Installation of reeds=leaner jets.Why is this??

BucKat

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#1
As taken from Canadian Dave's Web Site =
"Addition of Boyesen reeds or a Boyesen RAD Valve will require you to lean the pilot and main jet one size and readjust your air screw."

Can someone explain why this is?

Thanks

Buc
 

CaptainObvious

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#2
Because the PWK carburetor works on a vacuum principle (I can go into Bernoulli’s theory if you like). By creating more vacuum through the carburetor, the carburetor responds by supplying more fuel.

Remember the strange thing about 2-strokes, the leaner you get the mixture, the more power you’ll make (to a point, of course).

After I had my engine ported this year I had to lean the mixture. At first this seemed counter-intuitive until I start to think about the theory behind 2-stroke combustion.
 

BucKat

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#3
Ah yes.....Bernoulli’s theory .. No need to rehash that old stuff...
Process instrumentation/flow dynamics 101..Been there done that..


I guess what I'm asking is......
1.Do the reeds respond quicker therefore the resulting vaccum is increased,,, thus a richer condition exists?

and secondly......a slight off topic but hopefull related question
2.If your KIPS was not fully open(open to the RESONATOR/closed to the exhaust) during low rpms ,,,could/would the same rich condition occur on the pilot circuit?
I noted that I had lost bottom end and had to turn my air screw out near 4 turns to get a 'decent' response.
Thought I had cracked reeds.Inspection proved they were ok..
Pulled the pipe off to have a look at the KIPS and realized that they did not ALWAYS fully snap open when manually operated.The main exhaust valve was not extending down fully( reducing the effective size of the exhaust port) and the right and left exhuast valves where slightly cracked open allowing flow through the sub ports to the pipe..
I have since fixed that and will test tomorrow..

Will post result tomorrow night.


I had no consistancy with bottom end pull or response.Sometimes it was lean,,,other times it was rich...Sometimes it pulled like a tractor,,,,other times I was nose diving over the hanlde bars when the power just wasn't there...

Prior,,,,I tried pulling the air box snorkel off and found the bike ran even richer....( but that's another story somewhat related. More on that later)..


Thanks for the info....The quest contines..

Buc
 

CaptainObvious

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#4
Since the newer reeds are stiffer they "snap" faster. This results in less overlap and therefor more vacuum.

The KIPS sure do sound as if they are causing your troubles though. If the drums are hanging open it will just kill throttle response. While not common on your bike, you might want to inspect the gears to make sure they aren't stripped.

Don't even bother changing your jetting for the new reeds until you resolve the powervalves. BTW, who's your compression?
 

BucKat

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#5
Originally posted by RV6junkie
Since the newer reeds are stiffer they "snap" faster. This results in less overlap and therefor more vacuum.
QUOTE]

Wonderfull...that's the kind of response I was looking for.....A definite,,,postive answer. :thumb:


My reeds are not new nor replaced...They are the orginal stock units....
I was just researching unknow territory in an attempt to resolve another problem I've incountered..That being the loss of bottom end and low end response.

My KIPS are fine and no gears are stripped...They work correctly however they did not snap fully open ( closed....take your pick..) during low rpm operation..
That was a result of re-assemble. This time I preloaded or tensioned the governor shaft before I put the gear on ...and then tightened it....See buykawasaki.com for details.
Now the KIPS valves snap fully in both directions..:yeehaw:

Tomorrow will tell all..

Thanks for all the advice and help.


Buc

I'll let you know how tomorrow's ride goes.

P.S.
Compression is good...As far as I know.I'll check that soon.
My 90 200 gave me great grief with respect to the KIPS.
 
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BucKat

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#6
Alrighty,,,,,,test ride proved that the KIPS was the problem causing the loss of bottom end.
A/S set to 2 turns out,,,( very,very humid day ) and I have re-gained the tractor like,,,crackl'n crunch the KDX200 is soooooo known for....Yes,,,,,,,,,,even though I have the rev pipe on....

Whooohooo lets ride...

Buc
 
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#7
Hey there BucKat,i see you have a 220,would you mind telling me what jetting set up you use that works for you, cheers :thumb:
 

BucKat

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#8
Sure,,,no problem.But keep in mind,,,,what works for me may not work for you..

Current set up...well yesterday anyway,,, is as follows.
This is for current temps of approx 20-24'C with varying humidity.

FMF rev pipe
stock needle --- 3rd clip position from the top
40 pilot
a/s 1.5 to 2
145 main

I will change the pilot,air screw setting and needle position depending on the humidity....
On a really dry day with temps just below 20'C,,,I have been known to bump the main up as well..
The humidity changes greatly from day to day in my neck of the woods.


I have just installed my new torque pipe and will test that tomorrow.Jetting should not require changing.
I also have a CEK needle kicking around that I may be temp'd to try aswell.


Buc
 
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#9
re: 'Jetting should not require changing.'

a change from my rev (-30) pipe to my torque (-35) pipe with no other changes will result in a fouled plug in short order.

Jetting certainly will need to be adjusted.

Besides the vacuum issue keep in mind that a 2-stroke has a tuned exhaust system that is designed to scavenge and pressurize the combustion chamber at a desired rpm band. How well (or not) that system works will have a large effect on what jetting is required.

It doesn't all suck.

....a reference to negative pressures.......;)


An aside pick.....reeds don't 'increase' vacuum. Any vacuum results from piston movement. Said vacuum can be applied earlier/later/faster/slower to the carb based on reed design...but reeds don't 'make' vacuum. Yeah...bad reeds can certainly effect the piston's ability to make vacuum (like when they leak). Still...they don't make vacuum.
 

BucKat

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#10
CC.....The humidity here,, in my neck of the woods,, has drop'd dramatically over the last week...hence jetting may not be required....Guess I should have stated that in my previous post.
In fact,,after the installation of the -35 pipe,,,,,I was still running a bit lean.

I found the installation of the -35 pipe( with a 13-47 sprocket) had a similar effect as my -30 pipe with a 12-47 sprocket combo.
Yes the power/torque curve was moved but,,,,,in both cases there was an increase in lower end and,,,,the top end fades out quicker.
Interesting stuff...Must tweek more,,,must play more..dang,,,,,,I'm obsessed.


Agreed.... reeds do not create vaccum... but I do buy into the idea that they will help preserve the created vaccum.

Buc