1977 Chevy Truck poor performance under load

TSGFECK

MEMBER
1977 CHEVROLET TRUCK
V8
4WD
AUTOMATIC
95,000 MILES

My 400 is less than 30000 miles old, in a K30. I have checked plugs, wires firing order, fuel pump, and timing.
It seems to idle fine but when I put it into drive it acts like it's going to die as is sputters and spurts under load.

Am I dealing with a stuck valve? Someone suggested that. Carb was rebuilt when engine was new.

Please ANY help is valuable. It is my work truck and I can't use it for work.

5 Replies

HMAC300

MECHANIC
48,601 POSTS

If you have a stuck valve, you wuld know it at idle. Check for a vacuum leak and if you have 15" of vacuum or less then it maybe a plugged converter or exaust.

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Thursday, September 2nd, 2010 AT 6:09 PM

GEEKFECK

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19 POSTS

How do I tell if the valve is stuck at idle?

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Tuesday, December 7th, 2010 AT 4:08 AM

HMAC300

MECHANIC
48,601 POSTS

Check your compression. Also it was supposed to read 15" of vacuum. If it's like that check for a plugged exasust or converter

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Tuesday, December 7th, 2010 AT 1:39 PM

GEEKFECK

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19 POSTS

Compression checked, when looking at front of truck the left side (2, 4, 6, 8) has (front to back) 134, 127, 130, 117. Right side front to back(1, 3, 5, 7) has 105, 104, 103, 88, Now what? Check for a stuck valve? And how to unstick? The motor is only a few years old with about 20,000 max miles on it probably less.

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Sunday, July 31st, 2011 AT 9:55 PM

HMAC300

MECHANIC
48,601 POSTS

On a chevrolet V8 the left bank(drivers side ) is 1-3-5-7 and right bank is 2-4-6-8. Your your right side is down on compression. Put some oil in the cylinders and then check compression. If it goes up your rings are bad otherwise it looks like you have a valvle problem. It may be bad guides or receded valves or both. Also check for a bad camshaft. Take the rocker cover off and start the engine andlook for one of the rockerarms not going up and down as much as the others. That is usually an indication of a worn cam lobe and you'll need to replace the cam and lifters as well as probably a valve job w/guides.