I own a Case 530 backhoe that has always run well up until now. The loader has the 159 cubic inch gas engine. When I try to start the tractor it will start only if the throttle is wide open. It will run rough, back fire sporadically with some blue & black exhaust. When the problem first started I noticed the carburetor float was sticking causing the engine to flood so I thought that was the problem and it was going to be an easy fix. I was wrong. I sent the carburetor out to a local shop and had it rebuilt which didn't correct the problem. Since then I have replaced the spark plugs, plug wires, rotor, cap, condenser and ignition coil all to no avail. I checked all 4 plugs and they are all getting a good blue spark. I checked the compression which is 125, 140, 150 & 130 psi from front to rear. I don't think anything is internally broken in the engine. I checked the distributor to see if it might have become loose causing the engine to be out of time but it hasn't. If anyone has any ideas as to what the problem could be I would greatly appreciate your assistance. Thanks.