220 with a jerky throttle response

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220 with a jerky throttle response

Postby jbroom » 04:04 pm Feb 25 2008

i've got a stock '03 220 that i've had out on the trails 2 times now. that makes 3 times total that i've ever been out on the dirt, but i've been racing 2t and 4t road bikes for the past 4 years, so i do have bike experience.

my problem is that the throttle response seems jerky and unpredictable sometimes. i know this is kind of a characteristic of a 2t, but seems like it could be smoothed out. sometimes i'll get on the throttle and it'll lug along, some times it'll just flat take off. i understand the concept of the powerband on a 2t but i think this might have more to do with loading up at about mid throttle. i wasn't totally paying attention to it, so sorry that the details are vague.

any suggestions on what to do/adjust for this, or is it just me being a newb with poor throttle control? its ran pretty darn good otherwise, so i haven't even messed with the bike much yet. i'm not sure what size the jets are in the carb.
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Postby KarlP » 04:31 pm Feb 25 2008

I'd take a look at the jets, if only to get the numbers and know what you got in there. Same with needle and clip position. Besides, you may well dislodge a troublesome bit of grit.

In an open area it ought to pull clean, in gear, from idle to full throttle.

I've found it usefull to mark the throttle handgrip with 1/4, 1/2, 3/4 positions to help determine in what areas it is acting up. Its pretty easy , and unconscious, to figure out how to ride around an engine that is running poorly at certain throttle positions.

I find third to be the most revealing gear. Idle along in third and snap the throttle to 1/4. Pull clean? Try 1/2 throttle, same thing?

How's the air cleaner?

If you don't think it's running right, it probably isn't. You'll know when it is. :wink:
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Postby jbroom » 04:50 pm Feb 25 2008

thanks

i just realised i forgot a couple details. i took out the snorkle and cut the top of the airbox. judging from the rest of the bike, i'm about 95% sure that everything in the carb is stock.

the air filter might be dirty though. its due. too bad i don't have a spot near my house to test things out :? cops pull up as soon as i start it up.
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Postby canyncarvr » 05:16 pm Feb 25 2008

Re: 'sometimes i'll get on the throttle and it'll lug along, some times it'll just flat take off.'

The difference being....what?

Between when it's first started..and it's good'n warmed up?

Temp changes over the course of a day?

'Jerky and unpredictable' is not a 2T thing...it's simply a bad thing. Absolutely, it can be smoothed out.

Have to ask..you are familiar with a choke-cold start (4-stroking probably)..and that any throttle response judgement during that warmup timeframe is going to be skewed?

Karlp's right about the jetting part. You need to find out what's in there now.

A number of common problems other than improper jetting can cause twitchy throttle response: Orientation of the downstream intake air-guide (180º out), a KIPS issue are two that come to mind right off.

What's the reported history of the bike? It doesn't have a 'fresh top-end' does it?

There is some freeplay on the throttle?

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Postby Colorado Mike » 08:21 pm Feb 25 2008

sticky floats too.

While CC makes a good point about the KIPS, that requires a tear down to thoroughly clean. Tell us what premix has been used, and what ratio. certain oils are better suited to being glues in the KIPS. this is made worse by bad jetting.

Clean that carb out really well when you're doing the filter. Especially check the float action and the little valve that they operate. Better yet, make friends with someone that really knows jetting on a 2 stroke. Buy him a bunch of beer and spend the day tuning. You'll need a bunch of spark plugs and some jets.

Be mindful that screwing with the carb without RB's mods on it is mostly a huge waste of time. I say this cuz the difference in non-RB to post-RB makes you feel retarded for riding the thing without it. Better off just sending it out to him and get the thing worth your time working on it in the first place.
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Postby jbroom » 11:15 am Feb 26 2008

messed with the bike some last night. the air cleaner needed a cleaning, but it wasn't too bad. possibly bad enough to start causing what i was experiencing though.

the carb looked to be in good shape. i cleaned it up some anyways and had a look at the jets.

its got the stock needle - R1173L and is in the middle position. clip is 3rd from top.

main is 145 and the pilot jet is 42.

i've got a stock exhaust, no snorkel and half of the top of the airbox cut away. that sounds about right for texas to me.... thoughts?
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Postby canyncarvr » 01:11 pm Feb 26 2008

CM wrote:Be mindful that screwing with the carb without RB's mods on it is mostly a huge waste of time. I say this cuz the difference in non-RB to post-RB makes you feel retarded for riding the thing without it. Better off just sending it out to him and get the thing worth your time working on it in the first place.


:hmm:

So....what do you think? :wink:

I wasn't headed toward a KIPS cleaning..just a check to see if it's working.

What you list is OEM 220 jetting (right??..you BigBore guys?) While it can be improved, it's probably not too far off for Dallas TX.

Cable freeplay?

While you had the carb off was the time to verify that the downstream block is assembled correctly. No mention of it leads to the presumption that that didn't happen?

Observe:

Image

With the carb out of its boots you can look into the downstream side and tell easily enough if it's in backwards.

Note the orientation tab on the lower left? Yours is correct?

And, please, an affirmation regarding 4-stroking..what it is..and that it's NOT an issue in this case?

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Postby KarlP » 01:48 pm Feb 26 2008

145/42 is the stock jetting for a 220
I was real happy with 140/38, all else stock. I ride alot of single track, very little fast stuff. Please don't take my jets as a suggestion for your bike.
I'd pick up a few at the shop. Say 142,140 and 40,38. Play around a little.
You can change jets without removing the carb. Loosen the clamps, shut off gas, and rotate the top of the carb inward, bowl outward. Watch you don't bust the little piece of pipe the throttle cable runs through at the top of the carb.
Clean air filter, clean plug, clean carb with the right jets and it will run well enough to start working on the suspension :supz:
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Postby kawagumby » 02:23 pm Feb 26 2008

I agree with Karl, I suggest a 142 to start, even if you are near sea level to 1500 ft elevation, and also drop the needle one notch to start. Usually uneven throttle action is due to the jetting being too rich causing loading followed by a burst of clearing/acceleration.

My jetting is shown below - and was used with the stock engine before the reed, head and pipe mods (which did not make enough difference to rejet). This is based on a 40:1 blend of Bel Ray H1R premix.

So, another thing to consider is the fuel/premix. Are you using similar proportions and premix type to that of the previous owner?
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Postby canyncarvr » 02:39 pm Feb 26 2008

Kind of btw...but another rider summed it up very well:

bmase wrote:I agree with "Jeb". I usually bring down the size of the jets when the weather gets hot. A 142/40 or 140/40 should be about right with the 220. I also run it without the snorkel, and just check the filter regularly. The throttle response is night and day compared to the stock bike I bought. Now it is a lot of fun, but I don't really worry about the pucker factor. The power is very crisp and predictable.


Note the 'predictable' part?

Jerky and UNpredictable isn't how the KDX runs.

Oh, this comes from here.

It's not meant to be a jetrec for your situation. The point is the difference you can expect..and 'predictability' of it all.

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Postby jbroom » 03:37 pm Feb 26 2008

thanks for the info guys.

i'm running motul factory line 800—40:1
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Postby jbroom » 02:17 pm May 12 2008

update... for reference sake if nothing else.

i finnaly got to take my bike out again after making my adjustments. i dropped my main from the stock 145 to a 142 and cleaned/oiled my filter.

bike ran great. no more oil spitting all over my swingarm, and nice smooth throttle. i was on a bunch of really tight single track this time, so it was a little hard to compare to the more wide open trail riding i was doing when i was having problems... but it still felt really nice.

now i just have to improve my throttle control. i got screwed up crossing a crooked log, somehow grabbed a handful of throttle by accident, and found myself in the trees and over the bars... haha. busted my headlight. :oops:
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Postby canyncarvr » 02:32 pm May 12 2008

It's good to hear of a resolution to a posted question....doesn't happen all the time.

Thanks!

As long as no one had to get hauled off in a flashing red light vehicle...things like finding yourself 'in the trees and over the bars' is part of the fun of riding...those things get kind'a funny in hindsight. After the wounds heal and the hurts stop makin' you wince, anyway.

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Postby fuzzy » 03:57 pm May 12 2008

In addition to all that...

What's the "DEK" equivelant for a stock carb? Anyone ever try a "DEK" in a stock carb?

Jon, this needle is famed for nice linear power delivery, but mostly with the RB modded carb.
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Postby Indawoods » 04:21 pm May 12 2008

That would be a DEL
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Postby fuzzy » 09:28 am May 13 2008

There you go Jon, Throw a DEL needle in there now that you've got your pilot/mail working for ya....Needle profiles can and will alter the midrange power delivery....That's why there are like 200 of them that fit the PWK, but most people never (outside of this forum, or a works bike trailer) use anything other than OEM.

Another note on throttle control. Dirt bikes generally use a 1/4 turn throttle...That's 1/4 turn from idle to WOT, and the damn things can sure be tricky sometimes. I'd like a 1/2 turn myself....Especially on the 250. I believe there are aftermarket throttle cams available these days, but I've never tried one.
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Postby jbroom » 10:10 am May 13 2008

i put an aftermarket throttle on a motard xr100 to shorten the range for roadracing, but haven't messed with it in the dirt.
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Postby Dewey » 11:50 am May 13 2008

Once you get your jetting close, put in Boyesen 607 reeds, then fine tune the jetting. They really make things smoother, more predictable, and their cheap!

Keep tweaking on it, you can make that 220 ultra smooth with a little work.
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