Cup O Noodles Posted September 29, 2010 Share Posted September 29, 2010 1987 GL. I know they aren't supposed to be fast cars but it takes longer than I'd like to get up to freeway speeds. I give it what I think is a moderate amount of throttle and I shift at 4k-4500 rpms but if I give it any more throttle or if I get the rpms any higher it backfires. Yesterday when I got on the freeway, just to see what would happen, I gave it full throttle (or close) and shifted around 4500 rpms and it got up to 65mph pretty quick but the backfire was really loud. Is backfiring bad for the engine? It seems like it would be. To combat the lack of speed I'm going to put a Weber in when I can afford it until I can afford an EJ swap. GD drove me around in a couple of his cars that have Webers in them and they have the acceleration I would like to have in my car. How much horsepower does a Weber add? -Thanks Link to comment Share on other sites More sharing options...
NorthWet Posted September 30, 2010 Share Posted September 30, 2010 A question that may seem dumb, but I couldn't quickly find the answer in your other threads... and IMHO it needs to be asked. I am under the impression that you removed (and maybe replaced) your timing belt(s). If this is correct, are you sure that you got the timing marks correctly aligned when the belts were reinstalled? Link to comment Share on other sites More sharing options...
GeneralDisorder Posted September 30, 2010 Share Posted September 30, 2010 The backfire is a result of exhaust leaks. Plugging the ASV system will help or you can fix the leaks. Actual HP increase from the weber is minimal. It feels faster because the off idle torque is improved and acceleration due to the progressive linkage instead of the vacuum secondary of the hitach. GD Link to comment Share on other sites More sharing options...
Dirk Posted October 1, 2010 Share Posted October 1, 2010 What do your spark plugs look like? Link to comment Share on other sites More sharing options...
Subruise Posted October 1, 2010 Share Posted October 1, 2010 The backfire is a result of exhaust leaks. Plugging the ASV system will help or you can fix the leaks. Actual HP increase from the weber is minimal. It feels faster because the off idle torque is improved and acceleration due to the progressive linkage instead of the vacuum secondary of the hitach. GD please give me a nugget: ASV system?? whats that, how do i plug it? my 86 carby has a backfire most of the time i shift, not super loud but loud enough that i wanna know whats up. im sure thisll help the OP as well. thanx, RV Link to comment Share on other sites More sharing options...
True2Blue Posted October 1, 2010 Share Posted October 1, 2010 (edited) Air Suction Valve or anti afterburn system backfires....... GD is good but lets give you more options spark plug gap is incorrect weak valve spring/sticky valve the disty need adjustment or replacement more can be listed when you close the throttle or let off suddenly the engine is running rich at high rpms which causes backfiring because the high flow of air/fuel passes through unburnt to the exhaust and which is soon to be ignited and backfire. fresh air in you exhaust will cause backfiring any leaks as GD said will cause this when you let off the throttle to shift there is negative pressure which sucks fresh air into the exhaust and pop backfires understanding these things or having them explained should really help you pin point and fix it. LOUD or erratic back firing is a timing issue most commonly its worn wires grounded wires or failing coil not firing means lots fuel build up in the exhaust which gives you the loud POP's let me know if you need help - Kody Edited October 1, 2010 by True2Blue Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 1, 2010 Share Posted October 1, 2010 (edited) Air Suction Valve or anti afterburn system backfires....... The AAV does nothing to prevent backfireing. That's not it's job. if your exhaust pressure goes negative the ASV pressurizes it to prevent backfiring What? No. The ASV's job is to supply fresh oxygen for the catalyst. In conjunction with exhaust leaks it is very often the CAUSE of backfiring. In no way does it prevent same. when you close the throttle or let off suddenly the engine is running lean at high rpms which causes backfiring because the high flow of air/fuel passes through to the exhaust and collects which is soon to be ignited and backfire. No. Again. Durring a shift the throttle slams closed and the engine (taching several K) pulls fuel from the carb primaries due to high manifold vacuum under the throttle plates - causing a RICH condition. This exra fuel is mixed with fresh oxygen from leaks/ASV supply and ignites downstream in or near the muffler. Often blowing holes in the muffler in the process. The ASV just supplies an extra quantity of fresh air and thus oxygen. Cutting off this supply is typically enough to stop backfiring on EA's. Stick a quarter in the pipe that runs from the head to the ASV valve. Even with a leaky exhaust this will generally fix the problem and it's cheaper than fixing all the exhaust leaks. GD Edited October 1, 2010 by GeneralDisorder Link to comment Share on other sites More sharing options...
Cup O Noodles Posted October 1, 2010 Author Share Posted October 1, 2010 I have not yet replaced the belts but now that you mention it, they may not be installed correctly anyway. Will there be visual or audial evidence one way or the other? Where is the ASV and with what should I plug it? Is an exhaust leak just an opening in the pipe or might it be the head gasket? I haven't looked at the plugs since installing them but they're only a month or so old. I have one lifter that keeps making noise and I keep changing the oil so it'll shut up for a couple weeks but the problem is still there. Would a weak valve spring/sticky valve cause the lifter to knock? In a week or so I'll order me some lifters and take care of those while I'm replacing the oil pump seals and timing belts. I don't know about the disty but I changed the cap and rotor recently. -Thanks for the info. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 1, 2010 Share Posted October 1, 2010 Follow the metal tube from under the head to the ASV valve. Unscrew it from the valve, slip a quarter in the valve and thread the pipe back on. All your backfireing will vanish for $0.50 (do both sides). GD Link to comment Share on other sites More sharing options...
True2Blue Posted October 1, 2010 Share Posted October 1, 2010 yes on the ASV being a source of backfiring no its not a pressurizer i know this now i was reading bad info. on decel the engine creates alot of vacuum, the asv is hooked up to an intake vacuum line, so on decel the asv is opened allowing atmosphere air to enter the exhaust to counter the radical emission changes usually rich mixtures (lean it out)... Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 1, 2010 Share Posted October 1, 2010 The ASV works at all times - it supplies fresh air from the air filter to the exhaust stream (via a reed valve that is opened by the exhaust pulses) in order to improve catalyst effeciency. Newer style catalysts no longer need this extra oxygen to work properly. The ASV is Subaru's equivelent to a smog pump. Same concept. GD Link to comment Share on other sites More sharing options...
True2Blue Posted October 1, 2010 Share Posted October 1, 2010 Follow the metal tube from under the head to the ASV valve. Unscrew it from the valve, slip a quarter in the valve and thread the pipe back on. All your backfireing will vanish for $0.50 (do both sides). GD good stuff ive never heard of that one before. but IF he is required to pass emissions wont "plugging" the asv hinder just that, his ability to pass? Link to comment Share on other sites More sharing options...
GeneralDisorder Posted October 1, 2010 Share Posted October 1, 2010 It could, yes. But removing the quarter is easy enough when/if you need to go through DEQ and here they do an idle and 2500 RPM test with no dyno run so the backfireing wouldn't be an issue for the test. Then just replace the quarter and drive on for another two years..... Also - installing a new, $69, ebay 3-way catalytic converter would take care of the emissions and you could just remove the entire ASV system as the modern cats don't even need it. GD Link to comment Share on other sites More sharing options...
NorthWet Posted October 2, 2010 Share Posted October 2, 2010 Follow the metal tube from under the head to the ASV valve. Unscrew it from the valve, slip a quarter in the valve and thread the pipe back on. All your backfireing will vanish for $0.50 (do both sides). GD Do as GD said. Life will be good... and quieter. (I forgot about the darn ASVs... none of mine has that wonderful device.) Link to comment Share on other sites More sharing options...
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