engine back fires

I'm rebuilding a 1975 cj-5 with a I6 258. The problem i'm having is when i let up on the gas the engine back fires. I assume it the Carb. I know very little about Carborators. I would like to find out if this will be an easy fix that i can do or should i take it into the shop to have it fixed.

 

scamire35: First of all, welcome to the board. Drop by the intro section and intro yourself.

I'm not an expert on '75 I6's, but if this is a CA vehicle, it probably has a "smog pump" on it. If the pump, or the "anti-backfire/dump valve" is bad, it will backfore. So, if you have a pump, check the valve that dumps air into your intake manifold upon decelaration.

 

Thanks James I will check the smog pump. I did for get to introduce myself. My name is Scott Camire and from Central California. I Just bought my first Jeep, which is a 1975 cj5. I just can't wait to get in on the road.

 

Welcome Scott. I Used to own a '75 CJ-6 when I lived in CA. It too had a 258 I6.

Your best resource is the factory service manual. You can get a reprint from Turner 4WD http://www.thejeep.com or maybe an original manual from Books-4-Cars http://www.books4cars.com . These factory manuals are more expensive, but are worth it.

Jim's advice about the purge valve is good - without the purge/burp/dump/anti-backfire valve, the smog pump will dump fresh air into the exhaust manifold on decelleration. There's lots of unburned fuel in the exhaust gases when you decelerate, and it'll ignite and backfire if given enough air.

hth Tim

 

Thanks Tim, I've been trying to get a factory service manual for my jeep. I will try the sites you mentioned

 

Welcome Scott, from South Carolina. I assume that you have checked your timing on the engine. If not, you may want to make sure it's not too high. If it is, the motor will backfire when you let off the gas and also burn your valves, over time.