Looking at a 650 diesel.It runs excellent on diesel (pull start)..missing the starter the person has not heard it run on gas.What is the worst case scenario if it would not run on gas..Thanks in advance..

would be the regular spark or carb issues, nothing major. you can pull it on the gas side to start it thus not being so hard on the diesel if your using starting fluid, other wise it takes about 1/2 mile to get them going. dont forget engine parts are obsolete so make sure the engine is in decent shape.

It could be as simple as water in the carb. It is equally as simple to drain it off through the carb petcock. You will also have to clean the starting tank sediment bowl. I mention this because it happened to me the other day. Don't know where the water came from but it must have been in the five gallon gasoline bucket.

Standard gas engine troubleshooting procedures apply here. Check fuel and spark. You can get a rough idea of the gas side compression by comparing the cranking speeds while in gas or Diesel mode.

A 650D in good condition will start on Diesel with the starter if starting fluid is used. Don't think anyone would recommend that method as a regular procedure. They will also start on Diesel if hot. A high watt block heater might be hot enough.

I have never had to mess around the with the multiple linkages, valves, or switches on any of the three gas-starts I have owned.

When I got my 650D the little "cam" in the carb that shuts off the float when switched to deisel had come loose...was just a little nut on a threaded shaft that had worked loose. I realize that this probably wouldn't be your case where it runs on deisel but maybe not on gas, but who knows what's going on inside those carbs until you take 'em apart and look. They're very simple carbs, and OEM Tractor parts(I think) has a kit available for them. When I took mine apart the gaskets were still ok and I was able to reuse them.

First of all to check stuff, make sure your starting tank has gas in it, open the valve at the sediment bowl under the starting tank, then open the petcock at the bottom of the carb(with the switchover lever in the "up"(gas) position and make sure gas is getting to the carb.

If the only way to spin the motor is to pull the tractor, you can vice-grip a spark plug someplace visible to a good ground and hook a plug wire to it and watch for spark while someone pulls you...might have to rob a longer plug wire off something else, but this'll tell you if you have spark at the plugs or not.

If there's spark at the plugs and gas in the carb and still no start, it's time to start looking into the switchover mechanism to make sure everything's moving like it should. Since it runs good on diesel, it's probably a safe bet the starting valves are closing ok, make sure they open when the lever's moved to the gas side(pull valvecover to check this).

they can be hand cranked and started also,... if you ate enough pancakes. i start my WD9 with the crank at times.

I'll add in that the butterflies in the intake manifold are a major culprit for not starting on gas. Their job is to divert air from the main passages into the carb passages. They are not forced closed. The linkage just pushes the shaft past center and then a spring on the shaft (in the end of the manifold) pulls an arm over center and finishes the job. If the shaft develops a bit of a drag it won't snap closed. You can reach in behind the manifold and work the shaft manually to a certain degree. The feel will tell you if it isn't right.

Another FYI, the butterfly shaft kills the ignition when in diesel. There is a switch at the front end, presuming it is hooked up.