Help Needed.!! 1984 Nissan 720 Wont Start.!?

Replies to This Discussion

Permalink Reply by TigerRacing on March 30, 2011 at 2:24pm

Do you have fuel in the bowl sight window?  If not, you may have a stuck float valve, very common when they sit a while without running.  Take off the input fitting, clean the filter and squirt some carb cleaner down into the inlet, that may loosen it up if it's stuck.  If that won't do it, you may have to pull the cover off and take a look inside the carb, there may be deposits clogging the float, valve, or fuel jet inlets.

 

Will it start with starting fluid or a little gas poured down into the carb?

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Permalink Reply by Glenn Mitchell on March 30, 2011 at 3:39pm

It has fuel in the carb you can see it threw the site glass. And I've pulled all eight plugs and im gettin gas across. The cylinder that's why in at a lose and not sure where and or what im missing.!?

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Permalink Reply by TigerRacing on March 30, 2011 at 4:24pm

Ok, well, try pouring just a little gas down the carb, (it won't take much) then try starting it.  If it fires then, you probably have sediments in the bottom of the bowl which are clogging the jets.  If it doesn't fire doing that, it's time to check the compression on the cylinders and make sure the ignition and cam timing is correct.

 

One thing to keep in mind, if a vehicle sits for a very long time, ground squirrels, rats and mice can use the exhaust system as a place to make nests and store food.  If they have the exhaust completely blocked, no amount of fuel and spark is going to help, because the engine can't get any air.  Sometimes if you can get the engine running, it will run very rough.  I've had some strange things come flying out of an exhaust on a vehicle I had sitting for several years.

 

So, considering you know you have spark, if it won't run when you add fuel to the carb but your compression looks good, the ignition timing and cam timing look good, try disconnecting the exhaust at the manifold.

 

Good luck!

 

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Permalink Reply by TigerRacing on April 3, 2011 at 12:24pm

I forgot to mention, I had a 720 that I bought used, and couldn't get it started to save my life.  I went through and fixed all the obvious problems, wiring issues, corroded connectors, bad fuel pump, fuel pump relay, stuck float valve, bad ignition coil, blocked jets in the carb, and after all that, it still just wouldn't start even though I knew I had fuel, spark and air.  I checked the timing, compression checked the cylinders, changed plugs, and everything was good.  But, if I poured a little gas down the carb, it would start right up, run a short while, then die...

 

In the end what fixed it was draining all the gas from the tank, and putting in fresh gas.  This stuff was so old and oxidized, I couldn't get it to burn even if I poured it on the rag and tried lighting it with a lighter.  So, don't forget the basics like I did!

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Permalink Reply by Glenn Mitchell on April 3, 2011 at 4:09pm

Hmm.. Well I've poured fresh gas in the carb and it still wont start.. I haven't checked the compression on the cylinders yet but I don't have blown head gasket as far as I can tell with out pullin the head.. oil looks good not milky and full of antifreeze.. all four plugs are damp or smell of fuel so im gettin the fuel across the cylinders jus wont start.. ill eventually get it runnin if I have to tear it down piece but piece ha

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Permalink Reply by datzenmike on April 3, 2011 at 6:28pm

A bad or blown head gasket does not always leak coolant. They can blow between cylinders.

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Permalink Reply by TigerRacing on April 3, 2011 at 8:53pm

Well, I'd check compression before I'd pull the head.  Even with a blown head gasket, it should still be trying to fire on the cylinders that do have compression.  If you have no compression on any cylinders, it might be someone put in a cam and didn't time it correctly, best case there is you just have to align it properly, worse case it bent the valves from opening them at TDC and you'll have to have the head worked.

 

Have you moved the ignition timing around to see if it will try to start?  If the fuel pump shaft wasn't installed properly, the ignition timing could be way off.

 

What type plugs are in it?  Are the plugs wet all the time, or just when you poured fuel in the carb?  If they're wet all the time, you might have a float valve stuck open an it's fouling out the plugs.  I've had plugs fouled with gas that would never fire again even after being cleaned and dried.  Had to replace them.

 

Just keep checking off the basics, you'll figure it out.

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Permalink Reply by Glenn Mitchell on April 4, 2011 at 1:22am

I've move the distributor and it turns over and you can tell it wants to start best at where its was.. I put new NGKR E6 E5 plugs in it so they are good plugs and all eight are firing they haven't fouled yet anyways.. they are not really wet I shld say you can tell that fuel has hit them and more less dried instead for fully burning off.. now the four numbered notches on the cam gear are they to show when each piston shld be at tdc of its stroke.!?? If so I can easly check to see if if someone have had to timing chain off and not aligned the cam ba k properly..!?

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Permalink Reply by TigerRacing on April 4, 2011 at 9:12am

Hmm, you have four numbered notches on the cam?  Normally, there are only 3 on a stock cam gear.  It sounds as if you might have a motorsports cam sprocket on that.  It has 4 numbers, and 3 letters.

 

Those are for setting up the cam timing when you install the chain, you can't really use those to check the valve timing accurately with those once the engine's been spun.  And, you have to have the front cover off to set up the cam timing using those marks because there is a relationship between the bright links on the timing chain and the marks on cam and crank sprockets.

 

You can check basic cam/ignition timing with just the valve cover off.  Just pull the plugs on one side to make it easier to turn the engine over with a socket on the crank pulley bolt.  Its good to have a friend help with this.  Then turn it over clockwise until  #1 piston comes up to TDC on the power stroke (you can use a phillips screwdriver down in the spark plug hole to determine when the piston is coming up to TDC if you can't read the crank pulley timing mark, just don't leave the screwdriver in the spark plug hole and spin the engine over unattended or you'll damage things), both valves should be closed (up) at TDC on the power stroke, and your distributor should then be pointing to the #1 plug position under the distributor cap.  At that point, the numbered notch on the cam that is at about the 2 o'clock position is most likely the one it was aligned to.  Normally this is 2 on a stock engine (from my experience).  Each number represents a 3-4 degree of cam timing advance or retard.

 

It's very common with people who haven't worked with these engines much to get the ignition timing off when they remove and replace the oil pump.  You have to install the oil pump shaft in a very specific way in order to insure your distributor timing is correct because that shaft also drives the distributor.  This is somewhat difficult to do with the engine in the truck, more so on some years than others.  There a some good discussions in the forums on this topic,  you can try searching for "oil pump shaft".

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Permalink Reply by Sealik on April 4, 2011 at 11:27am

Here's the spindle position a TDC....11:28

Notice the offset at the top of it...?

 

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Permalink Reply by TigerRacing on April 4, 2011 at 12:28pm

Thanks Doug, I was hoping you'd chime in :D

Permalink Reply by Glenn Mitchell on April 4, 2011 at 1:33pm

Yea I can see what your sayn.. im the compression on the cylinders then if I don't find anything ima move on to checkin that and the cam and gear and see if it off or wrong.. either one of you guys happen to know when kinda compression numbers I shld be seein when I get the chance to check.!??

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