1967 GTO Running rough - Pontiac GTO Forum
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post #1 of 13 (permalink) Old 06-05-2014, 02:27 PM Thread Starter
 
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1967 GTO Running rough

Hi Everyone, I have a question about how you guys would start to troubleshoot a problem I am having with my new rebuilt 400, I put in the new motor and broke it in, but it is sputtering like crazy, we took it for a drive around the block and it has a top speed of about 30mph, and is just sputtering like crazy. I'm just wondering where you guys would start, timing?, Carburetor, adjust the valves, maybe even something as simple as a vacuum leak. Any thoughts on how to get started would be great, Thanks in advance. Also do you think I need to run a pcv valve to the carburetor, right now I just have it capped off.
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post #2 of 13 (permalink) Old 06-05-2014, 02:56 PM
 
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Exact symptom of a vacuum leak. Hook the PCV back up. Check all vacuum lines (carb, brake booster, etc). Especially check the nipple that goes into manifold in front of the carb. Mine wasn't tight. Car coughed and sputtered. Called in an expert. First words out of his mouth were "I don't know what else might be wrong but you got a vacuum leak". I couldn't hear it. JB weld on the nipple and all was well.

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post #3 of 13 (permalink) Old 06-05-2014, 04:23 PM
 
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I'd check the firing order. The first 389 I built I had the wires backwards. These fire the opposite direction of a Chevy 350 which was one of my first motors I built just before the 389.
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post #4 of 13 (permalink) Old 06-05-2014, 04:43 PM
 
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Quote:
Originally Posted by topfuel67 View Post
I'd check the firing order. The first 389 I built I had the wires backwards. These fire the opposite direction of a Chevy 350 which was one of my first motors I built just before the 389.
That too.
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post #5 of 13 (permalink) Old 06-05-2014, 06:25 PM
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Is the timing chain in properly, or clocked 180 out? Easy to do, and will act as described. Is the distributor in properly? Static time the engine (number one cylinder at TDC) dist rotor should point at #1 terminal on cap, and timing mark should be at zero on the balancer. A compression test will verify if valve timng is ok. What vacuum are you pulling on a vacuum gauge? Should be at least 18" at idle. A vacuum leak would not effect drivability off of idle very much. And not at all at WOT. (There is no vacuum at WOT). To me, it sounds like a timing problem, and very possibly a mis-installed timing chain.
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post #6 of 13 (permalink) Old 06-06-2014, 11:34 AM Thread Starter
 
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Thanks for the feedback, first i'll start by hooking the pcv up to the manifold, and then put a vacuum gague on it to check it, and then move on to the timing, is there any way to check if the timing chain is on correctly without taking the timing cover off, I don't think so but i'm not sure. Thanks again, I'll check it out and post what I find.
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post #7 of 13 (permalink) Old 06-06-2014, 11:39 AM
 
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Do you have the grounding strap from the firewall to the engine block? Did you rebuild the carb with new gaskets?
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post #8 of 13 (permalink) Old 06-06-2014, 01:29 PM
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If you static time the engine, and confirm that both valves are closed and the piston is at TDC on number one cylinder, and the timing mark and rotor line up as I described, the chain should be clocked correctly.
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post #9 of 13 (permalink) Old 06-06-2014, 03:06 PM Thread Starter
 
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Now that you mention it, I don't remember if I hooked the ground strap back up when I put the engine in, I'll have to check, also thanks again for the responses, i'm going to check to see if the timing chain is installed correctly as well.
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post #10 of 13 (permalink) Old 06-06-2014, 06:20 PM
 
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Garage
x2 with Geeteeohguy. Sputtering sounds like an ignition problem and not being able to get over 30 MPH. Fuel problems usually don't act like that UNLESS your choke is not fully opening and could be closed.

Do you have points? If so, check the gap and dwell.

A bad alternator/low charged battery will do this as well. If you are not getting full voltage to the ignition system it will sputter and not run very fast as you described -have had this happen. Check your charging system to ensure you have enough voltage, which includes making sure you have the correct voltage regulator/alternator, no broken/pinched wires from the engine install, and of course, the ground wire.
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