[ThreeNuts]

I owe you all a follow up!

Engine runs very smooth. Have put just under 200-miles on it and it runs great.

Two issues. The first is an older one, but still here after the rebuild: Has to be a carburetor issue: it's stumbling a bit when drifting along on neutral throttle at low speeds, and there's a momentary hitch that feels like the accelerator pump is starting to go bad when giving throttle...but while the engine was out, I cleaned and rebuilt the carburetor and it has a new pump in it (the old one was worn through at one point on the leather). The stumbling at neutral throttle - I replaced the metering rod springs - apparently, they should be done at every carb rebuild; this is the factory 4034S, I've had the car since 2000, and I'd never replaced them. They're not in a rebuild kit, so I got a couple sets (one from Mike's) and also picked up a couple pistons in case the springs didn't help. They didn't.

I pivoted first - acquired, cleaned, adjusted and installed another '66 4034S, transferring the accelerator pump (the piston was worn out the same way!) and new metering rod springs. The stumbling seems to be gone, but the slight hesitation is still there. May get another accelerator pump.

Second issue is new: cold start is fine, but at hot start, there's about a half-second of what sounds like valve clatter as it lights but before it catches fully. This is not a 'dry start from sitting' - type thing; only hot starts, and it is momentary.

I set the timing about 2-3-degrees retarded (no vacuum) at the recommendation of the builder, who found heavier wear at the top of the cam bearings and suspected detonation (valves & heads are fine). Is this causing that? Acceleration ain't what it was set this way, and the old man in me wants to advance it a bit.

I also never checked to see if it was actually at TDC for ignition or exhaust (the timing was set right a 0, and I verified visually that the #1 piston was at TDC before installing the distributor). Pretty sure it wouldn't run if it was wrong.

Thank you all for your inputs, critiques and wit! I now have a $7000 paperweight, but she's back running!

[SRGN]

Originally Posted by ThreeNuts

I owe you all a follow up!

Engine runs very smooth. Have put just under 200-miles on it and it runs great.

Two issues. The first is an older one, but still here after the rebuild: Has to be a carburetor issue: it's stumbling a bit when drifting along on neutral throttle at low speeds, and there's a momentary hitch that feels like the accelerator pump is starting to go bad when giving throttle...but while the engine was out, I cleaned and rebuilt the carburetor and it has a new pump in it (the old one was worn through at one point on the leather). The stumbling at neutral throttle - I replaced the metering rod springs - apparently, they should be done at every carb rebuild; this is the factory 4034S, I've had the car since 2000, and I'd never replaced them. They're not in a rebuild kit, so I got a couple sets (one from Mike's) and also picked up a couple pistons in case the springs didn't help. They didn't.

I pivoted first - acquired, cleaned, adjusted and installed another '66 4034S, transferring the accelerator pump (the piston was worn out the same way!) and new metering rod springs. The stumbling seems to be gone, but the slight hesitation is still there. May get another accelerator pump.

Second issue is new: cold start is fine, but at hot start, there's about a half-second of what sounds like valve clatter as it lights but before it catches fully. This is not a 'dry start from sitting' - type thing; only hot starts, and it is momentary.

I set the timing about 2-3-degrees retarded (no vacuum) at the recommendation of the builder, who found heavier wear at the top of the cam bearings and suspected detonation (valves & heads are fine). Is this causing that? Acceleration ain't what it was set this way, and the old man in me wants to advance it a bit.

I also never checked to see if it was actually at TDC for ignition or exhaust (the timing was set right a 0, and I verified visually that the #1 piston was at TDC before installing the distributor). Pretty sure it wouldn't run if it was wrong.

Thank you all for your inputs, critiques and wit! I now have a $7000 paperweight, but she's back running!

If there was witness marks on the upper shell of the rod bearings, that would be detonation. Upper part of the cam bearings is more likely an oiling issue or a bent cam. If you want to work on the tune, I have a wideband and a lot of diagnostic equipment. You are welcome to drive up to my little shop and I'll help figure it out. I'm usually up there when I'm not at my regular job.

[ThreeNuts]

Originally Posted by SRGN

If there was witness marks on the upper shell of the rod bearings, that would be detonation. Upper part of the cam bearings is more likely an oiling issue or a bent cam. If you want to work on the tune, I have a wideband and a lot of diagnostic equipment. You are welcome to drive up to my little shop and I'll help figure it out. I'm usually up there when I'm not at my regular job.

Thank you! Be careful what you offer; I just might!

I have all of the bearing shells (I always insist on retaining all of the old parts) - I'll check the rod bottom ends...not sure which one is the top one - I guess if they're scrubbed, I'll know...

I did order a new accelerator piston. The issue is not noticeable in Park.

The vacuum was right around 19hg, with a 1"-hg steady flutter, which I keep forgetting is normal for carbureted cars.

I may put the tach & vacuum meters in the car (with really long extensions) and drive it around to rule in/out it being ignition or fuel. It's running the Pertronix system I installed in 2001; I did replace the cap, rotor, plugs & wires along with the coil with this rebuild.

I'll push the timing up & see if the clatter goes away.