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Old November 20th, 2009, 03:30 PM   #1
Goat
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Carburated Chevy 350 question

I have a 85 GMC K1500 with a 350. It has a comp cam (don't know what the specs are atm) Was told it is bored 40 over. Rebuilt in 99 sat for 6 years til I bought it. It ran fine when I had glass packs and headers. Got pulled over a few weeks ago and had to put real mufflers on it. I ended up getting Thrush turbo mufflers. Since I put them on it has been stuttering and popping out the exhaust. Last night it was running real bad. Like it was not firing on 4 cylinders. I pulled all the plugs and checked them. All looked good except #6 had alot of scale built up on it. It was still nice tan color like the rest. I figured I should do a compression check.
Here is what I got -
#1 165psi
#2 170psi
#3 120psi
#4 170psi
#5 110 psi
#6 170psi
#7 170psi
#8 175psi
Your thoughts are appreciated. I'm not sure why only 2 cylinders would be low like that.
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Old November 20th, 2009, 04:36 PM   #2
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Quote:
Originally Posted by Goat View Post
#1 165psi
#2 170psi
#3 120psi
#4 170psi
#5 110 psi
#6 170psi
#7 170psi
#8 175psi
Your thoughts are appreciated. I'm not sure why only 2 cylinders would be low like that.
Possible blown head gasket or cracked head since the low numbers are side by side.
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Old November 20th, 2009, 06:30 PM   #3
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That is kinda what I was thinking. I check my coolant twice a week and it has been slightly low the last few times I have checked it. Maybe a 1/2 quart. Oil looks good and exhaust doesn't smell sweet so I have no idea where it would go. Thanks for your input.
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Old November 20th, 2009, 06:58 PM   #4
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do a cylinder leak down test. that will tell you where the problem lies. bubbling in the coolant means head gasket or cracked head, air past the carb means leaking or burnt intake valve, air out the exhaust means burnt exhaust valve.
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Old November 20th, 2009, 07:13 PM   #5
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I'm thinking burned valve or out of a adjustment valve. if you know how to adjust them running do so.
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Old November 20th, 2009, 11:40 PM   #6
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I have seen the head gasket burn between two cylinders and not lose anything but compression. Pulled the head and there was a 1/4" gap in the ring.
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Old November 21st, 2009, 11:41 AM   #7
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Thanks for the input guys. Now i just need to find a leak down tester to barrow before i start tearing it apart.
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