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300 Misfire when Cold

L

Lee Jr.

Member
I forgot to post my real challenge. I have a 300 that when it is cold I have to pull the choke all the way out and the engine pops allot until it warms up. Once it warms up, it smooths out and I can push the choke in some. I have ran it at idle and sprayed choke/carb cleaner around the carb connections to the manifold and the manifold to the block, but have not noticed any change or surge from the engine. It certainly seems to me it is starving for gas and possibly getting excess air. I thought it could be an intake/exhaust gasket or possibly a warped manifold becasue it smooths out when it warms up. Any ideas to check? Thanks
 
Those engines are slow to warm up, particularly in cold weather. Other than that, your carb could need cleaning. And, if you don't know, the main jet screw needs to be 5 turns out for maximum power. If it is out about 3 turns, it is too lean.
 
We had a 300 Utility that behaved that way in cold weather. Putting a piece of plastic over the grill to block air flow in cold weather allowed the engine to warm up sooner and run at a higher temperature. After it warmed up good, it ran fine!
 
OK and thanks. It runs with the missfire in warm weather also on cold start ups. Cold here today, I thought about covering the rad but did not. Only time it might not missfire is in warm weather when I first change plugs. They foul fast since I have to run the choke out allot, but if I don't it won't run/start at all. Takes a long time for it to start hitting on all 4. I'll check the carb closer and for sure the adjustment. Thanks a ton
 
You are supposed to have to choke it when it's cold. What the choke does is over-ride the mixture setting and makes it suck in a richer mixture.
 
I agree with CNKS and Cowman. These old girls are cold blooded, even in the summer. If you can lay your hand on the top of the intake where it meets the main manifold, you are NOT up to operating temp.

start with choke, then back choke off a little, run for at least 5 mins, then back out some more. run another 5-10 mins, and she is ready to start working. so, that is at least 5 mins of warm up in the summer and 15 in the winter (if not more).

If the intake isn't warmed up, they will cough and sputter without the choke.

PS. icing at the outside of the top of the carb in ANY weather is normal. I am talking about the manifold area where the intake meets the exhaust.
 
Thank You. I think I am not representing the cold starting condition correctly, or these 300's are more cold natured than my H's and C's. I'll double check all the primary/secondary components again to make sure that is ok and see where that leads. Appreciate the time to reply and thanks
 
I'll double check all that prior to tearing into it, just replaced the plugs and the wiring was done last year. thanks.
 
Yes, probably. The 300 is probably a little higher compression then the older letter series and is going to be more sensitive to correct fuel mixture. And every tractor is different. There are just so many variables to consider.
 
Ya Know, I was thinking coming home that my 300 starts fine with new plugs, but it darkens them (black sooty)as if running too rich. I have always thought it was because I ran the choke at cold too much, but now I am thinking possibly the carb is running rich fouling the plugs and like a dummy I give it more fuel cause that is what gets it running. I think I will clean the plugs and see what happens on another "cold" start. If it fires up a lot quicker, then I have a carb running too rich fouling plugs. make sense?
 
Either you are too rich, OR check your air cleaner. Make sure of 2 things: the bottom is clean and you are not using too heavy of oil. The manual says to use the same SAE oil in the cleaner as you do in the engine. so, in the old days, when it got cold enough to change the oil from SAE 30 to SAE 10 (or SAE20), that is what you used in the air cleaner also.

Bottom line, sooty plugs is either too much fuel or not enough air (for the most part).
 
Thank You. I would never have thought to check the air cleaner. We are going to be in the 30's today so I will check it this afternoon. I'll clean the plugs after taking care of the air cleaner, start her up and see if that cures the plug fouling. If not, then I guess I have a carb running too rich. Thank You again.
 
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