Newbie Problem

Hi All,

I have been perusing the the forum since I bought my 66cc engine from BGF to solve a number of problems I have encountered. I am new to this particular hobby but after about 50 miles of riding - I'm hooked. Nevertheless, I have had no luck with my most recent problem and am hoping to obtain the advise of those with way more experience and knowledge about these engines than I.

When the motor is first started, it will not accelerate past 20mph even the the throttle wide open. After about 20 minutes of riding, the engine will start to go faster but will bog momentarily and make a knocking noise. If I release the throttle and immediately give it gas again the knocking goes away and the bike will go faster. I surmise this is because an engine runs leaner once its warmed up - but cannot evidence that in any way. The knocking I also thought may be "4 stroking" but cannot substantiate that claim either. More recently, the motor seems to have periods of heavy vibration stemming from the head of the motor even during low rpm operation. It subsides and returns randomly. Along with this new phenomenon came a gurgling sound while decelerating. Moreover, the bike seems to be going through a tremendous amount of gas. In about 60 miles of riding I have filled up 4 times. I am not a math expert - but even on the conservative side I should have been able to go roughly 180 miles.

I did notice some oil-like substance dripping out of the exhaust and also around the exhaust mount. I do not know if this is normal.

I have read a lot about adjusting the carb - which I have tried. So far the best setting seems to be the 2nd notch from the top. Adjusting the C-clamp made relatively no change in the knocking sound or top speed. I also made sure the carb was level and secured properly.

Additionally, BGF supplied two different spark plugs, both of which I have tried. The second seems to make the engine run more smoothly, but that may just be my imagination. They are both chocolate brown.

In my research I have seen suggestions such as cleaning the exhaust, installing a new main jet, and removing the air filter. I wanted to see what you all would suggest as my next move in solving these problems.

Thank you in advance for your tine and help.

UPDATE:

I spent some time today experimenting with different settings. The I moved the c-clamp up to the top most notch in the carb. The plug is a nice chocolate brown color at 1/2 throttle. At WOT the plug becomes black and there is a lot of smoke... so I am going to assume its running rich. Is my only option to replace the main jet?

Also, the bike runs much better/faster once warmed up. Even still, the bike occasionally slows and makes a knocking noise. Could this be 4 stroking from the engine running rich at the top end?

Any advise would be helpful.

PS. I have a BGF RB80

Wayne Z - Shutting off the the petcock does boost the performance - so def running rich at WOT.

Is it better to solder and drill the existing jet or could i just buy a 6mm #73 jet? Do you happen to know the default jet size on a standard NT carb that comes with the BGF RB80? I want to ensure I am not leaning it out too much. Perhaps this is why drilling is better - trial and error?

I also noticed there was a little oil around the head gasket. I read this is normal - but should I take the a look anyway? I don't have a torque wrench so I am apprehensive of taking it apart. I know the right thing to do is to sand it down with a fine grit paper attached to a piece of glass - but will it cause damage/problems if it leaks a little?

Thanks for all the advise.

Okay. So I bought 3 different jets from sickbikeparts. .60 .65 and .68. I started with the .65 and immediately noticed the bike was running smoother but once I started riding i noticed the engine sounded a bit starved. Put in the .68 and things seem to be pretty good. Still not thrilled with the speed (20-25 mph).

Checked the plug and its dark brown. Maybe I'll start tinkering with exhaust next.