Fouled plugs

Have a 300 that starts to miss. If I pull the plugs they are black, appear to be coated with carbon. If I put new ones in, they last about 4-5 days of work. Can't figure out if the problem is the plugs, coil (spark is yellow), or something else. Any ideas?

Is your mixture set too rich?

Black fouled plugs? If you're using light winter oil like a 5-20 you could get some extra oil by rings and valve stems- try 15-40 or straight 30 low ash. Other well known reason is running rich- adjust carb leaner. Rich mix usually has some black smoke from exhaust, oil burning from worn rings ,etc has gray or whitish smoke from exhaust. Plug problems at times - running a cold range plug for light duty can result in fouling, switch to light duty 'hotter' range plug. Coil problem symptoms should show up even after changing plugs when hot. Distributer check- condensor going bad would cause a bit of miss and pitted worn points that would have a few missfires- fouling would be about same as rich run for next firing cycle. Points gap less than .010 would maybe cause misfiring also, had start and missfire on IHC 303 combine from wear and close gap that mostly went away after clean and proper gap- point gap should be .018/.020 inch. This should give a little idea of what to check. RN

Not sure if the mixture is too rich. How do you adjust it? Thanks

Sounds like it is running too rich or has a very dirty engine. Change your carb adjustments and see if that helps. What plugs are you using? I've had great luck with Champion D18Y.

There are 3 adjustment screws on the carburetor. One is for the low speed adjustment and the other 2 are for air/fuel adjustment. I have the manual for my Dad's 300, it is out in the pickup, I'll get it and tell you where the screws should be set.

Andy

Your carburetor may need a rebuild or at least some attention. Also, you may want to try a set of Autolite 3116 or even 388 spark plugs. I never have much luck with the Champions.

Hello,
To adjust the idle adjusting screw, turn it in until lightly seated and open it 1 turn. Start the engine and operate it at fast idling speed (without any load) until thoroughly warm. While the engine is running at fast idle speed, it is advisable to screw in the throttle stop screw a few turns to prevent the engine from stopping when the throttle is closed. Now close the throttle by pushing the throttle lever all the way forward. The engine will then be idling at a fairly high speed and the throttle stop screw can be backed out a little at a time until desired idle speed is obtained. If the engine misses or or rolls while backing out the throttle stop screw, the idle adjusting screw may be adjusted either in or out until the engine operates smoothly. Speed up the engine for a few seconds; then recheck the idle adjustment. A slight adjustment in or out will give the smoothest idle. NOTE: On Gasoline carburetors, turning the adjusting screw in makes the idle mixture leaner. On distillate or kerosene carburetors, turning the adjusting screw in makes the idle mixture richer. To adjust the main fuel adjustment screw, first warm up the engine. To regulate the main fuel adjustment, advance the engine speed control lever to fast idle position and turn the main fuel adjustment screw clockwise until the fuel flow is shut off and the speed of the engine drops because of the lean mixture; then open until the engine runs smoothly. After the engine has been put under load, readjust the the main fuel adjustment if necessary. Always adjust so that the engine operates smoothly with as lean a mixture as possible.

The main jets on the Super H-up carbs are not adjusted as you describe, if they have been maintained in original condition. Max power setting is 5 turns out. It can be turned in one or one and one-half turns for better fuel economy as long as it does ok under load. If you adjust it like the non-super series, it will stumble under load, or even going up a slight hill with no load. At 5 turns out the needle is not in the seat. That jet is what I would call a "fixed" jet than will operate with the needle partially inserted. I imagine some of those carbs have mistakenly had the non-Super series jets installed, so the adjustments can be tried both ways--whatever works. My Super H carb is 5 turns out. I don't use it much, but it is a gas hog.

Turn that screw back in a couple of turns and the engine will perform just fine and fuel economy will improve. The carb adjustments and components on the super series carbs are NO different than the non super series. I own an H with the C-164 engine.

Super H and standard M carbs have the same main jet and screw. I don't have SM manual and am too lazy to check numbers on the CaseIH site. Perhaps IH did this on the Super series for a richer mixture for more power. If I really used my SH, I would adjust it leaner as long as it pulled the load. I initially adjusted the carb on my SH to the so called "sweet spot" as Andy said. It did not have any power. I then read the manual, where the 5 turns out thing is. I have not fiddled with it. I am sure it will run 4 turns out, don't think it will run with 3. Perhaps I should turn my M main fuel screw 5 turns out and see if it will run. Or maybe there is some other differece in the carbs. All I know is what it says in the Operator's manual. I believe that statement is in every manual (Super H-Super M, up), until the 706/806? when IH began using a solenoid. I have not checked every part.

I will try both kinds of plugs. Just bought some Champions last night, haven't put them in. When I try to adjust the screw on the front of the carb it wants to run rough. Is their another way to change the fuel mixture? Thanks for the help, guys. Joe

That would be a huge help, Andy. I hate to start turning screws that I don't recognize! Joe

"Super H and standard M carbs have the same main jet and screw."

Looked up wrong number, the seats (jet) are NOT the same, the adjusting screw is. the Operator's manual says that SH seats are calibrated for the 5 turns out for max power. The M seat undoubtably fits so your C164 carb may not have the original jet. Who knows what has been done to a 56+ year old carb? In original condition they are different. The distillate/kerosene carbs are adjusted like the ones on the non-super series. I imagine that some of the aftermarket companies do not differentiate between the M/Super M/Super H carbs thus the replacement jets can be the same.