Dort

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I rebuilt the carburator on a oliver 70. The tractor ran great,but the needle and seat wasnt closeing. So I went through the carberator agian,needle and seat now close,but the tractor has a pop through the carburator. Ive tried to take the pop out with carberator adjustments and ignition timing. No such luck, any suggestions?
 
There's been claims before when it comes to carburetor vs ignition,that one would cause a backfire through the carb,the other through the exhaust? Does anybody remember which was which and know whether it's a real thing?
 
plus a compression check should be done so you have piece of mind that valves are good. you might have tight valves or one burnt. plus you must set the timing to factory spec. before adjusting the carb as that is always the order. I remember the instructor saying in school... "when I set things to factory settings she runs pretty darn good!" if your setting timing by ear that is out the window. there is spec's for a reason.
 
Won?t timing depend on the fuel used? Setting to original spec, if using a far higher octane fuel or unleaded, will not be optimal. Original spec is a fair starting point, but not necessarily for fine tuning with modern-day fuels.
 
all good advice,but it didnt develope this pop till I went threw the carburator the 2nd time. The tractor ran good when i first put the rebuilt carb on it. But the needle and seat wasnt shuting off the gas. After i went threw the carb the second time, is when it developed the pop in the carburator.
 
I haven't heard that before but it got me to thinking (look out LOL). The only way to have a backfire through the carb is to have spark when there is a valve open. That would be a stuck valve, mixed up plug wires, or spark arcing to the wrong plug under the distributer cap. So backfire through the carb about has to be ignition related. Backfire in the exhaust is unburned fuel in the exhaust ignited when an exhaust valve opens. That would be a dead or weak cylinder putting through unspent fuel (it would probably be missing while running), or over fueled on all cylinders. So that would carburetor related. My thought process, for what it's worth.
 

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