WD45 runs rough

I have recently aqcuired a WD45. This tractor has not been rebuilt since 1960. I found out just yesterday that it has the d17 kit for the motor. Anyways this tractor fires right up and runs great most of the time. When it is working underload it is as smooth as can be. But when its just driving around it tends to backfire and spit slightly. Enough to make it annoying. And it seems to do this more and more the longer you are running it. Sometime it will get so bad i have to stop the tractor and let it "catch it's breathe". I figured it was the ignition system. So i put all new, Points, Condnsor, Rotor, Cap, Wires, and plugs on it. It still does the same thing. I am thinking a carb rebuild kit now. But is there anything else i should be checking??

Change the coil.

Since the D 17 and the WD45 have the same bore and stroke, what exactly is a D17 "kit" ? I hear this over and over but nobody can explain how they know it has a "kit" and what is different. You could put WC flat top pistons in a 45 and have higher compression and probably more HP. There were differences in piston to wrist pin length, making compression ratios different but how can you tell without measuring the piston?

Thats what i forgot to mention. I changed the coil also. and i messed with the timing. Timing seems to be pretty much dead on. It never dies and it idles ok. just seems to have some hickups. How much play is ok with the distributor rotor? it has quite a bit of play in it.

Is the centrifugal advance working? If could be running advanced at idle which makes it rough. Or the idle circuit could be running either rich or lean from a plugged passage or a mistuned idle screw or too high or too low a float or some of all of the above.

Gerald J.

Lets do a little diagnosis. You say it gets to sputtering a bit. I also see where you have figured out if you give it a little choke at idle it smoothes out. That usually indicates a lean condition where the engine is not getting enough fuel to go with the air it is getting. When you choke it you're increasing the amount of fuel drawn in. That lean condition could be caused by unmetered air also known as a vacuum leak. You can find vacuum leaks with spray carb cleaner. With the engine running, spray a little cleaner around each gasket. If there is a leak, the engine will respond to the cleaner being drawn in. You could also have dirt restricting a passage in the carb or valves/rings that do not seal as well as they did the last time the carb was adjusted. On a Marvel Schebler carb, the idle mixture screw is controlling air only, not fuel/air as on a Zenith carb. The idle mixture screw is a small screw on the throat of the upper body of the carb. Turn it in to richen the mixture, out to lean it. The screw on the back is the idle speed screw.

DougS wrote: If flat tops are the key, why was the Power Crater such a more powerful engine?  It had dished pistons.  You would think AC would have installed flat tops on the WD45 right from the get-go.

Nobody said flat tops were the key but a WC flat top piston will give a higher compression ratio in a WD45 than the power crater original piston. Think of the crater as a volume added to the volume between the piston at TDC and the bottom of the head. Now fill in that dish and the compression is higher. This may be a little over simplified as the center line of the wrist pin in relation to the top of the piston is of great importance.
 I'd still like to know how people determine they have a D17 "kit" in an engine.

Charlie,I don't know any way to tell 45 VS 17 without having the head off and knowing the difference in the heights or shape of the two. 6.6 VS 7.25 or.3 is the comp difference but it doesn't take much to make that difference.

bdallman wrote: I am not sure what all it entails for the d17 kit. As far as whay the previous owner told me. A standarda wd45 crank wont fit in it anymore??? Now i took what he was saying with a grain of salt considering he was 90 years old and he had the motor rebuilt in 1960. I do know that instead of the 3/8" threads on the sparkplug it takes the longer reach 3/4" threads like the d17's used. That and the higher compression from the d17 pistons. He told me that you would have a hell of a time trying to crank it. He said he had a guy he knew try to crank it over back in 60's and he broke his arm. lol

Maybe you should look at the engine number. Look on the left side rear flange of the block and tell me what's on there. Could be a D17 block if a 45 crank won't fit it anymore.

Should be a felt seal. If you get a cheap kit it won't have the throttle shaft and many times the shaft is worn a lot.

bump

got the Carb REbuilt. It was the seal on the throttle input shaft. put the new seal on. Cleaned the carb a bit and slapped it back on. She is purring now!!! Gotta love that 45 sound. very distinctive and brings back memories of my childhood!!! Went and used the snap coupler blade to push some brush into a pile. Works like a champ!!!