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I have a 1985 MTD tractor model 145-810 I believe. It has the original gas cap which is missing the clear plastic top part. I am worried that if I leave the machine out when raining it will leak water into the tank. I would like to find a replacement cap. I don't require(or want) one with the built in gauge. I would like to find a vented unit to fit.
Here is a photo of my cap. The tank opening is just slightly larger than 1.75 inches.
Any suggestions?

Rotary, Stens & Prime Line all do replacement caps with & without fuel gauges.
In the mean time a fizzy drink bottle cut in 1/2 should be a reasonable fit over the top to keep water out.

Part number. 723-0346A