Heavy Shake at low RPMs

[Mymini]

Doodlebug with stock 2.5 is shaking pretty pretty hard during takeoff and midrange. When I take off on bike it shakes pretty hard until 15 mph then it smooths out. Seem a bit more than just regular mini bike vibration.
Haven't played with anything except the long govener screw

 

[olajoe808]

Check to make sure you flywheel didn't come loose. It could also be your clutch engagement to low.

 

[The Restore Kid]

Those thinngs are notorious for carburetor problems... It may be running to rich and loading up at lower speeds until the engine really gets going and can burn off the fuel it's getting...

Sounds like my dads chevy truck.. :laugh:

 

[Dudlydoodleright]

Is It a Thump-Thump-Thump, one for each piston stroke? Is it worce cold and not as bad hot?

 

[Mymini]

Which screw to adjust fuel on carb. ? Turn clockwise to lean out?

Those thinngs are notorious for carburetor problems... It may be running to rich and loading up at lower speeds until the engine really gets going and can burn off the fuel it's getting...

Sounds like my dads chevy truck.. :laugh:

 

[Mymini]

Yes,,, haven't noticed if it is worse hot or cold!

Is It a Thump-Thump-Thump, one for each piston stroke? Is it worce cold and not as bad hot?

 

[mmisterbungl]

Have you tried to shim your neck tube spacing where the forks mount to the tube?

 

[Mymini]

I did tighten chain too. Maybe too snugg.

Check to make sure you flywheel didn't come loose. It could also be your clutch engagement to low.

 

[supernova]

He's likely experiencing the same shake every one has with a larger rider on it, they eventually stop shuddering once you get to speed. I've had four and every one did it badly under acceleration with me on it. My son too and he's 150#, the stock engine is best for kids under 100#. My daughter rode two with the stock engine and they did OK for her. I still cannot believe they still use the little powerplants, they must get em for a very low price.:shrug:

 

[Dudlydoodleright]

If I'm right what it is is too little of gear reduction for the power of the motor vs. the mass it's pushing. Each thump is the piston pushing on power stroke. You need to increase the gear ratio or get more displacement. If it's better hot let it warm up, and not less air/fuel-more. You'll notice it less on down hill and more up. Basicly if you want that little motor to last change your gear ratio or over time you'll lose the motor.

 

[olajoe808]

I did tighten chain too. Maybe too snugg.

Oops, that might be it right there.

 

[jreid50]

Could be the clutch slipping due to what the above posts where stating, to much gear(or not enough depending on how you want to say it!) for your weight! The clutch cant fully engage at low RPMs! Go up on rear gear and I bet it will smooth out a bit for ya!

 

[delray]

more then likely the clutch is just fighting with the low power engine and your weight and the incorrect gear ratio from factory. the only thing that will really help is a jackshaft setup. that will help the clutch lock up better. problem will never really go away ,but it will help some.:thumbsup:

 

[Dudlydoodleright]

Even with total lockup there is a surge of power on each power stroke followed by the other 3 parts to the 4 cycles of a 4cycle engine. More mass in the flywheel, clutch, wheel, tire, chain, sproket and crank smooth things out-as dose more rpms. As for slip even if you ran a sprocket with no clutch- if the mass of the spinning moving parts are too low for the mass the motor is pushing it will do this and the lower the rpms the more you'll notice. Jackshaft or heavier motor.

 

[lonewolf57]

He's likely experiencing the same shake every one has with a larger rider on it, they eventually stop shuddering once you get to speed. I've had four and every one did it badly under acceleration with me on it. My son too and he's 150#, the stock engine is best for kids under 100#. My daughter rode two with the stock engine and they did OK for her. I still cannot believe they still use the little powerplants, they must get em for a very low price.:shrug:

Yep, same thing here. When we bought our red DB30, it would shake, vibrate when my wife or I would ride it, but not when our daughters (much lighter than us) rode it.

A week later I dropped a HF 6.5 hp "clone" engine in with a cjtmini install kit and the problem was solved....:wink:

Jimmy S.

 

[Mymini]

Found it: bike was put together at Academy sports. They forgot to put the upper and lower beveled washers on the front fork bolt. About 1/2 inch of space.

 

[balljoint]

Doodlebug with stock 2.5 is shaking pretty pretty hard during takeoff and midrange. When I take off on bike it shakes pretty hard until 15 mph then it smooths out. Seem a bit more than just regular mini bike vibration.
Haven't played with anything except the long govener screw

It is underpowered,the clutch is glazed from heat is my guess

 

[supernova]

Yep, same thing here. When we bought our red DB30, it would shake, vibrate when my wife or I would ride it, but not when our daughters (much lighter than us) rode it.

A week later I dropped a HF 6.5 hp "clone" engine in with a cjtmini install kit and the problem was solved....:wink:

Jimmy S.

Like I said, the engines tend to shake badly when stressed by a heavier rider. 100# is too much IMO for riding without a jackshaft. The last one I bought was already getting the 3hp briggs so we rode the 2.8 to death, it shook and dragged ass till it puked oil out the air cleaner. It did take a while but it never made good power, and I bypassed the governor altogether (not recommended). A kid can ride one for a while, adults have no business on one with a stock engine.:drinkup:

 

[Jason B]

He's likely experiencing the same shake every one has with a larger rider on it, they eventually stop shuddering once you get to speed. I've had four and every one did it badly under acceleration with me on it. My son too and he's 150#, the stock engine is best for kids under 100#. My daughter rode two with the stock engine and they did OK for her. I still cannot believe they still use the little powerplants, they must get em for a very low price.:shrug:

Yep, just got a yellow db30 and mine does the same thing. Glad I found this forum. I weigh 170, good to know it's normal when a heavier rider it on it.

Now, on the governor screw with the spring on it. I've loosened it up pretty far and it now goes around 25mph. I've been reading of some people removing the screw completely and they say it even goes faster? But it's not recommended to "remove" it??

 

[supernova]

Yep, just got a yellow db30 and mine does the same thing. Glad I found this forum. I weigh 170, good to know it's normal when a heavier rider it on it.

Now, on the governor screw with the spring on it. I've loosened it up pretty far and it now goes around 25mph. I've been reading of some people remving the screw completely and they say it even goes faster? but not recommened to remove it??

If you weigh 170# it's time to graduate to a more powerful engine, you'll never get the performance out of the 2.8 you need. :thumbsup: