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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: josh0325 on November 20, 2015, 07:08:54 pm
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Installed fresh Mark IV broke in flat tappet but I couldn't get it to idle under 1200 rpm, was running rich, tried adjusting timing but when I regard it it falls on its face. Fires up but fights against starter. No valvetrain noise at all. Please help I don't Want to screw up my new engine.
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most times when you cant get the idle low its because of a vacuum leak. take some starting fluid or carb cleaner and while the engine is running spray it around the mating points of the intake and heads and intake and carb. also make sure all your vacuum lines are in good shape and are connected to something on both ends.
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No intake manifold leaks anywhere, all vacuum lines are brand new and connected securely. I'm not sure if I have a n air/fuel misadjustment or timing adjustment issue . My buddy told me it could be valve springs binding but I don't know. It backfires through carb and exhaust if I let off the gas. When I rev up to 1200 or so it smooths out a little.
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how do you rev up to 1200 is you cant get the idle below 1200?
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I have to give it gas to keep it at 1200-1500. That's at about 1/4 throttle. If I take my foot off the gas it throttles down and dies. If I give it more timing it will run on its own at 1500, but it pings, and slightly backfires out exhaust. If I regard the timing it Will stumble from 1500 to 1200 pick up a little stumble and die. When I go to restart it , it will fight against the starter, I click off the ignition, and hit the key again and it starts. This is my first build so I don't know how to properly diagnose the issue. Thank you for your replies
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...Fires up but fights against starter....
...My buddy told me it could be valve springs binding.... It backfires through carb and exhaust if I let off the gas. When I rev up to 1200 or so it smooths out a little.
I have to give it gas to keep it at 1200-1500. That's at about 1/4 throttle. If I take my foot off the gas it throttles down and dies.
If I give it more timing it will run on its own at 1500, but it pings, and slightly backfires out exhaust. If I regard the timing, it will stumble from 1500 to 1200 pick up a little stumble and die.
When I go to restart it, it will fight against the starter. I click off the ignition and hit the key again and it starts.
Carbureted, TBI or other injection? Factory HEI or...? New plugs, wires, cap, rotor?
Recheck the firing order, 1-8-4-3-6-5-7-2.
Make sure you don't have any cracked spark plugs.
If you are concerned about coil bind, run a compression check or cylinder leak down test.
Check fuel pump pressure, draw and volume.
If you have a spare distributor and coil, swap them.
The foregoing steps aside, your narrative suggests a timing issue.
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It is carbureted...800cfm quadrajet, aftermarket H.E.I., new cap plugs and wires. Every component on engine are brand new.
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...Fires up but fights against starter....
...My buddy told me it could be valve springs binding.... It backfires through carb and exhaust if I let off the gas. When I rev up to 1200 or so it smooths out a little.
I have to give it gas to keep it at 1200-1500. That's at about 1/4 throttle. If I take my foot off the gas it throttles down and dies.
If I give it more timing it will run on its own at 1500, but it pings, and slightly backfires out exhaust. If I regard the timing, it will stumble from 1500 to 1200 pick up a little stumble and die.
When I go to restart it, it will fight against the starter. I click off the ignition and hit the key again and it starts.
Carbureted, TBI or other injection? Factory HEI or...? New plugs, wires, cap, rotor?
Recheck the firing order, 1-8-4-3-6-5-7-2.
Make sure you don't have any cracked spark plugs.
If you are concerned about coil bind, run a compression check or cylinder leak down test.
Check fuel pump pressure, draw and volume.
If you have a spare distributor and coil, swap them.
The foregoing steps aside, your narrative suggests a timing issue.
This.
Recheck the firing order. Make sure you are setting base timing with the vacuum advance disconnected and the vacuum line plugged. Vacuum advance should be getting its signal from a manifold source and not above the throttle plate.
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Make sure you also have your plugs gapped correctly. Don't assume they are correct. I picked up some from my truck and they were gapped for points ignition not hei and it ran like a horrid turd.
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Thank you all for the great advice. I had several issues, loose spark plugs, burnt plug wires, and a few vacuum leaks including the intake manifold. I didn't spray the starter fluid around the base of the intake, just near the carb. Hopefully these issues will solve the problem.