Problem at steady throttle...solved

[John_S]

Hi guys, new KDX owner and I'm loving the bike but having a frustrating problem. I'll give a little history and current set up below. First off I want to thank you guys from the bottom of my wallet (and heart) for all the info on this forum. I've been reading through all the different topics like it was a favorite book of mine for about a year now.

My bike has a problem at steady throttle inputs. If you jumped on it and starting ripping around always working the throttle you'd never know it and it rips. If I give it 1/8, 1/4, or 1/2 throttle (anything but wide open) as soon as the rpms taper off like you're going to start cruising at that speed the bike runs terrible in any gear. It sounds like detonation or pre ignition and it runs really rough. If you give it any throttle input its perfect until a second or two later when the speed steadies out. I've tried all three lines (base, retarding, and advancing) on the timing and it happens on all three settings. I guess its time to bust out the voltmeter and start going through the electrical but I have no prior experience other than checking a coil on another bike I have. I'm hoping someone has had a similar problem or a suggestion on where I should start to look first. I haven't tried any other spark plug but the BR8ES and tried a couple of those just to make sure it wasn't a fouled plug. Unfortunately I don't know anyone else with a KDX that I could swap coils, CDI, stator, etc to test. I've tried every pilot jet from a 48 to a 38 and DEK, CEL, stock, and JD jetting needles (in more clip positions than I'd like to admit) thinking I had a jetting problem. It sounds like its lean when it starts pinging at steady throttle. Although I love the bike and willing to work on it this is getting old. It runs so great as long as you're working the throttle so I'm completely stumped. Every time I take it out I'm tinkering with it to try to get it right way more than I am riding and enjoying it. I'm driving home from work yesterday and thought maybe I should I try to ride it with the headlight on and see if that helps haha. That's where I'm at with this thing. What should I try next?

The Bike:
2002 KDX 220 which I'm told sat basically brand new for years and then got a trail tech put on when the second owner bought it and it showed 39 hours when I got it. The original owner said it had 2 hours at most on it when he sold it. I was super excited to find this bike and stalked craigslist for a long time to find one in my area. I know KDX's don't fetch a premium but at $1500 I feel like its a steal compared to how much a new bike costs. It had a FMF woods pipe and turbine core silencer, oversized front rotor, barkbusters, and the trail tech. Since I bought it I've done;

New wiseco piston and cleaned all KIPS parts
New 35MM air striker
40 pilot 1 7/8 out on the AS
JD red needle middle clip position
150 main
607 reeds
leak down test showed good at 6 psi for 6 minutes after rebuild
Repacked silencer
New twin air filter, snorkel removed
I'm in Florida at sea level

[doctord23]

That seems like some pretty lean jetting that you have with a 35mm carb.
I would suggest trying a 42 Pilot or even a 45.
I run 42, 152 on my similarly equipped 220, 2nd clip from the top and I ride at fairly high altitude 2500 -6000 feet.
I have the desert pipe though. I think that it is a better match to the 220 engine.
You might have to play with it. Also try moving the needle clip up and/or down.
Have Ron Black cut the cylinder head for you. It is a worthwhile investment.

[John_S]

Thank you for the reply doctor. Earlier in the post I spoke of the jetting. The 35mm came stock with a 48 pilot and it wouldn't even think of idling. The 45 pilot took about 3.5 turns out to run and still was rich. The 42 which I had in there until this morning runs best 2 1/8 out, 2 1/2 out gets a lean bog when you whack the throttle. The 40 I put in this morning and its best at 1 7/8, anything more than that gets a lean bog when you whack it open. I've tried DEK (which came with it), CEL, the 220 stock needle, JD blue, and JD red. I messed with them all from the 4th clip to the 1st clip, just short spurts to see how it acted. Right now its good with the JD red at 3 or JD blue at 2. On the mains I started with the 160 that came with it which was way too rich, the 155 still rich, the 150 good, and the 152 decent but had the occasional rich stumble. It has the airbox lid on and even the snorkel until this morning. I tried jetting it without the air box lid and it was a mess. It was minute to minute whether it was going to run good or not. I put the lid with snorkel back on and it was a huge improvement and very easy and consistent to jet. Putting it back on and it running good makes me think that yes, I was lean in my settings without it. Right now it runs so good I'm just leaving it on and took the snorkel out this morning and didn't notice a change, with or without snorkel. With all that said no matter what jetting I have in it, it runs like crap, but ONLY at steady throttle and RPM. It idles good, roll on power is great, whack the throttle and the front end is up with no hesitation. The best way to describe it at steady throttle would be like if you unplugged one of the spark plugs in your car, runs really rough and knocks. The only thing electrical I've done so far is to swing the timing all the way between the lines and put a new NGK plug boot on and the voltmeter shows that is in spec according to the manual. I'm very much looking forward to sending off my head to Ron but I need to get this problem sorted and then that's the next thing on the list.

[Willbilly]

Lol sounds like doctord23 decided to give you advice without understanding your problem.

Have you checked your petcock and fuel line for blockage? Same w airway beyond filter? Reeds seat fine? Exhaust cleared of oil/ debris?

[John_S]

I flushed out the tank with fresh fuel, put a new fuel line on, and rebuilt the petcock (it wouldn't fully stop the flow in the off position). The reeds were new at the time of the top end (10 hours now). I ended up buying a new power core silencer because the turbine core had a leak where the bracket to bolt it up is welded and would spray oil onto the inner side of the number plate. I tried to JB weld it multiple times but it kept coming back so I thought maybe there was a back pressure issue with that leak (throwing money at it....good thing I'm keeping it). I didn't check the pipe real good but sprayed engine degreaser in there and flushed it out. It didn't have much carbon in it but I'm sure it's full of oil now from me idling it so much messing around with it. I took the air box out and cleaned it up real good too. At this point I might as well take the reed block out and see if there are any issues, thank you. I bought a br8eg plug today just to see if there is any difference. I haven't taken it out yet but notice it idles smoother with the ES plug than the EG.

[doctord23]

Regardless of what Willybilly thinks, I'm still leaning with fuel delivery via the carb as the likely culprit.
Either needle or the pilot circuit. Steady throttle is when those two circuits are functioning. The fact that you can adjust the air screw tends to make me go away from the pilot though. I had a new carb on a jet ski once that I could never get to run right. It happens!

What about the kips? Timing correct? functioning correctly? Valves not switched so the wrong side? Remember that the original repair manual was incorrect as to which side they went in.

[bufftester]

I'd have to agree with the Doc, this sounds like a fuel delivery issue, not an electrical one. Lots of good info in the first post about current settings and work done so far, but a few questions come to mind based on lots of years riding these and watching the travails of others. Have you ensured your intake/exhaust tracks are good (i.e.: no air leaks outside the engine, cracks in the boots, etc). A leak down is great for verifying the motor is sound, but you still want to check all the soft parts outside the motor and all the junctions. Then have you disassembled, inspected, and cleaned the carb yourself? Has the float level been checked and set properly? Have you done a plug chop? Once you're confident everything is mechanically sound follow the jetting process. Don't skip around, don't do a bunch of changes all at once. Just follow it through step by step, changing only 1 thing at a time. Yes, it is time consuming but it absolutely needs to be done anytime you change anything in the intake/exhaust tracks, and your bike has a lot of mods in those areas.

[John_S]

If I put the needle in the 5th clip or the 1st clip it would do the same thing. 45 to a 38 pilot, same thing. Frustrated one day, I took the stock 33mm carb with me and put it back on with the jetting set at stock, same problem.The KIPS was installed correctly (grooved valve and o ring valve on the right side, all the timing indicator dots all lining up throughout) and checked for function while putting it together and then again by removing the slotted cover and checking it opens and closes smoothly at around 6k rpms. It happens at 1500 or 7000 rpms, doesn't matter, as soon as I steady my hand. Its really weird! At this point I almost wish it didn't run because its easier to find a broken part than one that's acting up. I wish you guys could ride it and feel how great it runs and then...if you wanted to cruise...you would think its going to blow up with the spark knock.

[bufftester]

Yeah, it's not a KIPS issue. It can be completely inoperative and the bike will run just fine from idle to 6000 rpm, above that it will run fine, just lack power. You said it does the same thing with the stock carb, so there is a possibility it could be a CDI issue, though that would be a strange one. Have you checked the high tension lead from the coil, and the coil? Seems an unlikely culprit given the symptoms, but you never know.

[John_S]

Thanks Bufftester, I haven't tried spraying any starter fluid around while its running but did try with brake cleaner. Don't know if that has the same effect. I know it sounds like I jump all over with the jetting but I've jetted quite a few bikes over the years and even kind of like it the tinkering around aspect of it. I didn't change more than one thing at a time though. All that jetting I mentioned is hours and days of one thing at a time. One day messed around with pilots, the next with needles. A full throttle plug chop with the 150 main shows considerably better than the 160 and 155 but still on the dark side. Its about a 2mm ring at the bottom of the porcelain, chocolate brown. I started the pilot and needles as rich and then worked down to noticeably lean, then dialed them back up to seat of the pants feel and in between my rich and lean settings. I'm really confused with all this.

[John_S]

Yeah, it's not a KIPS issue. It can be completely inoperative and the bike will run just fine from idle to 6000 rpm, above that it will run fine, just lack power. You said it does the same thing with the stock carb, so there is a possibility it could be a CDI issue, though that would be a strange one. Have you checked the high tension lead from the coil, and the coil? Seems an unlikely culprit given the symptoms, but you never know.

I checked the coil with the plug boot on and not the second test from the manual. I haven't checked the CDI and I guess its time I start learning. Mechanical I'm not afraid to dive in, with the electrical I feel like its a foreign language to me looking at the processes of checking it out. Thank you so much for the advise. I really appreciate it!!

[John_S]

I just did some testing with the volt meter. The manual shows the coil primary windings should be between .16--.24. Mine is double that at .5.
The secondary windings should be between 5.0--7.6 and mine is at 6.07.
The exciter coil should be between 250 and 370 and mine is 315.
I unhooked the CDI and started to test it according to that table in the book and the results are basically nothing like that table, most of the readings between all the different wires just staying at 0. Might be my 20 year old radio shack tester. It looks like the coil primary windings being double what they should be is the place to start.
Would you guys go only OEM on a coil or one the $15-$20 ebay coils?

[Willbilly]

If the electrical doesn't pan out the next thing I'm thinking is the balance of the crank or other related bottom end items. I don't know much about the bottom end so I'm shooting from the hip.

[bufftester]

If it were me I'd do the cheap coil, but I'm not convinced that's the problem as you are getting spark, just erratic running on no throttle input (no change in throttle to be more precise). Generally when a coil goes bad it doesn't spark at all, or you see problems at just the higher RPMs but not the lower. Same with the CDI, if it's bad you would have either problems all the time, or at one end of the RPM band or the other. YOu said it does it all over the RPM band when you stop changing throttle input. That tends to make me think its a carb issue. I'd start there (for 2 reasons: 1. it seems the more likely problem, and 2. its cheaper than buying parts).

Another thought hit me: did it do this when you first got it before you did the top end? Is the piston facing the correct direction? I know, stupid questions, but leave no stone unturned...

[KDXGarage]

float valve rubber tip OK?

float height OK?

[John_S]

Excellent points about the coil and likely how it should be breaking up at high rpms if it was bad. After looking at the ebay coils I decided against it for now. None of them are a direct replacement with the blue wire coming off. I'm not ready to splice into the wires and change the connector on the blue wire. The guy who takes all those bikes apart on ebay charges more for his used coils that RMATV does for a new one. A new oem is $60 something.

I believe the bike did this before the top end but I thought it was bad jetting and because I wanted the stock piston out of there I didn't put much time on it and mainly just ripped it up and down the parking lot behind my shop (20 minutes) pretty much idling or full throttle :). I ended up taking the cylinder head back off of it to make sure I wasn't burning a hole in the piston with the pinging. The piston looks good and the arrow faces the exhaust. I'm going to double check the reeds and theres another thing I need to look into. I took the air striker apart when I first got it and blew out all the passages, I need to do that again. When I installed it I noticed that the carb would slow drip from the overflow even if the bike was just on a triangle stand. The floats came set at 14mm so I reset them to 16mm but twice now in the 10 engine hours since its been done it started pouring fuel out the overflow while the engine was running. Once I was putting around the lake and when I came back my daughter said dad your bike is leaking bad. Then today in the garage it was idling and I walked away for a minute and when I came back it had a pretty big puddle of gas underneath it. Could be that my float valve is not seating correctly? It shouldn't cause it to spark knock so bad though I wouldn't think. I have a few other PWK's and going to take the float valve out of the newest one and try it out., double check the floats and do the blow through air test again to make sure its sealing at 16mm. I sure hope you guys are right about the fuel issue. After jetting way rich to noticeably lean on the pilot and needle and it still doing it I had sort of written off a fuel problem. I took it out for a spin tonight and I definitely made the problem worse by retarding the timing all the way to the hash mark. When it would do its thing tonight at steady throttle you could really feel it in the grips and pegs. Back to base timing and more tinkering. Thank you again!!

[John_S]

float valve rubber tip OK?

float height OK?

Good thinking Jason. I was just replying back to bufftester about a possible intermittent float valve issue. Back to square one with the carb and going to give the 33mm another test run because I barely rode it when I put it back on. I took off and still in first gear about 15 mph it started pinging and I turned right back around and took it off.

[KDXGarage]

I think it would be worth checking.

I am not an expert, but well read on the old dirt bike forums in the last 15 years. The "only cuts out at high RPM" comment is often seen on failing coil, CDI works or it doesn't as best I remember. Anyway, if it were mine, I would not think it is the coil or CDI. As far as your measurements being off, I don't see many people getting service manual friendly checks on their readings.

[John_S]

I think it would be worth checking.

I am not an expert, but well read on the old dirt bike forums in the last 15 years. The "only cuts out at high RPM" comment is often seen on failing coil, CDI works or it doesn't as best I remember. Anyway, if it were mine, I would not think it is the coil or CDI. As far as your measurements being off, I don't see many people getting service manual friendly checks on their readings.

That's good to hear. With as much as I've read on this forum and I've seen your name for a long time now, you're an expert in my book :). I'll keep you guys updated and apologize in advance for my long winded posts. I'm just trying to have the good old KDX I've read so much about and wanted for a long time now. I'm determined (maybe obsessed is a better word) to get it right, its getting close. I got to ride a 220 once in Hawaii in the early 2000's and it went on my "I should get one of those someday" list.

[John_S]

I had a little bit of a breakthrough today but haven't ridden it yet. I took the carb all apart, blew it out, checked the float level, and installed a float valve from another pwk. Started it and it seemed the same, sort of rough idle like always. After doing that I decided to do another leak down because it has had a bad idle from the day I bought it, old top end and carb, new top end, carb, and reeds. The previous owner said it was cold blooded and I just figured it was the jetting which he said hadn't been touched since it was new. No matter what pilot or AS setting...I have to keep it running with the throttle for about 5 seconds before it will idle on its own. Take it out and run it and you may have a idle at 1200 wanting to die or could be 1900. But it doesn't seem to surge up and down like an air leak. Weird thing if you bring it in and the idle is up near 2000 you can hit the kill switch and then start it 2 seconds later and you have to keep it running with the throttle again for a few seconds and then it will idle fairly rough and low. Anyway I put the piston at BDC and pumped it up to 6PSI. Within 6 minutes it dropped down to 4PSI but I couldn't see any bubbles from spraying it with soapy water or hear any leaks. I took the right side KIPS actuator cover off and the left side slotted kips cover and pumped it back up. Behind the slotted cover by the gear was hissing where the kips valve goes through that seal in the cylinder. I've always just snugged that cover up and never really cranked it down. I'm going to get a new oring for the cover but in the mean time I greased the oring and cranked it down and the engine held to 5 3/4 over 6 minutes, much better. When I started it up it idled really smooth right away and even higher where I had to turn it down a bit. Hopefully we're onto something. I also cleaned up the stock carb and put in stock jetting so I can give that another (longer) try if sealing up that slotted cover doesn't work a miracle like I'm hoping it will :-).