Air leak doesn't make sense, crazy (new) vibration at high RPM

[ChristianF]

Guys, I really need some help. I've put off creating a username for this forum for quite a while, as I tried to find the answers I needed by using the search function and reading all the general stickies, but I have some problems I really need an expert on. My 66cc has been running fine for a few weeks, but the last few days it's been doing really strange things. First I noticed that the idle is really inconsistent - it's high, it's low, it's out of control high, it's so low it won't stay running, etc. I figured obvious air leak, and ended up sealing the carb-manifold joint with self sealing silicone flex-tape. However, with the engine idling, if I blow on the carb, the eninge quits. I don't even have to blow hard.

The next problem is that in the last 3 days or so, the bike has developed a very, very bad vibration and bad noise at high RPM. I initially thought it was pinging, but the videos I've watched that demonstrate pinging doesn't really describe it. The engine is making a knocking and vibrating sound at high rpm, but at an rpm that it ran comfortably at last week. Nothing really has changed. I'm running 32:1 full synthetic. The vibration and noise is really concerning me. This bike is my primary mode of transportation, and I can't really afford to have it down and out if it blows itself up. What do I do? I'm really frustrated and need some expert guidance. Thanks!

 

[Jag]

Does it have good compression? Try pulling apart the jug and looking at the cylinder walls for scoring. Blown base or head gasket?

 

[crassius]

first, make sure motor is tight in frame and frame isn't cracked

then find out why you have to seal a carb that never needs sealing on other bikes - air leaks can also be from base gaskets or crank seals

 

[ChristianF]

first, make sure motor is tight in frame and frame isn't cracked

then find out why you have to seal a carb that never needs sealing on other bikes - air leaks can also be from base gaskets or crank seals

I'm not sure what you mean. There's tons of threads about the NT carb needing to be sealed. Why would blowing on the carb cause it to die if the base gasket seal is blown? I don't understand.

 

[Jag]

Because it’s still running lean. Look for dark oil spots on the engine near where the gaskets are. Pull out your plug, is it whitish grey? I recommend pulling it apart and looking at your cylinder walls to check for scoring. Buy a new carb, and if your cylinders already jacked then buy a new carb and cylinder, hopefully your bearings aren’t going too. Spray soapy water where the intake attaches to the carb and to the jug, along with everywhere else on the engine that has gaskets, There should not be any air bubbles. Check to see if your spark plug is in all the way. And all your bolts are tightend.

 

[Jag]

Try looking at the magneto and make sure there is no rust and it’s tight

 

[ChristianF]

Because it’s still running lean. Look for dark oil spots on the engine near where the gaskets are. Pull out your plug, is it whitish grey? I recommend pulling it apart and looking at your cylinder walls to check for scoring. Buy a new carb, and if your cylinders already jacked then buy a new carb and cylinder, hopefully your bearings aren’t going too. Spray soapy water where the intake attaches to the carb and to the jug, along with everywhere else on the engine that has gaskets, There should not be any air bubbles. Check to see if your spark plug is in all the way. And all your bolts are tightend.

Okay thank you, I'll do all of that. I really hope the bearings aren't going, I've only had the engine for about 6 weeks.

 

[Jag]

where did you get your kit from?

 

[ChristianF]

where did you get your kit from?

Raw Motors thru eBay. Crapshoot, I know.

 

[Jag]

If your in the u.s.a make sure you check it out quick and order the parts. %25 increase in cost. Thanks Trump