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Discussion Starter #1
I have a 355 with 650 double pump,hei ign. Motor has less than 500 miles on rebuild and it recently started to have that rough dead cylinder idle shake. I did a cylibder balance and #1 is dead ,header is barely hot when running. Did compression and all cylinders have 165lbs + or - 5lbs. Swapped plugs,wires and cap all fine. Removed plug and let eng. run with plug wire hooked to plu and plenty of spark. Valve train seems to be moving fine as I removed valve cover and watched them all move freely.
I have recently rebuilt the carb to be safe but not a carb expert so could of missed something and also had a small vaccum leak at intake and so those gaskets were also recently changed. Seems the cylinder is not getting fuel ?? Its a rpm manifold and any help is apprecitted before I tear this down for no reason or to find a reason ?? Thanks, Chad
 

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Maybe a rocker on that cyl is too tight holding the valve off the seat?
 

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I had a lifter that acted normally, let the cylinder make compression for a compression test, but when the engine ran, it pumped up and held the valve open. To find the problem I backed the rockers for that cylinder off until I had about a quarter turn slack in the valve train, fired it back up, and the cylinder came back. It turned out that the lifter for one of the valves had internal check valve issues that allowed it to pump up when the oil pressure was up, as in engine running, but acted OK when no oil pressure was present. I found out it was made in Bolivia, sold as a "rebuilder's set" not a brand name set of lifters like they were supposed to be. I replaced all the lifters with a set of new brand name lifters, and all was well.

Regards,

Milton
 

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Discussion Starter #4
But if the valve wasnt seating how would I have the same compression as other cylinders ? Confused ??


Ok I reread the last statement and I guess it could pump up ? I will try that and back off the rockers before I tear anything apart.
 

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Discussion Starter #6
Wish it was that easy but I have installed 2 new plugs and same result. Even switched plugs and wires from other cylinders still no fire on #1. Will back off the rockers tomorrow and see what happens. Thanks for the help. Chad
 

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Discussion Starter #7
Ok, dug a little deeper. The rockers are not it, back them off until they ticked while running and still dead. The cylinder is only dead at idle, when I rev the eng. #1 cylinder hits fine. I am getting smoke out the tail pipe which I assume is just unburnt fuel once that cylinder ignites ? So it seems I am not getting fuel to #1 at idle any ideas ?
 

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Discussion Starter #8
Also its a 650 double pump carb I just rebuilt because I originally thought it was a carb problem. I dont know much about idle circuits but can a carb on a dual plane intake really cause 1 cylinder to not get fuel ??
 

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No can't be the carb...
The 2 primary barrels supply fuel and air for all 8 cylinders at idle and part throttle and there is no way that it could stop fuel from getting to one cylinder at idle.

Do you have any vacuum connections on the runner for that cylinder? You could try plugging them off.
 

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Yep, sounds like vacuum, but I would re-torque your intake manifold. A vacuum leak there is compatible with each of your symptoms.
 

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Discussion Starter #11
I just replaced the intake gaskets , but I guess I will do it again ?? The vaccum leak is about all I can think of at this point ? I did spray around the intake with no notice of a leak but dont know what else to do and its driving me crazy. Thanks for all the help.
 

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Bump. Anything new Chad?
 

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Discussion Starter #14
I guess when i get time I will pull the intake and replace gaskets again. May be a few days as I am very busy with work and a newborn baby. Thanks for the help.
 

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You said the spark was there. Was it yellow or blue? It should be blue, if not, bad dizzie tower? Or, (I know this is a stretch) bad lobe on the dizzie cam affecting the dwell/timing on that one hole?

alan
 

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New born baby!? Didn't you hear of the Mexico City earthquake back in the '80's? The maternity hospital collapsed. It took two weeks for rescuers to dig their way into the babies. ALL OF THEM were fine! We learned that human bodies, at that age, shut down to survive. Of course there's no way anybody but a Nazi would know that. We probably evolved that way because when we were cave men and a rival tribe would attack, parents would stash their kids and come back later. The kids who could survive the longest passed on their genes. Cool product of evolution, huh?
How does that relate to Camaro's? Easy. Don't sweat your kid screaming. The suspension on your car can be massaged with no harm to Jr.:yes:
 

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Only problem with that Andy is his compression is good across the board.
 

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Good cranking compression should indicate the engine is mechanically sound. Fuel issues are gennerally not going to cause one cylinder to miss on an engine with a carburetor. It seems strange to have a vacuum leak on one cylinder. Seems like it has to be electrical. Bad plug wire? Either shorting (should cause missfire, though), or have too much resistance. Check resistance compared to one of the others.
 
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