Solved-Carburation mystery

[RBMann]

I am having an issue with our '69 1600. The whole car will start lurching/bucking/surging after the transition from light or no throttle to very slight acceleration in 1st or 2nd gear. When I let off the gas coming down my street then turn into the driveway and roll into the gas to start the climb it will lurch so bad that it starts chirping the tires. That is the worst case and requires either full throttle or stop and try again. It makes low speed light throttle driving very difficult. It's as if the pistons in the SUs are flopping up and down without any damping.

This behavior started a couple months ago but seems to be getting worst. I have checked the carb tuning, float level, checked the timing and have played with the mixture. I used ATF in the pistons, I tried straight 30W to slow things down and I have tried driving without the plungers in the pistons. It performs the same in all three cases.

As I am writing this I remembered the electric fuel pump was changed but to a new one that was supposed to have the specs. as the one that has been in the car for ten years. Maybe I'll switch it back as it is the only thing I can think of at this point.

Thanks for any ideas/tips.

[Nissanman]

Just maybe it is spark not fuel.
Run the engine in the dark and look for any lightning display.
Check the points, if you have points, for correct gap and function.
As the saying goes, when your sure it is a fuel problem check the ignition and vice versa

[spl310]

Carb problems are often ignition problems and vice versa. I'm betting that the springs or posts for them on the mechanical advance in the distributor has a problem. They are under the breaker plate

[jrusso07]

i had a very similar problem years ago - it was caused by the little graphite button on the center contact (coil voltage contact) in the distributor cap had broke and fallen out so the coil voltage to the rotor was through the spring and spark was intermittent but car would run, but not well. (so spark was the problem). Not sure how the button broke - found pieces of it inside the distributor.

[redroadster]

You are in need of the old sun machine oscilloscope
Are the carb pistons slides moving smooth and free when you push them up ....maybe one is froze and your running on 1 carb
A spark plugs fuel fowled , or a plug wire arcing very possible too....carbon tracking in distr.
Check for vacuum leak , ign timing cetrifical adv

[keith0alan]

It may be a carb problem but I have never seen this.

[Gregs672000]

I would agree that on and off, lurching etc suggests more of an electrical issue than carbs. Usually if it's lean it will backfire through the carbs, and an overly rich condition will just make it boggy and slow.

[rwmann]

Broken throttle return spring?

[notoptoy]

I'm with electrical as well, look for arcing at the coil, cracked cap, loose or broken lead or ground wires.

[RBMann]

Thanks for the suggestions. Looks like I'll be going into the distributor.

It's that thing over on the other side of the engine right?

[notoptoy]

I can see how you would be distracted by this side of the engine - looks good!

[todd lorber]

The problem is that your engine is too clean. No car can run properly looking like that.

[itsa68]

A quick check of the points wire might be in order. The wire likes to break inside the covering and could be intermittently making a connection during timing advance. I have also had a brand new rotor with leak path to the distributor shaft causing an intermittent spark short.

Hope that helps.

Cheers
Ray B.

[Gregs672000]

Eye candy for sure, really really nice.

[redroadster]

The problem is that your engine is too clean. No car can run properly looking like that.

Ya looks like it was wire brushed & buffed
Hope you wore a respiratory and gloves