Hi All, hoping for some good suggestions.
Background:
1974 Mercruiser 888 (Ford 302), original block, heads. MC-1 outdrive, same vintage. FWC, no water in oil. Compression definilty on the "worn out" side (100-110 psi, spec 140). Over last season, I tore it down to the longblock, as the valves were leaking. After replacing 1 burnt valve and a poor man's valve job (griding), put it all back together. New Holley marine 2BBL carb (old one leaking at throttle shaft). Holley carb has a 6.5 in power valve, pink accelerator pump cam (same as on the old one), 0.60 jets, and 0.28 squirters. These look the same or similar as the old carb. Accelerator pump pumps a good stream when the throttle is pumped. New coil (old oil filled one overheated), new engine electerical and ballast resistor, new points distributor (Mallory marine, with stock mallory marine advance, old one had rusted advanced springs). New plug wires, new plugs, triple checked correct firing order (13726548, cam is 351 on the 888, confirmed by sequence of lifters when the valve cover and manifold was off), new fuel pump (diaphram on the original pump blow and leaking gas into the sight glass). Fuel system checked (new filter), fuel line to gas newer aluminum gas tank, removed and inspected correctly function antisiphon valve, removed and inspected intake fuel pick-up and metal screen, removed and blew through (with no resistance) fuel tank vent. New 87 octane gas (10% etoh) w/ marine stabil.
Starts fine cold and hot, has never idled well below 800-900 rpm w/o load (on muffs) or w/load in water in gear. I'm assuming this is because the engine is old and worn out, and there are slight imballences in the compression between the cylinders. I'm forced to leave it at ~1000rpm, else erratic surging at idle (up and down 800-1200). Base distributor timing at 10 BTDC, the advance on the mallory marine distributor is not as steep as the original merc, but the max advance is the same (24 advance to 34 total). From what I can tell at 1000 rpm, the distributor hasn't started it's advance yet, as if I set the idle lower (into the erratic 800-1000 range) it stays at 10 BTDC. Ilde screws are set about 4 turns out, set using vacuum gage for max vacuume at lowest rpm (w/o erratic idle). Vacuum at idle is steady 13-15 in.
Problem:
Will idle around fine in gear and slightly off idle. If I slowly increase the throttle at ~1500 rpm (in gear under load) it dies. Same spot, everytime. If I punch it to WOT from idle or off idle, it overcomes the dead spot (with a single backfire), and revs up to the correct max RPM at WOT (4000 rpm at WOT). Before someone says lower shift cable, it's definitley not, does the same thing with the ground disconnected on the shift cut out switch, plus, I'm allready in gear.
Any thoughts or suggestions?
Background:
1974 Mercruiser 888 (Ford 302), original block, heads. MC-1 outdrive, same vintage. FWC, no water in oil. Compression definilty on the "worn out" side (100-110 psi, spec 140). Over last season, I tore it down to the longblock, as the valves were leaking. After replacing 1 burnt valve and a poor man's valve job (griding), put it all back together. New Holley marine 2BBL carb (old one leaking at throttle shaft). Holley carb has a 6.5 in power valve, pink accelerator pump cam (same as on the old one), 0.60 jets, and 0.28 squirters. These look the same or similar as the old carb. Accelerator pump pumps a good stream when the throttle is pumped. New coil (old oil filled one overheated), new engine electerical and ballast resistor, new points distributor (Mallory marine, with stock mallory marine advance, old one had rusted advanced springs). New plug wires, new plugs, triple checked correct firing order (13726548, cam is 351 on the 888, confirmed by sequence of lifters when the valve cover and manifold was off), new fuel pump (diaphram on the original pump blow and leaking gas into the sight glass). Fuel system checked (new filter), fuel line to gas newer aluminum gas tank, removed and inspected correctly function antisiphon valve, removed and inspected intake fuel pick-up and metal screen, removed and blew through (with no resistance) fuel tank vent. New 87 octane gas (10% etoh) w/ marine stabil.
Starts fine cold and hot, has never idled well below 800-900 rpm w/o load (on muffs) or w/load in water in gear. I'm assuming this is because the engine is old and worn out, and there are slight imballences in the compression between the cylinders. I'm forced to leave it at ~1000rpm, else erratic surging at idle (up and down 800-1200). Base distributor timing at 10 BTDC, the advance on the mallory marine distributor is not as steep as the original merc, but the max advance is the same (24 advance to 34 total). From what I can tell at 1000 rpm, the distributor hasn't started it's advance yet, as if I set the idle lower (into the erratic 800-1000 range) it stays at 10 BTDC. Ilde screws are set about 4 turns out, set using vacuum gage for max vacuume at lowest rpm (w/o erratic idle). Vacuum at idle is steady 13-15 in.
Problem:
Will idle around fine in gear and slightly off idle. If I slowly increase the throttle at ~1500 rpm (in gear under load) it dies. Same spot, everytime. If I punch it to WOT from idle or off idle, it overcomes the dead spot (with a single backfire), and revs up to the correct max RPM at WOT (4000 rpm at WOT). Before someone says lower shift cable, it's definitley not, does the same thing with the ground disconnected on the shift cut out switch, plus, I'm allready in gear.
Any thoughts or suggestions?
.