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450 pop in exhaust

A

Anonymous-0

Well-known Member
I have a 450 that has a pop in the exhaust. I can run in right next to my 400 and an hear a difference in exhaust sound. The 400 rain cap will stay steady at idle. The 450 rain cap will bounce up and down almost as they do on john Deere two cylinders. My question is what to look for. Timing, valves? Would a compression test tell me if the valves are sealing good cause that was my guess was a bad sealing valve. Any help is appreciated. Thank you.
 
First guess would be a non-sealing or burnt valve. Second guess would be a miss and the un-ignited fumes from that miss are combusting in manifold or muffler (wich would be more like a backfiring sound). If you have heard both situations you could easily tell the difference. Hard to explain the difference in sound.
 
Try running some Seafoam through it and see if it changes or clears up the popping. If a valve just has some carbon on the face and isn't burned yet, the Seafoam should help break it up
 
It should unless the valve is only doing it part of the time. Like say it is sticking part of the time, but only at a normal running RPM. A situation like that would perhaps give you a normal compression test reading. If a low compression test, put a squirt of oil in the plug hole and then re-do test. If the result is a normal reading after being low, it is a problem with the rings. If it is low after being low it is a problem with valves most likely, but a chance of cracked head or bad head gasket.
 
After I rebuilt My Super A I had the same problem. Poping out of the exhoust. I checked timing,plugs,carb,valve timing, valve adjustment, compression, etc. I found everything good and in spec. I ran it like that for quite a while, all the while scratching my head for an answer. Then while ordering an unrelated part from this site I came across a set of new plug wires and thought to myself "I might as well get a set" because I had a mismatched set of carbon wires I had put on during the rebuild that were to long and didn"t look good. So I replaced the wires just for cosmetic effect and lo and behold the popping quit. Do you have GOOD COPPER wires on your 450?
 
That is a good point, it could be an ignition issues. Pops in the exhaust are usually unburned fuel that ignites in there.
 
Its been like this for years. So I doubt it's bad gas. It seems to run good. Just at those lower rpms it wants to pop out the exhaust.
 
To get the tractor to run smooth at idle, you have to have the timing so far retarded that it won't have any power when you go to work it.
 
id spray carb cleaner around the intake gaskets and carb to see if u have a vacuum leak that will make them pop at idle
 
Are you saying that if all else is correct that the timing cannot be set to give good idle and power as the manufacturer may have intended.

Well tuned and good running tractors are well known for there impressive slow steady idle are they not.

Is the tuning you are suggesting an adjustment for a bad centrifugal advance or do I have it backwards.

I am not trying to be a smart xss. Educate me.

Thanks
 
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