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Join Date: Jun 2012
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Compression Loss #4 cylinder

After rebuilding and adjusting the carburetors on my 66 912, I was trying to read the spark plugs. Cylinder numbers 1,3, & 2 looked minimally black. Number 4 looked brown. I kept trying to match the other mixture screws to get a brown look on all plugs. At some point, the # 4 cylinder plug started looking its metal color, no longer brown. I had only been adjusting on the 1,3, & 2 cylinder mixture screws. However, the # 4 cylinder is no longer firing. I cleaned the carburetor out, have spark, new distributor cap, adjusted points gap, set timing, and adjusted the valves. The # 4 cylinder is still not firing, and only tests at about 65 lbs. of compression. The other cylinders are around 100ish. Could I have burned a valve this quickly, during the approx. 12 hrs of run time (no high RPMS, or abusive running) after the rebuilt carburetors were reinstalled. Engine had always ran on all 4 cylinders before this. Any advice greatly appreciated.
Old 01-12-2018, 05:04 PM
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If I were you I would post your problem on the 912 bbs forum and join that as well- it's. Free and there are dedicated strictly to 912 and have a lot of expertise on their forum, all the time and every time
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Gordon

1967 912 Coupe
1985 911 Carrera
1967 MGB GT
Old 01-12-2018, 07:16 PM
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Quote:
Originally Posted by Greg Greer View Post
After rebuilding and adjusting the carburetors on my 66 912, I was trying to read the spark plugs. Cylinder numbers 1,3, & 2 looked minimally black. Number 4 looked brown. I kept trying to match the other mixture screws to get a brown look on all plugs. At some point, the # 4 cylinder plug started looking its metal color, no longer brown. I had only been adjusting on the 1,3, & 2 cylinder mixture screws. However, the # 4 cylinder is no longer firing. I cleaned the carburetor out, have spark, new distributor cap, adjusted points gap, set timing, and adjusted the valves. The # 4 cylinder is still not firing, and only tests at about 65 lbs. of compression. The other cylinders are around 100ish. Could I have burned a valve this quickly, during the approx. 12 hrs of run time (no high RPMS, or abusive running) after the rebuilt carburetors were reinstalled. Engine had always ran on all 4 cylinders before this. Any advice greatly appreciated.
check the 912 site as you have some answers to provide to slove issue
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Gordon

1967 912 Coupe
1985 911 Carrera
1967 MGB GT
Old 01-13-2018, 06:27 AM
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