Minnesota Classic Glastron Forum
General Category => General Discussion => Topic started by: Holymoses on March 18, 2020, 04:58:33 AM
-
I bought a 1973 CV 19 with the olds 455 pack a jet in it. The motor was supposedly just rebuilt. I have a problem with the motor popping back through the carburetor. There were also several other issues with water and oil leaks at the intake manifold so we removed it. everything looked fine so reinstalled correctly and tried again. One note is compression was checked all the way around and is good. Also replaced the carburetor, the one installed when I got it was for a car. Also the distributor which was also for a car. The timing is correct but the motor still pops. I will probably pull the heads next but hoped someone might have another idea before I do that. Thanks in advance.
-
Have you checked all the spark plug leads, are they hooked up in the correct firing order?
-
Yes. Actually new spark plugs, wires and distributor. We did that hoping it would fix the problem. Pulled the manifold off again last night and noticed gas sitting on the intake valve in cylinder 8. Turned the motor by hand and when we got to that cylinder it pushed bubbles up around the valve and popped. We think we have a valve that is not seating or maybe a bad cam lobe. Just not sure and hoped someone had run into the same issue. Thanks
-
Could be anything from valve train issue, to fuel lean, to ignition issues. You did a compression test, but this can mask some issues like tight or leaky valves. Second thing would be to perform a leak down test on all cylinders. If both tests come out clean, check ignition system for issues, timing order as Jeff mentioned. Is the ignition electronic? Points? Having a vehicle carb is a safety issue, but it would run ok on one. You could have a vacuum leak on one or more cylinders that can cause this condition. I use carb cleaner while running to find these leaks, the condition will clear when the leak sucks in the cleaner.
-
Sorry, you posted while I was typing. Check valve lift at that valve. If lash is ok, and lift is bad, likely a bad lobe. This does happen occasionally. Many budget priced cams are sourced from China, Howard's and Edelbrock still make theirs here in USA. If lift looks good, might just be a bad valve, faulty lifter, or lash set incorrectly.
-
From things that you checked I would guess that the cam was not broken in correctly and has a bad lode and lifter. Breaking in a motor is critical for cam and lifters. There are many videos on this.
-
Check and see if any push rods are bent. Check bottom side of intake
manifold if its the stock cast iron one for cracks at the exhaust cross over area
center of manifold.
-
Maybe when they rebuilt it they got the valve height
wrong if they replaced any valves . The stems should be
all about the same height within a few thousands .No adjustments
on the stock valve train. If a valve stem is too high,.025 or more
it will crack the Aluminum strap. A straight edge across the valve stems will let
you know if they are off too much. They sell a different set up if they are off .
-
You can open this area up to match gasket for better oil return
when you have the heads off. Top right hole.
-
You may want to look at the number 8 exhaust low back in the carbureted days GM head issues with soft lobes which would duplicate the same problem. If the cylinder cannot exhaust to the exhaust port it will have to exhaust through the intake interrupting the flow and creating a miss and backfire good luck