200 EXC Knocking at low RPM's and just after stopping

[PoopSock]

Hi all, I just recently purchased an '05 200 EXC and I just started hearing some unfun noises on my last ride. I bought it from an older engineer who took very fastidious care of it, but I know it's due for a top end soon (which I have on order), but I was hoping to get one more ride out of it this weekend.

The symptoms:

I tend to hang out in 3rd gear a lot, and just let it lug me around. At first I thought I was just hearing rocks bouncing off the skidplate, but when I'd stop to wait for others to catch up, it would rhythmically make the knock sound with the combustion of the engine only when it's winding down. After about 5-10 seconds, it'd go away. It seems to only happen after riding hard, I can't replicate by just letting it idle and revving it up. I've tried doing some searching and haven't found anyone with this exact problem, but reading some other threads it sounds like this might be unexploded fuel working it's way out?

Some background on the jetting/mixture:

The guy I bought it from was running it with stock jetting and 45:1 ratio, my can already had some 40:1 in there, so I gassed it up with that. Made it smoke quite a bit more, and wasn't quite as peppy. So the last time out, I put 44:1 in the can and topped off the tank (which was half-full) with that. The smoking went away and it was running really strong, but then I ran into this knocking sound, so I'm really not sure what to make of it.

Bonus question:

My gas can has indentations on the side to check the level for both gallons/liters, I used a "ratio rite" and for 44:1 for 2.5 gallons, and went by the pump to put exactly that into the can. But when looking at the side of the can, I noticed that it was somewhere between 2-2.5. Which reading do you trust more, the pump or the can?!

Anyways, aside from these issues I am absolutely loving my 200. Thumpertalk was a huge influence in my decision, and I just can't get enough of that bring ding!

Thanks for any advice you fellas can give.

[pdxhillbilly]

Confucius say "Bike make funny noise, don't take out into forest, may break down". Confucius also say "Parts on order, make repair before engine go boom" Confucius has no advice about gas can markings.

[gottaroost]

I also have a 2005 KTM 200EXC. I do not have that same effect as you describe on it, but I do have that issue on my 2006 KTM 250XCW. Actually I have never solved it with either jetting, ratios, mixing oils, etc. I have probably just gotten used to it and I have have had no ill effects other than it being a bit of a nuisance.

Now I have not checked my 250's reeds in a long time and I do remember their being a tiny tear on there a long time ago...so maybe it it got worse and needs addressing. My 2006 did not start out making that extra pong sound when I first got it, but it does now and has for over a year so your post has me curious on the reeds. It is as you describe, been running and happens when returning to idle.

Maybe your situation is different...I did not see what octane gas you use---I only use the premium fuel. I do not run any race gas.

[PoopSock]

I also have a 2005 KTM 200EXC. I do not have that same effect as you describe on it, but I do have that issue on my 2006 KTM 250XCW. Actually I have never solved it with either jetting, ratios, mixing oils, etc. I have probably just gotten used to it and I have have had no ill effects other than it being a bit of a nuisance.

Now I have not checked my 250's reeds in a long time and I do remember their being a tiny tear on there a long time ago...so maybe it it got worse and needs addressing. My 2006 did not start out making that extra pong sound when I first got it, but it does now and has for over a year so your post has me curious on the reeds. It is as you describe, been running and happens when returning to idle.

Maybe your situation is different...I did not see what octane gas you use---I only use the premium fuel. I do not run any race gas.

Yeah I should have specified, just running pump premium. I can scope out the reeds when I have it open, although some quick searching made it sound like a bad reed will be more of a backfiring/popping out the exhaust symptom. Sorry you're having the same issue, but kinda glad to know somebody else has it! Girlfriend noted that it sounds a bit more "tinny", but that may just be something to do with the slightly-leaner mixture. Like I said, that very subtle change affected the smokiness drastically.

pdxhillbilly: wise words

[pdxhillbilly]

OK a serious reply this time. I think what you describe as knocking may be a lean surge as the bike winds down. Try moving the needle up a notch (or 2) to richen up the midrange. My son's bike had a lean surge when it was hot and moving the needle up 1 notch got rid of it.

[PoopSock]

Okay, that would make sense since it didn't start happening till later in the ride. I started it up last night and rode it up and down the street to see if I could replicate it, and it was perfect. My brother (crf 250x rider) got on it for the first time, and now he wants one.

So I'll try moving the needle up and see what happens, will report back. Thanks

[PoopSock]

Hey, resurrecting this thread as I've done some work on the bike, and the knocking still persists.

Just tore it down and did the following:

• new piston/rings
  
• coolant flush with engine ice
  
• JD jet kit
  
• fmf turbine core 2 (spark arrested) pipe added
  
• gear oil etc
  

I checked the crank for up and down play when I had the cylinder off, and it's solid as can be, so I know it's not that. The cylinder walls looked great, pretty much everything checked out as a super healthy well-maintained 200.

Took out for a poker run over the weekend, and I got the knocks several times, I wish I'd had a gopro so I could just post that up for you folks to listen to. Anyways, I noticed that I mostly could hear the knocking sound when it's under load, like when on a trail that is consistently gaining elevation. During downhill sections it seemed to go away. I've looked all over youtube trying to find a video that matches the sound I'm hearing, and this is the closest I've found, albeit mine is less "tinny".

The sound starts around 20 seconds in, and is very similar to what mine would sound like when I'd stop before shutting it off.

http://www.youtube.com/watch?v=14HHB3qI_58

If I can, I'll try and get my own video/sound of it happening at some point, but this is the best I've got right now. Any thoughts?

[Lmiinch]

Sounds like it is really lean to me...try going up a size or two on your pilot jet

[PoopSock]

Sounds like it is really lean to me...try going up a size or two on your pilot jet

I'd like to, but I'm already running a 45 pilot (included/recommended by the JD kit) and I haven't seen anyone in the jetting threads running anything higher than that... all I see if 42/45.

[Shimjocky]

Does your idle hang like the vid as well? Because that seems to indicate a lean condition in the pilot circuit to me.

If that is the problem, and you are confident in the jet selection, then I would look for a blockage in the idle/low speed circuit as well as checking for air leaks downstream of the carb. Perhaps the boot, reed body, main seals etc.

[acer01]

Did you check the x dimension? If the base gasket is too thin (negative x dim), it will knock no matter the amount of jetting change.

[PoopSock]

I didn't check the X dimension, actually just had to give that a google to see what you meant. Definitely can't rule that out completely, but I can say that the knocking was happening the same before and after the top end, so I hope it means I won't have to tear it down to that again.

That said, it sounds like I should pull the carb and go through it and make sure everything is clear, then take a look at the reeds and that whole area. Thanks a bunch guys, this is just one of those &%$#@! gremlins that is tough to nail down.

It's worth it, though. The 200 is just crazy amounts of fun, every other bike I ride seems boring in comparison.

[braap916]

Does your idle hang like the vid as well?

[PoopSock]

It does a bit, not as severe. When it's doing the knocking, it will wind down and knock in time with each ding-ding-ding, similar to the video.

Edited July 9, 2013 by PoopSock

[zotis777]

Just thought id throw some random knowledge at the bonus question, - trust the can, like 98% of gas pumps or something ridiculous are miscalibrated, read somewhere there's only around 300 people in the entire U.S. who calibrate pumps, never trust the gallon reading

[dryz250]

I think it is you X dimension is above the required "0"mm, causing higher compression, or that the previous owner had shaved the head without modding the bowl for pump gas. Wher do you have your air screw set at. A 1/2 turn richer can solve your knocks!

[braap916]

It does a bit, not as severe. When it's doing the knocking, it will wind down and knock in time with each ding-ding-ding, similar to the video.

This indicates a lean condition then

[Ud_Luz]

Sounds lean to me too.

[pdxhillbilly]

3 things you might do:

1) Make sure the float height is correct. Check the pin that holds the float in the carb. I had one of the holes in the stanchion get oblongated so that the float height would look correct but the pin could move up and down and change the real float height.

2) The casting where the main jet and pilot jet get screwed into is removeable from the main carb casting and there is a "Jet Block O-ring" that goes between this casting and the main carb casting. If the carb has ever been dipped in carb cleaner, this O-ring is probably ruined. This can let air into your pilot circuit. The casting is held in place by 2 theft-proof screws so you need a driver for that. None of the Keihin parts diagram show this O-ring, they'd rather sell $250 replacement carb bodies. You need some special adhesive that won't eat up the rubber to hold it in place when you install it.

http://www.motorcyclecarbs.com/_P12161.cfm

3) Smear black RTV silicone all over the outside of the intake boot to seal up any air leaks due to cracking in the rubber.

[pdxhillbilly]

One other thing, coat the gasket between the intake boot and the reed case with some RTV sealer since air can leak past the gasket.