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hwp

Timeing on AC 720

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hwp
how do you set the timeing on the Onan? And what should it be. I Just put another carb on mine, and cant get it to adjust right. It runs, but spits and spudders. sounds like it is loading up and running real rich. Can I use my timeing light on it? Carb is in good shape. How do I set the float level on a spring loaded float? Is there some port I am missing that might be cloged. I have sprayed to look for air leaks, sometimes it will run great for a few seconds and then start the rough running once more. I have no rust in tank, new fuel lines, new filter, pump is working. no dirt in carb that I can find. I know this is a funny carb to work on, so any tricks for solving the problem would help.

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D-17_Dave
There should be a timing make and tab off the pto side of the engine on the belt clutch. Yes you can use your light. I normally find that the correct timing is almost all the way to one side of the points box. Care should be taken when tightening the box back down so as to not move the setting. Also it is critical that no moister or oil residue be inside the points box and make sure there are no exposed edges from the circuit close enough to ground out. ie, the connections and points spring inside the box next to the outside of the box. Just a note on the carbs. If you are still using the old diaphragm fuel pump there is a good chance that the diaphragm is disintegrating and putting small rubber debris into the carb float needle. This will restrict the fuel flow and starve the engine. Put on a good electric pump and loose this old pump with all it's problems.

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hwp
I have been trying to get this thing to run, and have thought it was the carb. (still might be) I have rechecked the timeing with a light. this time I got my good timeing light out and found it way off. Then found the 2 allen bolts that hold the box down to be very loose. I have slid it all the way over to the right hand side of the tractor. the timeing marks almost line up, but it jumps around quite a bit. on a car, that might meen the distributor is bad. What might cause this? and how can I get the box to move over more? Oh yea I am trying to get them to line up at 20 deg BTDC (right?)

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D-17_Dave
To your question, yes. 20% BTDC is the recommended setting. In the case of a worn engine, as close to this as you can should be OK, + or - a few degrees. If the timing come up erratic you'll need to dig a little deeper. Look for any sort of loose part, scuffed wire, grounding out condition in and around the points box, etc. If the box is warped and won't tighten up properly then some sort of repair or replacement is needed. Pay close attention to the plunger also. If it's worn convex on the bottom then it could rotate and throw of the timing occationally.

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hwp
Ok, Points and condenser are new and gap it set right. If i idle it low, it runs like a watch. when I rev it up to cut grass, it loads up and spits and pumps out black smoke. I cant get it to run good at high rpm. I do have it steady at 20 deg BTDC. At low idle timing stays right on.

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D-17_Dave
Check the air filter then adjust the carb. a little leaner. Sounds as if it's running rich. Some of this goes back to the fuel pump issue. If there is trash in the float needle seat then the fuel pump is flooding the engine and you won't be able to adjust the carb. correctly.

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hwp
The one thing I cant seem to find out is the adjustment on the float. My carb has the preload spring on the float, but I know the tab on the float has been moved from the org. The information I have shows a adjustment for the ones without the spring. But there must be a adjustment for the preloaded one also. That might be my problem. You can use a drill bit for most adjustments. Anyone have any idea as to what this one is? There is no trash in carb. I put a filter on the line when I got the tractor, and have changed it about 4 times. Each time I pull the carb, I find no trash dirt or water in the bowl. but if the float is out of adjustment, that could be a problem.

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D-17_Dave
The spring is to force the needle to the open position when the float goes down. This keeps the needle from sticking in the seat if it were a gravity flow system. The float adjustment is the same as any other carb. Float needs to be level on the needle height with the carb inverted.

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