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1978 Chev G-Series Van Other - Engine
Question: Chevrolet 400 motor would run well only when timed at approx. 20 degreses BTC. for last month. Had new long block built. Same situation. Checked for TDC with pencil in #1 and found balancer and timing numeral plate seemed to line up perfect at 0. Does this indicate timing gear installed properly? Removed balancer and found it matched up correctly with new one in relation to mark and keyway. Placed back on, same problem. Had distrutor placed on machine at auto repair facility and it checked ok. Replaced distributor. Same problem. Checked routing of vacuum lines with Mitchell Manual. All appeared correct. (Backfires at 4 degree markand runs ROUGH). Still runs ok @20 degrees. Can't pass smog with this timing condition. Machine shop "re-clocked" distributor drive. Same condition. Maximum intake manifold vacuum is @ approx. 20 degrees BTC.
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Technican: I'll give it a shot. Do you know if you have a single plane intake or dual plane. If dual plane and a quadrajet it might have an internal crack. Also try spraying some WD40 around the intake area and see if you notice any difference in rpm. This could lead to a warped intake.
Owner: I believe it's what is called a dual plane though I don't really know. It do know it does have a quadrajet. Short of replacing the carb or manifold (which one are you implying may have the crack, the carb, the manifold, both?) by changing them out how can these be tested? To change each of these is worth it of course if this is the problem, but it's so much work and expense if not quite certain before hand. But, of course, if replacing is my only option I will eventually and if this solves the problem I will ok payment immediately. I have tried spraying carb cleaner on the intake manifold and there was no change in RPM's. Did placing at TDC and the timing marks lining up at zero prove the timing gears are lined up (synchronized) correctly? Again, please be assured that if this does indeed prove to be the problem I will authorize payment immediately. Thank you. P.S. For ease if you would like you may call me at (760) 753-0034, Thanks again, Robert
Technican: If you have a dual plane intake, you can do one check that will nearly pin point the problem. Take and turn your one idle adjusting screws all the way in. This should kill half of the engine. If it does not turn the other all the way in and see if it does kill the engine. E-mail me back with results. Thanks
Owner: Les, I turned one of the idle speed screws in all the way (Rochester 4mv is the carb.) and the motor ran a little rougher. I left it in and then turned the other one in all the way. Motor ran even rougher but still did not die, though it acted as though it was sick enough that it might want to. Intake manifold vacuum dropped from 20 to 14 after both screws were turned in all the way. I did not adjust the fast idle screw on the primary throttle valve contact lever (I didn't think that that was the one you were speaking of). Hope this is right. Thanks.
Technican: Hi Robert;
This is. It seems like there is more than I can explain. I work Nights so give me a call at work at about 6:00pm. I'm in central time. The phone number is 1-800-646-8933. Talk to you later. Here's How To Get Guaranteed Solutions In Minutes
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