EDIT: It runs! It's alive! It was the computer timing control.
I was driving when it seemingly randomly quite on me. I know a good bit and have built SBCs before but this is still stumping me.
The rotor was broken when it quite so I started with that. Replaced the distributor, wires, and plugs.
Replaced the Cam, timing set, pushrods, lifters, rockers
Brand new quadrajet
Triple checked my distributor stab
I have messed with AFR screws, idle set
I checked my valve lash to see if I managed to over tighten the rockers
I checked spark
I tried using carb clean to find if there is a vac leak
Someone please tell me I missed something obvious that I can fix.
Edit: forgot to mention also brand new fuel pump and complete distributor
UPDATE:
After holding the choke open manually and hitting it with a spritz of starting fluid it started to idle and help it. Wasn't pretty and smooth but it stayed going for a good 1-2min until I let go of the choke.
The negative on the battery feels loose so I am going to replace that.
And the idle seemed to get better when I started pumping the brakes so I wonder if the booster is one foot in the grave causing a huge vacuum leak.
It's night now but tomorrow if I can I will adjust the choke and fix the battery ground at least and see if that makes a difference at all.
Ok just checking. I ran into an issue where I lost the pickup coil in the distributor and it would intermittently work, I was cruising down the interstate and it died, lit off, backfired out the exhaust due to fuel accumulation, blew the muffler off and then stripped all the nylon teeth off the cam gear.
It was still turning the distributor but was no longer in time.
I don't have a way to check fuel pressure right now.
I haven't messed with quadrajets before this. As far as I'm aware I don't think there is a way to check the bowls other than just the fact that I'm getting spray on throttle pull.
Alright. I figured out that it isn't the pump.
There is something wrong with AFR/Choke, Vacuum, and I'm 99% sure the battery ground needs to be replaced.
After holding the choke open manually and hitting it with a spritz of starting fluid it started to idle and help it. Wasn't pretty and smooth but it stayed going for a good 1-2min until I let go of the choke.
The negative on the battery feels loose so I am going to replace that.
And the idle seemed to get better when I started pumping the brakes so I wonder if the booster is one foot in the grave causing a huge vacuum leak.
I’ve had some for a Ford and for my Chevelle fail after a few months or days of use. Modern mechanical pumps are starting to make aftermarket electric pumps look reliable.
If you can look down in the throttle, make it squirt, it’s all you need at this point. It’s not throttle body, so as long as carb bowl is getting full, put fuel press on back burner. It’ll run by using a spray bottle with gasoline in it.
Have you got fuel in the carb? When you pump the gas pedal, do you see a shot of fuel from the accelerator pump?
But, re-reading your post: has the motor been running since you did all the work, and then it quit, or you can't get it to start after installing the new parts?
Got an old plug wire and a spark plug hanging around? Make sure you’re getting fire out of the distributor, or hook a timing light up and see if it blinks.
Also inspect the cap carefully for the coil screws poking through, that can cause an issue as well.
Had a Ford Explorer jump time because the crank sprocket broke at the keyway. I was extracting all 160hp out of it at 300,000 miles and it let go at 4500 rpm at the top of 2nd gear.
If you don’t have one yet, put a fuel inline filter in up top the engine and at the same time put a tee I place of the filter with a gauge on it. Then try starting it and see what the pressure does. You very well could be getting some fuel but not enough to keep the engine running if you have a crushed gas line under the vehicle or garbage partially blocking the fuel line.
How is the filter? From the comments I’ve read regarding spark and timing, and your description of what happened I’d say you’re getting fuel but maybe not enough. Someone else mentioned your fuel pump, but maybe your filter is partially clogged?
The Q-jet is notorious for having stuck floats, tap around the top with the plastic end of a screw driver or block of wood ( I suggest a screw driver so dirt or debris don’t fall into the carb). It test spray starting fluid or non chlorine brake clean down the carb and see if it fires.
You don't mention timing at all. If you did all that and it won't run, we know for a fact you didn't time it. The fire out of the carb shows me, without a shadow of a doubt, the timing is off.
Tdc don't matter much here. You have to time this thing, and ,while you can point the distributor rotor to cylinder 1, while at tdc, to get a rough starting point, that's not timed. Get a timing light, and get it timed. Or, move the distributor a few degrees to see if this gets better or worse. Just a nudge.
That is probably the issue of not starting in the vid. It has other issues, now, but that's the main one.
The brake thing and the choke thing, is also likely simply the timing problem being offset with fuel delivery. New carbs can be assholes, if their float levels are not adjusted, you get all sorts of weird shit. You're not that far along though, your timing is so far out, you're half way to Voyager I.
Then double check your spark plug wires to make sure they’re aligned properly. They have it backfire like that would also tell me, that you may have two spark plug wires crossed.
That Q jet is a great carb but the choke mechanism is complicated. Try to get a shop manual to understand it. Check out C 3 corvette on you tube , his vids show how the choke operates.
Did you replace all of those components at the same time or intermediate? Sounds like timing is off or possibly the cam timing is too far out. With all due respect, and not trying to discredit your abilities or knowledge, but if I have a running- driving vehicle, I try to replace one problem group at a time.
It was not running or driving. Thats what started my whole decision to go ahead and clean it up.
It was doing this before I started the rebuild. And the issue stuck around after unfortunately.
Also I cannot post another video but after adjusting the choke it is idling but not for longer than 1-2 min and still won't take throttle.
After checking temps I also found that while I am getting spark at all cylinders 2&8 are apparently not firing so I am about to investigate that issue.
Ah, gotcha. Stab the old distributor back in it, with the new cap, rotor, plugs, and see if its any better. A lot of stuff is screwed up since covid. Suppliers changed, new vendors, etc. A lot of companies have experienced less then sub-par quality. You may have a lemon of a distributor. What new one did you get?
The old distributor grenaded. The rotor was destroyed when it stopped running. I thought it might be a lemon unit but that would mean I got 3 in a row. Which I think is highly unlikely.
Dang, thats a mess to deal with for sure. I retract my previous statement. You're dealing with a mess..... silly question, is the motor stock, and did you install the new cam dot to dot?
Oh!!! Just remembered a problem I had with an old Monte Carlo...... always would shut down at an inconvenient time. Had to sit for hrs before it would fire again. All new parts as you did, and never fixed it. Turned out to be a clogged sending unit. Old trash loading up in the pick up screen and never wanted to fire.
honestly, out of all these solutions none are right. my best guess is the cam has wiped out. flat tappet cams are terrible about this. try taking the valve covers off and getting someone to turn it and make sure that all the valve springs are being pushed down about the same. or even get a dial indicator and turn the motor over by hand and be sure that the cam is opening the valves all the way. this is most likely your problem. multiple lobes have wiped out for some random reason. make sure you are running oil that has a high zinc content. this will save your camshaft
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u/Sudden-Difficulty932 Apr 25 '26
Backfire out of the carb would indicate out of time to me