Help needed with a 327 ,backfires / coughs back up the carb with or with out the filter on ,we get a flame then cuts out when you pull away or just sat in my workshop and opening the throttle.The engine has had both heads reworked new valves, guides and hardened seat . Rv very mild cam ,+ .30 bore and pistons ,oil pump main ,big ends . New point less distributor, new leads,new coil with a ballast resistor, new plugs . Had a 600 cfm edelbrock carb and an edelbrock torker manifold unsure about carb so purchased a New 600 cam edlebrock carb ,had the timing at 14 BTDC have tried it at 10 BTDC Now set to 4 BTDC all with vac pipe to distributor clamped ,have check for air leak in manifold none clamped modulator hose to transmission, clamped servo vac pipe . Still the same losing the will to live PS I live in England
Are you absolutely positive you’ve got the firing order correct? If it’s not that then I’d say it’s a sure bet that you’re not actually setting the timing at 4BTDC, what timing marks are you using? if it’ll idle have you tried just setting the timing by ear?
Do you have access to a different manifold to try? perhaps a dual plane? But first run a compression test. And triple check the firing order and you might try more timing advance, instead of less.
When you say it’s had head and valve work, that tells me a couple of valves might be adjusted too tight. They’re hanging open so combustion is coming back through the intake. check the valve lash
@verr1908 Like other have said, A list of things to check first ,Good gas , No vac leak ""Lean '""" car adjustment Then what ever order Needs checked if cam was installed correct Your more likely initial is going to like 15 - 18ish deg BTDC , That's "If" TDC mark IS correct , Firing order Valve ajustment , bad lifter , to tight of lifter , bent push rod , coil bind , Broken spring ,wipping of cam lobe, Sticking Valve A None firing order swap cam ? Compression check , for bent or open Vavle , leak down test . Bad wire , Plugs What Brand distributor & type ? We know none points . Then if all checks out start looking into ignition Last carb , adjustments cracks vacuum leak accelerator pump enrichment screws lean / rich Correct intake gaskets for No vac leak
It won't run with it 180 out. Sounds to me like it runs, but it has a bad hesitation off idle. if so the usual suspects are being too lean (like accelerator pump not working), retarded timing, or something in the valvetrain keeping valves open or closed when they shouldn't be single plane intakes have lousy fuel distribution at low speeds, is what my suggestion is based on
Ok guys quick update , I got it wrong points distributor new (too many projects ) ,checked TDC with bores scope line up with zero on tv damper ,all plugs lead on correct will start an idle from cold if I manage to feather the throttle to get past the cough will drive , when warm and cuts out diff to restart thanks guy
might try replacing the condenser, if you can find another one somewhere. New point distributors are suspect.
Update from England, pushed the timing to 14 BTDC with vac line clamped ,revs out at idle ok , still not smooth on light throttle . Would you push the time out more to say 18 BTDC
Backfiring through carb... my first thought is that with hydraulic lifters and a decent cam you can't run 1 full turn tension on the rocker arm nuts. You need to go 1/2 turn or you can get into a scenario of the valves hanging open and backfiring through the carb. A leakdown check would confirm that via air blowing out the intake. 14-18 BTDC will be the correct range for this engine, vacuum advance disconnected. Then run ported vacuum once its not backfiring. The wrong coil will make it run TERRIBLE. that depends on what electronics you have. Most need a 3 Ohm coil or a 1.5 Ohm coil with an external 1.5 Ohm resistor. If you put the resistor with a 3 Ohm coil it'll fall on its face and be virtually undrivable. Make sure the factory ballast isn't still in place when you add the additional one near the coil! You COULD have a massive phasing problem if your aftermarket distributor was assembled with the gear installed incorrectly. Chevys are set up in a specific way. If you put the gear on the shaft 180-out, the spark has to jump off the corner of the rotor to the side of your cap terminal, and those terminals will burn up pretty quickly and run awful. A quick inspection will verify if it is right or wrong via the "dark spot" burned on the edge of your rotor. If this is all 100% correct, you're likely running VERY lean. Are you using a properly adjusted choke?
anything dual plane...either a factory intake, or something like the Performer, or it's predecessors. But make sure the ignition system is working right before you get too far along. Most carb problems are caused by the ignition system. and like he said, make sure it's not too lean. With two different carbs giving the same results, not real likely, but let us know about how you adjusted float level and idle mixture with both of them?
18436572 CORRECT ? Double sure ? And you know were # 1 is and the direction the rotor spins . Sorry to be elementary but Id start from scratch and check every thing . I jsut was teaching a kid this stuff last week and he had the wires going the wrong direction. I just went through this my slef with a 331 hemi that had wires crossed and was being driven that way when I pulled from the car . I was about to tear it apart thinking it had a bad cylinder and then thought hmmmmmmmm Id also be looking for a vacuum leak maybe the intake beibg to lean can cause this some one mentioned condenser and Id also check that on a points ignition I just had that on a guys olds and check the point cap/ dwell as well . Id re run the valves might have one to tight . turn the distributer way retarded and advanced and see how it acts .
My dad had his wired with a resister all the time and no 12v from the starter when cranking and it would not start well especially on a slightly weak batter due to to much voltage drop . His fancy new mini starter had no 12v when cranking stud so I had to add a in a relay. SO I was also thinking no resistor should be there but I had the old instructions, and it clearly said to use a resistor or it would fail . I was surprised it needed one .
I'll add in that the Edelbrock carbs don't like anything over 5.5 lbs fuel pressure, not sure what measure that is in crumpets lol
You said new cam . HMMMMMM Any chance the new cam has the 4-7/2-3 swap for SBC that means it uses a LS firing order and not the normal 18436572 order I know one guy who found out he had a non standard cam in a car he bought and there getting more and more popular these days .
Had it running tonight after 10 hour working day , loss my spark so I will pull the distributor and fit a patronix kit ,unless I can find a small hei I am one p****d off guy
The engine is so tight to the recessed fire wall ,that I have to drop the engine off the mounts to remove the distributor cap ,so if I use a patronix kit no more maintenance of the points
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