Thoughts on a backfiring 60

Royse

Well-known Member
I went to look at a 1954 60 today. With the engine running
anywhere under half throttle, it backfires through the exhaust.
They're fairly constant at between 10 and 15 seconds
apart but then it may not backfire for a minute or two.
Above half throttle it doesn't backfire and has good power at
all speeds comparing it to my JD 50.
Seller says he just had the valves ground and replaced the
manifold. He doesn't know if it was backfiring before having the
valves ground. He couldn't run it with the cracked manifold.
Thoughts on what it could be or a good place to start looking?
 
Sloppy throttle shaft /bushing will also cause it. Usually can't open idle fuel enough to make up for the air leak/lean mixture.
 
i would be checking the valve lash adjustment first thing. who knows who set the valves? backfiring is a valve problem, not a carb or timing problem. wont hurt to check the compression first also.
 
Backfiring can be caused by a valve issue or misfires that fill the exhaust with unburned fumes.

Could be most anything.
 
Well it could be several things. Condensers can cause all sorts of weird problems and are simple to try another one.
I would also not discount a bad left hand cam bearing from what I have seen in the past on models A and 60.
 
When my 70 gas did it new plugs would fix it. When distributor turns engine speed and plugs fire on exhaust stroke too it can happen. Weak plugs won't fire under compression, but will during the no compression exhaust-intake overlap firing the fuel charge that should have burned earlier.
 
I will throw a question out to those who have responded to this question. I have a friend of mine who has a 1949 A, while I have a 1951 A. As I recall, his tractor was running similarly to what has been described here. I want to emphasize this recollection goes back around 20 years ago, so my memory may not be entirely accurate. His tractor about drove both of us nuts in trying to diagnose the issues he was having with it. Out of curiosity, we took the carburetor off mine and put it on his, and the tractor ran much better, and sounded normal. I had noticed wear in the throttle shaft and bushing on his tractor. He had his carburetor rebuilt and it didn't make a difference in how his model A ran. He had it timed and the timing was okay. He changed plugs and plug wires. He had his coil checked. He replaced the points and condenser. He talked to an older man who skinned up a lot of knuckles turning wrenches on 2 cylinder John Deere tractors. His recommendation was to change the oil in the crankcase, as he suspected there was enough gasoline in the crankcase to cause some issue, and he recognized the oil in the crankcase had been there for some time. That was it! Could this possibly be the situation with this 60? Just a thought, based upon an experience I had some involvement in some years ago.
 
So it backfires at low throttle but straightens out once you go past half throttle. That does sound like it is lean while running on the idle circuit but once the engine gains enough RPM to activate the load circuit, it then has a good air/fuel mixture. I'm a big believer in checking the simple stuff first and checking the idle mixture is pretty simple and easy.
 
Thanks for all the replies. He called me back tonight, it sold.
He was asking $2000. Poor to fair tires, decent paint, no 3pt,
good fenders, ratty seat pads, bad battery and muffler.
Starter and generator he said were both rebuilt in the last year.
I didn't make him an offer yesterday, so I don't know if he
would have taken less or what it sold for. Wasn't meant to be.
 
I had a early "D" that did that . started hard did everything but run right . Overhauled the engine sent carb to ROBERTS CARB. nothing worked . This went on for 4 years I would work on it every so often . One day I went thru the valve lash ,valve lift ,right in speck . Mag was good timing was right . Drove me nuts . Long story short the CAMSHAFT was OFF about 90* . I don't know why it even run . Gott'er timed and started like a champ, no more back fireing .
 

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