Rough stumbling cold idle, Kymco Yager GT 200i

[Yager200i]

Hi, all.

Ok, got a problem that's been vexing me on my 174.5 cc liquid-cooled fuel-injected 2010 Kymco Yager GT 200i running on 87 AKI octane gasoline from Costco, and using Royal Purple 15W-40 synthetic oil. It's got an NGK DPR7Eix-9 Iridium spark plug in it.

On cold startup, the engine seems to only hit on half the cycles, then as it warms up, it sounds like it starts hitting on all the cycles. It never dies, engine speed is normal idle speed, there are no DTC (Diagnostic Trouble Code) codes and everything looks good when I hook up the Kymco Diagnostic Tool. *Everything* is just as it's supposed to be, according to the Diagnostic Tool (fuel injector pulse width, coolant temperature, ignition dwell time, etc.).

So it starts out with a "rum-dum-rum-dum-rum-dum" sound that slowly smooths out to a "rum-rum-rum-rum" sound over 30 seconds or so. It also smells like it's running rich when cold.

There are no starting problems. Just a touch of the starter button and it fires right up, warm or cold.

When it's warmed up, it runs like a champ, no hesitation, no power loss... in fact, it's got so much power it's super easy to hit the rev limiter, despite running heavier than normal variator weights (18 grams instead of 16 grams).

Even when it's cold, it runs like a champ, but the power definitely climbs as the engine warms up... max speed when cold is about 68 MPH, then as it warms up, it'll go up to the rev limiter at about 77 to 78 MPH pretty easily.

I've replaced the O2 sensor, but that didn't make a difference on the cold start issue. I cleaned out the Idle Air Bypass Valve with some throttle cleaner from Kragen, but that didn't make any difference. I used the Kymco Diagnostic Tool to reset the Air Per Cycle (APC) valve and engine idle speed (for some reason, engine idle speed was set to 1716 RPM, when I reset the APC, it dropped back to the factory 1660 RPM).

None of that helped.

The spark plug comes out looking good, there's just the tiniest bit of light brown buildup on the flat edge of the plug below the threads, the insulator is an off-white color, no bubbling or cracking of the insulator. This spark plug is one heat range cooler than OEM, which should make it more prone to fouling, but it's definitely not fouling.

My fuel mileage has actually been getting better and better... I'd almost resigned myself to only getting about 65 MPG, but lately it's been climbing. The last tankful was 74.6 MPG, an all-time-high MPG. It's hit all-time-high MPG the last three tanks as the MPG climbed.

I've been running Startron Enzyme Fuel Treatment (one ounce per tankful), and that's helped the lumpy cold idle a bit, but not much.

So I got to thinking... could it be the Secondary Air Supply System pumping too much air into the exhaust pipe while idling, thereby tricking the ECU into richening the mixture? I've got heat wrap on my exhaust pipe, but that shouldn't matter on a cold startup.

Remember that the SASS injects air into the exhaust upstream of the O2 sensor as a means of pollution control, sort of a smog pump... but if that's what's causing this, why is it only happening on cold idle, and under no other conditions?

I'm stumped, so I'm looking for others who've experienced the same and figured it out already.

[Yager200i]

Just had another thought... if the spark coil is weak or the spark plug wire is leaky, it could cause missing... and the unburned fuel would actually trick the ECU into thinking it's a *lean* condition, making it richen the mixture.

But why only when it's cold?

[Yager200i]

In chasing down this lumpy cold idle gremlin, I was watching YouTube about motorcycles with lumpy cold idle. One of the guys said it was due to his valves being misadjusted. So I checked the valve clearance, the secondary air injection control valve, the spark plug and the timing chain today.

Nothing out of the ordinary to report.

I cleaned the spark plug, using an emory board to shine up the J-hook, just in case the spark was having trouble jumping the gap due to carbon buildup on its landing zone. Then I made sure it was gapped to 0.9 mm. I put a dab of copper antiseize on the threads, and torqued it to 10 ft-lb. I know the manual says 6.5 ft-lb, but that seems awfully loose... it barely crushes the crush washer at that torque. The good news is I started the spark plug threads 180 degrees from where it'd been put in last time, so the J-hook isn't shrouding the spark from the intake valve anymore, the plug's open gap is pointing almost directly at the intake valve now. No indexing washers needed.

The secondary air injection control valve was a bit carboned, but not bad. I cleaned it up and put it back together.

The valves were at exactly 0.09 mm, just as I'd set them. I know they're supposed to be set to 0.1 mm, but that ever-so-slightly tighter valve clearance gives me just a tad more valve lift, which gives the engine a tiny boost in power, without unduly risking slamming the valves into the piston.

The timing chain and chain tensioner look practically new. No wear, no problems.

I also went through and tightened all the clamps on the intake manifold and the various tubes, just to be sure there wasn't a leak on one of them.

Unfortunately, the problem persists.

[BettinANDlosing]

Is there an air bypass screw on the throttle body on the Yager? That might solve your issue. It'll be on the left side with a tiny rubber cap over it. Turn counter clockwise about 1/2 turn see if that helps.

[Yager200i]

I'll check that first thing tomorrow morning, and get back to you. It's a promising lead, as in perusing the service manual, a picture of the throttle body shows a cylindrical metal protrusion on the left side of the throttle body, with a black rubber stopper in it, just the right size for an adjustment screw. It's not labelled at all in the service manual, though.

I'll keep you apprised of what I find.

[Yager200i]

Wow, you know what? You're right. There's an adjustment screw under there. I didn't touch it, though... I found what was causing the rough idle.

I tore into the bike pretty deeply today. I took apart the entire intake from the air filter to the engine, cleaned up all the parts, ensured everything was in good condition, and put it back together. I did the same for the fuel system from the fuel hose to the fuel injector.

I found some very, very fine grit covering everything from the fuel hose, the fuel injector, the intake, etc. It was pretty apparent it came in via the fuel, you could see in the throttle body where it'd been sprayed on the walls by the fuel injector. So a bad batch of gas is the culprit. That means I'll have to replace the fuel injector, as it's partially clogged with the stuff and no amount of cleaning will fix it.

And I'll have to find better fuel filters. The ones I'm using are Wix 33031 / Napa 3031 filters, with a metal canister body and paper filter element. They have a 12 micron filter rating. So the fine grit getting through the fuel filter was finer than 12 micron. But it clumped up everywhere.

I stripped every part down as far as it'd go... the fuel injector actually comes completely apart. But I nicked the O-ring when I was taking it apart (it was really stuck together), and that tiny, tiny nick caused it to leak fuel when I'd gotten it all back together. So I went to Kragen and got a Viton O-ring of the same size and put it in. Leak fixed, problem solved.

I found the Throttle Position Sensor can actually be pivoted back and forth to adjust the sensed throttle position. I got the bright idea that if I slid it all the way toward the forward position, the ECU would think the butterfly valve wasn't fully open, even though it would be, and hence it'd feed the engine less fuel, improving fuel economy.

It works, but there's a side effect. At a certain RPM, the engine just cuts out. The closer you are to adjusting the TPS so it reads 100% when the throttle is 100% open, the lower that RPM will be right off of idle. I started with the TPS all the way forward. The Kymco Diagnostic Tool showed the throttle position sensor as reporting the throttle only open 91%.

"A 9% fuel savings!", I think to myself, "Great!". I buttoned it up and took it for a test ride, whereupon I discovered the flaw in my brilliant plan. The engine was cutting out at around 4500 RPM, which is right where the RPMs are when I'm taking off from a stop with light throttle.

Apparently the ECU switches between "open throttle" and "closed throttle" modes, and there can be no gap in throttle position between the two, or the ECU just shuts off the fuel injector in that gap.

So, I went back home, and adjusted the TPS so it was showing 96% open when the throttle was actually 100% open. Another test ride revealed the engine would cut out if I just barely cracked the throttle. I kind of like it like that... it allows me to coast in traffic without using fuel, and the engine cuts out at 3000 RPM, an RPM that isn't even usable given that the clutch doesn't start engaging until 4500 RPM. Cracking it just a slight bit more makes the engine jump to 4500 RPM.

But, knowing that it ought to be seamless between idle and open throttle, I carefully adjusted the TPS position until it was exactly correlated with the actual throttle position, then I did the TPS reset procedure. Just can't win. Heh.

See attached pictures.

[Stig / Major Tom]

Two thoughts....off white plug and increase in mpg's.....running lean? But that doesn't jive with running one grade colder....or fuel smell upon starting.
I cleaned my injector by soaking in a bowl of Techron and then air hose.
Check for small air intake leak?
My $7 quick fix is a new plug. Can't hurt.....and is cheaper than whatever you're making per hour as a scooter mechanic!!  :-) :-)
Stig

[Yager200i]

Curiosity got the better of me today, so while I had the Met-In Box off for measuring free space for a new 5 micron fuel filter (my current fuel filter is 12 micron), I popped the little rubber plug out to access the adjusting screw on the intake plenum, as discussed here:
http://www.kymcoforum.com/index.php?topic=12666.0

I turned it all the way in, just so I knew how far to turn it back out when I was done playing. It was exactly two turns out.

Turning it all the way in gives that rough, stumbling idle *all* *the* *time*... so that gave me a clue that this might be the last little bit that needed cleaning to completely smooth out the idle. I'd already cleaned the fuel line, fuel injector, intake plenum and put a new 12 micron fuel filter on previously.

So, I screwed the screw all the way out while the bike was idling, and removed the screw. It's a needle screw, obviously for adjusting the idle fuel:air mixture... even though we've got an Idle Air Bypass Valve, I guess this is the fine adjustment.

I sprayed some throttle cleaner into the hole, cleaned the needle, then popped the upstream hose off the Idle Air Bypass Valve and sprayed a bit of throttle cleaner through it as the bike idled. It died a couple times, but started right back up.

Taking the engine's response from when I'd turned the needle screw in all the way, I gauged where the rough idle started, then backed it out until it was idling smoothly. It's now only 1 turn out, instead of 2, and the idle is smooth as butter.

I'll adjust as necessary in the future if I find it's necessary.

[Louder North]

Yager200i, the next time you have the floor board off, could you measure the resistance of the two leads for the fuel pump? It should be 1 ohm (+/- 0.2) to be 'in spec'.   

thanks

[CROSSBOLT]

Have not heard from Yager 200i since about 2015.....