Can a carb be bad/worn out

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throttleout
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Can a carb be bad/worn out

Post by throttleout »

Can a carb get to a condition to where no matter what jets, float, seals, gaskets, ect have been replaced that it still makes the bike run like crap...think bad gas?

Story, brother bought a 04 kdx200 that "needed the carb cleaned" well we cleaned it, rebuilt carb, had the cylinder replated, new top end (not new kips but it's working), played with jetting and needle position, and checked power valves. No matter what it still runs like crap. But, it does get a little better with leaner jetting. Jetting now is 40 pilot and 152 main.

Thanks,
Wes

Edited to add jetting info
Last edited by throttleout on 08:59 am Apr 03 2017, edited 2 times in total.
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Re: Can a carb be bad/worn out

Post by Tyl3r »

How did you clean the carb? Did you dip it in a cleaning solution? If so, the valve block 0-ring is likely toast. I would try replacing that first and see where that gets you (https://www.jetsrus.com/individual_part ... 32_su.html). Its a common problem with these carbs. Just do a search on here, you'll see lots have ran into this. Also, you physically verified that the kips are operating? Did you clean all the gunk and everything off them when you did the top end so nothing hangs up?
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Re: Can a carb be bad/worn out

Post by throttleout »

Tyl3r wrote:How did you clean the carb? Did you dip it in a cleaning solution? If so, the valve block 0-ring is likely toast. I would try replacing that first and see where that gets you (https://www.jetsrus.com/individual_part ... 32_su.html). Its a common problem with these carbs. Just do a search on here, you'll see lots have ran into this. Also, you physically verified that the kips are operating? Did you clean all the gunk and everything off them when you did the top end so nothing hangs up?
Just regular can carb cleaner, all new gaskets, and cleaned the kips good. The kips are definitely opening.
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Re: Can a carb be bad/worn out

Post by G22inSC »

You may not have "dipped" it but no telling what a previous owner did before you.

Yes, carbs can wear out over time. The slide is constantly moving within the carb body and some people's ideas about air filters differ from others.
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Re: Can a carb be bad/worn out

Post by John_S »

YouTube "pwk idle fix". It's a 1 minute video and it's the first thing I would do. Although that guy was able to move his jet block and get it to seal, if you have bubbles I would just order a new jet block oring. It'll run like crap for sure if that's leaking. Jets R Us.com has them for $4 or $5. Go to the parts exploded view and it won't show it on the picture but will have it down in the parts listings. The only thing that truly makes a pwk wear out is if the needle jet gets out of round but that's not too typical. Definitely first on my list would be that oring test. Next would be manually blowing air into the fuel inlet through a hose and working the floats to make sure when they are at their set height, no more air can be blown through. That would be a float valve problem which is about $20. Fresh fuel and plug right?
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Re: Can a carb be bad/worn out

Post by Tyl3r »

throttleout wrote:
Tyl3r wrote:How did you clean the carb? Did you dip it in a cleaning solution? If so, the valve block 0-ring is likely toast. I would try replacing that first and see where that gets you (https://www.jetsrus.com/individual_part ... 32_su.html). Its a common problem with these carbs. Just do a search on here, you'll see lots have ran into this. Also, you physically verified that the kips are operating? Did you clean all the gunk and everything off them when you did the top end so nothing hangs up?
Just regular can carb cleaner, all new gaskets, and cleaned the kips good. The kips are definitely opening.

If that's the case, I'd personally replace that jet block O-ring first before trying anything else. If you order a carb rebuild kit, they don't come with that o-ring because its not listed as a "wearable item". Even if the PO didn't dip the carb, they still degrade over time.
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Re: Can a carb be bad/worn out

Post by throttleout »

So it's not the carb. We put my RB carb on there. Boosted power but still felt like how your bike feels when it's cold.

Should we do a vacuum test on the bottom in to see if that's causing it to run rich?

Could it be an electrical issue?
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Re: Can a carb be bad/worn out

Post by G22inSC »

throttleout wrote:Should we do a vacuum test on the bottom in to see if that's causing it to run rich?
A vacuum/air leak would cause a lean condition, not rich. With an air leak, you are pulling in additional air. Normally causes a surge or fast idle.
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Re: Can a carb be bad/worn out

Post by throttleout »

G22inSC wrote:
throttleout wrote:Should we do a vacuum test on the bottom in to see if that's causing it to run rich?
A vacuum/air leak would cause a lean condition, not rich. With an air leak, you are pulling in additional air. Normally causes a surge or fast idle.
How do you test the wet crank seal to see if it's pulling in clutch oil and causing a rich condition?
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Re: Can a carb be bad/worn out

Post by KDXGarage »

Vacuum / pressure test

Check transmission oil level to see if it is getting lower over time.
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Re: Can a carb be bad/worn out

Post by G22inSC »

I've heard if the RH crank seal fails on the pressure test you could possibly see bubbles if looking into the trans oil fill hole. Not sure if that's completely true or not or would always be the case. As Jason said, failing on vacuum and you should notice a drop in the trans oil level.
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Can a carb be bad/worn out

Post by throttleout »

Update, did a little swap-shooting. Ran the coil and cdi from the bad bike on my bike and it ran fine. We ohmed out the ignition coil on the stator and it read 315ohms; manual says 247-350 ohms is normal. So, we are assuming that we're good electrically.

Only thing left is the bottom end seals. Tranny is topped off to check fluid level after some rides.

This is disconcerting though, I was telling my brother in law about the kdx and how we might a bad wet crank seal but the bike hasn't wet fouled plugs just runs bad. Well his bike has been wet fouling plugs. He does the fluid check on his bike and lost half of his fluid in two rides! But, bike runs like a beast :blink:

Anyways, hopefully we'll figure this out.
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Re: Can a carb be bad/worn out

Post by canyncarvr »

The answer to your OP is, 'Yes.' But..that's water under the bridge at this point.

You're stuck with nutting this out from worse than only the beginning...because you don't know what has been done to the bike before you got into it.

Not to impugn your level of expertise in any way...but some basics that will result in exactly the performance you indicate follow. Sorry. I have no idea what you know and what you don't.

A couple of common errors/mistakes that are worth checking:

Intake reed valve alignment. The assembly can go in upside-down just as easily as upside-up. Looking down the throat of the intake boot, you should NOT see any flat surface of the white phenolic/nylon air guide. Without taking anything apart you can see if the guide is installed correctly by its shape. Check an IPB or a manual if you are unsure what you are looking for.

Like this!

Ignition timing. If the flywheel has ever been off, maybe the woodruff key slipped on re-assembly. That leads to the flywheel slipping and incorrect timing. Remove the cover, stick something like a paper clip into the slot to verify the key is in place. Might as well check the timing while the cover is off.

Head gasket. You say the top-end was done. With a new head gasket? Re-using what appears to be a perfectly good head gasket...aluminum painted or not...is not efficacious.

Carb hookup. Make sure the nylon retainer is properly seated around the needle retainer nut.

Is WOT via the throttle actually WOT at the carb?

I read, 'The KIPS is definitely opening.' How do you know that? Observing the actuator rod moving by looking under the KIPS cover does not mean the sub-valves are working. Manually activating the system via the governor rod and observing 'things' to move does not mean the bike is moving the governor rod.

Aftermarket silencer? Service it. Whether improperly packed or not recently serviced, a poorly packed S/A will result in crap performance. If you end up with packing left over in the FMF bag it came in, you didn't do it right.

Good luck!

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