Detonation?

hobgoblin351 · 05-11-2003, 08:14 PM

I was driving yesterday and started backfiring through the carb. Or what sounded like a backfire. Got it home and checked it out. If you rev it slowly it's ok until about 1/2 throttle, then pops. Slap it open and it pops right away. I played with the timing and it still pops. It's a relatively new engine, about120 miles, and running 10.25 compression. I did'nt have this trouble last season. I took ti out of storage and ran it with the old "winter" gas and it ran fine. I put in some fresh Mobile 1, 93 octane and it started soon after. Haven't tried octane boost the stores were closed. Could it be detonation? How would I know for sure? Thanks

66StangGuy · 05-12-2003, 02:29 PM

check your carb settings. i had a similar problem and ended up replacing the carb. do you have a 4 or a 2 bbl? in my 4 the secondary metering rods would get stuck and run it rich almost chocking out the motor. mine did the same thing how if you would rev fast it would pop but if you did it slowly it would be ok.

hobgoblin351 · 05-12-2003, 09:24 PM

It's a Holley 700 double pumper with mech 2nds. So you think something is stuck or gummed up? It could be it's been running on the gas that has been sitting all winter. I'll check the levels and clean it up. I dont think it's detonation, it ran last year fine and 10.25 is not really that high. But the pops are that loud and it's not the timing. No flames out the carb, just a pop and a shot of mist.

66StangGuy · 05-13-2003, 01:04 AM

yeah sounds like carb. try setting everything again or maybe even run carb cleaner though it to see if that helps at all. if anything get a gas can and run your fuel pump directly to that and see how it runs and maybe you just have bad gas? dont know..i had a similar problem and i just bought a new carb and everything was perfect after that. fired right up and no problems ever since. look into the carb more and see if everything is ok.. also check that the advance on the dist is ok.. maybe one of the springs for the advance came off and its firing the spark at the wrong time once the engine gets to a certain rpm??

hobgoblin351 · 05-13-2003, 09:38 PM

Yeah everyone is telling me the carb is off. I'll give it a good cleaning. I do forget this though. I think that it will pop if its running too lean, or is it too rich. All my books are still packed from moving. Yeah I know too lazy to unpack them, hey at least I can get to my tools right! Thanks

05-11-2003, 08:14 PM	#1
hobgoblin351 Registered Member Join Date: Sep 2002 Location: NYC Posts: 245	Detonation? I was driving yesterday and started backfiring through the carb. Or what sounded like a backfire. Got it home and checked it out. If you rev it slowly it's ok until about 1/2 throttle, then pops. Slap it open and it pops right away. I played with the timing and it still pops. It's a relatively new engine, about120 miles, and running 10.25 compression. I did'nt have this trouble last season. I took ti out of storage and ran it with the old "winter" gas and it ran fine. I put in some fresh Mobile 1, 93 octane and it started soon after. Haven't tried octane boost the stores were closed. Could it be detonation? How would I know for sure? Thanks __________________ 1970 Stang Conv: en:Boss351 (balanced/blueprinted) mech cam(240*@.050/.540 lift) Scrw in studs/comp cams rllr rkr Mldn valves 2.19in 1.71ex ported polished cc'd hrdnd ex Keith Black FT pistons(10.25/1) Weiand Excellorator manifold Holley700 DP mech 2nds MSD 6 box and Dis Headers/2 1/2 inch duels tr: modified FMX re:9-inch/3.89 limited slip

05-12-2003, 02:29 PM	#2
66StangGuy Registered Member Join Date: Feb 2002 Location: Diamond Bar Posts: 258	check your carb settings. i had a similar problem and ended up replacing the carb. do you have a 4 or a 2 bbl? in my 4 the secondary metering rods would get stuck and run it rich almost chocking out the motor. mine did the same thing how if you would rev fast it would pop but if you did it slowly it would be ok. __________________ 66 mustang-292-Holley 4160-World Castings Windsor Sr.-Hooker super comp headers-MSD box & Coil.3.55 gears. B&M Z-Gate-Black leather racing seats with 4pt harnes.

05-12-2003, 09:24 PM	#3
hobgoblin351 Registered Member Join Date: Sep 2002 Location: NYC Posts: 245	It's a Holley 700 double pumper with mech 2nds. So you think something is stuck or gummed up? It could be it's been running on the gas that has been sitting all winter. I'll check the levels and clean it up. I dont think it's detonation, it ran last year fine and 10.25 is not really that high. But the pops are that loud and it's not the timing. No flames out the carb, just a pop and a shot of mist. __________________ 1970 Stang Conv: en:Boss351 (balanced/blueprinted) mech cam(240*@.050/.540 lift) Scrw in studs/comp cams rllr rkr Mldn valves 2.19in 1.71ex ported polished cc'd hrdnd ex Keith Black FT pistons(10.25/1) Weiand Excellorator manifold Holley700 DP mech 2nds MSD 6 box and Dis Headers/2 1/2 inch duels tr: modified FMX re:9-inch/3.89 limited slip

05-13-2003, 01:04 AM	#4
66StangGuy Registered Member Join Date: Feb 2002 Location: Diamond Bar Posts: 258	yeah sounds like carb. try setting everything again or maybe even run carb cleaner though it to see if that helps at all. if anything get a gas can and run your fuel pump directly to that and see how it runs and maybe you just have bad gas? dont know..i had a similar problem and i just bought a new carb and everything was perfect after that. fired right up and no problems ever since. look into the carb more and see if everything is ok.. also check that the advance on the dist is ok.. maybe one of the springs for the advance came off and its firing the spark at the wrong time once the engine gets to a certain rpm?? __________________ 66 mustang-292-Holley 4160-World Castings Windsor Sr.-Hooker super comp headers-MSD box & Coil.3.55 gears. B&M Z-Gate-Black leather racing seats with 4pt harnes.

05-13-2003, 09:38 PM	#5
hobgoblin351 Registered Member Join Date: Sep 2002 Location: NYC Posts: 245	Yeah everyone is telling me the carb is off. I'll give it a good cleaning. I do forget this though. I think that it will pop if its running too lean, or is it too rich. All my books are still packed from moving. Yeah I know too lazy to unpack them, hey at least I can get to my tools right! Thanks __________________ 1970 Stang Conv: en:Boss351 (balanced/blueprinted) mech cam(240*@.050/.540 lift) Scrw in studs/comp cams rllr rkr Mldn valves 2.19in 1.71ex ported polished cc'd hrdnd ex Keith Black FT pistons(10.25/1) Weiand Excellorator manifold Holley700 DP mech 2nds MSD 6 box and Dis Headers/2 1/2 inch duels tr: modified FMX re:9-inch/3.89 limited slip

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