Help, buggy goes *pop*

Posts: 46

I would love to get another opinion on what just happened this evening with our buggy.

The buggy: 150cc American Sportworks 7150 with a TJ Powersports engine (very much a Twister GT200 mechanically)

Modifications: 115mm variator, 10g rollers, 1500 clutch spring, UNI filter with about a 10" long "redneck" intake, 130 jet, blaster rear shocks.

Goes 39mph with me and my 12 y.o. son in it. Running slightly rich but my Twister pipe from Reliable was arriving on Monday so I thought that would even things out.

Tonight: My son is flying around the yard, just hauling around corners, whipping the rear end around spinning tires and throwing dirt (16 / 32 axle with 21" rear tires and a nice clutch / variator combo equal torquey goodness) running as fast as the cart would go back and forth for about 10 minutes.

He comes to a fast, jerking stop in front of me when suddenly there's a decently loud *pop* (like someone popped a sizable balloon inside a kitchen cabinet - know what I mean?) He did not shut it off, it quit immediately following the *pop*.

I am a car guy, and it sounded very much to me like bad timing firing back into the intake.

Buggy does not restart. Assume it's flooded perhaps? Wait over an hour - still does not start - not even the slightest hint of firing.

Ok - tool time. I drain the carb bowl, quite a lot of fuel comes out. Attempt to start - nothing - but carb bowl does refill, so gas is being delivered.

Remove carb to check diaphragm and floats. Floats are ok, diaphragm appears intact, needle appears to move up and down smoothly and sits all the way at the bottom when at rest. The diaphragm is supposed to look like a deflated balloon right? And the needle and tube are supposed to be all the way down when at rest, right?

Compression check (with carb removed from intake) - 145psi - is that about right?

Spark check - intermittent. Sparks once when turning key to "accessory" (dash lights come on), sparks once sometimes when turning key to off. Spark is smallish and blue. Plug is brownish, moving to black (right where I want it prior to putting on the new pipe). Buggy turns over strongly, battery does not seems weak.

I was testing the spark by laying the plug on the frame (I tried this in more then one place). Because it sparked so easily and repeatable when flicking the key, I would assume the grounding was sufficient.

I switched out the CDI for a spare, same behavior with the intermittent sparking.

The *pop* seemed like such an intake sort of noise to me - is there something else I can test on the carb? Or is this just a case of the coil blew up at just the right moment and it sounded like an intake "back" fire?

What is the test for the coil? I have a DMM if someone can tell me what the specs should be.

Perhaps it's a bad ignition switch? Doesn't explain the *pop* though...any thoughts on what I should test / check next?

Thanks for the diagnostic help.

Posts: 1889

Download the GY6 service manual at http://spiderboxperformance.com and follow the electrical troubleshooting section. report back what you find.

If you hold the pedal to the floor and crank the engine. the plug should be wet when you remove it. If not, you have an air or fuel problem. Check for leaks between engine, carburetor, and air filter.

Posts: 46

Thanks for the quick reply and the pointer to the testing procedure.

Results:

Ignition coil: .7 ohms across terminals, probably ok

Stator (remember, I have the odd wired & triggered CDI):

Blue / Yellow (on my kart this is Blue / White): 0.2VAC
Black / Red: (not used in my ignition): 128VAC (no, that's not a typo)
Green and Yellow: 0.0VAC

This does not seem right some how. Looks like I'll be ordering a new stator. Is there any how-to on replacing it?

I've attached my eletrical diagram as a refresher if necessary.

Thanks for the help so far, any additional thoughts?

Posts: 1889

Ohm out the stator coils to ensure they really are bad. When you crank the the engine will the lights glow while the engine is turning? If they do not, then you may have a blown stator. Look for signs of wire damage or shorting that could have resulted in component failure. Check your regulator for proper resistance (I have seen many fail and melt the connector).

Posts: 46

Stator tests:

Between White and engine block - 0 ohms (should be 0.2 - 1.2)
Between Yellow and engine block - 0 ohms (should be 0.1 - 1.0)

Regulator tests:

Yellow to Green - 546k ohms, should be 5k-100k
Red to White - 540k ohms, should be 3k - 50k

Something bad happened. Sad

Posts: 1889

Most likely the regulator failed and took out the stator. Check your wiring for damage and order the above items.

Posts: 46

Thanks, I have ordered a new 8 coil stator and a rectifier. The 8 coil was stock already.

I also ordered a new flywheel, because before I realized that I needed a special 27mm left threaded puller, I tried to use a set of regular hinged jaw pullers. Who knows if I bent it in my attempt to remove it. Are these things properly balanced new out of the box?

Is it possible that anything else was "taken-out" in the process? Should I get a new coil? I have a back up CDI already, but maybe it's time to upgrade. Is there really any performance to be gained with a "red" or a "9,000rpm", or a "20 degrees advanced over stock" CDI?

Anyway, I ordered a puller too. Wink

Ebay item, Scooter Assassins is the only place I found to get it.

I ordered the stator and flywheel from gy6usa.com - it was the most reasonably priced online ordering place which had both the 8 coil stator and the flywheel. I'm getting the rectifier from Reliable because their "Twister" part is visibly an *exact* match to mine (I keep saying, my ASW 7150 is a Twister GT200 underneath). Smile

The only semi-exposed wire I found, was the the unhooked red / black high voltage AC wire - right near the rectifier inside the black plastic electronics box. The rubber covering it had pulled back and and near as I can figure out - when my son came in real fast and braked real hard it threw everything loose forward. This probably caused that exposed wire to come into contact with something. I have found no other explanation and the kart is only about 30 days old.

Thank you again!

Posts: 46

After replacing the stator and the rectifier (stabilizer to some people), the kart is running again. Thanks for your help!

Also replaced: Coil (but I do not think this had any affect)

Observation: Not all 8 pole stators are created equal. The 8 pole stator part I removed was "beefier" then the replacement I got from gy6usa.com. There were more "plates" and the winding were slightly larger in the old part. The only voltage measurement I can compare between the two is that the old one made 128VAC and the new one makes 108VAC. The price was slightly better with gy6usa, but you always pay for you get.

Expensive work to do, but well worth it. I learned how to do all the diagnostics and the actual buggy type work (I'm a car guy). Plus my son and I did it together so it was nice to spend time in the garage with him teaching him how to use tools not to injure himself or the part he was working on. Smile