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Old 04-22-2012, 03:06 PM
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SBC 350 missfire at idle in gear

I have a rebuilt 350, heads have been machined, all 8 exhaust valves have been replaced, the intakes were in good shape, I have a .442 intake and .465 exhaust lobe on the cam, Stock hei distributor, new crank, new .030 over pistons, new pushrods, rockers, and lifters as well. I started it up for the first a few days ago and it was popping out the right side pretty bad. Adjusted all rockers and changed wires, cap, rotor, and even went and bout a new HEI dizzy. Still have a misfire on the passenger side banki of motor and dont know what it could be, I do Know that when it pops back through the exhaust its blowing fire into the pipes, could it just be a bad spark plug, or is it something worse that means tear down and reassemble.

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Old 04-22-2012, 07:09 PM
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Run a compression check. Also try isolating by pulling each plug wire, finding one cylinder that behaves differently when the wire is pulled. This will all help isolate the issue.

Pat
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Old 04-23-2012, 04:45 AM
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im going to check the compression on it today, also could it be a bad coil. A couple years ago i had a bad alternator that was putting out 16 - 18 volts volts and was driving it, I am basically having the same problem with the new 350 that i had with the old and tired 305. could it be electrical.
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Old 04-23-2012, 05:24 PM
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Make sure your timing is right with a timing light
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Old 04-23-2012, 10:07 PM
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Quote:
Originally Posted by ragee517
I have a rebuilt 350, heads have been machined, all 8 exhaust valves have been replaced, the intakes were in good shape, I have a .442 intake and .465 exhaust lobe on the cam, Stock hei distributor, new crank, new .030 over pistons, new pushrods, rockers, and lifters as well. I started it up for the first a few days ago and it was popping out the right side pretty bad. Adjusted all rockers and changed wires, cap, rotor, and even went and bout a new HEI dizzy. Still have a misfire on the passenger side banki of motor and dont know what it could be, I do Know that when it pops back through the exhaust its blowing fire into the pipes, could it just be a bad spark plug, or is it something worse that means tear down and reassemble.
Briefly, what procedure did you use to break in the cam?

Did you use break in lube on the cam/lifters and a break in additive in the motor oil (or oil made for break in)?

Did it start doing this after cam break in or was it doing it during break in?

What procedure did you use to adjust the lifters?
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Old 04-24-2012, 12:22 AM
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I used the break in lube that came with the cam. Applied it to whole cam and lobes. It was piping as soon as it fired once the engine gets to about 150 degrees the pop goes away and then comes back at normal running temp. When I first tried to fire it the spark plug wires were in correct order but had them one plug advanced on the cap so engine didn't fire. Changed wires to correct location on the cap and it started with a nasty miss. I changed the wires, cap, rotor, then the whole dizzy since I noticed that mine wouldn't spring the weights back. Still has pop on passenger side bank. Has about 150 psi compression on all 8 cylinders and valves are operating properly. I had the valves adjusted by my father who has built engines for years and the method he adjusts valves is loosen till clacks then slowly tighten to clack goes away and then give an extra 1/4 turn on the wrench and they are good to go. Valves were adjusted with a warm engine so there should be no issue there. I did find a little oil on the number 8 plug and it smell of gas so I don't think its firing. I am running the stock copper prone to foul if flooded plugs. And I flooded the engine the first two times I tried to start it.
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Old 04-24-2012, 01:03 AM
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What cam did you put in it? Part #?
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Old 04-24-2012, 01:56 AM
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Its a summit cam ill have to look up a part number when I get home. Im pretty sure that my issue is electrical due to recently found out the truck was totaled in an accident but some one welded the frame and bent it back straight. Wish I would have known that before I bought the truck.
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Old 04-24-2012, 03:42 AM
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Cam part number is: sum-1103
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Old 04-24-2012, 07:26 AM
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Most likely it is valve adjustment. A tight valve is a very common cause of popping through the exhaust especially if it seems to be isolated to 1 cylinder.
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Old 04-24-2012, 07:45 AM
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Well it was isolated to one cylinder then I changed the dizzy since I couldn't get the timing down lower them 12 degrees btc without the times becoming iradic jumping from 4 degrees after tic to way off the chart btc. Then I found that the rotor could bounce cause the weights weren't being held by the spring. So I switched the dizzy and forgot to recheck the timing to see if I could get it to set where it needs to be. So ill get some new spark plugs on friday and try to set the timing. Ill keep you guys informed on what I find out
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Old 04-26-2012, 08:19 AM
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Well I got it all fixed up. Np more popping. It was bad spark plugs and timing was off a little bit
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Old 04-26-2012, 02:13 PM
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new problem

Now it has a knocking or pinging like sound above high idle it doies not do it at low idle or at high idle but about 1500 rpm it starts making noise. Oil pressure is above 80 psi at that rpm so its not an issue with oil not being circulated around. could it be my fuel pump going bad. the pump is mechanical and probably has 155,00 miles on it like the stock 305 had.
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Old 04-26-2012, 05:05 PM
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Quote:
Originally Posted by ragee517
Now it has a knocking or pinging like sound above high idle it doies not do it at low idle or at high idle but about 1500 rpm it starts making noise. Oil pressure is above 80 psi at that rpm so its not an issue with oil not being circulated around. could it be my fuel pump going bad. the pump is mechanical and probably has 155,00 miles on it like the stock 305 had.
I would take a hard look at the distributor again. Put a light on it and see what the timing is at 1500 rpm
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Old 04-26-2012, 05:14 PM
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Timing is around 30 or 50 its not near the mark. Don't know if its helpful but with the vacation advance unhooked it still makes the noise. It sounds like its up front of the block or by the trans. It doesn't always seem to be in the same spot and as soon as I let off the throttle its gone.
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