Hi all, my 250.6 Mopar L Head 6 in my 1955 Fargo pickup has a vacuum reading of 18-19 inches, but the needle vibrates. My timing seems decent, set it with vacuum gauge, adjusted carb for best vacuum, off the line performance and acceleration is very good for this type of engine. Idle is slightly rough, and these engines are known for being very smooth and low RPM idlers when stock. I did replace plugs and wires and verified points and cap, all appears in really good condition. Anybody have any ideas? Here is the you Tube link to see the vacuum test and engine running.
Thanx, tried that, it only lowered the vacuum reading, idle was not any different. Most likely I am dealing with the signs and symptoms of a well used engine, that is 60 years old....thanx
The fluctuation should be a lot more, but yes that could very well be the issue, with this old girl...thanx
A compression test and/or leak-down test will tell the story. If you come up with one low cylinder, pump shop-air to that cylinder with both valves closed. If an intake valve is burnt [or adjusted too tight] the escaping air will be heard in the carb..if it's an exhaust valve, noise will come from tail pipe.
Thanx Rocky will do, was going to do a compression test today, but my tester fitting is too long, will hit the valves, so need to get another. See your 650 miles straight south of my place, you feeling this cold too....
Thanx man, did a compression test on Saturday afternoon on a warm engine, but certainly not a hot engine. All 90-100, acceptable for this old low compression beast. Last night after a 12 hour day shift, I got out the timing light again, wanted to make sure vacuum advance was working, and it is. But the timing was way advanced at idle. I could only adjust back to about 2 btdc, and the dizzy ran outta room, then I shut off engine, moved top bolt setting to the middle of the range and loosened bottom adjustment bolt and set timing to TDC. I was then able to tweak timing and set her about 2 btdc. I proceeded to set carb and idle again, it is running much smoother and slower at idle about 500 rpm. I then had to go for a drive, and proceeded to drive her like i stole her, and did the 1/4 mile to the neighbors to 60 mph, on dry frozen gravel..... ps it was darn near 0 Fahrenheit outside and dark, but I was happy.
Are you picking up vacuum at the carb or at a port on the intake? If it's at one end of the intake your reading could be normal.
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