Why does my 225 run so rough cold?

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You've probably got choke problems. The choke thermostat may be faulty or missing, or the choke pushrod bent or otherwise brutalized. The choke pull-off may be faulty or its link improperly adjusted. See choke adjustment info here, though your '75's choke thermostat is not adjustable (if you want an adjustable one—which, really, you definitely do want—get a #1234 Electric choke kit). Check and make sure the thermostatic air cleaner system is intact (including the flex duct from the bottom of the air cleaner snorkel down to the sheetmetal heat stove surrounding the central collector portion of the exhaust manifold) and working correctly (flapper in the snorkel blocks the front/cold-air entrance of the snorkel, so all the air has to come through the sttove and flex duct). Another thing to check on this: cracks or leaking gaskets at the exhaust manifold central area. If there are, this will feed exhaust into the intake and make the engine run very poorly when cold. The heat riser valve is a good thing to check, too; with the engine cold, find the 3" diameter round disc facing front, on the central portion of the exhaust manifold. Grab and rotate it counterclockwise (viewed from front). It should turn easily and spring back clockwise when you let go.

Make sure the distributor vacuum advance is working (diaphragm not blown, hose not cracked or holed). Route the hose from the distributor directly to the carburetor's spark advance/OSAC port, without stopping at the widget on the side of the air cleaner housing.

The carburetor is likely due for some attention. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. Tune-up parts and technique suggestions in this thread. And don't forget these engines need periodic valve adjustment.

You will want to get the three books described in this thread as quickly as you can.
 
Start with the choke. Does it close but not to tight? Does the choke pull off work? Start were ever you want-it all works together. Did it have this problem before the new carb?
 
I too would suspect choke. you maybe able to test if it is a choke problem by manually adjusting the choke when its cold and see if you can get it to run smoother.

I've recently read the carb chapter in the stockel book dan is recomending above and compared that with my carb manual and carb rebuild guide. This along with rebuilding my carb a couple times to get familiar with its mechanical parts and connections/movements and troubleshoot along with a bit of just plain playing with the carb has taught me a lot.

point being, Dan has good advice above, I'd really recommend reading that very accessible Stockel book (at least chapter on carbs), plus I recommend some manual experimentation with the choke

Where to start: manually open and close the choke by the choke shaft. but dont put your hands in the carb bowl... explosions occur down that hole and they dont always stay down there like they should
 
Ruadhd2 said:
This is good stuff. The carburetor is brand new. So where do I look first?
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Brand new as in never ever used before, new old stock? Or "brand new" as in a "remanufactured" item from a parts store? If the latter, it's probably part of your problem; "remanufactured" carburetors are junk.
 
Is there anyone near Silver Spring, MD who I can pay to check out my carb and whatever else is making my car so rough and cold? I am mechanically challenged.
 
Ruadhd2 said:
Is there anyone near Silver Spring, MD who I can pay to check out my carb and whatever else is making my car so rough and cold? I am mechanically challenged.
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Im about 50mil west of you and would be more than glad to look at it for you if you bring it up....Artie
 
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