Motorized Bike Lurching a Bit

angus · #1 (**permalink**) 03-01-2008, 08:22 PM

Hey everyone!

I just got my bike up and running! I'm very pleased (new build)! 48cc 2 stroke on an old cruiser frame - a 1985 Murray.

As I ran it up and down the road, I noticed that it lurches a bit. The engine runs smoothly without a load (clutch disengaged); however, under load (clutch engaged), it tends to lurch or buck. I'm pretty sure that it is the drive train. In fact, I tightened the chain a wee bit which helped, but it continues to do it. Any thoughts given my very brief description?

By the way, I used Norman's approach to sealing the intake manifold and it works like a charm! Thanks Norm!

angus

deacon · #2 (**permalink**) 03-01-2008, 08:27 PM

I have that lurch from time to time and have never found a real answer.

I hope someone can help you with it. My chain was too tight and I think that might be it, but you said tightening yours seemed to help. I thought mine might be the sprocket not centered but it doesnt seem to happen often enough to be that. I mean if the sprocket is the problem it is always off center if thats it. It only lurches now and then.

angus · #3 (**permalink**) 03-01-2008, 08:47 PM

Quote:

Originally Posted by deacon

I have that lurch from time to time and have never found a real answer.

I hope someone can help you with it. My chain was too tight and I think that might be it, but you said tightening yours seemed to help. I thought mine might be the sprocket not centered but it doesnt seem to happen often enough to be that. I mean if the sprocket is the problem it is always off center if thats it. It only lurches now and then.

The chain tightening definitely smoothed out the power transfer to the wheel. I aligned my sprocket with the drive sprocket during the build; it also appears to be true - in the same plane as the drive sprocket. I'm hoping that as I get better at adjusting the throttle, the lurching will diminish.

Funniest thing: I was taking great care during the initial start-up but forgot to turn on the switch (I installed an on/off switch on the black wire to the CDI). I pedaled like crazy... fuel on and showing flow... no luck with a start!!! Took me several attempts to figure out that the switch was in the off position. I have to laugh at myself... being so excited by the start-up and forgetting to turn it on! Feeling like a kid.

**Norman** · #4 (**permalink**) 03-01-2008, 08:55 PM

I know the feeling you are talking about very well. Is the jerking at low rpms? if it is then try ot run it a little faster I know sometimes I get mine to jerk when I goof on start up up to the point of knocking me off the seat. I have to look around to make sure no one is watching when that happens as I feel dumb.

norman

deacon · #5 (**permalink**) 03-01-2008, 08:57 PM

I set mine up the same way with the on off and have done that more than once since. The dumbest one for me was I set everything up and then ran up and down my drive. nothing, checked all the wiring then the plug and finally it downed on me. I had the throttle shut down to idle. I opened the trottle and it fired right up. one of those Duh moments.

**Norman** · #6 (**permalink**) 03-01-2008, 09:04 PM

We all have our midol moments.

norman

angus · #7 (**permalink**) 03-01-2008, 11:22 PM

Quote:

Originally Posted by Norman

I know the feeling you are talking about very well. Is the jerking at low rpms? if it is then try ot run it a little faster I know sometimes I get mine to jerk when I goof on start up up to the point of knocking me off the seat. I have to look around to make sure no one is watching when that happens as I feel dumb.

norman

Now that you mention it, it is at lower rpms that I see the lurch. I'll try giving it more throttle tomorrow (...I was trying to take it easy today for the initial run...). I'll let you know how it comes out. Thanks guys!

angus

**RedB66** · #8 (**permalink**) 03-02-2008, 02:44 AM

I'd like to jump in on this thread. My lurching is at high rpms. As I'm motoring along the lurch feels like I'm running out of gas. It is very suttle and quick. As I'm riding I can hear and feel a momentary drop in the rpm's. Sometimes it will happen 4-5 times in a mile.

**Bikeguy Joe** · #9 (**permalink**) 03-02-2008, 06:04 AM

Quote:

Originally Posted by RedB66

I'd like to jump in on this thread. My lurching is at high rpms. As I'm motoring along the lurch feels like I'm running out of gas. It is very suttle and quick. As I'm riding I can hear and feel a momentary drop in the rpm's. Sometimes it will happen 4-5 times in a mile.

Carb float height?

**Bikeguy Joe** · #10 (**permalink**) 03-02-2008, 06:06 AM

On my kits, I noticed a "lurching" on the run down. I always pulled the clutch in when I was off the throttle, whether on a downhill grade, or when coming to a stop.