I'm trying to start a freshly rebuilt SBC. It'll pop and snort but won't run. It will occasionally backfire through the carb. I've loosened the valve lash to zero lash to eliminate the backfire. ( I'll adjust the valves once the engine is running). 1. I've tried rotating the dist. 180, 2. I've triple-checked that the plug wires are in the correct firing order. 3. I've checked the timing gears are properly installed. 4. I've got plenty of fuel (fuel squirts down the carb when I open the throttle. What am I missing?
pull the number 1 plug. stick your finger in the hole, bump the starter until you feel compression. continue to turn the same direction by hand until the timing marks line up to 10 degrees before , check that the rotor is pointing at the number 1 terminal at the cap, verify that the firing order on the cap (going clockwise from 1) is 1 8 4 3 6 5 7 2 . Hook up the timing light, turn the key on and rotate the dist until the light flashes. put the number 1 plug back in, and start her up
Agree it's a timing problem. Follow the advice of previous replies. You will figure it out. Sent from my SM-A102U using The H.A.M.B. mobile app
Used to be one of our hands on tests for new hire mechanics. Pull the dist and crank the motor over then get it back in time and drop the dist. We would allow 30 minutes on a 350 Caprice. some guys did it in less than 5 minutes other guys never got right. You can guess who never got hired.
This is probably one of the most common problems that home mechanics run into. Getting the engine cold timed for an easy start up is a huge time saver.
============. Sounds like the old Plymouth trouble shooting contest. And, what the step-by-step instructions in the trouble-shooting sections of OEM Shop Manuals are meant to diagnose ASAP.
Sound like a 180 out dist, I once stabbed a dist three time, kept putting it in 180 once correct varrrooom
I had a new cracked distributor cap once that caused havoc on initial start up, somehow the spark was jumping terminals causing it to act like it was out of time, I scratched my head on that one a couple nights lol
Over at a friends one day to give him a hand on a no start; interesting to learn that an inductive timing light would flash even tho the rotor was laying on the bench. He swore it was in there when he put the cap on. Gremlins, no doubt.
I can't write the instructions any better than this. It is almost word for word what I would have written. In the 70's when I built my T bucket with the 283 in it it was the first Chevy V8 I ever owned. I had had a 322 Buick and then my 69 Cutlass with a 350R After I rebuilt the 283 I stuck it in the chassis an got it all wired up and hooked up and went to fire it and got some real nice flames out of either the carbs or headers. A couple of days of fighting with it off and on and abut 02:30 one night/morning it hit me I had wired the distributor backwards. Out in my bath robe to the garage, rewire it and fire it up at 2:30 in the morning. I didn't run it long but sure slept good the rest of the night. When I was teaching auto shop in the 80's we had a 289 Ford engine in a stand that Ford had donated as a training aid. Each year I would have my classes have contests as to how fast pairs of students could put the engine in time, adjust the points, drop the distributor in and wire and fire it. It had to start and run. Several teams got it down to under two minutes and I think one pair did it in a minute and 30 seconds.
I chased my tail in the same way. Being young and taking poor advice, after an intake change I put the distributor in with all the wires running the wrong way around the cap. My dad came home and asked a few questions. Never even looked at the engine. A few minutes later he came back with a MoToRs manual and said “read this”. Sure, he could have told me what I did was wrong, but after reading that manual all night, the light bulb came on. I liken it to bumping your forehead on a low beam. After your learn, you never make that mistake again
Yep,,, I’d question my dad, he said read this while handling me a motors manual. He’d say read this so we both know what we’re talking about and if you still don’t understand “IT”. I’ll walk you thru it. Now comes 10th grade, “hey dad, I think I want to take auto mechanics. It’s a 2yr vocational program all day.” My dad said, Why? I’ve already taught you everything they will teach you,,, hell I bet you could almost teach most subjects- take the welding and fabrication vocational course.
Lol. I dropped my auto shop class in HighSchool. After 3 weeks of being told “this is the oil plug, this is the filter, etc”. I didn’t make a career out of working on vehicles, but in 40+ years of owning them I never have had to pay some one or a shop to fix an issue. Well, other than machine work.
One of the things that causes a lot of 180 out timing is when assembling the engine (this applies to chevs) and the timing marks are dot to dot. This #6 firing not number one, number one firing is both dots strait up.... So, has the OP got his running yet???
I will use the thumb over the plug hole sometimes. I haven't seen it mentioned, that when the #1 intake valve closes, just rotate the crank 'til the timing mark comes up. If the valve covers are off, I like this better than the thumb method.
Thumb over the spark plug hole works if the valve cover is on engine and has stuff in the way for easy removal. Otherwise looking at the valves is a sure fire way to ensure you have TDC on #1. (intentional pun, sure fire) It is also important to ensure the plug wires are entered on the cap the correct way clockwise or counterclockwise; and in the correct firing order.
I don’t have enough arms to rotate the motor and keep my finger over the plug hole, so I wad up toilet paper and twist it into the threads abit. When it flutters or pops out I then take the balancer mark to a bit before TDC.
I didn't see this mentioned.... check for a big vacuum leak. At the back of some carbs there are large ports to run a vacuum brake booster or a large port in the intake manifold. If they are open (or if you question the booster), plug them and try it. I've seen this myself on a friend's truck he couldn't get started.
I need to add... I have no idea of your mechanical capabilities, and I mean no disrespect but if you're not mechanically inclined, that's ok because we all need to learn. I'm mentioning this only because you said in the thread it is a rebuilt engine? Are you aware of how to best break in a camshaft? This is very important on a new camshaft (depending on type). I just don't want to see a fresh engine have a failure if you're not aware of some things mechanically. Again I mean no disrespect, I have no idea of your capabilities.
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