popping through intake

[qaztwo]

351w just put back into boat when running I get a popping through the intake, like a hammer hitting the back of the flame arrester. Thought it was a valve sticking, compresion test ok. Replaced dist and wires, no change. Will a over tighten rocker cause a popping sound through the intake.

 

[jeff13601]

Re: popping through intake

Are you talking about popping back out of the carb? Have you checked the timing, tune up, etc?

 

[qaztwo]

Re: popping through intake

Through the induction side, can hear it through the carb, and not through the exhaust. timing fine, replaced cap because I thought it might be arcing. I'm concern about the rockers because the manual says to use a lifter bleed down tool then gap the distance with a feeler gauge. I do not have the tool that is used to collapse the lifter so I adjusted like a 302. Turned engine to that cylinder then tighten down and backed off the rocker nut. I heard a to tight rocker arm miss before but never pop.

 

[jeff13601]

Re: popping through intake

I dont know about the rocker but even water in the gas can make it spit back out of the carb as can the timing being off and bad plugs or wires

 

[xltier]

Re: popping through intake

the popping your hearing is the compression in the cylinder coming back up the intake.can be a sign that the exhaust valve isnt opening.so when the intake opens again,theres compression still in the cylinder.

 

[cardude]

Re: popping through intake

a lean fuel mixture can also cause a backfire

 

[Mahoney]

Re: popping through intake

I had same issues caused by a lean condition in the secondary system. would idle fine, but in the water under load when deploying enough throttle to require secondary carb operation, the circuit was running to lean and popping out the carb. it is a very tricky fix, I ended up fixing it with a new carb of the same type so I could retain parts from both units.<br /><br />I had a Rochester and was able to verify this condition by raising the secondary metering rod hight to allow more fuel to enter during secondary operation, it ended up causing a bog, but I got rid of the lean backfire, so at least I knew what I was working with. Maybe something you might want to give a shot too before you start pulling heads and adjusting valves, rockers, etc.<br /><br />Good luck

 

[Reel Poor]

Re: popping through intake

Will a over tighten rocker cause a popping sound through the intake.

Yes. A loose adjustment will also cause this. A worn lobe on the camshaft can cause this.<br /><br />

water in the gas can make it spit back out of the carb as can the timing being off and bad plugs or wires

a lean fuel mixture can also cause a backfire

How does the motor run at idle? Rough or smooth?

 

[Haut Medoc]

Re: popping through intake

Are you sure you put all the push rods back in the same place? Ford is not easy like Chevy when it comes to push rods. They are not adjustible. The rocker arms get torqued to 20 #. If you mixed any up you will need to go through the measurement process again. A wrong stick in the wrong spot will really sscrew thins up.

 

[qaztwo]

Re: popping through intake

A couple of the rocker arms where so loose I was able to spin them 360 deg by hand. Tighten them up and started the engine ran greet for a minute, then same thing. Pulled the valve covers again and the same rockers where lose. Put a tad of rtv on the nuts, will see if that works. Never thought that a loose rocker would cause such a noise.

 

[LubeDude]

Re: popping through intake

Originally posted by qaztwo:<br /> Pulled the valve covers again and the same rockers where lose. Put a tad of rtv on the nuts, will see if that works.

If your cam is going flat and wearing rapidly, you could be having this problem. You may need to pull your intake and have a look at your lifters in those holes as a last resort. RTV isnt going to do squat.

 

[Reel Poor]

Re: popping through intake

Pulled the valve covers again and the same rockers where lose.

Check the rocker studs, they may be pulling out of the head.