Chasing carb prob. on D17, suggestions?

Been tinkering off and on for a week or two with my D17 series 4.  Can't seem to figure out what is going on.  When I got this thing home, it hadn't run in some time.  Cleaned the carb, cleaned sediment bowl, and added gas and she fired up.   At that time it ran really nice and smooth.  Starting fixing all the other things, one being the manifold top by the exhaust port was cracked.  Put a new threaded cast piece on and tried to weld it but the old manifold was really pitted so ended up brazing it on so I could just use the existing manifold to run it and keep going.  Put it back on with some new manifold gaskets.  It leaked at the rear exhaust port, so I took it apart and ground some of the other ports and checked with a straight edge and put back on.  Still leaks a hair but not bad.  Ever since I tinkered with the manifold it has run like crap.  I pulled the carb nine or ten different times to clean it and check it and all is good.  Put an inline fuel filter inbetween just to make sure no more junk is getting to the engine.  Still runs like crap.   The only time it runs good is when I choke it halfway.   I don't think it's the carb but it could be.  What else could be causing this.  Someone suggested to run it and spray WD40 around the carb and the where the intakes meet the head to see if it sucks any in which I did not see any.  Is it possible from brazing the manifold that it warped and it still isn't sitting right on the head?  Could I take it to a machine shop and have them surface grind it to make sure it is true, or because it is worn and somewhat pitted, when it gets hot, it will warp bad again?   I don't mind spending the $ on a new manifold if that's what the problem is, but I want to make sure before I do it.  I did reuse the existing bolts and nuts but I did put new gaskets on.    Was wondering what your suggestions are to look at. 

Check the air cleaner, might be plugged. Mine was. Jim

If the air cleaner were plugged, it would run rich. Can't help with the manifold question except to ask: Are you sure that you didn't affect something else when r&r carb? Good luck......

I called the local shop and I am going to bring the manifold in and have it milled.  He said it should cost no more then $60.  Be a couple days to get it back.  I know what you mean about the head Charlie.  I had a WC head that I sent in once to get new frost plugs put in as one popped out.  By the time I was done, it was that, valve job, and milled the side of the head as it was burnt out.  I don't even want to remember what the bill was. 

you gonna spend more welding & trying to repair something that needs to go in the scrap pile than it's worth...you can buy a new aftermarket manifold for less than $150 ...you got a bad intake leak....if you can't afford a manifold ...you can't afford the tractor...take care ...Kent

 I was wondering what ever came of this. Did the milled manifold fix the problem? I think I have a very similar problem with my wd45 so I wanted to know if it was an intake leak. Thanks

check the small passages that are in behind the venturi on the carb. Had this happen many times.

I have had tractors sit for only a few months and ran like crap until I drained the carb and got to some fresh gas.  Make sure you have good, fresh gas before you give up.  

This winter I am thinking about storing most of my stuff with carbs run dry.

I did have the manifold milled and it fixed the problem.   Runs good now.   But I agree that it should get a new one.   I haven't worked on this tractor much this summer, but I didn't want to dump alot of money into it unless I got a chance to go through the transmission, rearend, hydraulics etc.   From what I have diagnosed, all is good which means a new manifold is on the wishlist on this one.   The shop that I had the milling done was cheap, but they didn't mill it straight, so the outlet on the top is tipped, as welll as the carb inlet.   Not that big of deal, until you put the muffler and try to put the hood back on and the hole doesn't line up again.   Like I said, lesson learned and I will buy a new one for it soon, as this tractor is getting a loader on it in the next month, so it can clear the snow out of the driveway.