Re: any ideas what would cause a motor to run wide open with hood off but..
The air intake on that hood is probably at the lifting handle on the top, back of it. Any chance that you got something clogged in it from the inside, when you had the hood off?
I agree that exhaust gases getting into the enclosed cowl will affect performance quite a bit, but that's not something that would be expected to begin, just because to hood was off and the carbs were worked on. That said, just as air full of spent fuel/exhaust gases will degrade performance, so will lack of air at all. If plenty of air is not getting into the cowl from the outside, engine performance will suffer greatly.
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