good pull at the bottom - flat flat flat - then cleans out and runs strong.
I have an 82 IT175 with very similar power delivery (except no bottom), should the KDX be better?

Thanks the input

pkenney · Post by **pkenney** » 04:53 pm Jun 27 2015

6DP1 needle solved it!

I ran out of options on the jetting with nothing making much of a difference at all in the midrange.
I am storing a buddy's mint 87 and decided to try his carb on my bike but it acted the same.
In fact his bike had the same stagger through the midrange so I was starting to think I was expecting too much from an old bike.

Just as a last try I put the 6DP1 on my bike and what a huge difference, very linear power until the top end hit - no flat spot.
330Main/30Pilot/6DP1 clip P3/Uni Filter Works for me!

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