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rharm78

78 Datsun 620 Smog help

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So im trying to get my 620 smogged. I have a friend who has a CO meter and it seems to be ok until i take it to get it tested and then it fails, by alot. The plugs are okay air filter ok and it has a new smog pump. Any ideas appreciated, but I will not be putting a weber on it and it needs to pass. Thank you!

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Well one of those meters is bad. Try another station. If similar results your buddy's is no good.

 

CO is incomplete combustion fuel. Running too rich or more fuel than there is air to properly burn it. Here are some things that will cause or contribute to it. In no particular order....

 

Poor ignition.

This could be old or fouled plugs, (use only NGK BP6ES-11 gaped to 0.038"-0.042") 

Bad plug wires, cap or rotor.

 

Cold engine.

Thermostat should be 180F. Gauge should be reading half way up into the run range. A cold engine does not burn fuel efficiently.

 

Choke.

Improperly set and or sticking partly on, forcing a rich condition.

 

Flooding

Several things can cause the float chamber to over fill. The float may be set to high, it might be damaged, the needle valve may have something stuck in it not allowing it to close properly.

 

Idle mixture

Set too rich.

 

Air filter

I've never seen one so badly dirty it would affect anything.

 

Catalytic converter.

Lost/removed or worn out. The Cat doesn't do everything but it does help clean up what little fuel is not burned.

 

Valve lash

 Toooooo tight exhaust valve lash, not allowing exhaust valve to close and seal properly. During compression stroke gas and air are pushed out unburned. Left, this can cause a permanently 'burned' and damaged valve.

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Mike, it already failed smog. Hence write up of smog test. If in Calif., then Sacramento has records already.

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The combination, (High HC, High CO, low NOx) along with extremely low CO2 numbers (should be 15%+) tells me it's running REALLY rich.  Like the choke is on, or it's overflowing the float chamber.  Or leaking internally. The zero O2 numbers indicates it's not an ignition or misfire condition.  Numbers like that tell me too much fuel/too little air.

 

But it could be burning oil.

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I originally had worn out rings, damaged piston or worn out valve seals but removed them. It would probably have to smoke noticably for that?

 

 

Mike, it already failed smog. Hence write up of smog test. If in Calif., then Sacramento has records already.

 

I know it failed but he said his buddy's tester showed a pass.... one must be wrong. I would guess the buddy's.

 

California jets are 101 primary and 158 secondary. These unfortunately, can be mistakenly swapped when rebuilding.

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I do agree this looks like it's running a bit rich..

 

High CO can also be caused by an exhaust restriction.. plugged cat/muffler.

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How does ur spark plugs look after idling for a few

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I can check the spark plugs right now since i just let the truck warm up. 

 

Burning oil could be a possibility but compression is good, could it be burning that much?

 

Thermostat does not open until just before halfway on temp gauge, i warmed it up to check that. 

 

As for the carburetor i sent it to a carb shop about 4 years ago. It was completely overhauled then and passed smog soon afterwards, but the Cat was also brand new at that time

 

Pretty sure the choke isnt sticking. That would also cause the high idle to be on which it isnt. 

 

As for the jets i have no clue like i said i left that to a shop. I tried rebuilding it once, and did not do a good job so i had it sent out. 

 

It seems to me that at my friends shop it seems fine because it is under no load, the engine is in neutral because he doesnt have a dyno, just the CO meter. Once it gets on the dyno for the test, it fails. But he works on vintage 911's and he checks all of them that way. 

 

I will pull the plugs right now and post a picture. 

 

Also spark plug wires are less then 4 years old, but i have new ones that im gonna install. I'll double check cap and rotor. Truck has electronic ignition because it is a 78'

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Front of the truck is towards the left, spark plugs in order

BP5Es-11, its what the manual recommended for a hotter spark so its what i used

I did not check the gap, but i will when i get home

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It's not a hotter spark. The plug runs hotter with a lower number and self cleans better is all. A 'hotter' plug is used when it fouls more often using a standard 6 heat range. Fouling can be from burning oil to carbon fouling from a poorly set up carburetor. A hotter heat range can keep them cleaner but it's not fixing the original cause of the fouling problem.

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It's not a hotter spark. The plug runs hotter with a lower number and self cleans better is all. A 'hotter' plug is used when it fouls more often using a standard 6 heat range. Fouling can be from burning oil to carbon fouling from a poorly set up carburetor. A hotter heat range can keep them cleaner but it's not fixing the original cause of the fouling problem.

NGK: smaller numbers are colder plugs. BP5 is one step colder.

 

 

I'm with everyone else...ignition is working, running way too rich.

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When u did compression check, did u warm up car to operating temp., open throttle all the way and used screw in type not plug in type, better reading with screw in type.

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Touche. I will need to talk to my parts personal about his misinformation.

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 Champions Autolite, Bosh are higher number hotter heat range.

 

Here's something else. My '84 FSM for the Z24 shows the exhaust plug a 5, intake a 6. I was always under the impression the 5 was colder because of it's location near the exhaust valve.also.

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NGKs are backwards from most in how the heat range is numbered, though it's similar to Denso (might be a Japanese thing...).  Lower number=hotter plug, higher number = colder plug.  You rarely, ever, want a hotter plug.  Oil fouling is one of those instances, but it's a band aid, not a permanent fix.  And it won't solve the emissions problem.

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yeah i know theres lots of oil on the plugs, more then i expected :(

 

last time i did a compression check i had just adjusted the valves(this was less then 300 miles ago) and i believe it was cold and i did not hold the throttle wide open. If i should retest it under these conditions i may have time to do that this weekend. 

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I went with the hot type plug because i figured if i had a hotter plug it would burn more or cleaner? I replaced them awhile ago but the truck has not had too many miles since then either, like maybe 1,000 but i doubt that. Probably more like 600 ish. I thought regardless if it made a difference it was still a plug that is recommended in the factory service manual i have so it should be ok. But it was just something i thought i would try, i did not expect it to solve my engine issues. I know the engine is worn out, but it still has some life in it. If i can get it smogged and drive it once a week(if not more) that would be awesome. Yes the engine does consume oil, but i did not think it was to the point to where it was fatal. and if it is then its rebuild time

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I also run 91 because its what the manual says with all the emissions crap. 

 

And thank you so much for all the replies so far!

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NGKs are backwards from most in how the heat range is numbered, though it's similar to Denso (might be a Japanese thing...).  Lower number=hotter plug, higher number = colder plug.  You rarely, ever, want a hotter plug.  Oil fouling is one of those instances, but it's a band aid, not a permanent fix.  And it won't solve the emissions problem.

I knew there was some correlation to my thoughts.

 

I don't work on cars that require plugs that are not NGK or Denso.

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I also run 91 because its what the manual says with all the emissions crap. 

 

And thank you so much for all the replies so far!

 

91 octane RON.  US pump octanes are typically displayed as R+M/2 (RON + MON /2).  The MON of most "Regular" unleaded is around 82, which is a pump R+M/2 of around 87. 

 

Running higher octane than necessary can cause lower economy (more fuel use).  My '76 runs best on 89- on 87 it pings badly, but running premium kills the mileage by about 10%.  I also have a higher compression head, though. 

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I went with the hot type plug because i figured if i had a hotter plug it would burn more or cleaner?

 

No, just keeps the plugs cleaner but risks preignition since the plug retains more heat.  You really want the coldest plug that doesn't foul.  Unfortunately since you're burning oil that does mean a hotter plug, but if you're burning enough oil to throw the emissions off, I don't think anything short of a rebuild will make it pass.  And no, it doesn't have to smoke to be burning enough oil to throw off the emissions.  One of mine was burning a quart every 500 miles before it started showing smoke, and that was WITHOUT a catalytic converter, which will mask it to some extent.

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