A. . . hem, help me clear my kdx's throat, please

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pastorbuck
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A. . . hem, help me clear my kdx's throat, please

Post by pastorbuck »

Hi guys. Three years ago I bought an '03 kdx 220 that was bone stock and in mint condition with less than 100 miles on it. Every year I add another couple mods, as my funds will allow. As far as the engine is concerned, all I have done is added the gnarly woods pipe and spark arrester silencer (which I did last year), and I was very happy with the improved performance.

This year, however, I have noticed a significant change in how long it takes to "clear its throat" when warming up. As well, if I cruze along at 1/8 to 1/4 throttle for only a short time, when I get into it to take off or pull a 2nd gear wheelie, it again spits and pops to clear its throat before it becomes nice and crisp and smooth. This didn't happen last year or the year before. I could lug it around all day and not have a problem. I didn't change a thing this year, so what might be causing this? Do I need to clean the power valve?
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A. . . hem, help me clear my kdx's throat, please

Post by pumpguy »

First thing I would do is to pull the carb and thoroughly clean it. Just do a search, there is plenty of info on that subject here on the site. If that doesn't help, I would try going through the jet checking process posted here also.

Do you still have the stock OEM piston? If yes, you really should change it to a forged Wiseco. There's alot shown here on the site about how the OEM 220 pistons just go to pieces unexpectedly. And when they do, it's real costly to repair the engine.
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rbates9
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A. . . hem, help me clear my kdx's throat, please

Post by rbates9 »

Spark plug?
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bufftester
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Re: A. . . hem, help me clear my kdx's throat, please

Post by bufftester »

If it sat through the winter, then at the least it needs a carb cleaning and new plug. That should be part of post hibernation maintenance anyway. Sounds like an issue in the low speed circuits.
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Re: A. . . hem, help me clear my kdx's throat, please

Post by KDXohio »

Did you re-jet for the pipe last year when you put them on?
If not once you clean the carb and change the plug as already mentioned Id try going through the jetting process for sure.
1990 KDX200 FMF Fatty, Answer VFC silencer, VForce 3 Cage, Wiseco Piston, KX125-J series KYB USD fork conversion, Race tech goldvalves, J series front brake assembly, air-box snorkel removed, Acerbis Headlight, KX450F Front fender, Pro Taper RM bend bars, ASV front Brake lever, MSR Clutch perch and lever, RB Head mod, 36mm PWK carb, Trail Tech Kickstand.
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A. . . hem, help me clear my kdx's throat, please

Post by pastorbuck »

Let's see if I can address everybody in this responce.
- Swapped out the piston for a wiesco when I first got the bike 3 yrs ago
- It's not the plug. I've changed it and the result is the same with a new plug
- I didn't re-jet it when I put the gnarly pipe on because fmf said I didn't need to. Also, the bike ran great after I put the pipe on, with no issues
- I have not tried cleaning the carb yet, so that's what I'll try first

Thanks guys. I'll clean the carb and give an update in a few days.
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Re: A. . . hem, help me clear my kdx's throat, please

Post by KDXsg »

might also be a leaky crank seal contaminating the stator coil, causing a spark issue?
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Re: A. . . hem, help me clear my kdx's throat, please

Post by bufftester »

KDXsg wrote:might also be a leaky crank seal contaminating the stator coil, causing a spark issue?
Very unlikely, even with a bad crank seal all you're going to get is some premix, you have a greater chance of having water in there from an old flywheel cover gasket or around the rubber grommet for the wires. And since it is running you can pretty much rule out the spark issue. It's a classic carb fouling symptom, a quick search of posts here will net you a lot of "tried everything else and it turned out to be a gunked up carb" stories.
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A. . . hem, help me clear my kdx's throat, please

Post by Gotanubike »

Did you fill it with fresh gas this season?
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Re: A. . . hem, help me clear my kdx's throat, please

Post by Roadhazardguy »

Have you checked the reeds? I guess not if you haven't even cleaned the carb yet..
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pastorbuck
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A. . . hem, help me clear my kdx's throat, please

Post by pastorbuck »

- Does have fresh gas. I've gone through several tanks this year.
- I thought about the reeds. I'll check them when I clean the carb. Hopefully I'll have some time later today to do it.
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A. . . hem, help me clear my kdx's throat, please

Post by pastorbuck »

Ok, guys, here's the update:
I cleaned the carb and checked the reeds. Reeds are fine. I took it out for a test and it ran the same. I did a plug chop and it was bright white - very lean, as you all know. I then raised the needle one knotch and did another chop and it was still lean. I then raised the needle all the way (lowering the clip to lowest knotch) and still super lean. I'm talking bright white, like I'm burning straight gas with no oil. My premix ratio is 36:1, which I've runned for three years with no issues.

So, what do you think? Bad rings? I heard somewhere that when rings go bad it mimics a lean situation. Remember, it runs like it's rich - all choppy and stuff until I'm screaming in the powerband. It starts fine and idles fine, runs smooth and powerful in the powerband, but not until it "clears its throat" so to speak. And it does it even after it's warmed up and seems to be worse now than it was a month ago. In other words, it's getting worse.

So, let me know what you think.
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A. . . hem, help me clear my kdx's throat, please

Post by rbates9 »

I would make sure the carb is clean. Remove everything you can and spray through all the passages and make sure it comes out somewhere. Then go through the jetting. The needle was basically nothing to do with full throttle.

It might be worth checking the crank seals and intake for a leak.
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A. . . hem, help me clear my kdx's throat, please

Post by pastorbuck »

rbates9 wrote:I would make sure the carb is clean. Remove everything you can and spray through all the passages and make sure it comes out somewhere. Then go through the jetting. The needle was basically nothing to do with full throttle.

It might be worth checking the crank seals and intake for a leak.
- I took the carb completely apart and blew cleaner through every jet and vent hole possible. That thing is 100% clean.

- I think you're wrong about the needle. Everything I've read tells me that a WOT plug chop is the way to check the needle height.

- Why would I have to rejet it now? For three years, it's been running great. I'm riding at the same locations, same elevations, etc. Something has changed to make the bike start running poorly. It can't be the jetting unless the jets somehow got worn larger from three years of fuel flowing through them. And if that is the case, then a plug chop would show rich, not lean.

- I plan on doing a leak down test as soon as I can get to a hardware to buy the stuff to make a tester. I think I might also get my hands on a compression tester to test compression. I want to analyze this from every angle to really isolate the problem.
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Re: A. . . hem, help me clear my kdx's throat, please

Post by KDXohio »

If you have some starting fluid you can do a quick intake leak test spray all around the intake boot between Carb and and engine if the idle changes you have a problem
1990 KDX200 FMF Fatty, Answer VFC silencer, VForce 3 Cage, Wiseco Piston, KX125-J series KYB USD fork conversion, Race tech goldvalves, J series front brake assembly, air-box snorkel removed, Acerbis Headlight, KX450F Front fender, Pro Taper RM bend bars, ASV front Brake lever, MSR Clutch perch and lever, RB Head mod, 36mm PWK carb, Trail Tech Kickstand.
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Re: A. . . hem, help me clear my kdx's throat, please

Post by bufftester »

WOT plug chop will give you an indication of whether or not you're jetted correctly, but does not indicate proper location of the needle. The needle is in play from about 1/4 to 3/4 throttle, and is usually checked by doing roll ons off idle. At WOT your main jet is the biggest contributor. You do need to rejet for a new pipe, especially since FMF specifically states :
We developed these specs with a 32:1 fuel to oil mixing ratio of a 50/50 mix of race fuel and super unleaded, 0 - 1500 ft altitude at 70 degrees outside temperature.

Please note: There are way too many variables in jetting to give you a recommendation that works perfect. Use these specs for a reference to help aid you with your specific bike.
You may well find that you have low compression, but I'd at least run through the jetting guide to make sure my baseline was good.
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A. . . hem, help me clear my kdx's throat, please

Post by pastorbuck »

Thanks, guys, for all your input so far. Here's the latest:
- I did a compression test and got 140 psi. Pretty darn good I think.
- Did a leak down test and engine is tight. It lost about 1 psi per 2 minutes or so. From what I've read, that's very good.

So, I guess what I'm gonna do is order a set of jets and rejet it. While I'm waiting for the jets to come, I'm gonna try one other thing. I'm gonna switch to Belray MC-1 mixing oil and go to 50:1. According to the bottle, it says that it is formulated to work best at 50:1 and that rejetting may need to be done. I've been using a cheap, generac 2 cycle mixing oil that may be part of my problem. So we'll see what happens by going to better oil, a leaner oil/gas ratio, and rejetting. I'll give an update in a couple weeks.
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A. . . hem, help me clear my kdx's throat, please

Post by pastorbuck »

Well, I've runned through about 5 gallons of gas so far mixed at 50:1, using Belray synthetic oil and it has made a world of difference. The bike runs soooo much better, it's like night and day. I still think I need to go one size smaller with the pilot jet to be perfect, but it's pretty darn good right now.

I've learned a valuable lesson through this whole experience: The brand of oil makes a HUGE difference. I will never buy the cheap stuff from my local hardware again. I know that the Belray synthetic is expensive, but the performance of the engine is so much better that it's worth it to me. The cheaper oil made my bike run so poorly that I actually thought something was wrong with the engine. Hense the reason for trying to pinpoint a problem that didn't actually exist. If I were more experienced, it probably would have dawned on me quicker that it was just the cheap oil.

Live and learn, my friends, live and learn. Some day I'll be perfect. Until then, I'll continue to trip over my ignorance.
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Re: A. . . hem, help me clear my kdx's throat, please

Post by KarlP »

Thats funny-

i run my motorcycle mix in my chainsaw and weedeater. They run MUCH better, almost zero smoke, very crisp.
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