Long dormant 1600 now running, but POP POP !!!!

[Greg Stout]

I 'rescued' this T-5 with 1600 (600122), that was sitting for YEARS...and I have changed oil/filter, adj valves, PO rebuilt the Zeniths and the fuel pump.
She started and ran pretty well, for a few days. Now she has started to backfire quite a bit. I Know I will have to replace the plugs, and I have checked the static and dynamic timing....even switched out the SP wires, but....still, random "POP POP" !!!! I do have a spare 022 & 050, but the timing light showed steady and appropriate advance....Gas tank was completely cleaned and petcock 'rebuilt'd by me. New premium Chevron gas.
Stuck float? burnt Valve? Bad plug? Pissed off for having to sit for so long?
Any Ideas out there??? I'd really like it to NOT be a burnt valve....and no, I have not done a comp test (but should)....

Thanks
Greg

[WilliamVaughan]

maybe clogged idle jets from dirt from lines between fuel pump and carbs?
Inspect your float bowls to see if they contain new sandbars of dirt.

[David Jones]

Don't take a chance, rebuild the carbs. After sitting for years the gaskets and seals will dry out and as Robert said there is a good chance of crap from the lines in the carbs. Do not make the mistake of adding another inline filter. There are already 3 in the fuel circuit.

[Thomas Sottile]

check the fuel pump for crud. you will be surprised with what you find.

[Doug McDonnell]

I have seen this due to distributor also.

[Jim Karaba]

Pop Pop from where. Carbs or exhaust? Makes a difference in troubleshooting. backfire out the exhaust can also point to an exhaust leak. Even a small leak can cause an occasional backfire.

[John Lindstrom]

My engine does that too, because my carbs are out of adjustment. I think maybe it's the idle circuit. One of these days I'll get around to fixing it. In the mean time I keep a fire extinguisher handy. I think I'm just going to mount it on the grill and leave the lid permanently open about an inch, just in case.

[Paul Ahnell]

Greg: If this is a constant popping, I recommend you do a compression test. I have a '60 Normal that recently began popping. Did a compression test and compared to earlier test. Found #2 had dropped from 160 psi to 115. Thought it was a burned exhaust valve. Did a leak-down test and immediately found air blowing out of the carb. When I got the head off I found carbon had built up and I suspect gummed up #2 intake valve. See pix. Machine shop cleaned up the heads and installed 8 new valves since most of the stem ODs were out of spec.

Point is, do that compression test.

[C J Murray]

I bet Paul is right.

If it was full of Rice Krispies it would make snap crackle pop noises.

[Martin Benade]

After a 25 year rest my car did that when cold, but eventually cleared up. I am guessing the intake valve was sticking/leaking very slightly and managed to clean up from driving.

[Jan Kolm]

If the centrifugal advance weights in the distributor are gummed up, they will retract very slowly upon deceleration, which can also cause popping, as well as a fast idle.

Pieces of rotted fuel line in the Zenith needle valve chambers will also create issues.

[Geoff Fleming]

Often, something as simple as synchronizing the carb down-links will stop the popping. Both carb throats should open and close as nearly the same as possible. Work the linkage from behind the shroud and watch as each down-link starts to open the throats. Working from behind the shroud replicates how the linkage exerts pressure, rather than simply pressing down on one side or the other.

[Mike Ruddy]

My two penneth, could this be a symptom of a dodgy condenser ? Failing condensers have been a hot topic here on the Registry recently, perhaps it could be that simple ?

[GregVandenbussche]

PaulAhNell check date on the heads, 1959 ones valve seats have the tendency to recess so much that valve end up loose, had the problem and it was described perfectly by another member
Burned exhaust valve tend to whistle too (burned mine due to the previously described problem)

[Al Zim]

You have no idea what the inside of the engine looks like! It would be prudent to strip the engine down to the rod bearings to see if they are in the copper and to check the condition of the pistons, rings, oil cooler and oil pump. I graduated from high school in 1960 that was 58 years ago. al zim