What can cause sputtering
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 751
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From: Woburn,ma ma
What can cause sputtering
It's a 383, Holley 650dp Installed a new carb, intake and distributor...I removed my proflow, as it sputtered even worse.. with the carb it does feel much better, but none the less, it should not do this, the engine has approximately 1500 miles, and it has been running like this from the start.. just before I removed the proflow I noticed when I pull out of my garage I could just use the clutch, no gas pedal, and then depress the clutch all the way the car would abruptly idle high, then come down to set point.. it does this with the carb setup also. I thoroughly checked for vacume leaks... the coil and wires were new when the engine was installed... Any suggestions on what to test, or look into? There is no unusual valve train noise, but I am going to pull all plugs, try another coil I have, and pull the valve covers . I will add, yesterday I set the timing adjust the carb. Sounds good, today when I started even after it was fully warmed up it was idleing 200 rpms less than it was set at, also at times it will out of no where idle rough.. this is a lot to take in.. yes, I changed the intake gaskets, as the edelbrock gaskets leaked at water passage..
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I'm confused with the issue. Are you fighting a inconsistent idle? Or a slight misfire? Or perhaps both?
You removed your proflow for a undersized carburetor?
I'm totally confused.
You removed your proflow for a undersized carburetor?
I'm totally confused.
Thread Starter
Burning Brakes
Joined: Aug 2000
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From: Woburn,ma ma
Yes, I am fighting both.. I got the 650dp as to summits recomedation, I use to have a 750dp..prior to that, I had 650dp, it just felt better with the 650dp.. it's also more than a slight misfire..with the edelbrock proflow it was more pronounced..
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From: Sunshine Coast, Queensland, Australia
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A miss fire sounds more like leaky plug wires. A bad distributor cap. That type of thing. Not induction.
Yes if things are wrong it's more noticeable with fuel injection. Double edged sword I guess. But that doesn't mean the injection is at fault.
I'd be looking for a pinched or burnt plug wire. Checking all of them with an ohm meter, checking the cap and rotor, those types of things for a misfire. As per inconsistent idle. How did you install those intake gaskets? Etc. I think I'd fix the misfire first. And if the inconsistent idle persists. Then chase that.
Yes if things are wrong it's more noticeable with fuel injection. Double edged sword I guess. But that doesn't mean the injection is at fault.
I'd be looking for a pinched or burnt plug wire. Checking all of them with an ohm meter, checking the cap and rotor, those types of things for a misfire. As per inconsistent idle. How did you install those intake gaskets? Etc. I think I'd fix the misfire first. And if the inconsistent idle persists. Then chase that.
Melting Slicks
Joined: Apr 2021
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From: Minnesota
What does your ignition curve look like? Total/initial mechanical advance? What RPM is it all in at? Do you have a vacuum advance? How much advance does it pull and how many inches of mercury is it all in by?
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I agree, good questions
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 751
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From: Woburn,ma ma
A miss fire sounds more like leaky plug wires. A bad distributor cap. That type of thing. Not induction.
Yes if things are wrong it's more noticeable with fuel injection. Double edged sword I guess. But that doesn't mean the injection is at fault.
I'd be looking for a pinched or burnt plug wire. Checking all of them with an ohm meter, checking the cap and rotor, those types of things for a misfire. As per inconsistent idle. How did you install those intake gaskets? Etc. I think I'd fix the misfire first. And if the inconsistent idle persists. Then chase that.
Yes if things are wrong it's more noticeable with fuel injection. Double edged sword I guess. But that doesn't mean the injection is at fault.
I'd be looking for a pinched or burnt plug wire. Checking all of them with an ohm meter, checking the cap and rotor, those types of things for a misfire. As per inconsistent idle. How did you install those intake gaskets? Etc. I think I'd fix the misfire first. And if the inconsistent idle persists. Then chase that.
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 751
Likes: 32
From: Woburn,ma ma
Once I could here the miss, at idle that should not happen.. I just stopped there, if proflow did it, now it's doing it with carb, except with proflow base is 12 degrees then you lock it in.. once warmed up these are your numbers.
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What idle speed are you using?
Are you adjusting the mixture screws when engine is fully warmed up?
When adjusting mixture at idle do you turn one mixture screw a 1/4 turn clockwise, check for an RPM drop, if no drop go to other side and adjust 1/4 turn clockwise, and continue going side to side until drop occurs and then turn back counterclockwise 1/4 turn.
Are you adjusting the mixture screws when engine is fully warmed up?
When adjusting mixture at idle do you turn one mixture screw a 1/4 turn clockwise, check for an RPM drop, if no drop go to other side and adjust 1/4 turn clockwise, and continue going side to side until drop occurs and then turn back counterclockwise 1/4 turn.
Melting Slicks
Joined: Apr 2021
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From: Minnesota
That isn’t too bad, but a little on the low end for your 110 LSA cam 388. 18 initial with a mechanical advance distributor sounds about right. 10-12 degrees of vacuum advance on top of that you should be idling with your timing being in the high 20s if not 30.
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 751
Likes: 32
From: Woburn,ma ma
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 751
Likes: 32
From: Woburn,ma ma
What idle speed are you using?
Are you adjusting the mixture screws when engine is fully warmed up?
When adjusting mixture at idle do you turn one mixture screw a 1/4 turn clockwise, check for an RPM drop, if no drop go to other side and adjust 1/4 turn clockwise, and continue going side to side until drop occurs and then turn back counterclockwise 1/4 turn.
Are you adjusting the mixture screws when engine is fully warmed up?
When adjusting mixture at idle do you turn one mixture screw a 1/4 turn clockwise, check for an RPM drop, if no drop go to other side and adjust 1/4 turn clockwise, and continue going side to side until drop occurs and then turn back counterclockwise 1/4 turn.
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 751
Likes: 32
From: Woburn,ma ma
I did a compression test and a leak down test, it held compression, no signs of leaking, compression test was consistent 180's across the cylinders. I also tried my best at using a dial indicator for lobe lift, the numbers were very close to one another.. I replaced the wires and coil still fouling in those 2 cylinders, I readjusted the valves no change, I did notice a couple of poly locked were very easy to to turn to one full turn before locking down, all others were feeling snug at the 1 turn mark.. it's a comp cam roller.. For this cam u need to go one full turn, per comp cam, I tried a half turn and it clanked loudly.. any other recommendations, I really don't want to pull this engine,
Drifting
Joined: Jun 2025
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I did a compression test and a leak down test, it held compression, no signs of leaking, compression test was consistent 180's across the cylinders. I also tried my best at using a dial indicator for lobe lift, the numbers were very close to one another.. I replaced the wires and coil still fouling in those 2 cylinders, I readjusted the valves no change, I did notice a couple of poly locked were very easy to to turn to. one full turn before locking down, all others were feeling snug at the 1 turn mark.. it's a comp cam roller.. For this cam u need to go one full turn, per comp cam, I tried a half turn and it clanked loudly.. any other recommendations, I really don't want to pull this engine,
Suggest rule out burnt and/or leaking valves. Vacuum gage can help a lot. Also compression test & leakdown test; both with and without oil. Closely watch for any differences with/without oil and accurately record those values
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 751
Likes: 32
From: Woburn,ma ma
Suggest revisit this BUT this time With Oil squirted into sp holes. Go through all eight again & again
Suggest rule out burnt and/or leaking valves. Vacuum gage can help a lot. Also compression test & leakdown test; both with and without oil. Closely watch for any differences with/without oil and accurately record those values
Suggest rule out burnt and/or leaking valves. Vacuum gage can help a lot. Also compression test & leakdown test; both with and without oil. Closely watch for any differences with/without oil and accurately record those values
Drifting
Joined: Jun 2025
Posts: 1,715
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Has your block ever been decked ? Have the block surfaces where heads rest upon (decks) ever been milled aka shortened ? If so how much was removed ? Do you KNOW your current "deck height" ?
I ask only because it's commonplace that decking a block often requires concordant milling of intake manifold ( to help it realign with heads' intake faces ).
A slight angle-mismatch there can cause persistent leaks between intake & head.
I'm NOT saying yours is leaking, but it seems you're investigating any/all possibilities.
Yes, if a head were dropped on a corner, that could raise its intake gasket surface enough to prevent intake from laying flat against head; suggest check it with straightedge.
I ask only because it's commonplace that decking a block often requires concordant milling of intake manifold ( to help it realign with heads' intake faces ).
A slight angle-mismatch there can cause persistent leaks between intake & head.
I'm NOT saying yours is leaking, but it seems you're investigating any/all possibilities.
Yes, if a head were dropped on a corner, that could raise its intake gasket surface enough to prevent intake from laying flat against head; suggest check it with straightedge.
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 751
Likes: 32
From: Woburn,ma ma
Has your block ever been decked ? Have the block surfaces where heads rest upon (decks) ever been milled aka shortened ? If so how much was removed ? Do you KNOW your current "deck height" ?
I ask only because it's commonplace that decking a block often requires concordant milling of intake manifold ( to help it realign with heads' intake faces ).
A slight angle-mismatch there can cause persistent leaks between intake & head.
I'm NOT saying yours is leaking, but it seems you're investigating any/all possibilities.
Yes, if a head were dropped on a corner, that could raise its intake gasket surface enough to prevent intake from laying flat against head; suggest check it with straightedge.
I ask only because it's commonplace that decking a block often requires concordant milling of intake manifold ( to help it realign with heads' intake faces ).
A slight angle-mismatch there can cause persistent leaks between intake & head.
I'm NOT saying yours is leaking, but it seems you're investigating any/all possibilities.
Yes, if a head were dropped on a corner, that could raise its intake gasket surface enough to prevent intake from laying flat against head; suggest check it with straightedge.
Drifting
Joined: Jun 2025
Posts: 1,715
Likes: 597
Back in 2005 the block was decked to zero.. I have many times over the years pulled the intake, cam swaps and never seen that.. that was the first thing I noticed when I removed the intake to pull of my proflow, today I pulled the roller lifters out there were a few with no oil in them, I try to depress the lifters with the pushrod some were extremely hard to depress slightly.. I adjusted my valves, started the car and it was clanking, it sounded like it was just a few, but the car was running horribly.. I am thinking the lifters are bad, this is the second time adjusting them, each time several were extremely easy to go 1 full turn after preload... I also for the heck of it put some intake sealer on those ports, normally I don't ever use it on the intake side, but I had to see if that could be a problem. It wasn't..so I can I be sure that my lifters are bad before replacing them????
suggest you prepare a very clean & well lit work bench. If you need additional magnification; do so. Do use lint-free towels. Then perform complete disassembly of those hydraulic lifters (not the roller wheels). Do Not mix the parts from one lifter assembly with another. Look closely for Any foreign material, dirt etc inside lifter & it's valve. Clean everything with brake or carb aerosol & blow dry compressed air. Reassemble with just enough fresh ATF to coat all surfaces. This job Not hard to do; but can be tedious and must not be rushed.
Also, closely inspect all 16 lifter bores for abnormal wear, scoring, spalling, galling etc.
Also, closely inspect all 32 tips of Pushrods. Collapsing, Fracturing (axial & radial), Scoring, Chipping, Spalling, Galling etc. Of course, roll each PR on a glass pane to ensure none bent.
Verify no valves are sticking/binding in valve guides.
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 751
Likes: 32
From: Woburn,ma ma
Deep-Clean Your Lifters:
suggest you prepare a very clean & well lit work bench. If you need additional magnification; do so. Do use lint-free towels. Then perform complete disassembly of those hydraulic lifters (not the roller wheels). Do Not mix the parts from one lifter assembly with another. Look closely for Any foreign material, dirt etc inside lifter & it's valve. Clean everything with brake or carb aerosol & blow dry compressed air. Reassemble with just enough fresh ATF to coat all surfaces. This job Not hard to do; but can be tedious and must not be rushed.
Also, closely inspect all 16 lifter bores for abnormal wear, scoring, spalling, galling etc.
Also, closely inspect all 32 tips of Pushrods. Collapsing, Fracturing (axial & radial), Scoring, Chipping, Spalling, Galling etc. Of course, roll each PR on a glass pane to ensure none bent.
Verify no valves are sticking/binding in valve guides.
suggest you prepare a very clean & well lit work bench. If you need additional magnification; do so. Do use lint-free towels. Then perform complete disassembly of those hydraulic lifters (not the roller wheels). Do Not mix the parts from one lifter assembly with another. Look closely for Any foreign material, dirt etc inside lifter & it's valve. Clean everything with brake or carb aerosol & blow dry compressed air. Reassemble with just enough fresh ATF to coat all surfaces. This job Not hard to do; but can be tedious and must not be rushed.
Also, closely inspect all 16 lifter bores for abnormal wear, scoring, spalling, galling etc.
Also, closely inspect all 32 tips of Pushrods. Collapsing, Fracturing (axial & radial), Scoring, Chipping, Spalling, Galling etc. Of course, roll each PR on a glass pane to ensure none bent.
Verify no valves are sticking/binding in valve guides.
Thanks