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Subject: Exhaust Soft Pop

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Max    Posted 10-15-2018 at 20:41:34 [URL] [DELETE]        [Reply] [Email]  
  • Exhaust Soft Pop
  • Hello all, I have a question about my 1949 8N. It starts easily every time and runs good. However, when it idles or any time the engine is under no load there is a soft intermittent pop from the exhaust pipe. I would like to know if this is normal or not. The tractor is a front mount distributor and still has the 6 volt system. The entire tractor appears to be factory correct according to the documentation I have acquired from this web site. This is slightly long winded, but here is a brief history of my time with the tractor. When I brought it home last Spring I had to pull it behind my truck and pop the clutch to start it. The tractor had been sitting for several years without being used. I replaced the battery, battery cables, spark plugs, spark plug wires, starter solenoid, pulled the starter and cleaned the mating surface between it and the flywheel housing, replaced the points, condenser, coil, distributor cap, distributor and coil gaskets, set the points gap and timed the distributor as described in a 1948 8N Owner's Manual, verified continuity of the wire between the ignition ballast resistor and the coil primary, cleaned and rebuilt the Marvel / Schebler carburetor, adjusted the carb jets by a procedure I found on this site by Bruce (VA), cleaned the fuel screens in the gas tank and the carb, and verified I am getting gas to the carb. I purchased quality replacement parts from sources recommended on this site. Thanks to you all for sharing this knowledge. After doing all of this I still have the soft pop. If this is normal then I'll call it good. If not, I'd like opinions on what I have missed so I can correct the issue. Any advice is appreciated. Thank you all.

    K.LaRue-VA    Posted 10-16-2018 at 09:26:08 [URL] [DELETE]        [Reply] [Email]  
  • Re: Exhaust Soft Pop
  • I assume this is at slow idle less than 500 RPM. At a fast idle, the tractor is already running on main mixture, so the idle air mix adjustment screw does nothing. Random pop at idle is usually slightly lean, try pulling he choke slowly out. If a little choke makes the problem go away, that confirms engine running too lean. Adjust small idle air mix screw in and see if that fixes it. If engine is idling at slow idle and turning mixture screw in does nothing, the engine may be sucking air past a loose throttle shaft, other leak, or the carb idle fuel passage is restricted or blocked. The idle mixture screw controls idle air, so cranking that screw in as far as it will go is as rich as it will go. If pulling choke a little still clears up intermittent popping, spraying wd-40 around likely leaks may identify the problem, or the idle fuel passage needs to be cleared or maybe enlarged. Idle fuel jet may be too small, but problem with idle fuel flow is usually restriction in the fuel passage.

    If pulling the choke slowly makes the problem worse, it's running too rich. Turn idle air mix screw out a bit. If turning the idle air screw all the way out does nothing, the engine is most likely not running at idle, it's running on the main mixture. Without a tach to gauge engine rpm many people don't realize how much slower a 450-500 rpm idle is. Many cars and trucks normally idle around twice that.

    Dave Smith    Posted 10-16-2018 at 07:08:30 [URL] [DELETE]        [Reply] [Email]  
  • Re: Exhaust Soft Pop
  • Give it a compression test. Wet and dry.
    That might give a clue what is happening.
    Dave <*)))><

    Larry Holbrook    Posted 10-16-2018 at 04:42:41 [URL] [DELETE]        [Reply] [Email]  
  • Re: Exhaust Soft Pop
  • My 48 front mount did exactly the same thing. I've sold it and bought a 3000. It ran fine though for years and started right up. I asked the same thing once and some suggested it could be a valve problem I believe.

    Randy(PA)    Posted 10-15-2018 at 22:41:48 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Exhaust Soft Pop
  • If your soft pop is what I think it is, my experience would say that it is caused by extra rich fuel mixture. Try leaning it out a little.

    Joe in Texas    Posted 10-16-2018 at 18:39:11 [URL] [DELETE]        [Reply] [Email]  
  • Re: Exhaust Soft Pop
  • I'll second that on the fuel mixture. It only took about a quarter turn toward the lean side on the carb.

    duey    Posted 10-15-2018 at 21:00:18 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Exhaust Soft Pop
  • Sounds like most Ford tractors I have heard... including my own...

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