Does this plug look alright?

[gary55]

So when it drops down from 29 to 23 when it hits 23 does it start running good again without no change in throttle position? Then pick back up to 29, then drop back to 23. If it will oscillate back and forth like this with no change in throttle position you could have a vibration issue.
If the mounts are a little loose sometimes it will allow enough vibration to cause the fuel in the carb bowl to foam, and the needle to vibrate violently in the tube. This usually happens at the higher end of your rpm and the interruption of even fuel flow causes the engine to die down until the vibration dies down then the engine will speed up. The cycle of speed up, slow down, speed up, slow down will continue with no change in throttle position. Just a thought to check out because form the looks of your plug I would be reluctant to jet leaner.
I only mention this because of the 6 mph drop is a big change, and is probably not the case since it only has a small drop with the 70. I would stick with the 70 and get it as close as I could with needle adjustments till I got the new pipe on and then go from there as anything your doing with the stock exhaust on will quite likely change with the new pipe.

 

[Kpi890]

So when it drops down from 29 to 23 when it hits 23 does it start running good again without no change in throttle position? Then pick back up to 29, then drop back to 23. If it will oscillate back and forth like this with no change in throttle position you could have a vibration issue.
If the mounts are a little loose sometimes it will allow enough vibration to cause the fuel in the carb bowl to foam, and the needle to vibrate violently in the tube. This usually happens at the higher end of your rpm and the interruption of even fuel flow causes the engine to die down until the vibration dies down then the engine will speed up. The cycle of speed up, slow down, speed up, slow down will continue with no change in throttle position. Just a thought to check out because form the looks of your plug I would be reluctant to jet leaner.
I only mention this because of the 6 mph drop is a big change, and is probably not the case since it only has a small drop with the 70. I would stick with the 70 and get it as close as I could with needle adjustments till I got the new pipe on and then go from there as anything your doing with the stock exhaust on will quite likely change with the new pipe.

Unbelievable I just came in from the garage to read this post. I literally just finished tightening up the motor mounts as I realized all of the studs were loose as hell. I tightened 'em up and waiting for the loctite to set. I am thinking what you said here may just be exactly what was happening! I am still pretty new to the motorized bicycle world, but I'm trying my best to learn from people such as yourself. Okay well now that the engine should be mounted securely should I try putting back in the 70 (stock) or the 72 jet? Could this vibration issue have been causing the engine to run lean at WOT because I couldn't seem to get a dirty oily plug like a lot of people that are trying to lean out their mix, I've been trying to run it richer but every time I pull that damn plug it's looking lean to me? Thanks so much for your help!

 

[Kpi890]

I would stick with the 70 and get it as close as I could with needle adjustments till I got the new pipe on and then go from there as anything your doing with the stock exhaust on will quite likely change with the new pipe.

Also, I am running the stock exhaust without the cap on if that makes a difference in how I should continue to approach this? Does a better pipe need a richer mix and what pipe upgrade would you suggest because that's the next thing I am looking at doing?

 

[CrazyDan]

2 strokes need backpressure to keep the air/fuel mixture from passing out the exhaust port. You should put that cap back on.

 

[Kpi890]

2 strokes need backpressure to keep the air/fuel mixture from passing out the exhaust port. You should put that cap back on.

Correct they do need back pressure, but it has plenty within the stock exhaust itself without the cap on. I've read many, many, posts covering this topic. The only downfall is the absurd amount of noise it creates, which where I live is not an issue.

 

[Kpi890]

Folks I think we’ve done it! 33.4 MPH with a beautiful coffee colored spark plug! A big thanks to everyone that’s helped me along the way on this thread I really appreciate it! I took the carb apart, moved the c clip to the 2nd notch from the top, and left in the 75 jet. This is all after I cranked down on the engine block mounts and used loctite on all the studs (I am started to really believe this is where my issue was Thanks Gary55!). While the carb was off I trimmed back the carb intake manifold gasket, which by the way was blocking probably 30% of the air coming from the manifold into the head. After reassembly I didn’t have my hopes up. Fired her up and let her warm up for about 5 mins or so and took off down the road to my “testing drag strip” as I like to call it lol. Hit about 31 MPH with the 75 jet in so dropped it to a 72 since I could hear it 4 stroking. Once I put the 72 jet in this little Chinese Chica sounds better than it ever has and feels much smoother to ride. I may still mess around more with the Jetting to see if I can get a little faster but right now the throttle response is great and my top end hit 33.4 MPH fastest I’ve ever been on a bicycle! I did notice as I was riding at WOT at some points of the vibration got bad or road got bumpy there was a definite slight (1-2 MPH) drop in speed which I’m still curious how to fix since these motors will always vibrate? Is there a way to stabilize the carburetor separately from the motor with an offset intake or something? Regardless of that minor issue the bike finally has hit what I think is going to be the top end for what I have on it. It’s a completely stock Ebay clunker minus the exhaust cap but I couldn’t be happier. If anyone has any other simple mods I can do to gain either more torque or a little more top end I would love to hear them. My dream for this bike is to get more low end torque and have it top out at 35 MPH. Thanks again!

 

[CrazyDan]

Get an mx-65 pipe.

 

[gary55]

You will notice a instant improvement with either of these pipes. both are from mzmiami parts on ebay, but they sell out quickly so you either have to pay attention to their listing of contact them to see if they do pre sales. Top is the mz65, comparable to the mx 65 Dan mentioned. Don't remember what the bottom one is called. Top one has more top end, bottom one has more low end torque and mid range power. Both are lowed unless you add a muffler.View media item 60557View media item 60733View media item 60733

 

[CrazyDan]

Yeah I meant mz65, didn't notice the typo.

 

[Kpi890]

You will notice a instant improvement with either of these pipes. both are from mzmiami parts on ebay, but they sell out quickly so you either have to pay attention to their listing of contact them to see if they do pre sales. Top is the mz65, comparable to the mx 65 Dan mentioned. Don't remember what the bottom one is called. Top one has more top end, bottom one has more low end torque and mid range power. Both are lowed unless you add a muffler.View media item 60557View media item 60733View media item 60733

Ok great thanks I’ll look into that! How do I find MZmiami stuff on eBay? Do I search the name or?