Post by hooligan on May 6, 2013 1:32:09 GMT 1
Pretty much everyone with a 4LO is familiar with the 5500 - 6500 rpm mid range stumble or flat spot before the engine comes on the pipe. It is especially annoying in the higher gears as the bike won't pull across the flat spot and requires dropping a gear or two to accelerate above it.
With only a simple modification I seem to have completely eliminated this midrange flat spot on my LC.
My bike is running OEM pipes and carbs, the stock airbox and filter and is pretty much stock except it has an o-ringed head and the squish has been set correctly. The main jet is a 220 and the needle is one clip down from the middle position IIRC.
Over the winter I extensively cleaned the carbs and replaced all the seals. The air screws and idle settings were matched and carbs synched to ensure everything is working properly.
The only two things changed from stock is a set of Boysen dual stage reeds (which I don't think is the solution to the midrange stumble) and the addition of a pair of 6mm reed cage spacers (which I do think is the reason for the elimination of the flat spot).
Today had the bike out on the highway and the midrange flat spot is simply gone. The bike will easily pull across the 5500-6500 rpm in any gear. Most impressively it will actually do a 6th gear roll on at 5000 rpm without the need to gear down. I even did one on a slight uphill section. The only time I had to gear down was when we hit a bit of a headwind. I rode nearly 50 kms of highway and hardly had to gear down at all. Anytime I wanted more speed just roll on the throttle. It's like a miracle.
At this point I am totally happy with the bike. I still have a boost bottle to try but I'm not sure it can make much of an improvement. Hopefully the midrange stumble will remain a distant memory when I get the expansion chambers installed.
With only a simple modification I seem to have completely eliminated this midrange flat spot on my LC.
My bike is running OEM pipes and carbs, the stock airbox and filter and is pretty much stock except it has an o-ringed head and the squish has been set correctly. The main jet is a 220 and the needle is one clip down from the middle position IIRC.
Over the winter I extensively cleaned the carbs and replaced all the seals. The air screws and idle settings were matched and carbs synched to ensure everything is working properly.
The only two things changed from stock is a set of Boysen dual stage reeds (which I don't think is the solution to the midrange stumble) and the addition of a pair of 6mm reed cage spacers (which I do think is the reason for the elimination of the flat spot).
Today had the bike out on the highway and the midrange flat spot is simply gone. The bike will easily pull across the 5500-6500 rpm in any gear. Most impressively it will actually do a 6th gear roll on at 5000 rpm without the need to gear down. I even did one on a slight uphill section. The only time I had to gear down was when we hit a bit of a headwind. I rode nearly 50 kms of highway and hardly had to gear down at all. Anytime I wanted more speed just roll on the throttle. It's like a miracle.
At this point I am totally happy with the bike. I still have a boost bottle to try but I'm not sure it can make much of an improvement. Hopefully the midrange stumble will remain a distant memory when I get the expansion chambers installed.
