300 Carb help

I rebuilt the carb on the 300 I have this weekend. It seamed to be in real clean shape. I think I was the first person since the factory. Anyway I have a couple questions. First is what would make the tractor burn fuel quickly? I mean it seams that I use much more fuel that I should for the work I do. I thought it was the carb but it seamed to be in great shape. I didn't have any passages pluged. Jet was almost new looking. Just am stumped.
Second question is what would make it carbon up from between the air cleaner and upthrough the venture. I am not talking about alot of carbon but just a fine dusting. Is this normal? didn't think that there would be exaust comming back through but maybe. If so would you think it wasa bad valve. Tractor seams to run good.
Third and last question is after rebuild I'm not sure what to set the adjustment too. I also see that I have three places to adjust. One being the bottom needle. The second is the governer adjustment. The third is another needle at the flange by the manifold. Have never seen on there but it's there. What's it for? What do I set them to and get it back to factory?

Thanks guy for your help.

Ed – A light coat of black inside the venturi is pretty much normal. It comes from an occasional light backfire in the manifold (not unusual when starting a cold engine). Also some gasolines will leave a light residue inside the venturi as the gas evaporates. Don’t be too concerned about it.

Regarding fuel consumption, if the exhaust is clear (no trace of black) and the tractor has good power and runs smoothly, there's not a lot you can do to improve fuel consumption.

However here's some possible causes of high fuel consumption:
- Ignition timing (should be TDC at idle)
- Ignition advance (should advance to around 30 deg TDC by 1,200 RPM).
- Dirty or plugged air cleaner
- Dragging brake(s)
- Hydraulic system malfunction. If the hyd reservoir gets hot after running a few minutes there’s a problem here.
- Engine running too cold (missing or broken thermostat)
- Operating in too low a gear. (If load permits, better fuel economy can be had by “gearing up and throttling down”)
- If you are using fuel with a lot of ethanol in, fuel economy will be less (ethanol has less energy that straight gasoline)
- Excessive idling. These engines can burn a lot of gas “just doing nothing”

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Carb adjustment:

The upper screw with its head facing the front of the tractor is the idle mixture
The upper screw coming in from the side of the tractor is the idle speed adjustment.
The bottom, angled screw is the power mixture.

Initial mixture settings are 1 turn open for the idle and 3 turns for the power.

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To set the carb first get the engine fully warmed up and make sure the choke is fully open. Then:
1 – With the engine idling turn the idle mix screw in/out as required until you get the best (smoothest, fastest) idle.
2 – Reset the idle RPM if required with the idle speed screw.
3 – Now open the governor all the way. Turn the power screw out until the engine just starts to run rough. Now turn it back in slowly until the engine again runs smoothly.
4 – Close the throttle and repeat #1 and #2 if necessary.
5 – With the engine idling snap the governor open as fast as possible. If the engine stumbles as it picks up, open the power screw and additional 1/8 – ¼ turn or so.

Well I always thought that black soot from the exhust was the norm. Are you saying that the pipe should be clean? If so mine is not. If it isn't smoking then I'm sure there is some but under the work and age of the tractor (some 50 years) and any hard work or neglect prior it seams normal. Puff here and there mostly after getting into a load or just giving her the gas.

I haven't really done a timming to the old girl and maybe that should come this summer. I think I understand the concept but where on this tractor is the tdc location? I could check that with a light? Or is it something I need to see in a hole or something?

Thanks for the advice regarding getting the carb to some spec before I put it on. I will have to get it fine tuned in before I really run it this spring. Now if other things are done say with better timming will the carb also need to be adjusted to the new settings? If so I guess the fine tunning will be for just this install.

It will be sad but the best part on the tractor right now is the carb. I took the time to really give it the going over. New paint and all now the rest of the tractor looks like it's old and in need of something. Think I have started something? Maybe bad? I think so. Thanks for your help.