Lean Surge???

[Zman]

Last autumn my Godson had his 2002 EC200 scream (high RPM) itself to death. He noticed that its throttle revved while going over whoops. He was playing in a big mud puddle/pond prior, but the issues stopped after he left the whoops. Then he went back to the mud pond and the engine revved and it would not stop. He was soaked and the single wire kill switch was shocking him so much he could not press it to kill it. He ultimately pulled the gas line to stop it but it melted the top end and crank bearings.

I inspected the bike immediately after the melt down and the throttle was fine. I rebuilt the entire engine but never found a cause. The crank seals were fine, the intake gaskets were fine, the throttle cable was fine. The carb to intake boot had some minor dry cracking but none went all the way through, but I replaced it anyway.

I checked the carb float bowl and it was clean. I did not have one of the Motion Pro cables with the threaded ends so I applied a little JB weld epoxy to the cable sheath end to secure the sheath in the throttle adjuster screw. I drove the bike for a few miles over some hills and trails but no whoops and it ran great!

The first ride for the rebuilt ec200 was a local enduro. The first mile of the enduro had a whoops section. My Godson's father was riding the 200 this time and was lagging behind so I waited for him to see what was up. He told me that the bike went wide open on the whoops. I was shocked. I spent several minutes to double check the throttle cable and it was still rigidly secure at both ends and the cable sheath was routed correctly. It was not binding and the throttle worked perfectly.

I started the bike and it rode fine across the flat corn field. I normally ride a big bore XC300 and the 200 runs well but it is not an unmanageable amount of power. I took it on the same whoops section again and I was riding with a constant 1/3rd to 1/2 throttle in 3rd gear. The bike acted normal for the first three whoops and all of a sudden the bike the bike revved like it went WFO and it shot out from between my legs and looped itself down the trial in front of me. It happened very fast. I know this sounds silly but it happened. I did not open the throttle to WOT (where it could get stuck) it went WOT or revved on its own.

I just got through riding it hard across the field and the engine did not seem ti have the same amount of power I just witnessed on the whoops.

Again the throttle, cable and ends were fine. Prior to the whoops section the bike had not seen water for 8 months.

I started thinking that maybe the bumps caused enough force to bounce the slide up so I am going to replace the throttle spring but I think that is wishful thinking.

This does not make sense to me and I am starting to wonder if this event could be related to the carb being a little rich in the 1/3 to 1/2 throttle range and if it went leaner over the bumps and had a surge of power.

Another possible option may be that the float level is slightly low and it could similarly cause it to go lean over bumps.

I have not found a good answer for this event and I would appreciate your thoughts. I will install the new spring soon, check the float height and record all of the jetting details.


Entertaining side note- My friend was standing 200 ft away watching the event. When he came over to help, I could not help myself so I told him, " I don't know what you are talking about. The bike runs fine!" I was wearing my GoPro and the video is rather interesting.

 

[(F5)]

This probably needs some careful investigation. If you can only work out how to harness this outrageous power increase you could be onto something big here. Think about the aftermarket possibilities and the revenue stream you'll generate. You'll probably have to think about moving into a bigger house & consider hired service.

But maybe I'm getting a bit ahead of myself.

Only thing I can think of (after thinking I bet the throttle cable is hooking up a few times whilst reading, but I believe you've checked now you mentioned it so many times) is perhaps the throttle slide. My EC200 never had such problems & neither did my KDX.

But it (KDX) did have a PWK carb & the slide on that was badly worn so I replaced it thinking it was only a matter of time before it hung up. Looked like a 1/2 moon shape worn into the slide from rattle at idle I guess.

Lean revving usually only occurs under no load. Turn the gas off & run the bike & it will rev a little high, but not crazy, If it was being ridden it would just die under load.

 

[Jakobi]

I'd be closely inspecting the slide and return spring.

Get the bike running on the stand and modulate the airbox and other parts and see if you can get any change in the way it runs. Flex the intake boot/manifold a bit and make sure its not opening up under certain actions.

Maybe open up the throttle body and have a quick check in there aswell. Did you replace the throttle cable or just make sure it wasn't pulling out?

I think you'd be hard pressed to have the carb run dry in the whoops. You may be loosing some fuel due to splash, but the same splash should also be directly fuelling the engine and also causing a richness. I've seen bikes run away a bit as they run out of fuel, but its not something that happens in an instant.

 

[Zman]

This probably needs some careful investigation. If you can only work out how to harness this outrageous power increase you could be onto something big here. Think about the aftermarket possibilities and the revenue stream you'll generate. You'll probably have to think about moving into a bigger house & consider hired service.

LMAO!!!!! I know and yes the thought did cross my mind.

I pulled off the top of the carb. The #7 slide looks pretty good. No significant wear and the plating is still fully intact.

The needle is gold/brass looking in color and it has been ground just below the clip notches. We bought the bike used so I wonder if this is an old LTR needle? The clip is in middle position. There are some scratches in the needle as was mentioned in other posts on the stuck throttle topic.

The spring shows a good bit of wear on the outer surface where it contacts the bore. It is 3/8" shorter than the new return spring and softer potentially due to the wear.

I will double check the float height and other jetting when I pull the bottom off this weekend.

I will try the idea of poking and prodding the air filter boot when I put it back together. The air filter boot is on the hard side.

I will also compare that needle to our other EC200 and will probably just order up a new needle for it. I need to check the jetting posts for the most recommended needle type.

I did not install a new cable, but I will install a new KTM Motion Pro with screw ends while I am at it.

 

[bergerhag]

I had a similar thing happen to my 300 while pressing it hard on a sandy mx course. I identified it as a lean out condition, caused by too little flow through the hose mounted ball valve on the fuel tank cap. You know the one that is supposed to stop reverse fuel flow if you drop the bike. This got worse with a topped up tank, as the small air pocket made the pressure drop too fast and preventing proper flow to the carb. When i removed the valve the symptoms were gone. I had a long track side mech session finding this out, tearing down every part of the fuel flow and throttle cable. This never happened in my normal woods riding of course.

 

[Zman]

How long did that take you to figure out?

 

[Brian VT]

I identified it as a lean out condition, caused by too little flow through the hose mounted ball valve on the fuel tank cap.

I was just thinking the same thing. I learned of these symptoms when I was a kid and I didn't pay attention that I had twisted the fuel cap vent hose when turning the cap back on. When trying to pull a lot of fuel it couldn't suck enough air through the hose.

 

[bergerhag]

How long did that take you to figure out?

It took me two sessions on the MX track to identify that I really had a consistent problem. Then perhaps two hours of trial and error, going through the fuel supply and test running between the various operations.

When removing the little valve, the bottom side of it has a holed plug in the end to keep the ball in place, and to let air past. The four holes in this plug were very small, and I have now enlarged them to allow better flow of air. I have not tested it this way yet, but blowing through it clearly shows the flow is improved.

 

[bkwdc]

I had the same thing occur during two hare scrambles. Was always during a rough section while hard on the throttle.
Correctly routed the throttle cable and safety wired both ends more securely than before and no problems since.
Was fun trying to tame a 300 while wfo in the woods.
I probably should be considering a longer throttle cable.

 

[hamilton]

I've had the same thing happen on other brands of 200's. Hard to believe just how fast they are if this happens. I have always found the cause to be a small grain of sand some where in the carb. Most always shows up when riding whoops with the fuel sloshing around. A thorough cleaning of carb, new vent hoses and new throttle cable is much cheaper than a trip to the ER. I now install small pieces of foam in the vent lines.

 

[(F5)]

Well I'm surprised to hear lean effect producing power, but if others have then I'm happy to admit to being wrong.

well not so much wrong as less right.

but I think the take away message here was that I was right.

anyways, yes the LTR needles weren't plated, but either are some others. My PWK 35s I bought new for my RZ had DEK needles bare brass from new.

No chance anyone has put a shorter needle in it? that would be a dangerous combination if it came out of the 'ole. I doubt you wouldn't spot that though.

 

[Zman]

All great information! The gas cap has an open piece of hose for the vent line but I will double check that the cap flows air well. I will pull the carb and do another thorough cleaning. I have a No-Toil that air filter that fell apart that I can use to filter the vent / overflow hoses.

I checked the needle and it is the correct length .

Thank you all for the info, feedback and support for the notion I may not be totally crazy!

(F5) - I think you are making good progress on coming to terms with your correctness!

 

[Zman]

Well I pulled apart the carb and found more black grains in the bottom of the float bowl. This was very odd since I pulled out the petcock and cleaned the carb when we rebuilt the engine. I had previously separated the carb vent lines and ran two high and two low. I replaced the black fuel lines for good measure.

I also found that the pilot was jetted way rich. I took it from 48 to 40 and it seems to run well now.

I also put in the new heavier return spring.

To wrap this one up I think it was running rich and going over bumps debris would get sucked into the main jet and the debris leaned out and corrected the air fuel ratio which made the bike "happy!"

 

[skidmarx]

Wow, all the above describes a couple of incidents I've had recently. 1/3 throttle over whoops and the bike wants to rev out. Even when I shut the throttle it still revs up. Have checked the usual cable/spring but all appears fine, so I will have all the jets out and cleaned.