Odd stalling issue

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Odd stalling issue

Postby 90SDKDX » 11:48 am Jun 22 2017

I've got a 1990 KDX200. It's been a while since I've posted here, but you may have seen my previous thread on this issue and installing the Jaguar performance CDI. Anyways I've been having an ongoing stalling / hard starting issue with this bike. Some mornings I can walk out, kick it once or twice, and it will start. Other days, it won't start to save it's life. I previously had a bad source coil that I replaced twice(first coil was wound incorrectly). I do currently have spark. My plug will get wet and my carb looks clean and I can see through all jets. Air filter is clean and oiled.

This past Sunday I tried taking it out for the first time this year. It was hesitant to start again, so I decided to try and unplug my kill switch. Right after I did this, the bike started first kick and was running well. About 3 miles into the trail the bike bogged down badly and died. The bike would not restart by kicking. The bike would start when pushing and popping the clutch, but if any gas was applied it would bog badly. On the side of the trail I did check my plug and it looked brown/black. I also checked for spark and confirmed it was sparking. Once I got the bike back home it fired off first kick.

I'm at my wits end on this thing. My only last thought is low compression, which I have yet to check. However, if compression was my issue I don't believe it would be an intermittent fault.
Am I wrong in thinking that compression should raise as the engine gets warmer, therefore it would be hard to start cold and run well hot, if my compression was low?

Thanks for any help.
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Re: Odd stalling issue

Postby doakley » 02:44 pm Jun 22 2017

Doesn't sound like compression to me. I would look at electrical things for intermittent problems, especially if you know the carb is clean.
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Re: Odd stalling issue

Postby 6 Riders » 02:46 pm Jun 22 2017

Low compression will cause an intermittent starting issue. If you've looked at everything else, it might be time to pop the cylinder off and have a look inside.
This is IF you've looked at everything else. Check your float, reeds and if necessary, the rest of the carb. It sounds like a fuel issue (to much) but I've had the same symptoms on a worn out piston/cylinder before as well.

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Re: Odd stalling issue

Postby 90SDKDX » 02:55 pm Jun 22 2017

6 Riders wrote:Low compression will cause an intermittent starting issue. If you've looked at everything else, it might be time to pop the cylinder off and have a look inside.
This is IF you've looked at everything else. Check your float, reeds and if necessary, the rest of the carb. It sounds like a fuel issue (to much) but I've had the same symptoms on a worn out piston/cylinder before as well.

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Can you explain how compression would have an intermittent effect on starting? I could see how a warmer temperature outside would possibly bring motor temp up, thus causing easier starting and vice versa for a cold day. I would think if compression is low it would not start at all, not on and off, but I've definitely been wrong before. I replaced the reeds when I purchased the bike a few years ago so they should be good to go still. Also why would the compression issue cause the bike to stall out on the trails?
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Re: Odd stalling issue

Postby 6 Riders » 03:27 pm Jun 22 2017

The piston expansion changes cylinder pressure. Also, since the piston is also the intake valve and exhaust valve you really have a bunch of parts that aren't working to full efficiency. You might not get any fuel, then the bottom end loads up and you have to much fuel and etc.

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Odd stalling issue

Postby 90SDKDX » 11:04 pm Jun 22 2017

So I did some more work on the bike tonight.

I started by doing a compression check. I did two back to back tests and got 150 psi, well within the specified range.
I then checked my float needle and float height, both looked great.
I then put everything back together and tried starting it.
Of course, the bike did not start. I tried with choke, without choke, holding the throttle open.
The only thing that seemed to change was the bike was kicking back hard and backfiring a bit when opening the throttle, which I know can happen when throttling on starting.

So I then got back to the stator and rotated the plate to retard the timing as far as possible, thinking the timing may be advanced too far with the new source coil (this one is from electrosport, new plate and all). Buttoned it back up and still nothing. Next I tried swapping my stock CDI back to the Jaguar adjustable CDI. No luck. All the while I was doing this I continued to check for spark and never lost it.

So in summary I have:

Good compression, 150 PSI (checking on cold motor since it won't start)
Fuel flow to cylinder (plug continually gets wet)
Clean and oiled air filter.
Spark when checking on cylinder head.
Completely new stator.
Testing with two CDI's.

What am I missing here? At this point I'm thinking it's got something to do with spark timing but who knows. I may try putting my old stator back in and see if it changes anything, but I don't see why it would.
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Odd stalling issue

Postby SS109 » 12:32 am Jun 23 2017

I would assume the crank key is on there since you had to pull the flywheel to adjust the stator timing, yes? So, from the plug being wet, it sounds like you are possibly flooding the engine to some degree. Have you checked the condition of the reeds? The backfiring makes wonder about them. How about checking to see if the carb float actually floats? What jetting do you have in there? Did you try a brand new plug? Even though you have spark have you tried swapping to another known good ignition coil?
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Re: Odd stalling issue

Postby Jaguar » 02:49 am Jun 23 2017

take the float bowl off and check for adequate fuel flow. a trickle of flow will starve it for gas when you open the throttle.
Also make sure the tank cap breathes correctly. If not then after riding a while the lowering level of fuel in the tank causes a vacuum in the air space which greatly limits fuel flow out of the tank.
A stator coil can connect/disconnect intermittently with heat/cold.
check your crank seals.
start with new gas because if it has any alcohol content then the alcohol will combine with moisture to settle to the bottom of the tank and float bowl.
when you take the float bowl off look at the gas in it and see if there is a "bubble" of water at the bottom.
also you could have an intermittent high voltage coil.
also your spark plug may need replacing.
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Odd stalling issue

Postby 90SDKDX » 08:57 am Jun 23 2017

In response:

I have not recently checked the reeds. I replaced them when I bought the bike roughly four years ago, so I'd hope they are fine still.

When referring to the carb float, would I simply need to pull the bowl off with the carb and turn the gas on to ensure it's flowing?

Jetting wise I have stock pilot jet I believe and a leaner main jet.

I have not tried a brand new plug after the stall on Sunday, but the plugs I've been using have very light use.

I have not tried swapping ignition coils as I do not have a spare and don't know of anyone in the area with one.

With the gas cap I've tried starting with and without the cap on, so I don't think it's an issue.

Obviously the stator coil is new, so I'm ruling that out right now.

I have not checked my crank seals as I don't have a leak down tester.

The fuel is less than a week old and from a gas station I use on a regular basis.

I'd like to touch back on the ignition coil. I have read that it is possible to have spark outside the cylinder but once the plug is under pressure it goes away. I would assume this would be an issue with the secondary windings in the ignition coil not producing enough resistance to spike the voltage high enough to overcome the added resistance from compression. Can anyone confirm this theory?
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Re: Odd stalling issue

Postby Friedom » 09:53 am Jun 23 2017

How's your spark plug cap? Could be being loose/corroded leading too inconsistent firing (may have visible spark, but under compression is a different environment).

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Re: Odd stalling issue

Postby 6 Riders » 09:53 am Jun 23 2017

You most likely have a fuel/air problem. Clean your air filter and CAREFULLY check the reeds. Use light and make sure there is no light leak.

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Re: Odd stalling issue

Postby 90SDKDX » 11:39 am Jun 23 2017

6 Riders wrote:You most likely have a fuel/air problem. Clean your air filter and CAREFULLY check the reeds. Use light and make sure there is no light leak.

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Now that I think about it, when I took the carb off to drain it, there was a sort of weird vacuum sound coming from it when the gas started coming out of the vent tubes. I made sure to blow out all those lines before I put it back on, but maybe I have a blocked air passage in the carb that isn't allowing enough gas to flow to the motor. Just a thought I had.
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Re: Odd stalling issue

Postby KDXohio » 03:38 pm Jun 24 2017

Throw a new plug in rule out a fouled plug.
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Re: Odd stalling issue

Postby 90SDKDX » 04:58 pm Jun 24 2017

KDXohio wrote:Throw a new plug in rule out a fouled plug.


Tried this last night - nothing changed.

I've got a spark tester on order so I can check the spark per the service manual. Looks like it should be able to cross a 7mm gap with the tester, so we will see.
If it's not that, I'll move on to reeds.
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Odd stalling issue

Postby 90SDKDX » 08:33 pm Jun 28 2017

Well I got my spark gap tester today and kicked her over. Got a spark that jumped the 7mm, appeared to be blue in color as best as I can tell. I don't know what a "fat" spark looks like as some say you need, but it looked okay I suppose.

I guess the only thing left is to clean my carb out and check reeds. Considering I have spark, compression, and a clean air filter, that's the only thing that's left.
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Odd stalling issue

Postby Dekon » 12:58 pm Jun 29 2017

The in tank fuel filter could be clogged as well. You might want to check that.
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Odd stalling issue

Postby 90SDKDX » 03:39 pm Jun 29 2017

Fuel flow out of the tank is spot on.

I ordered some reeds this morning so I can replace them if needed. I feel like 6 riders may have been correct earlier. I didn't know reeds could cause hard starts, but you learn something new everyday. It's just weird to me that they would fail while on the trail, but I suppose it is possible.
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Odd stalling issue

Postby B737driver » 05:53 pm Jun 29 2017

Dekon wrote:The in tank fuel filter could be clogged as well. You might want to check that.

+1

Debris may be jostling around in the tank and intermittently clogging the in-tank filter. I also always start with a blip of the throttle. 4 stroke guys :roll: usually have a hard time starting my bikes because they leave the throttle closed. It'll start eventually, but not on the first kick.
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Re: Odd stalling issue

Postby 90SDKDX » 10:50 pm Jul 05 2017

Update:

Got the time tonight to inspect / replace my reeds.
Upon disassembly I found that they looked perfectly fine. None of them were chipped or cracked anywhere and I could not see light through them. The only thing possibly odd was a couple of them were a little black in color, most likely from fuel-oil. I went ahead and replaced them as I bought some of the dual stage reeds in case mine were bad. Once all assembled again I tried starting and still nothing. I sort of figured this would be the case considering my old reeds were fine. It backfired really loud the first kick and nothing after that.

I took my carb apart and plan on cleaning it at work tomorrow. My pilot and mains were both clear, but at this point the only thing I can think of is a clogged passage somewhere. I did notice a tiny bit of green varnish in the bowl, but nothing horrible. If this doesn't fix it I may be leaning towards a bad crank seal.

Here's a little video of when it happened. You can hear it's running great and then it just bogs out and dies. Feel free to watch some of my Beta videos as well (I'm slow so you may fall asleep).
https://youtu.be/ZM7RApR3Q8A
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Re: Odd stalling issue

Postby Jason » 11:11 pm Jul 05 2017

In case you have not already, read up on dipping carbs and the jet block gasket.
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