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1976 sportsman 440 rv backfires through carb Steve taylor 4-29-17  
Ok. I did a toon up on the r.v. plugs, wires, cap, rotor. Before I did it the r.v. ran fine, no popping, no backfiring, no noticable lack of power. After the tune up it backfires through the carb and exaust. I checked and rechecked the wires. Even t.d.c. the #1 cylinder (1 top left if in the drivers seat) on comp. Stroke. And put the wires according to that.( were not the same as they were originally). Now when I start it, it idles great no misses no pops just smooth idle. Under a load ( ie foot on gas and brake, in gear, or with emergency brake applied it pops and backfires. If I advance the timing (spin the distributer clockwise from the drivers seat) it runs even better but backfires worse. If I retard the distributer (counterclockwise from the drivers seat) it almost comepletely stops the backfire but is extremely sluggish. I have adjusted the carb. Checked and rechecked all the vacuum lines. Am getting ready to check the fuel filter, even pull off the valve covers and check for worn springs, bent pushrod. I even took out the distributer cleaned and examined it.(looked ok) and put it back in. Correctly ( it isnt 180 out). Any thoughts on possible fixes? I heard it could be a worn timing chain and i could find out with a timing gun if the timing jumps around on the gun.... Hope its not that... My funds are limited... Thank u in advance for any and all ur thoughts.
Re: 1976 sportsman 440 rv backfires through carb Bubba The Bus Tech 5-1-17  
First guess is the firing order has cylinders five and seven reversed. Very easy to do on Chrysler stuff.

From there did your tune up include new cap and rotor? New spark plug wires? Those are the next most common issues casing your symptoms.

Good Luck
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