Originally Posted by grizz1

There is nothing wrong with the Gen 5 or 5.5 motors, trust me. We ran heaps of those motors here and they got hammered. Tuning and lean bog was not an issue, once tuned correctly. The people having difficulties with the motors are not tuning the long needle carbs properly.
Most people are under the impression, or have been taught to tune the top end needle first followed by the bottom end needle - WRONG. The best way to tune any carb on these motors (long or short needle), or any micro 2 needle carb actually, is to set the idle gap and tune the bottom end first. Then tune the top, then revisit the bottom.

With the long needle carb it's all about having the top end needle rich enough - so if you tune by cranking on the top end needle first to get a nice crisp WOT setting, YOU WILL GET LEAN BOG.
With the long needle carbs, because the tapered end of the needle stays in the reciever jet even at wide open throttle, you need the HSN set rich enough to let enough fuel past the needle tip at WOT. The slightest bit lean on the top will result in lean bog. This is why you must set the bottom end first for good power right through the rev range, thus making sure the HSN is rich enough to allow this, then fine tune the very top end if required with the HSN by only a screw driver blade width at a time. Then go back and re-visit the LSN if you did need to tweak the HSN, as this will have a direct effect on LSN performance too.

I go back to my garden hose analogy - Think of the HSN as the tap, and the LSN as the nozzle.

If you only have the tap open a little (think lean HSN) you will get a nice steady trickle out of the hose (normal running). Now if you open the hose nozzle suddenly and quickly (stab the throttle out of a corner), will you get a good jet of water ? - no you won't, because there is not enough pressure due to the tap being shut.
What you need to do is open the tap up more so you have all the water you will need, no matter how wide open the nozzle is (richen the HSN), then control the flow of water from a trickle to a jet by adjusting the nozzle (tuning the LSN). Make sense ??? Well that's exactly how your GO carb works !!!! It's no more complicated than that. It just requires a little thinking outside of the square, and away from conventional tuning methods that have not kept up with innovations over the years.
Tune the bottom first, then the top. Hope this helps.

By the way - check your exhaust header. Had a customer who was having a devil of a job getting and keeping a tune. Turns out his exhaust header had a hair line split in the bend. New header = problem solved.