Vehicles

sonett - troubleshooting mid throttle miss - plugs, carb, fuel

The Sonett has a pretty severe hesitation at anything other than idle. The problem is inconsistent. Sometimes it hesittates very badly, other times it is mild. I have yet to nail down the behavior. In addition to the hesitation, it also idles all over the place. Sometimes it idles at 2k rpm, othertimes around 1k, and sometimes it just dies. This is all even once fully warmed up. 

It is strange behavior for sure. Then again, I have no idea what the history is of this engine as I have never driven the Sonett before just recently. For all I know, this is how the car was running when the prior owner last parked it.

It is time to start checking off items as known working condition. I started with the spark plugs by installing NGK BPR6ES plugs. Suprisingly the old plugs didn't look that bad except for the extreme tan/whitish color. This would seem to indicate that the car is running lean. Maybe the hesitation is fuel related.

I cleaned the fuel filter after the fuel pump. As it turns out there is a fuel filter integrated into the fuel pump body so I cleaned that too. I then installed another disposable filter before the fuel pump itself. While in the area I found the fuel line had a split in it just after the pump. This could have allowed fuel to escape under pressure. I replaced all the flexible fuel line.

All of that did not solve the hesitation.

I have since replaced the distributor rotor and cap and have started cleaning the carb. I hope that solves the problem. If not, I will move on to installing an electric fuel pump, replacing the spark plug wires, and keep going until I find the issue.

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choke is just a coil that heats up and moves that lever, brilliant
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I will only remove one of the two arms connecting the choke to the carb body
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tiny gasket, carb kit came with a new one
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number plate from carb, 72TF KFA 4AC
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old gasket looks good, no tears, I will replace regardless
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bowl not too dirty. I have seen much worse
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fuel shutoff visible just above float, not sure what the needle on a spring does
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current main jet size = 140. Maybe 135 better for this altitude, then again plugs show lean
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FoMoCo carb model 72TFKFA 3MA. I wonder why it differs from the orange stamped tag
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I don't know what this valve does, but I got a new one in the kit so time to dissamble
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wide spring side goes towards the carb
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I love my ultrasonic cleaner with
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brass float tested ok, no leaks
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funny needled surrounded by shimmed spring, looks important, don't know what it does
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got new ones in the kit
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after 8 minutes of ultrasonic cleaning.
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