Where to start..... .
Bob, did you buy this thing from someone you trust to know what it is, or some jockey?To start with, I don't think you have a 7600. You have the forward sheet metal of a 7600 piled on top of a 7700 as suggested by the large instrument cluster. I'm assuming that the tractor also has suspended brake and clutch pedals like a car would have as opposed to conventional straddle pedals like the 7600 would normally have. I don't see foot boards for the 7600 OR a flat deck that the 7700 should have but the pics are a bit distant for my eyes.
It also has the row crop front axle with hydrostatic steering rather than the utility axle with an integral power assist and drag link that the 7600 should have....
It appears to have the 7600's fenders.
It would be good to know exactly what it is should you need parts since there are differences. I'm also curious about how or where you put fuel into this beast? Is the filler under the hood? Since you can't trust what's on the hood tag, look for a horizontal flat spot to the rear of the starter on the transmission housing. You should see three lines of numbers stamped there. Get them if possible and post them and hopefully someone will decode them. I'd have to look in a book myself to decode that model number. It also will not be a '75 model. It will be at the earliest a 76 model that might have been built in the last quarter of 75... Now, to the problems you have. The miss is most likely due to either a bad injector or a bad cylinder (rings/piston issues). You could start the tractor and open the lines one at a time when it's running rough and see which cylinder produces the LEAST stumble when you open the injector. That will be the poor cylinder. From there you can switch that injector with another injector and see if the problem follows the injector. If it does, you have a bad injector. If it doesn't, you have a bad cylinder. The fact that it clears off once it warms up would suggest to me that it's more likely low compression on one or more cylinders.
If it's not burning oil in any appreciable way I wouldn't fret about it too much unless you expect everything from that tractor. 1 quart in 100 hours would be moderate oil use for that engine. They shouldn't use any, but when they start getting tired, they burn about that much.... If it got to be more than that I'd be worried about broken rings, and then you shoud deal with it. The hydraulic problem probably isn't a problem. Look at the system selector rather than the quadrant lever. You should see Draft towards the front, Position in the middle and Load Monitor to the rear. This one is probably in Load Monitor, and it will respond to every movement of the clutch since the Load Monitor is a driveline torque sensor that affects the three point hitch position.
If it doesn't work correctly in position control then you'll need to pull the lift cover and go through the linkages and probably reseal the lift cylinder while you're in there...
This is probably not the news you wanted to hear, but get a little more info and we'll figure out what you have there. Rod
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