Mailbag: Talking Timing for Small Block Chevy V8s
Got questions?
We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re answering questions about timing for small block Chevy engines.
W.H . • Temple, TX
Q: Which way do you turn the distributor on a small block Chevy to advance the timing? We’re having a family debate—I say one way, and my boys say the opposite! Also, I believe advancing the timing on a carbureted engine (without a choke) will help it start easier on cold mornings. The boys disagree saying the spark should be retarded. And, if the engine backfires through the carb under acceleration (only when cold), is the timing excessively advanced or retarded? Finally, I think you should be able to install a distributor 180 degrees out of sync, and my sons don’t believe the engine will start, let alone run this way. How would you even know if it was installed 180 degrees out of sync?
A: Chevy distributors rotate clockwise, so you’d want to turn the distributor counterclockwise to advance the timing. Advancing timing to aid in cold starting will only help if the timing was retarded to begin with. Retarding the timing can help the starter turn a hot engine but that’s about it, so excessive timing one way or the other is not the answer.
Generally, advanced timing (up to the point of detonation) will make the engine run cooler. A vacuum advance that’s connected to the manifold vacuum rather than the ported vacuum can also reduce the engine’s operating temperature at idle. Not utilizing the vacuum advance can make an engine run excessively hot at any throttle position other than wide open.
When a cold engine backfires through the carburetor, it’s most likely an indication that your air/fuel mixture is too lean, not excessive timing.
If the the distributor is installed 180 degrees out of sync, the spark will occur during the exhaust stroke, so the engine won’t start, plus it’ll backfire out of the exhaust and possibly out of the carburetor as the intake valves open. If the rotor points to the #1 cylinder post, and the cam-gear alignment mark is at 6 o’clock, the distributor is 180 degrees out of sync with the crank. When the distributor is properly installed, the cam-gear alignment mark will be at 12 o’clock when the rotor points at the #1 cylinder post (you can use any of the eight posts for #1—the distributor won’t know the difference.)
Good info but not completely true. I have experienced and engine with timing 180 out. It will run. Just not like it should. I bought a truck with a 305 and after fighting with it trying to figure out why it ran like crap I figured out they had it timed 180 out lol.
I also have a 305 chevy silveradodoing same thing backfiring and then not wanting to turn on havevto hold gas to keep on could it also be 180
Why do we have to read stuff like this. It is completely accurate to say neither the letter writer nor the guy who left the comment about an engine running when it was 180 degrees out should be working on engines.
Agree. Why doesn’t all the commenters just shut up!!! The answer was concise, accurate and correct.
hey guys i have a 1984 Pontiac trans am Firebird, i am new to carb engines and it has a 88 c4 corvett engine (350 chevy small block) engine swap, i replaced the distributor plugs wires and rotor when i was thinking it had the oem 305 sbc , and it was throwing gas out the carb, not like shooting out but almost misting out if that makes any sense, so after finding out what engine was really in her i exchanged for the correct plugs wires ect.. just put some new gas in thinking it dint want to start cuz low fuel, still bursting gas out the carb i dont want to ruin anything so now im at a stand still, like i said im new to carb engines and cars in gerneral so when i intially took the distributor out i may have spun the distributor this way and that way.. my girl and i took the pullys apart and reset the harmonic balancer to tdc or the 0 degree mark thinking this would help set the initial timing and get her started but like i said still wont turn over and still shooting gas out carb. was running like shit when i got it so i did the initial tune up and it hasent started since im thinking its a timming issue seeing as i spun the distributor around like an idiot, ive read the question above and think i could have pointed the rotor the rong way but how would i know wich way it is suppose to point? i know it says post 1 so when i wired the spark plugs i looked up the firing order, the engine cast number did NOT come back with the exact year and so im thinking its an 88 but not a 100 percent. is there another way to detrime year of motor? distributor years vary 87 88 use the same but 86 and 89 pepboys said was a bit diffrent, would the carb spit if it has the incorect distributor in it or wouod timming be where i need to be focused? really need some help gents, my chick is in her 3d year of auto classes but for newer electric systems ect, so she knows but dosent lol. help help help help help help pleeeeeeeeeaaaasssseeeee!
You’re absolutely sure your timing marks are correct and you can get to TDC (Top Dead Center) on cylinder one (you can watch this to see how), correct? If so, when you install your distributor, make sure the pointer is located at the no. 1 cylinder position with the distributor cap.
Then set your timing–a good place to start is around 8 deg. before top dead center (initial timing), and then adjust from there.
After you’ve done that, if the carb still spits, then it may be another issue.
I was having simaler issues and it turned out my gas line was heating the fuel [e-10]and the carb bowl would boil it off. I changed the fuel line and double insulated it then got a small duct to go from a cooler spot (upfront to the side) under the hood to the air filter housing… so far so good!