Weird GY6 Ruckus engine 150CC Issue with random engine dying  By  userix (Read 19,951 times)

I flipped the carb around already from last time you stated it was backwards. But the fuel starvation issue is something separate. Even with the carb mounted facing backwards, I still have fuel delivery issue, as evident in the carb bowl being almost empty after a long wot session.

In reality, even though I was idling around 2500-3000, my bike wasn't moving by itself at a standstill. I could get off my bike, without any of the brakes on, and it would stay put and not move at all, even though it was idling so high. I know it's not suppose to idle that high, but just letting you know, it wouldn't move by itself in spite of the high idle speed.

But now that I see the carb bowl is nearly empty after a long wot session, I know it's a fuel delivery problem. It seems like the pump isn't getting enough fuel to the carb on extended wot sessions. I read somewhere else in this forum that the vacuum pressure of the GY6 engines at high RPM produce considerably less vacuum pressure, thus reducing in the amount of fuel pumped by the mikuni vacuum pump. Not sure how valid that is.

But like I said previously, I checked all the vacuum lines for leaks and the fuel lines as well. There are no leaks. It seems that the gas tank is working because if I disconnect the fuel line going into the mikuni pump, gas freely flows out, which means there is no obstruction to the free flow of gas from the gas tank. There is no gas leaking out from any of the lines either, so I'm not sure where the bubbles or air in the fuel line from the pump to carb are coming from. The mikuni pump is brand new, so I know there are no tears in the diaphragm of the pump.

Well, the carb is a stock 24mm keihin carb.  I have both my vapor speedo and TTO tach hour meter set to PPR of 1 (Pulse Per Revolution of the crankshaft).  Not sure how to fit a vacuum gauge to the small 3/16" vacuum hoses.  But I do have the problem of air bubbles getting into the fuel line between the pump and the carb.  I'm not sure where air is getting in.  The vacuum hoses and fuel lines are well sealed to the connectors and there are no leaks anywhere.

A new problem has arisen. I have the vapor speedo installed along with the TTO tach hour meter. The vapor speedo has the tach wire hooked up to the connector at the ignition coil coming from the CDI. The TTO Tach hour meter has its sensor wire wrapped around the ignition coil wire right before the spark plug. I just recently started having weird stuttering issues while riding. It's random stuttering that comes usually during WOT, but can occur throughout the throttle range as well. There are no popping or backfiring sounds and it idles fine. It doesn't feel like a fuel delivery issue or carb tuning, since nothing has changed in those aspects when it was running fine. It started having the stuttering issue after I removed the spark plug from the engine. After I reinstalled the spark plug and the boot securely, that's when I started having the weird stuttering issues randomly throughout my ride.

What I do notice because of my dual tach setup, I'm getting two different readings for my RPM during my rides at greater than 50% throttle. For instance, when I'm at ~8000rpm according to my vapor speedo, the TTO tach hour shows 4300rpm, almost half of what it should be. But at standstill idling, both tach reads correctly ~2000 rpm. I rode around longer and the problem is consistent, the RPM reading at the coil wire near the spark plug is almost always half of what I am reading from the CDI unit. The PPR setting is the same for both TTO hour and vapor trailtech, which is set at '1'.

So do I have a bad ignition coil? Or can the spark plug boot go bad? I notice the spark plug boots sold online have different type of resistance on them. Does the resistance matter for our gy6 engines? I currently have an NGK spark plug boot installed.

Yeah, I checked the gap, it's still the same, I didn't bump it while putting it back.  I mean, if the RPMs are reading correctly from the CDI right before it connects to the ignition coil, that should mean everything before the ignition coil is working correctly?  So my problem has to lie either in the spark plug, spark plug boot, or ignition coil.

If the wire is loose to the spark plug boot, can I just cut off an inch or so to expose fresh coil wire and thread that into the boot?

Ok.  Now this is something weird I noticed.  Here attached is a picture of two spark plugs that I have used.


The spark plug on the left is the stock A7TC plug I have been running perfectly fine in my engine with no issues whatsoever.  I believe the chocolately brown color indicates that the jet tuning is pretty good, not too lean and not too rich. 

Now here's the weird part, I decided to switch the plug to a brand new NGK C7HSA (Cross-referenced plug for the A7TC stock GY6 plug) to see if there were changes in the performance of the engine.  During my test rides, I noticed after long WOT sessions, I would experience very sluggish acceleration from a stand still.  But top speeds and mid-range acceleration still remain great, no sluggishness at all.  Also there is no popping on decel or backfires at all, so another sign it is not running lean.  I then pulled the plug after letting the engine cool down and noticed the plug looks very dry and has white ash deposit on the tip (the NGK spark plug on the right).  This, I assume is indicative of a very lean tuning or condition.  I verified there were no leaks at the exhaust gasket area, the carb and intake manifold area, and the head gaskets on the cylinder body. Does this mean the plug is too hot of a heat range?

Everything else on the engine remain unchanged.  The carb tuning was left untouched as well.  The valve cover has a small leak due to a worn o-ring gasket, but I wouldn't think that could affect the spark plug condition.  Does the sluggish acceleration from a stand still be a result of really lean conditions?