Plug Chop

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TWMOODY
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Plug Chop

Post by TWMOODY »

After reading Indawood's old post on Jetting a carb I rejetted today and
am not sure If I am a tad rich on the main.
I tested at 40 degrees/50% humidity/800ft elev/air box open/fmf rev pipe/TC2/VF3, No other mods and started with OE 160/48 jets.
Started with
AS screw 2.5-3 turns to start and only noticed and big change under 1 turn
Replaced pilot with a 45 and retested air screw still at 2.3 and no notable change. Changed needle position from 3 to 4 and then to 2.
4 seemed to chug/knock intermittently just off idle and 2 seemed to bog
occasionally.
Still seems to me that with 2.3 turns I may need a 42 but my plug came out pretty clean after riding on a plug for about 30 minutes.
I have no bogs or complaints except plug fouling before rejetting.
I did two chop tests and I think they are borderline rich but would like
an experienced opinion.
I am also thinking of replacing the needle and have read some of the threads on the CEK/DEK I think, any suggestions ?
I posted the plug chops here:
http://www.kdxrider.net/forums/modules. ... _album.php
Last edited by TWMOODY on 11:13 pm Dec 27 2006, edited 1 time in total.
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Indawoods
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Post by Indawoods »

The CEK and DEK only work with the RB modified carbs. You will want to use a CEL or DEL needle.

I have never had a use for a 160 main jet or a 158 for that matter. The fattest I have ever used is a 155.

You pilot at a 45 is the smallest I would go since temps are low but would try a 42 when temp warm up.

The plug chops are acceptable IMHO.
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Post by Jeb »

I don't consider myself experienced yet I feel rather confident that you aren't going to hurt anything - and probably note a performance improvement - if you go down one size on your MJ.

And don't be surprised if you go down two (if not you'll wanna check again when it warms up).

How'd you do the chop?
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Post by TWMOODY »

Thanks Inda
whats (imho) and your saying the chops are acceptable so leave the
160 in you think?
Also I sent you an e-mail yesterday did you get it?
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Post by Indawoods »

IMHO = (In My Humble Opinion)

Yes... I would leave the 160 til temps warmed up. A 158 wouldn't hurt it eiither though....

Yes... I did get your email, I replied this morning. Did you not get it?
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Post by TWMOODY »

Chop was done on the airport runway behind my house, the township
decided to grade my road today and it gets pretty harry at about 40mph.

Wide open throttle from 1-6 gears and about 6 seconds in 6th
pulled clutch/let off throttle/kill switch all at once
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Post by TWMOODY »

Nope didn't get it.
Was just wondering if the Debra thing was legit.
With all the **** going on on line these days just making sure
it was cool
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Post by Indawoods »

Yep it's all good Tom! :wink:
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Post by Jeb »

RE: chop conditions -

THANKS!

I was interested because of how distinguished and clear the carbon ring is.

If and when you do go down any on the MJ size it'd be useful to comment on how that ring changes when you do the next chop (a picture would be worth a thousand words!!)
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Post by TWMOODY »

Jeb wrote:RE: chop conditions -

THANKS!

I was interested because of how distinguished and clear the carbon ring is.

If and when you do go down any on the MJ size it'd be useful to comment on how that ring changes when you do the next chop (a picture would be worth a thousand words!!)
I will be sure to do that Jeb !
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Post by canyncarvr »

Re: 'I think they are...rich...'

Yep.

Re: '..you aren't going to hurt anything - and probably note a performance improvement - if you go down one size on your MJ.'

Yep.

Re:'And don't be surprised if you go down two.'

Yep.

You noted a lot of changes for the two pics that are labeled with the same jetting. ?? What about all the other setups?

Do take note of Inda's comments on needle choice.

I'd drop the pilot to get the airscrew down from 2.3.

Re: 'I have no..complaints except plug fouling....

Considering the bike to be mechanically sound, there is no reason to foul a plug ever. Lug it around all day, go downhill for ten miles..no matter.

What is your filter oiling procedure? OEM filter?

IMHO and all that (which I take to be 'HONEST' opinion....it's both ways. Slightly different connotation I guess...).

You're on the right track. Kudos to you for gettin' it done!! What you learn in the process will be an invaluable tool now AND in the future..this bike AND any other bike. You are putting yourself MILES ahead of most other riders that don't take the time to do the kind'a tedious job jetting can be...let alone learn anything about their bike.

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Post by TWMOODY »

Thanks CC
Both plug chops were done at the same time to make sure they were uniform on both tests.
Amazing you can't see any carbon on the porcelain until ya cut it apart.
The filter is a K&N clean and lubed just till it turns red.
On the AS screw and pilot jetting the only real difference I noticed
adjusting the AS was under 1 turn in ran kinda crappy.
Over 1 turn to 3 turns or so not much difference.l
If I lower the pilot to a 42 I would assume I would also need to drop the
needle clip to the 4 position?
You ever hear of a 1/2 throttle chop test?
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Post by Mr. Wibbens »

I kinda confoosed :rolleyes:

I'm no jetting guru, but...

You did a WOT plug chop, which (IMHO) checks the main jet, but you are changing and fiddling with the other circuits and not the main? well so far at least

re: 'You ever hear of a 1/2 throttle chop test?'

Yes, somewhere there's instructions on how to check all the circuits of the carb with plug chops, I believe it's in here http://justkdx.dirtrider.net

I've never done it though, I'll test the main once in awhile but the rest is pretty much seat of the pants
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Post by canyncarvr »

I just agreed with what was already said. Being my basic agreeable self!

:hmm: OK...maybe it was something else.....

Your filter sounds good. I've never been a fan of the (with foam filters) soak-n-squeeze method.

Wibby is right. You can do a plug chop test on any circuit you want.

I didn't check CDave's site to check if it's still there..but mark your throttle so you know where the different ranges of the different circuits are (say, use masking tape and a felt tipped pen). Run the test the same way for however many ranges (one at a time) you want to.

Putting in a 42 pilot does not necessarily relate to having to do a clip change. One does not follow the other. Maybe you will end UP there, but they aren't tied together.

A BTW...but jetting from the top-down (main to air screw) and from the bottom UP (air screw to main) are both useable choices. Some prefer one method over the other. I know that a poorly chosen main can mess up the idle..so my personal choice is top-down. EITHER method will get you BACK to the same circuit more than once most likely. With a given setup (other jetting selection) you know that clip-4 is better than a clip-3 because you TRIED both in that setup.

A further aside..but the 5mm throttle slide does seem to work about as well as the rest of the OEM configuration...not too. Riders that have used a 6mm slide in an otherwise modified carb I recall were happy with it. Problem with that is the cost of a slide. If you're going to spend $50 for a slide, why not put that $50 toward get the whole carb modified?

Again, your process/method is good. You will get it jetted correctly I'm sure.

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Post by IdahoCharley »

>|<>QBB<
canyncarvr wrote: Wibby is right. You can do a plug chop test on any circuit you want.

I didn't check CDave's site to check if it's still there..but mark your throttle so you know where the different ranges of the different circuits are (say, use masking tape and a felt tipped pen). Run the test the same way for however many ranges (one at a time) you want to.

.
I agree with CC on this although many will say - only the Main can be checked on a plug chop. My opinion is that if you are doing a 1/2 throttle or 3/4 plug chop just be sure that your engine has some load on it. Running it on a 10 degree or better uphill area works for me.
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Post by TWMOODY »

I replaced the main 160 to 158 this AM and did 35 miles in tight hilly terrain 1-3 gear mostly at 40 degrees.
I noticed a slight improvement in WOT for the short seconds I could
open it up however after lugging around it sputtered the first time
I would crank up the revs then cleared up till the next time lugging
around.
I took it home at dark washed it up and fired it up and crapped a plug
10 seconds after starting.
Plug was loaded with carbon after todays ride and I started with a
fresh one.
I need to go down on my pilot from the 45 to a 42 I guess
and try again.
I did the tape on the throttle yesterday trying to get the AS and needle
adjusted.
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Post by canyncarvr »

This is about the time to maybe remember something...but I'm not having much luck. It was only six years ago...:hmm:

Anecdotally speaking (my experience) I do NOT recall getting my bike to run clean (re: 'after lugging around it sputtered the first time
I would crank up the revs') with the #5 (OEM) slide. I'm not saying I know I didn't, but that I don't remember one way or the other.

I know that issue was a PITA and it took awhile to get rid of it after I had my carb modified, but that was before a good bit of test-n-tune led the way to the C and D needles.

I remember trying to get a #6 slide and having trouble with that (got the wrong one twice)..before I knew the OEM PWK took an Air Striker slide.

How many KDXers on this board with an UNmodified carb with the #5 slide have no plug loading problems..say after long downhills or 'lugging it around'?

...or simply remember one way or the other??

Re: 'just be sure that your engine has some load on it.'

Obviously a plug chop is harder to do with the throttle under WOT, because of the load issue. You can drag the brake. For as long as it's necessary (to get a readable ring on a plug), it won't hurt anything. Make a habit of it though, and you will be changing pads kind'a often.

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