I have a 1969 Dodge 361 wedge head with a 670 cfm Holley Truck avenger carb on ot. My issue is as follows. Driving it today, it would randomly start bogging down backfiring one and a while and almost die, unless I either shifted up or down a gear. At one point, I could only go 30-35 mph and thought the engine was about to cut out completely. If I give it full throttle, it does bog way way down and will start backfiring. It did this once before about 3 weeks ago, same exact systems. I thought the carb had some dirt int it or something else. The carb is only a few months. When it started last time, I removed the carb (PIA in this vehicle) and took the end covers off and it looked fine, I blew the jets out as well to make sure they were clear. The thing I did notice was a fairly thick brown lacquer on the bottom of the carb and just inside the intake manifold. I used a spray carb clear to remove it and it came right off, but now I'm havering similar issues again. When I had the carb out last time, I put a inline fuel filter in as well. What causes the brown lacquer deposits to be all over the underside of the carb. amd frp, , memory, the secondary was sticking or wass stuck closed because of this. Once I had the carb completely cleaned, it worked great and I drove it about 20-430 milses, put it up and then drove it to ta show about 5 miles from the house and on the way back, it started doing it again. What causes the laqucer to build on the bottom of the carb? What can i do to prevent it. Right now I'm going to spray the inside of the carb's secondaries and then go for a drive and see what it does.

Thanks for your time and assistance with thes>

 

Welcome. I would think old contaminated tank and lines.

 

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old gas ! Clean the fuel system/tank , replace any rubber hoses..