521newbie Posted December 9, 2009 Report Share Posted December 9, 2009 When I am driving my 521 and at about half throttle my engine seems to loose power. If I keep the accelerator there or try to get back into it after letting off I get the loudest backfire. any ideas folks. Quote Link to comment
MAG58 Posted December 9, 2009 Report Share Posted December 9, 2009 Does it actually backfire (through the tailpipe) or does it kick back through the intake? And that sounds like a timing problem. Is the engine timed to factory specs? Are the weights in the dizzy free? If they've frozen it could cause a solid timing problem. And does it do it free-revving, or only under load? Quote Link to comment
datzenmike Posted December 9, 2009 Report Share Posted December 9, 2009 Exhaust backfire, or intake? Quote Link to comment
521newbie Posted December 9, 2009 Author Report Share Posted December 9, 2009 Does it actually backfire (through the tailpipe) or does it kick back through the intake? And that sounds like a timing problem. Is the engine timed to factory specs? Are the weights in the dizzy free? If they've frozen it could cause a solid timing problem. And does it do it free-revving, or only under load? Only under load. I'm not sure where it's coming from. It scares the crap out of me it's so friggin loud. Quote Link to comment
benzo Posted December 9, 2009 Report Share Posted December 9, 2009 check your ignition wires and see if the distributor cap has a crack in it. also make sure the ignition wires are not loose or hanging off the ignition coil partly. Quote Link to comment
datzenmike Posted December 9, 2009 Report Share Posted December 9, 2009 Do you have the stock air filter on it still? If you do, an intake backfire sounds like a 'CHUG' sound. An exhaust backfire sounds like a shotgun fired under the truck. My first guess would be ignition. Do as benzo suggests. Check the wiring to the plugs and coil; must be clean and without cracks in the rubber, dizzy cap; must be clean, dry inside and no visible 'carbon tracking': this is where a spark has worn a burnt path to another wire or to ground. Check the coil tower for carbon tracking and moisture also. Check the condition of the points. Are they all eroded and worn? How are the plugs? Quote Link to comment
banzai510(hainz) Posted December 9, 2009 Report Share Posted December 9, 2009 (edited) ck your timming. How about ck the point gap. espcially the 2nd set of points. Sometime just pulling the wire to the 2nd set of points might help. I think the 2nd set of point work under load in 3rd gear and that might be the proplem of backfiring. the main points will have the bigger capcitor on the outside of the distributor. also a worn distributor might cause this also, If the bushing is bad the dizzy shaft can move side to side thus opening the points up by itsself also. olddatsuns.com Loose Power? explain more. Like running out of gas Power or what? block fuel line? dist bolt gone where the dizzy is offset on the timming plate to one side and going out of time thus loosing power. Edited December 9, 2009 by banzai510(hainz) Quote Link to comment
72240z Posted December 9, 2009 Report Share Posted December 9, 2009 My d21 backfires like a motha, when I gun it and let off. There is an exhaust leak at the collector I cant get at. Quote Link to comment
521newbie Posted December 10, 2009 Author Report Share Posted December 10, 2009 My d21 backfires like a motha, when I gun it and let off. There is an exhaust leak at the collector I cant get at. This sounds like what's happening with my truck. It is loud and comes from underneath. I'll check the timing but it should be solid from when I did the electronic ignition conversion. It backfired the same before I did the ignition upgrade so I'm thinking it's the exhaust. Quote Link to comment
MAG58 Posted December 10, 2009 Report Share Posted December 10, 2009 The difference here is the timing of the backfire, his comes from the compooter dumping too much fuel into the motor for a revolution or so and this extra unburned gas catching some oxygen in the exhaust leak and lighting off. Your seems to be coming from somewhere else. If you push through the back fire (keep it planted) will it keep backfiring throughout the rev range? Or will it smooth out? Quote Link to comment
datzenmike Posted December 11, 2009 Report Share Posted December 11, 2009 (edited) Nissan trucks didn't have TBI compooters until late in the '86 model 720. All carb vehicles will go slightly lean when the throttle snaps shut as there isn't enough idle mixture for the air being sucked past the throttle plate. Also there is no vacuum advance at idle so the plugs would be late firing for this lean mixture, and would be burning (off and on) as it left the cylinder. Edited December 11, 2009 by datzenmike Quote Link to comment
johny5 Posted December 11, 2009 Report Share Posted December 11, 2009 I had a toyota that burnt a valve and it would pump raw fuel down the exhaust. then it would explode , blew my muffler up:eek: Quote Link to comment
MAG58 Posted December 11, 2009 Report Share Posted December 11, 2009 Nissan trucks didn't have TBI compooters until late in the '86 model 720. All carb vehicles will go slightly lean when the throttle snaps shut as there isn't enough idle mixture for the air being sucked past the throttle plate. Also there is no vacuum advance at idle so the plugs would be late firing for this lean mixture, and would be burning (off and on) as it left the cylinder. I was referring as to why 72240z's d21 kicked back, but yes. Quote Link to comment
Braden Posted December 11, 2009 Report Share Posted December 11, 2009 i too am having a problem with backfire, it doesnt do it except when under load, i just rebuilt the carb and removed all of the smog shit, im running stock hitachi, and the non heat riser manifolds, new gasket no intake leaks or anything, when i try and take off from a stoplight or when im driving under load it wants to spit and backfire, then when the motor winds up say, 3 grand it quits and goes fine, as long as im romping on it its fine but if i drive it easy it backfires and shoots flames out the tailpipe with that being said and excluding the possibility of intake or exhaust leaks, (just redid my exhaust) is timing the number one culprit? when i had the intake off i felt the intake valves and they were all intact, my guess is timing, also when i take off sometimes the engine feels like it is winding in a rubberband then if i hold it to the floor it will keep doing it, when it reaches a higher rpm maybe 3 or 4 grand it just takes off like nothing is wrong, now when it does feel like it is winding up i can let off the gas and ease back on it and it will quit but if i romp on it it will get worse, its almost like the engine is caught in a bad spot and it wont get out of it or make any power, also i have run 87 on up to 93 octane having worse issues with the 93 Quote Link to comment
521newbie Posted December 11, 2009 Author Report Share Posted December 11, 2009 The difference here is the timing of the backfire, his comes from the compooter dumping too much fuel into the motor for a revolution or so and this extra unburned gas catching some oxygen in the exhaust leak and lighting off. Your seems to be coming from somewhere else. If you push through the back fire (keep it planted) will it keep backfiring throughout the rev range? Or will it smooth out? It smoothes out. Quote Link to comment
MAG58 Posted December 11, 2009 Report Share Posted December 11, 2009 HMM... Is the vacuum advance still on the dizzy? and what condition is the vacuum diaphram in? Quote Link to comment
521newbie Posted December 14, 2009 Author Report Share Posted December 14, 2009 HMM... Is the vacuum advance still on the dizzy? and what condition is the vacuum diaphram in? Yes and it's new. Quote Link to comment
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