Assuming you have adequate fuel level and flow and mixed at 32:1. If you are premixing.
After heat cycles was cylinder base abd head gaskets retouqed? Was a leakdown test performed? You may have an airleak(s)
Check spark plug color for an idea if it is fouled (wet or black in color) replace plug
Or white with no color at all which would indicate a lean condition ( airleaks,wrong jetting or carb)
How was it running when you drove it.?
The more information the better we can try to nail down your problem.
Can you run a compression test?
Was an egay rebuild kit used?