Bike suddenly won't idle?

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DenverKdxRider
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Bike suddenly won't idle?

Post by DenverKdxRider »

Hi Everyone,

I bought a JD jet kit put in and per their recommendations ran it at 4th clip, 42 and 158 for the elevation I was at. Was running fantastic (2 days) but towards the end of our trip it just wouldn't idle anymore. Adjusting the air screw and idle knob had no effect. The air filter was a bit dirty but nothing too crazy. I came back home, cleaned the air filter, and cleaned the carb and it still won't idle.

I've recently just cleaned the carb and am dumb founded. The idle screw and air screw have no affect at all on the idle and barely idles then dies. Is the JD jet kit here completely wrong? It's weird that it ran fine then suddenly wouldn't idle. I've heard that it could be the pilot gasket? Is the piston going bad? Any ideas would be appreciated.
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Re: Bike suddenly won't idle?

Post by KDXGarage »

Did you change elevations during this time?
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Re: Bike suddenly won't idle?

Post by kdxdazz »

Go back in the carb and recheck everything you did, check the pilot jet isn't loose, check the clip on the needle
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Re: Bike suddenly won't idle?

Post by DenverKdxRider »

I cleaned my carb by dipping it in parts cleaner which apparently is a bad idea. I am 90% sure that it's my jet block o-ring. I ordered one and gonna replace it. I definitely think that's it because at camp I adjusted the air idle screw and it worked but after it suddenly stopped idling at camp it did nothing. I've checked and rechecked the carb and this seems the culprit.
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Re: Bike suddenly won't idle?

Post by KDXGarage »

Uh oh.

Worth checking into. Security (tamper proof, etc) T-20

What model / year KDX is it?? You might want to make a signature with your KDX year and model in it.
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Re: Bike suddenly won't idle?

Post by bufftester »

Yeah, kind of sounds like the jet block gasket finally gave out after being dipped. Worth a check to verify everything else while you have it apart to replace the gasket.
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Re: Bike suddenly won't idle?

Post by kdxdazz »

Out of interest, what was the solvent in the parts cleaner, I sprayed degreaser on a shock once and it completely destroyed the bump stop within a matter of minutes
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Re: Bike suddenly won't idle?

Post by bufftester »

Berrymans Chem-dip (which is representative of many carb cleaners is primarily Methylene Chloride w/ Xylenes, Cresylic Acid, Ethylbenzene and
Sodium Dichromate
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Re: Bike suddenly won't idle?

Post by KDXGarage »

Berrymans strikes again!
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Re: Bike suddenly won't idle?

Post by PacificNWRider »

EDIT: This is probably NOT your problem, because I think the bike had a high idle, instead of dying..... Sorry, its refreshment time around here.

Also this might sound stupid, and if it is just ignore me.... but I had this problem a while ago on a little XR, turns out the throttle cable was binding ever so slightly.... It REALLY SEEMED like it returned as normal, maybe I just didn't look at it close enough at first, but it had the exact same problems, and the idle screw had no effect. That is a big time sign of massive fuel or air leak. Turns out I some how put a small twist in the cable when I twisted it to change the jet. It had the slide raised ever so slightly. Easy way to check is look into the carb before attaching to airboot, and adjust the idle screw make sure it is raising and lower the slide, and make sure the slide is at the bottom completely.

I made the mistake once before that, leaving the idle screw in when dropping in the slide. It stopped at the idle screw, I set my throttle free play accordingly (I like very little play). With the new pilot and the idle being set pretty high previously- when I went to drop the idle/ idle screw the slide couldn't seat all the way because of the free-play wasn't enough. Same result, air screw did nothing because throttle was cracked. I think both times the bike's were at a high idle though

so my procedure is - Back idle screw out all the way, look in carb to make sure slide is seated, adjust free play, then raise idle screw as needed.

ILike I said, if you know all this then just ignore me....

You could be several jet sizes off and you would still get action from the idle screw, so I doubt its the kit.. main & needle aren't part of the idle circuit..

I think you guys got it figured on the o-ring, It's probably that or float height / (water/oil in float) or gas not flowing freely from petcock?

I just wanted to throw that in, because I had a flash back when reading your post, so just wanted to offer up any info that may help you or any others that come across this in the future!
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Re: Bike suddenly won't idle?

Post by DenverKdxRider »

Hm...well I checked the gasket and it was fine. I replaced it for good measure but it's still not idling. Since I am in Denver and elevation is around 5000 feet. I tried to add in a bigger pilot jet. I ran a 48 and 150 and still won't idle. The idle and air screw still do nothing. I am still baffled that it was working fine all weekend and then all of a sudden it just won't idle.

Could be a sign of my top end going bad? Not sure the last time it was replaced by the previous owner. He was a bit of an older gentleman and I ride her pretty hard..
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Re: Bike suddenly won't idle?

Post by DenverKdxRider »

I was fed up and paranoid so I completely took apart the carb and cleaned everything. I looked at the jetting guide from JD and since I am currently at around 5200 feet it recommends my current jets 42 / 150 but to be on the 4th clip red needle. With poor idling I was using the same jets and 2nd clip. Adjusted the needle and made a big difference. It's actually idling now.

The JD jetting guide recommends 2nd clip for elevations above 8500 and last weekend the area I was going to ride was around 8000-10000 which is why I used their 2nd clip recommendation but it just wouldn't idle at all when I got there. I guess every bike has it's own "personality". I am gonna try these settings this weekend and fingers crossed it runs like a champ!

Thanks for the help.
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Re: Bike suddenly won't idle?

Post by KDXGarage »

Thanks for the follow up.

I strongly agree that each bike is somewhat unique on the jetting.
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Re: Bike suddenly won't idle?

Post by bufftester »

So did you change the needle clip setting when you were riding? If so you didn't mention that in your original post. As with most things if you change something and it gets worse, it was the last thing you changed that did it.
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Re: Bike suddenly won't idle?

Post by PacificNWRider »

Well thats good news! I don't understand how the needle clip could affect the idle, am I missing something?
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Re: Bike suddenly won't idle?

Post by DenverKdxRider »

Ya...so I drove 3 hours and was super excited to finally get out on the trials and bike still won't idle. When I first start it up I get a decent idle (A bit lower than I'm use to) but when I rev it up it starts to idle but then after a few seconds goes to barely idling and wants to die. I rode a few miles on the trail and every time I pull in the clutch the bike barely idles and wants to die. I have to hit the throttle a little bit to keep it alive. Adjusting the air screw and idle screw have no affect. It was just weird how it ran great with the jetting setup I had for 2 days even with elevation changes and then suddenly wouldn't idle anymore.

I started to rebuild the top end over the weekend as I've been meaning to do this for a while because I have no idea when the last time it was done but going to try this and see if it makes a difference.
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Re: Bike suddenly won't idle?

Post by PacificNWRider »

Well, the Top end will be nice to have done either way. Its possible once the bike gets good and hot there is a lack of compression, but the bike would be hard starting and noticeably under powered/smoking, I would think?? So it is definitely possible the top end will fix your problems, but not certainly.

Did you compression test it first?? Suppose it doesn't matter now, but would have given some information on whether or not your on the right track.

If your top end job doesnt fix the problem then- Ill take one more stab at it, because I don't think a worn top end would make your screws do nothing, unless it got burnt up. If you try this list it should take you like an hour tops and you will have the problem figured, if not already.

I stand on my previous statement, if your close enough to stock jetting and your screws do nothing you have a massive air or fuel issue.

1. Quit changing the needle clip and jetting, it will not affect the idle. Get it close to stock or last good working config, and forget about it
for now. You are looking at the pilot Jet only (42) and air/fuel problems. There is the possibility your 42 Jet has minor blockage, its almost
impossible to tell.. Also, if it has screw driver marks in the head or a piece of wire has been jammed in it (im guilty of doing this in earlier
years)...then for peace of mind, I would get a new 42 jet. Could be simple.

2. Check TO MAKE SURE YOUR CHOKE IS CLOSING OFF & SEATING PROPERLY, remove it, clean it up.

3. Start by spraying something flammable around spots that could leak air. I use propane its less messy, and won't dry out and crack your air
boots like you see on many bikes. Be careful. If Idle raises, address found leak.

4. Replace the petcock, unless it flows very good every-time, on both RES & ON, and you are very confident its not the problem, or hasn't
clogged previously... The cheap china ones seem to work great.

5. Confirm, and then DOUBLE confirm your float height using the correct procedure, NOT the "tilt over and that looks good method".

6. IF - after #1, #2, #3, #4 you have no air leaks, and your fuel flows fine, and #5, your float is within spec to 1 mm,, THEN connect slide to
carburetor - Confirm, and then DOUBLE confirm your slide is seated all the way with the IDLE screw all the way out, AND there is still play
in throttle. Adjust as needed.

7. Turn throttle screw in WHILE looking in the carburetor and watching the slide. When the slide begins to slightly move stop.
NORMALLY, the bike will run with IDLE screw all the way out, it will idle low and may die, but it will try to idle if the bike is in
decent running order. For starters Turn it in a half turn from where you stopped, that should give you a moderate idle. Turn the air screw
out 1-1/2 turns from gently seated.

8. Start the bike, it should idle, if it doesn't, try turning the throttle screw a little bit, half a turn, if it has no affect, something in steps #1 -
#6 are not right. If it idles decent, continue.

9. I suggest you use the INDAWOODS carb tuning guide - Here is a quick guide- If the bike runs and idles OK, THEN WARM IT UP FULLY. Turn the
IDLE screw in until you reach a good high idle. Now adjust the AIR screw slowly in either direction SLOWLY 1/8th at a time, wait for 8-10
seconds after adjusting BEFORE adjusting again, adjust it until the idle gets higher, when you reach the highest idle then lower your idle
to the correct idle speed. Ride the bike around for a minute, making sure it is nice and warm, confirm idle speed, adjust as needed, and
then follow proper tuning guide of needle and main jet.

Aside from replacing the petcock you should able to do this list fairly quickly. If you blew the petcock out with air to begin with, instead of rinsing the tank & replacing, I might start there. Other possibilities would be Reeds, TOP END (hopefully you got'r), sinking float (crack or hole), crank case seals? BAD GAS/BAD MIX/Mix settling.

In my experience, jetting the SAME two bikes differently is usually because of a few factors - Altitude, Compression, Air volume (leaks, air filter/air box volume, reeds, Pipe), Mix Ratio or Worn parts (needles, jets,slide)

In an OK running dirt bike - Air leaks, Reeds, fuel condition (mix ratio, bad gas, or unstable fuel delivery, addressed above) and Altitude are typically the only things that can have a MAJOR same day impact, unless the bike was run hard lean all day or no air filter/no mix.

I know this is a long post, but I wanted to give clear direction on what I suggest you should do. If you are adjusting the needle clip for idle then I think you may be a little bit confused on the process, no big deal, I just want to help guide you in the right direction. Hope this helps...
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Re: Bike suddenly won't idle?

Post by DenverKdxRider »

Welp finally found the issue. I spent all day on a Friday rebuilding the top end in my hot and sweaty garage. I cleaned the heck out of the top end, power valve , etc. Put in a new piston and rings, gaskets and checked and rechecked the air boots and carb for air leaks. I also changed out the jets with new ones just for good measure. Fired her up...seemed to idle great.

Then I took her up to Rampart which is about 45 minutes away. Started riding it and then it started to do the slow idle thin again but this time I noticed a ton of gas leaking from my gas cap and from the float. Well it turns out the piece of crap Clarke gas cap had disintegrated! This has got to be the culprit. The glue and seal probably started to come apart on the two days of riding over the 4th of July weekend and kept getting worse until today when it really bit the dust.

Image

Of course the stock gas cap doesn't fit the Clarke tanks so had to order another gas tank from them. This one will be a billet one as I am not taking a chance on their cheap plastic caps it looks like are giant piles of crud. Thanks for all the help guys and hanging in with me!
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Re: Bike suddenly won't idle?

Post by KDXGarage »

Could you not just order a new plastic cap or metal cap for the current tank??
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Re: Bike suddenly won't idle?

Post by DenverKdxRider »

KDXGarage wrote: 09:36 pm Aug 15 2020 Could you not just order a new plastic cap or metal cap for the current tank??
Yep just ordered one. My stock cap doesn’t fit the Clarke at all. I’ve heard a lot of the universal caps have different thread pitches so I ordered A billet one from Clarke. Their website says 5-6 weeks so really hoping it doesn’t take that long!!
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