Loud Tick or Pop at WOT

[Shugalou]

Hey guys,

I'm trying to diagnose an issue I've been dealing with for a bit.

The motor is a 305 with a Q jet 4 barrel and at WOT I get a loud tick sound almost like one loud pop, and power will cut out and I get out of the pedal. Everything returns to normal once I get back into mid and light throttle but when I hit WOT again I get the same thing.

Could this be a spark issue? I think my lines might overlap near the distributor or could this be the coil ontop of the distrubtor? Or is it something worse?

Any help is appreciated

Thanks guys

[Dead Parrot]

Spark is one possibility. WOT = highest cylinder pressure = needs best spark.
wires, plugs, cracked cap, worn button under coil are frequent suspects.

Could also be fuel starvation. WOT = max fuel need.
fuel filter, weak pump, suction line from tank to frame line are possibilities.

[Ziegelsteinfaust]

What he said.

Make sure everything in the ignition is good. Then your secondaries are probably not opening.

[Bluestep]

I would check the secondary air flap adjustment and the secondary enrichment circuit. If the flap is set too loose the secondaries open before the engine can utilize that much air causing the engine to fall flat.
The brass tubes on the secondary enrichment circuit can sometimes fall out. This circuit works like an accelerator pump. When the flaps begin to open the holes are exposed and siphons a shot of fuel. Remove the top of the carburetor to see if the brass tubes are in place or laying in the fuel bowl. If they have fallen out tap them back into place.
I believe that the "pop" you hear is a lean misfire.

[Shugalou]

Thanks for the suggestions guys I think I'll start with wires first and see if that solves the issue and if not move on from there.

The carb was recently rebuilt so I'm hoping that it is in good operating order.

Parrot - do you have more info on what the button under coil is and what I should be looking for?

Thanks guys

[Dead Parrot]

Assuming an HEI distributor, the 'button' is what the center of the rotor spins on. It provides the connection between the coil output and the rotor. It eventually wears out. Pull the cap off and look inside. In the middle is the button in the middle of a rubber type disk.

Might park it is as dark a place as you can and look for blue sparks where there shouldn't be any. Quick cheap test for ignition spark escaping to where it shouldn't

[3drburb]

Double check your firing order before you get to deep into it and go from there.

[Shugalou]

Thanks again guys,

I noticed a plug style of ground on the drivers side of the block in between spark plugs 1 & 3 was disconnected, any chance this is related?

I'll try to upload a picture if you guys aren't sure what I'm referring to.

Parrot I replaced Cap and Rotor last year but I'll keep that in mind when trouble shooting, I also like the test in dark method.

Burb - Good idea I was planning on doing this, I'm probably going to throw a new set of wires on so I'll be checking it all very shortly.

[3drburb]

While you are taking the picture to post, make sure the bolt holding the distributor in place is tight.

[Shugalou]

Burb - checked firing order and that has been done correct.
I know the distributor bolt was loose enough to hand turn to adjust timing I left it loosened while test driving I didn't think that would have made a difference but am I wrong?

I'll get that picture up shortly

[Shugalou]

[attach][/attach]
Hi guys,
The first picture show the wires and how some of them touch each other, the second is that ground area on the side of the block.

[Bluestep]

The loose wire is your temperature sending unit.

[Shugalou]

Thanks Blue that makes sense.

I'm researching a coil and wires now

[Shugalou]

I had someone else share a tip with me that I thought I would share with everyone incase someone else runs into this in the future.

In the dark run the motor and mist water onto the wires to see if there is leakage - if so you will see blue sparks - similar to what Dead Parrot had suggested but adding mist to exaggerate the effect.

[Bluestep]

Since you are getting into the coil, check to make sure that the mounting screws for the aftermarket coil have not punctured the distributor cap. If they have that provides the spark a path to ground. Also check the polarity on the coil wires, these can be installed wrong.

[3drburb]

If your distributor bolt was a bit loose I would guess your timing is off unless you have since checked with a timing light.
And yes that temp unit should be plug back on.
Good luck.

[Shugalou]

I'm planning to check the timing again tonight and set between 8-10 degrees and while I'm at it I'll be testing the water mist method.

Wondering if this could also be related to older gas, I'll try and burn some off tonight so I can top up with fresh gas.

[Bluestep]

Shugalou, I think that the very first thing I would check is also one of the easiest, and that is the secondary airflap adjustment. It is even more suspect because the carburetor was rebuilt recently. Your description of the symptoms really points to that. Poke the airflap with your finger and if it just flops with no spring tension it is a sure thing. You can find descriptions of the adjustment all over the internet, so I won't repeat it here. Use a small mirror to look at the lock screw until you become familiar with it.
All these other things should be checked out as well, but a loose airflap is my prime suspect.

[Shugalou]

Blue - thanks for repeating the importance of that - will do.

I did test it earlier and there is tension on the secondaries - they don't just flop open.

[Shugalou]

Hi guys, I've been tied up and just got to tinkering a bit last night. I bought a new timing light and set the timing to 9 (while in N, and with vacuum advance disconnected in the past I always did it in P). I took it out and couldn't repeat that loud tick backfire, I think I need to adjust my idle screws with the carb a bit still as there feels like there is a touch of hesitation when flooring it.

Thanks for the assistance guys