My brother is looking at an 1800, not sure of year, but from pictures it looks like a series B or C.  It's a gas, with a Minneapolis Moline trip loader on it.  Seems to be mechanically sound, but it doesn't want to go any higher than 1600 or 1700 rpm.  Could this be just an adjustment issue?  How much would this loader be worth if he were to sell it?  Anything particular to check out on it?  Thanks.