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Discussion Starter · #1 ·
SO my sbc 350 is running very rough and choppy. I did a head gasket change and when i reassembled it, it sounds bad. checked the timing, the valve sequences, it idles for a little bit and sounds more like a lawn mower or a motorcycle than a chevy engine. the Carb backfires and ive seen flames a few times and can smell burning oil. i feel like this whole swab job has been a big mess and i dont know where i went wrong. Please, any suggestions or solutions. Thanks!
 

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Go back to basic's..
Check the timing,, is the distributor rotor pointing at #1 cyl when it is at top dead center..


Is the firing order correct on the cap to wires..?


do you have a huge vacuum leak?


Did you stab the distributor in a tooth or two off..?
 

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Discussion Starter · #4 ·
Go back to basic's..
Check the timing,, is the distributor rotor pointing at #1 cyl when it is at top dead center..


Is the firing order correct on the cap to wires..?


do you have a huge vacuum leak?


Did you stab the distributor in a tooth or two off..?
Check all that. The distributer is set in basically perfect right now. I want to avoid pulling it back out if I can because I don't think I'll get it seated the perfect again. Only unknown is a vacuum leak. What would cause a huge vacuum leak like that?
 

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Let's start by going back to the beginning. Read this Wiki article then find TDC of your engine. http://www.crankshaftcoalition.com/wiki/Determining_top_dead_center Here is another article on the three most common locations for the timing mark on the damper. http://www.crankshaftcoalition.com/wiki/Timing_tabs_and_damper_TDC_lines_SBC If you want a timing tape for your balancer here is instructions on how to make a timing tape. Finally here is a Wiki article on how to set up your ignition advance. http://www.crankshaftcoalition.com/wiki/Hot_rodding_the_HEI_distributor This article also has some other tips that will help you like adjusting the idle transfer slot. Have you used a vacuum gauge to run some checks on your engine since changing head gaskets? If not you definitely need to.
 

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Check all that. The distributer is set in basically perfect right now. I want to avoid pulling it back out if I can because I don't think I'll get it seated the perfect again.

that makes no sense at all, either you want to fix it or not????

pull it out and re verify all timing steps if it was perfect then you would not be having a problem
 

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Most likely you have some valves lash too tight on some cylinders... if cam was 180 degrees out, it wouldn't run at all... backfire at best... do a compression test on all 8 cylinders and the ones with lash too tight will prolly leak down badly...
 

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Check the simple things first...maybe you have crossed a couple of plug wires. If it was the drivers side head it's easy to cross #'s 7 & 5.
 

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Discussion Starter · #9 ·
Most likely you have some valves lash too tight on some cylinders... if cam was 180 degrees out, it wouldn't run at all... backfire at best... do a compression test on all 8 cylinders and the ones with lash too tight will prolly leak down badly...
Yeah I'll check that next. Thanks
 

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Do you have a compression gauge or can you borrow one? Since you said you changed head gaskets do a compression check. Remove the coil wire before starting. The have someone sit in the car and depress the gas pedal and crank the engine over until you get the highest reading on the first cylinder. Do all the others the same. Record the reading of each cylinder, there should be no more than 10% difference between each cylinder. If you have a low reading on a cylinder squirt a little oil in the cylinder and crank it again. If still low the ring is wore or broken. If the numbers increase think valve problems.
 

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Everyone has made excellent diagnostic recommendations and each one of them should be checked with timing and spark plug wire checks at the top of the list. I'll throw in that a vacuum gauge reading is going to help identify the issue as well. If the gauge is randomly jumping at light throttle, 1100-1300 rpms, and the timing is close and the wires are located correctly, then readjusting the valves should be the next step. Checking compression can help identify which cylinder(s) are the issues, but I'd recommend rechecking all of the valve adjustments if you find an issue with a certain cylinders during the compression check. To be clear, when I say rechecking the valve adjustment I mean marking the adjuster nut prior to readjusting to see if your readjustment has led to change in the adjustment.

Lastly, I hate to ask so as to not open up a can of worms, but how did you adjust the valves? I STRONGLY recommend using the E.O.I.C. method. It takes some extra manual spinning of the motor, but it works. And many will recommend jiggling the push rods rather than spinning them until resistance is felt. I use both on every valve to confirm that I'm getting the adjustment from both methods.

Good luck - Jim

edit - forgot to mention, is your spark good? New cap and rotor? New wires or have you performed a resistance check on the current wires? A bad cap, rotor or weak wires will cause exactly what you're experiencing. A quick check of the ignition system is a low budget inline spark tester hooked up to the spark plugs to confirm that you 're getting consistant spark to every spark plug.
 

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Discussion Starter · #13 ·
Everyone has made excellent diagnostic recommendations and each one of them should be checked with timing and spark plug wire checks at the top of the list. I'll throw in that a vacuum gauge reading is going to help identify the issue as well. If the gauge is randomly jumping at light throttle, 1100-1300 rpms, and the timing is close and the wires are located correctly, then readjusting the valves should be the next step. Checking compression can help identify which cylinder(s) are the issues, but I'd recommend rechecking all of the valve adjustments if you find an issue with a certain cylinders during the compression check. To be clear, when I say rechecking the valve adjustment I mean marking the adjuster nut prior to readjusting to see if your readjustment has led to change in the adjustment.

Lastly, I hate to ask so as to not open up a can of worms, but how did you adjust the valves? I STRONGLY recommend using the E.O.I.C. method. It takes some extra manual spinning of the motor, but it works. And many will recommend jiggling the push rods rather than spinning them until resistance is felt. I use both on every valve to confirm that I'm getting the adjustment from both methods.

Good luck - Jim

edit - forgot to mention, is your spark good? New cap and rotor? New wires or have you performed a resistance check on the current wires? A bad cap, rotor or weak wires will cause exactly what you're experiencing. A quick check of the ignition system is a low budget inline spark tester hooked up to the spark plugs to confirm that you 're getting consistant spark to every spark plug.
Yes I used EOIC method. I'll double check everything. Haven't thought to test the spark plugs though so I'll definitely add that to the list. Thanks a lot for the advice. Hopefully one of these will get it running
 

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Talking about spark plugs if your engine has flooded for any reason your spark plugs will need to be changed. I found this out a long time ago when I converted my 72 Monte Carlo to HEI. It had a 400 c.i. engine with a q-jet. My wife went to start it one morning and came back in and said it wouldn't start. Well I went out to check it out and almost thought it had jumped time. But I got it up on #1 cylinder and popped the cap to check the rotor it was pointing to #1 spark plug wire's post. I removed the air cleaner and saw the choke closed. I opened it and used a screwdriver to hold it open while I tried to crank it. It popped and spit but would not start. I went and bought a new set of spark plugs and installed them and the car started right away. It has happened several times on different cars. I don't know why the resistor spark plugs are not any more good after flooding so I throw them in the garbage and replace them with new ones. It is a cheap price to check on yours.
 

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Talking about spark plugs if your engine has flooded for any reason your spark plugs will need to be changed. It popped and spit but would not start. I went and bought a new set of spark plugs and installed them and the car started right away. It has happened several times on different cars. I don't know why the resistor spark plugs are not any more good after flooding so I throw them in the garbage and replace them with new ones. It is a cheap price to check on yours.
I've flooded engines lots of times, held it wide open and cranked it till it started, and continued on my way with the same sparkplugs for years... of course, new, dry sparkplugs also works...
 
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