Not a Nikki Master here. They seem to Master over me.
Just some things I've seen about Nikki's hunting/surging/spitting.
When working on one for myself trying to avoid spending big bucks for a NEW OEM carb.
If I was working one equipment for a customer they would have the choice of buying a NEW OEM Nikki (some replacements at over $200) or going somewhere else, because they are most generally themselves the cause of the bad carb due to poor TLC with fuel and their equipment.
For my own use When I find one of the dual throat Nikki's for a twin cylinder engine hunting I can usually just use a can of carb cleaner with the small nozzle and blow out the jet holes and replace the emulsion tube jet o-rings if the o-rings are not snug fitting. If the inside is really nasty they go to the Usonic first I've found GENERIC China clone kits for the dual throat Nikki's for around $15 that have all the o-rings although not all the Nikki's are the same inside. (one size does not fit all even though they look the same on the outside)
Most generally if I give one a
good cleaning Only both the single cylinder type and the dual throat type and put one back together and it still surges I have to go back and replace the o-rings associated with the emulsion tube area, especially if the emulsion tube has the two itty bitty jets.
I recently bought a $20 china clone dual throat Nikki to replace a OEM surging Nikki I had cleaned and did not have a kit and the NEW China clone was surging worse. After re-checking the intake and all else I removed the CHINA Nikki clone bowl and seen that the emulsion tube was same as the OEM, so I used the clone emulsion tube and associated parts for parts into the OEM and got a good run.
I suspect that most generally PEOPLE are using the somewhat[b][color=#0040FF] LOWER PRICED ethanol fuel and causing lots of the carb problems even the Nikki o-rings going bad faster than normal.[/color][/b] (and at $5
plus/gallon for non-ethanol fuel now days most people are going to use the somewhat lesser priced ethanol fuel which weakens/hardens fuel lines and o-rings and makes moisture and the
majority of the China Clone carbs will rust inside the bowls very fast
even with good fuel.)
I always try to use non-ethanol fuel and external in-line fuel filters and do not have very many carb issues unless the equipment is left un-used for long time without a fuel stabilizer. I sometimes seen lawn tractors that have a large style fuel cap that the top of the cap will trap/puddle rainwater and the gas tank fuel will eventually get contaminated with moisture. (gas tank vent in the cap will eventually take in little bit of the water from the top of the cap)