Why do engines shake and stutter at low rpm/higher load?

[Rough Edge racing]

Ok, finally watched your suggested video.  Thank you! 

Low Speed Pre-Ignition.

That at least makes sense to me as a potential source of what otherwise seems like inexplicable shuddering.

 The video..... Low speed pri ignition is a problem with modern turbocharged engines. Oil formulas have been changed to make sure the tiny bit of oil getting into the combustion chamber doesn cause it.And the enginner is talking about creating lugging by fully opening the throttle at low rpm....I'll stand my ground and say an air cooled bike engine can suffer from pri ignition but it won't be at low rpm's with light loads...And pri ignition in an air cooled engine will punch a hole in the center of the piston in a blink of an eye...Anyone really familiar with old Brit Bikes, 2 strokes or even Harleys may have experienced it..

[wirespokes]

I don't get there's anything wrong with the OP's bike, yet everyone's trying to fix it. 

As far as I can tell, he's asking what causes the shuddering. I thought he wanted to understand the physical phenomenon behind that feeling of when an engine is lugged, but nothing came of the explanation I gave. So I don't know what's wanted here... 

[SmithSwede]

I don't get there's anything wrong with the OP's bike, yet everyone's trying to fix it. 

As far as I can tell, he's asking what causes the shuddering. I thought he wanted to understand the physical phenomenon behind that feeling of when an engine is lugged, but nothing came of the explanation I gave. So I don't know what's wanted here... 

Wirespokes.  Correct.  I’m not complaining or asking for a cure.  It’s easily avoided with a bit more revs. 

I’m just trying to understand *why* this phenomenon occurs.  I’m a curious but ignorant fellow.  Not sure I’m satisfied with all the answers given.  Maybe the question is too weird. 

I’ll try again.  One thing that seems odd about this is it is basically a non-continuous or binary phenomenon.   It either shakes and bucks a LOT at lowish revs, and then it doesn’t AT ALL at slightly higher revs.   

Why this binary behavior?   

Seems to me that if it had to do with fly wheel weight or some of the other factors being cited, the effects would be continuous, not binary.  It would buck badly at 2,000 rpm, a bit less at 2,200, and a bit less still at 2,500, etc. 

Rough Edge doubts it is low speed pre-Ignition.  Ok.  But I could at least understand why LSPI might occur under load L at 2,000 rpm causing obvious bucking, but then LSPI simply doesn’t occur at all at 2,250 rpm, hence no bucking.  Thereby explaining the non-continuous or binary effect. 

[oldbike54]

 From what I know about the issue , it isn't pre-ignition , it is incomplete ignition . Go back and read what I posted earlier .

 Picture a sump pump , when you first turn it on you get some *blooching* initially until the water supply is sufficient to fill up the pump. An IC engine is really just a pump , at low engine speeds the combustion chamber can't fill up with fresh charge , until it gets spinning fast enough to completely fill the chamber with fresh charge and expel the already burned mixture , you are getting *blooching* .

 Dusty

[Rough Edge racing]

Rough Edge doubts it is low speed pre-Ignition.  Ok.  But I could at least understand why LSPI might occur under load L at 2,000 rpm causing obvious bucking, but then LSPI simply doesn’t occur at all at 2,250 rpm, hence no bucking.  Thereby explaining the non-continuous or binary effect.

 I did mention the Ducatis having a fair amount of valve overlap and the lopey idle that goes with..The overlap causes a lot of tuning issue like intake charge dilution...This continues up the rpm scale until it fades away, on that era Ducati, about 2500 rpm...Careful tuing of the carbureor can minimize it so at 2500 in lower gears the bike runs reasonably smooth at light load....If you roll on the throttle at that rpm in the upper gear the engine will shake it's head...
   LSPI was never mentioned or a factor before small tubocharged cars became common place. With the long duration cams in a Ducati the low speed cylinder pressure is far far less than a modern turbo engine designed to have boost at low rpm to increse torque...In my opinion , the Ducati  engine cannot creat the conditions required for LSPI....

[SmithSwede]

Dusty, I’m offended you called my wonderful Ducati engine a sump pump.

 

[oldbike54]

Dusty, I’m offended you called my wonderful Ducati engine a sump pump.

 

 Reality kinda sux at times Prescott 

 Dusty

[LowRyter]

Dusty, I’m offended you called my wonderful Ducati engine a sump pump.

 

9k rpm "sump pump"