I just got this motor a week or so ago. I was unsure of its history so I rebuilt the carb, new plugs and did a decarb treatment. It does this weird popping/surging like the video shows. Any ideas what it could be? I know the video may not show it but it kinda backfires through the carb when it happens. It seems to be intermittent it may stop doing it for a few minutes then it will start up again. I've tried adjusting the low speed carb needle from 1/2 turn out to 6 turns out and this made no difference in the popping. Did the the decarb with seafoam cause this? Is this a fuel pump issue?
the changes in the rpm at about the 40 second mark was me idling it down. sorry for the video quality....
thanks for the reply cofe, you always seems to have an answer. I was reading through my manual and it said a broken reed valve may cause this type of popping. what are your thoughts on that possibility? I just cant understand why it would be intermittent though, to me if one was broken it would be an all the time problem. I just put it in the tank and ran it for probably 30 minutes without a hiccup. This is really bizarre!
If it just ran fine for 30 minutes, there may have been something in the carb idle circuit. A reed valve has similar symptoms, but would be very constant. Sounds like you may have got the cobs out. Time to fish?
If you turned the low speed needle 6 turns out and it didn't stall, you have a problem with the carb and it should be disassembled and cleaned. The popping is often caused by too lean a mixture at low speed. Disassemble and clean all passages in the carb with carb cleaner before moving on to more complicated fixes.