Iam going to look at a 650 that runs on gas not diesel..the guy said he has to many irons in the fire no time to diagnose the problem..other than looking for anti freeze in the oil what should I look for that would indicate there is something seriously wrong with this tractor?thanks in advance..

If there is a misfire in gas mode, the engine could have valve issues. If when switched to diesel, it just does nothing but slow down and no attempts to run happen it could be a stuck injection plunger, or other injection related issue. A gas side compression check in the neighborhood of 85 to 120 psi that is fairly even across the cylinders shows that it is probably not a disaster internally.
Water in the oil is bad, check the drain plug by loosening it till a tiny bit of fluid comes out. Oil good/coolant bad.
Cracked heads and poor maintenance on injector pumps and fuel systems are the most problematic issues. They are reliable engines, and economical. They are costly to repair due to expensive parts. Warming on gas side for two minutes gets them happy when starting the diesel run mode. Cooling down on diesel for 5 minutes after it is worked in the field is very important for avoiding a cracked head. (my opinion is that it should not be switched to gas operation for cool down, as it cools less than idle diesel, and opens the starting valves heating them for no reason.
If it produces no white smoke when switching to diesel mode, it is not getting fuel. Jim

Mr Nicholson are you available to take a look at this tractor sometime? it is near Montevideo.MN.thanks (56260)

The on site analysis would not make as much difference as answers to the following questions:
1) look at the intended value to your operation or intended use (it is pretty big to be dragging around to parades and shows)
2) The asking price might be 20% more than scrap price as the utility of these work horses is limited to drawbar like work and tillage.
3) it is going to take several hundred dollars to have the Injection system rebuilt if that is the issue.
4) The examination I indicated in my first response is easy to do, and really tells the story of the potential.

A local mechanically inclined friend would be more economical. A "non running on diesel" IH is a challenge to a pretty good mechanic. I am teaching this summer, and will not get a chance to roam very much.
Jim

First you need to establish if fuel is making it to the cylinders. If, when running on gas, you get white smoke upon advancing the throttle, you know the injectors are spraying fuel into the cylinders. At that point, I would start suspecting a compression on the diesel side problem....starting valves perhaps not closing. Listen closely to what the seller says about his trying to diagnose the problem.