[hillbilly357]

I have a 289 that is misfiring on:1-4-6-7. They are all in the same plane in the manifold. I've changed the plugs,wires,points,cap & rotor. I checked the rocker arms and they're all working. Any ideas where to look next?

[454me]

I had a similar problem on my 350, 2 cylinders with a dead miss and a pop back through the carb under light acceleration. I checked cap, rotor, wires, points, carb, rockers for lift and compression. I still had a miss and every test I ran said there was nothing wrong. What I finally found was 3 broken valve springs. One intake causing the pop in the carb and 2 exhaust causing the miss. I am not saying that is your problem but if you check everything and cant find it take a look.. By the way I ran mine with the valve covers off and you couldnt see or hear it. I only found it after I removed the spring.

[TechnTool]

If they are all on the same plane of the manifold, and you have a dual plane manifold, then half of your carburetor is not giving gas, or there is a major vacume leak on one side of the carb.

Simple test: While engine is idling, take a can of propane, like for a small torch for sweating plumbing pipe, and feed the suspect barrel some propane. Since you are feeding 4 cylinders, give it a decent amount. If the engine starts to hit on those cylinders, then fix the carb. Do not, and I mean DO NOT discharge the propane next to the cap and rotor and wires. A stray spark could flash the propane and you'd lose all your hair & your eyes and maybe your lungs if you are breathing in at the time. Also, wear protective facegear, and protective gloves, and wear a cotton shirt. If a polyester shirt catches fire, then it will melt onto your skin, but a cotton shirt will only burn your skin.

[97Z28]

lol... thats one hell of a test. if it were me i'd just take some gas and pour down that side of the carb... not pour, but get like a squirt bottle and give it a few good squirts. wouldnt that work too?

lol, beats getting flash burned if that propane ignites and losing all your facial hair and your shirt.

[KULTULZ]

The propane bottle is to be held uptight at all times. THEXTON makes a special wand or one can be fashioned from hose and a spark plug boot. You merely move the wand to the carb air inlet, open the valve until the idle begins to stabilize then move the wand around until you find the leak.