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My new to me 1984 (4/84) Nissan 720! Pic heavy! (we like pics right?!)


Kyle84

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Well, the truck is fucked. torsion bar bolts are taken all the way out (sitting in the cab). the engine sounds like a fucking hardcore sewing machine. and it idles really low... ill be happy if i can get rid of it for a grand... :'( 

 

 

i dont even want to touch it. im done.. 

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Well. i put the torsion bolts back in. rides SO much better. who does that? who likes banging their head on the ceiling every time they hit a bump? just silly i tell you... had to pay 9$ for a new u bolt since the pin sheared off the lowering block. and the guy that had it decided to cut off one of the long ends on ONE of the ubolts. and it got stripped out.. cut of a bolt to stick in the lowering block so it wont shift around. put that back together... rides SO much better. now.  :confused:  <_<  :frantics:  :no:  :fu:  :blink:  :wacko: all of my expressions... now to figure out its running condition.... i saw a flame/spark shoot out of the tail pipe earlier!!  :hyper: seems to do it when i press the gas, and then let go. while crusing. sometimes i can get it to do it standing still. makes a pop noise.  :unsure:

 

Flamethrower mod engaged????  :rofl:

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I grabbed this off the Google:

 

Backfiring

I can't remember where most of this came from.

Backfiring is in no way related to fuel and a properly tuned engine should not backfire. Backfiring usually occurs during acceleration or slowing down. It is commonly caused by ignition of the air/fuel mixture while it is still in the intake manifold. This usually happens because the inlet valve is sticking or leaking or because there is an ignition system fault. Unburnt air/fuel mixture passing through the exhaust and igniting also results in backfiring. This is usually caused by a temporary loss of ignition or rich idle mixtures in combination with exhaust air leaks. If there is only moderate backfiring it may be because the exhaust valves are leaking or the tappets are tight.

Most of the following came from f650.com - Backfiring FAQ


Now, an engine is not supposed to backfire and, when it is persistent, I am not convinced it is harmless to the engine. If there is an explosion in the exhaust pipe when the cylinder is trying to exhaust its spent combustion products a back pressure is created which interferes with the next cycle. This could result in incomplete extraction, irregular charging with the fresh mixture, and overheating. In addition valves are not designed to seal against pressure from their backsides and a broken valve head rattling around in the combustion chamber at 10,000 rpm engine speed is not something I am desirous of experiencing.

There are quite a number of different causes for backfiring. What this FAQ will try and do is to help you isolate the cause of it.

What causes Backfiring
  • "Deceleration Backfiring" is the most common backfiring that occurs when you change down and throttle off. This extract from the Virago Site explains it succinctly.

    "In general, backfiring on deceleration (as opposed to acceleration) is generally caused by a lean condition in the pilot circuit. What happens is that the mixture leans out enough to where is fails to ignite consistently. This, in turn allows some un-burnt fuel to get into the exhaust pipes. Then when the engine does fire, these un-burnt gasses are ignited in the exhaust pipe, causing the backfire. Newer Virago carbs have an 'enricher circuit' which cuts in on deceleration to help this problem. Earlier carbs do not have this. I would say check the pilot circuits, and set them a bit richer. It is hard to do this right without some equipment to test where you are. Aftermarket pipes often increase backfiring, probably because they may the bike run leaner."

  • Some riders have also experienced Backfiring on up-shifting. An exhaust gasket is the most liekly culprit.
So, how do I fix it?
  1. Idle screw

    Some folks cure backfiring by turning up the idle slightly. If you have mild backfiring, you can give it a shot.

  2. Idle mixture

    No this is NOT the same thing as the Idle Screw. The Idle Screw just limits the minimum throttle when you take your hand off the throttle. The Idle Mixture screws actually control the air/fuel ratio at idle.

    Many riders find that enriching the idle mixture by backing off the screws by 1/8 to 1/2 a turn will eliminate popping. Enrichen as little as necessary, work in small increments, and test the results before backing out the screw another 1/8 turn.

  3. Exhaust Gaskets

    This is another popular cause of Backfiring.

Most of the following came from fordfestive.com - Possible casue of Backfiring


Backfiring can be casued by the following:

  • Internal carburetor problems (on initial WOT acceleration, this can be caused by a defective accelerator pump).
  • Weak or broken valve spring (Usually severe. When it is exhaust, backfire will occur in the intake)
  • Low compression
  • Cam to crank timing off (rare, usually result in hard/no start condition)
  • Burnt/damaged valves or seats (sever usually)
  • Worn cam lobes (lack of power, can be severe backfire, often through carb)
  • One or more valves adjusted too tight (heard through carb then intake is usually too tight, heard through exhaust then exhaust is too tight)
  • Preignition (caused by deposits or lean engine conditions)


Notice some of the possible causes may be tied to your low cylinder pressure.  Fixing the head might fix the backfiring

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