bottom end sputter

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bottom end sputter

Postby kinganu » 03:31 pm Jun 16 2017

Hi there folks at KDX rider. I have been all over this site and learned much useful info about my top favorite ride....my kdx 200.
I have a bottom end sputter that I just can't seem to get rid of. Have tried every low end jet from a 40 to a 50 with no result. Turning the airscrew has no effect at all when it is idling. from 1/4 to WOT it rips yer arms off and runs great but it has this sputter from idle to 1/8 throttle. Also have tried all the needle settings and the clip is now at the highest point on the needle (dropping the needle to its lowest position) the needle is the one ending in 73. It is stock with an FMF gold series pipe on it. Right now it is running a 45 low speed jet and a 150 high speed jet.
The air box is clean and the crank seals seem to be ok as when it is running at high rpm there is almost no visible smoke and I am running it at a 32 to 1 fuel mix. Nothing I have done seems to have any effect on it.
If you have any advice or suggestions I would be much grateful.

And....I love this site....you guys have done GREAT JOB.
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bottom end sputter

Postby SS109 » 05:58 pm Jun 16 2017

Make sure your idle speed (not idle mix) screw isn't adjusted too high. If too high you are always running on the main jet and the idle mix screw would have no affect.
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Re: bottom end sputter

Postby bufftester » 11:35 pm Jun 16 2017

Agreed, your airscrew should be affecting changes when adjusted. Needle is not really in play below about 1/4 throttle. Ensure your intake and exhaust tracts are mechanically sound then follow the jetting guide.
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Re: bottom end sputter

Postby Jason » 01:33 am Jun 17 2017

Welcome to the forums.

Which year model??

Which country is the bike from??

reeds ok? dirty carb?

ethanol / gasahol??

let the fuel set long in the bowl??

float height is ... ??

TMI is not enough. :grin:
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Re: bottom end sputter

Postby jjavaman » 10:10 am Jun 17 2017

I would check your float height. I had the same problem with my 220 blubbering at low throttle.
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Re: bottom end sputter

Postby kinganu » 01:47 pm Jun 17 2017

Thanks for the replies guys.....
The carb is clean and spotless, The reeds are perfect and the float level looks fine. I went over your jetting guide till I have it memorized (very useful guide indeed). I have ordered a jet block gasket just in case. It is a 1992 American model. I am running standard grade regular gasoline as I havent had any problems with it in the past in my other 2 strokes.......hmmm....first time for everything maybe?.......I am also at about 4500 feet elevation. The engine case is clean and dry with no leaks anywhere.

The silencer does not have any packing in it but it looks it never was supposed to have any......just a turbo looking insert in an aluminum housing.
Lots of black spooge dripping on my swing arm and brake caliper....very annoying...
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bottom end sputter

Postby kinganu » 01:54 pm Jun 17 2017

SS109 wrote:Make sure your idle speed (not idle mix) screw isn't adjusted too high. If too high you are always running on the main jet and the idle mix screw would have no affect.


I will go play with the idle screw and see if that gets any results........
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bottom end sputter

Postby Jason » 06:39 pm Jun 17 2017

Which silencer or spark arrestor is on there? In stock form, it did have a bit of packing in it. Check out the parts diagrams online if you have the stock one.
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Re: bottom end sputter

Postby kinganu » 03:15 pm Jun 23 2017

Well....I played with the idle screw and still no results from it or the airscrew. I have to push start it when it is cold. the other night it got a bit cool around here and it would not start with the kick starter so I had to push start it. It started right up but it should have started easily with the kickstart. I wanted to test out the new LED headlight replacement I got off of Amazon which kicked butt it works so well.
Anyways.....I am still waiting on the jetblock gasket and that is about my last idea before just going ahead and tearing down the engine for complete rebuild. I'm going to pressure test it as soon as I get the time before I tear it down. It smokes way to much when it is at an idle and when twisting the throttle (when in neutral) it bogs like it is fouling out but then cleans itself out after about a second or two and makes a pretty good cloud.
Sorry I could not get back sooner but I'm working 6 days a week so not much time........

Thanks guys at KDXrider.........
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Re: bottom end sputter

Postby kinganu » 03:18 pm Jun 23 2017

I still don't know what kind of silencer is on it but I think the problem is way to bad to be just a silencer packing problem.
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bottom end sputter

Postby kinganu » 02:34 pm Jul 06 2017

Well.....I found the problem. I took the head off of it and the aluminum KIPS valves are wasted beyond recognition and came out in pieces so distorted you could not even recognize what parts they were. I ordered a set of steel ones.
I thought it was strange how no matter what I did there was no change in throttle response on the bottom end.. But even with the KIPS valves fried, it still screamed in the upper end of the throttle.
Can't wait to put those steel ones in even though they cost a pretty worthless penny and are coming from England. I got them off of ebay.
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bottom end sputter

Postby kinganu » 03:24 pm Jul 06 2017

If I could figure out how to upload images I would post some pics of my wasted KIPS valves........where do I start?
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Re: bottom end sputter

Postby bufftester » 07:50 pm Jul 06 2017

Don't be surprised if that doesn't fix your original problem. Even with the KIPS system disabled generally the bike will run fine, just won't have much punch above 6k RPMs (unless of course the valve failed full open which is rare). This is why the jetting guide is prefaced with make sure everything is mechanically sound prior to jetting. If your air screw is making no difference at idle you have a problem somewhere in the idle circuit, whether its and air leak or a blocked passage or something.
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Re: bottom end sputter

Postby Jason » 09:59 pm Jul 06 2017

Sorry to hear that the engine had that problem.

After installing the valves, you can get a fresh idea of how it is running, knowing that the power valve system is in order.
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bottom end sputter

Postby kinganu » 06:56 pm Jul 19 2017

Hi ya'll......well...I got the new steel kips valves in and they are working fine now. But you were right Bufftester.....it did not fix the problem.
After putting it all back together it started on the 3rd kick, but that bottom end sputter is still there. When sitting still in neutral and hitting the throttle wide open from an idle it bogs really bad before it finally clears its throat and revs up. Its not quite as bad when there is a load on the engine as when I hit 2nd gear. It really goes a lot better now that the kips is working but I just can't get rid of that bottom end sputter.
I just got the jet block gasket so i'll go change that and see if that makes any difference.

I'm running out of ideas.
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Re: bottom end sputter

Postby david » 11:40 am Jul 20 2017

Did you ever replace the jet block gasket?
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bottom end sputter

Postby kinganu » 08:14 pm Jul 20 2017

Well...my oh my......I replaced the jet block gasket and it had no effect at all........nothing I have done so far has had any effect on it. Turning the airscrew has no effect either.....I can turn it all the way in or all the way out and it makes no difference.

Whenever I start it up when it is cold it revs really high before it settles down to an idle.....and it seems to idle just fine whether warmed up or cold once it is running.

I have never had a problem that gave me so much trouble on a two stroke before.......

Any more ideas as I am about out of them.......I want to keep thinking maybe crank case seals but if it was the crank case seals it would be sucking oil and smoking and starting hard I suspect. Everything on the bike works great.....except that you can't pull the front end up at all in the lower 1st and 2nd gears because it sounds like it is fouling a plug but it isnt.......then it clears out and takes off like a rocket.....

Help..........
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Re: bottom end sputter

Postby bufftester » 11:40 pm Jul 20 2017

If everything else is fine then you still have a jetting issue on the idle circuit. It clears on the throttle because you're now engaging the mid and high speed circuits. That also accounts for why your needle position is where it is as well. You have to know what jets are in there and get a couple on either side. My guess is you need to go smaller on the pilot given your altitude.
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Re: bottom end sputter

Postby david » 07:31 am Jul 21 2017

Maybe it's time for a new carb. There have been a couple of members that couldn't get theirs tuned and ended up buying a new one...problem solved. Trying pilot jets from 40-50 and still having no response from your air screw is not normal (you know that already). It is possible that a previous owner has modified the carb and screwed it up.
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bottom end sputter

Postby kinganu » 11:53 pm Jul 21 2017

When I replaced the jet block o-ring I could tell someone had been there before me as I could see that they had used a light coating of some kind of dark (perma gasket maybe) sealant. Unless that was from the factory and I suspect it was not factory. It did not look like any of the sealant had oozed out enough to plug anything up....there was just enough applied that I could tell it was there almost like an ink stain....it was definitely not rubber residue from the old o ring.

What do you guys think about one of these Chinese keihn 34mm knock offs for around 25.00 to 50.00 bucks brand new? If anything for a test carb before I blow the big bucks on a genuine keihn.
I put a link to an ebay page below with the one I was considering. I tested the link and it took me right to the ebay page. Genuine keihn carbs are not cheap....even on ebay the best deal I could find was 100.00 for a used one. They also have a 38 MM replica.

http://www.ebay.com/itm/Motorcycle-34mm-Carburetor-Kit-for-Kawasaki-Yamaha-Honda-Suzuki-ATV-UTV/182607675147?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D2%26asc%3D41451%26meid%3Decc10e253f7a449299aa1b8522767b52%26pid%3D100005%26rk%3D4%26rkt%3D6%26sd%3D232309042739
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