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720 carb running rich

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Hitachi (stock) or Weber? Nope don't know a carb guy. I would still recommend that you figure it out. It's gonna go a lot easier and be significantly more enjoyable if you can figure out maintenance and stuff out because paying somebody else doesn't always work out.

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Looks like an '85 in the avatar. California would be the ECC carb with O2 sensor and the 6 wire round electrical plug at the back.

 

I have to assume this is a rich smell... at idle.  Some things that can cause an over rich idle...

 

 

Float has sunk or stuck or inlet needle valve is obstructed and not closing and the float chamber is over filling and flooding. Look at glass bull's eye on front of carb. Fuel level should be half way up. Look also down the primary barrel while running for gas dripping from the venturi.

 

Choke is on or part on. Take top of air filter off and look when engine fully warmed up. Choke plate should be fully vertical when off.

 

I've seen some pretty dirty air filters in my time but never one that choked the air supply enough to lower the mileage.

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Looks like an '85 in the avatar. California would be the ECC carb with O2 sensor and the 6 wire round electrical plug at the back.

 

I have to assume this is a rich smell... at idle. Some things that can cause an over rich idle...

 

 

Float has sunk or stuck or inlet needle valve is obstructed and not closing and the float chamber is over filling and flooding. Look at glass bull's eye on front of carb. Fuel level should be half way up. Look also down the primary barrel while running for gas dripping from the venturi.

 

Choke is on or part on. Take top of air filter off and look when engine fully warmed up. Choke plate should be fully vertical when off.

 

I've seen some pretty dirty air filters in my time but never one that choked the air supply enough to lower the mileage.

We had one on a 79 C10 that was so clogged up that it wouldn't even run.

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I've seen some with oily blow by wetting half the filter.

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Not in California. It has to pass emission testing doesn't it? Can't replace anything but with stock parts.

 

 

Guess I had better ask now before we go farther. Is your 'carb guy' familiar with carbs or EFI? EFI would have much less tailpipe smell than a carb vehicle. What you smell may be normal for a 720.  

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I dont know anyone out here with a nissan carb that can pass emissions. They're making harder each year to pass. vehicles from 1974 and older , do not need to have a smog check in California.

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75 and older don't need smog in California. If you do install a weber, it won't pass. 1st is visual, then performance.

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If u can't tune the carb, you have to find a mechanic that knows carbs, specially import ones. Most mechanic s that know carbs are retired or too old. Try adjusting urself before taking it to get smog.

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Float has sunk or stuck or inlet needle valve is obstructed and not closing and the float chamber is over filling and flooding. Look at glass bull's eye on front of carb. Fuel level should be half way up. Look also down the primary barrel while running for gas dripping from the venturi.

 

Choke is on or part on. Take top of air filter off and look when engine fully warmed up. Choke plate should be fully vertical when off.

 

I've seen some pretty dirty air filters in my time but never one that choked the air supply enough to lower the mileage.

 

 

 

Check these first and eliminate the obvious causes.

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I dont know anyone out here with a nissan carb that can pass emissions. They're making harder each year to pass. vehicles from 1974 and older , do not need to have a smog check in California.

 

Mine passes, just passed last year.

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First be sure there is a problem. Has it failed emission testing?... you haven't said. Otherwise smelly exhaust isn't much of a sign.

 

Are the plugs black?

Does it blow black smoke?

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Was this idle or revved up?

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