SOS! Need help

[Runslikeapenguin]

I just grabbed a 1979 Datsun 620 for a daily runner my room mate could use. His Kia took a shit and he just needed some basic transportation until he could find a better car to invest some money into. I grabbed this Datsun because it was only $800, had 90,000 original miles the dash was perfect and everything worked. It started first crank and idled right away every time i started it. it did run a little rough once it got warmed up but it would clear up with a few taps of the gas pedal. I figured that it was just a tuning issue and i could iron it out. Well i drove the truck to my work and it scooted along perfectly the whole way. But as soon as i started it up to go home everything went to hell.

 

It started perfectly as usual and then suddenly as i took off it died. Nothing. i started it again and tried to rev it up and it would rev for a second and then cut out %100. I soon figured out that the only way to keep it running was to pump the gas constantly. I figured that the mains were plugged if i could run it off of the accelerator pump. So i pumped it into the parking lot of an ORileys and started poking around with no luck. I finally managed to get the air cleaner off, by removing all 400+ hoses that were attached to it. What i was met with though was not a carb, it was something far far more sinister.

 

Soon some guys coming out of the parts store stopped and gave me a hand. We tested the fuel pump first and it was a little weak, but certainly working. They were convinced that it was the fuel pump not putting out enough pressure. Which seemed weird to me because the truck had run fine earlier that afternoon and a mechanical pump just wouldn't cut out like that. But i went into the auto parts store and bought a universal electric pump and put it inline hoping it would do the trick. No luck same BS. So i took it off, hooked the mechanical pump back up and walked to a gas station to get a drink and to calm down.

 

When i got back i started playing with the carb again and i figured out a way to keep it idling. I jammed a piece of cardboard between the choke and the air cleaner holding it shut. This let the car idle and rev all the way through the RPM's strongly for about a second before it started dieing and doing the same BS with the accelerator pump. But the good news was that with my little cardboard brace the pump technique was much much more effective and i was able to drive all the way home like that.

 

so now i sit with a bum truck out front of my house and a cramped leg, wondering to myself what to do. I was planning on ditching all the smog nonsense from this car but i was thinking i would have a little time to find all the parts i needed. I already have a weber 32/36 progressive and an Offenhauser manifold but they are in Cali right now and i would have to get them shipped. And from what i hear it wont work with the stock exhaust which looks like it has a bunch of junk for the air injection on it any way.

 

 

So essentially i need one of two things.

 

1. i need a simple fix, if this is easily answered then by all means i will go trouble shoot it real fast. Anyone got any ideas?

 

2. a place where i can get the parts to ditch all the Smog BS so i can rush to get it all off. And if someone could tell me exactly what i can ditch that would be amazing.

[datsunaholic]

That really just sounds like plugged main jets. I've had that problem many times, usually due to getting some water in the system.

 

But I'm not sure what you mean by "What i was met with though was not a carb, it was something far far more sinister."

 

I mean, what does it have?

[hang_510]

1. KISS, fuel filter???

 

2. what state? if it needs to be smogged, you may be SOL...

[Braden]

I just grabbed a 1979 Datsun 620 for a daily runner my room mate could use. His Kia took a shit and he just needed some basic transportation until he could find a better car to invest some money into. I grabbed this Datsun because it was only $800, had 90,000 original miles the dash was perfect and everything worked. It started first crank and idled right away every time i started it. it did run a little rough once it got warmed up but it would clear up with a few taps of the gas pedal. I figured that it was just a tuning issue and i could iron it out. Well i drove the truck to my work and it scooted along perfectly the whole way. But as soon as i started it up to go home everything went to hell.

 

It started perfectly as usual and then suddenly as i took off it died. Nothing. i started it again and tried to rev it up and it would rev for a second and then cut out %100. I soon figured out that the only way to keep it running was to pump the gas constantly. I figured that the mains were plugged if i could run it off of the accelerator pump. So i pumped it into the parking lot of an ORileys and started poking around with no luck. I finally managed to get the air cleaner off, by removing all 400+ hoses that were attached to it. What i was met with though was not a carb, it was something far far more sinister.

 

Soon some guys coming out of the parts store stopped and gave me a hand. We tested the fuel pump first and it was a little weak, but certainly working. They were convinced that it was the fuel pump not putting out enough pressure. Which seemed weird to me because the truck had run fine earlier that afternoon and a mechanical pump just wouldn't cut out like that. But i went into the auto parts store and bought a universal electric pump and put it inline hoping it would do the trick. No luck same BS. So i took it off, hooked the mechanical pump back up and walked to a gas station to get a drink and to calm down.

 

When i got back i started playing with the carb again and i figured out a way to keep it idling. I jammed a piece of cardboard between the choke and the air cleaner holding it shut. This let the car idle and rev all the way through the RPM's strongly for about a second before it started dieing and doing the same BS with the accelerator pump. But the good news was that with my little cardboard brace the pump technique was much much more effective and i was able to drive all the way home like that.

 

so now i sit with a bum truck out front of my house and a cramped leg, wondering to myself what to do. I was planning on ditching all the smog nonsense from this car but i was thinking i would have a little time to find all the parts i needed. I already have a weber 32/36 progressive and an Offenhauser manifold but they are in Cali right now and i would have to get them shipped. And from what i hear it wont work with the stock exhaust which looks like it has a bunch of junk for the air injection on it any way.

 

 

So essentially i need one of two things.

 

1. i need a simple fix, if this is easily answered then by all means i will go trouble shoot it real fast. Anyone got any ideas?

 

2. a place where i can get the parts to ditch all the Smog BS so i can rush to get it all off. And if someone could tell me exactly what i can ditch that would be amazing.

[DanielC]

Do the basics first. Check compression. Check valve clearances. Is the ignition strong, at the right time. Is the Carb getting fuel? Is the fuel clean, and not contaminated by water?

My opinion, just ripping out emissions equiptment with out fully understanding how each piece works, and how it contributes to the engine will create more problems.

 

It ran well when you first drove it. Find out what the root cause of the current malfunction is, and correct that.

[Guest kamakazi620]

sounds like a vacuume leak,when you jammed the choke shut it cut off the air and let it run(cuz air is getting in somewhere else)you need to buy a can of carb cleaner jam the choke shut run it then spary the carb cleaner around and on the carb look where you spray it when it runs different you found the leak,fix the leak, it could be as simple as a vacume hose or as complicated as a gasket on the carb+make sure all the bolts are tight,also check your plugs/wires/cap and rotor

[67411sss]

I'll just throw this out there, how old is the gas? Is there water in it maybe? Was the truck a daily driver before you got it or with 90,000 miles i wonder if it's been sitting for a while.

[Braden]

i wish you had come to the oreillys where i worked, i probably could have rebuilt your carb in the time it took you to drink your coffee at the gas station, anyways if your getting fuel and spark, it souds to me like you are getting one hell of a vacumm leak through one of your 400 plus hoses, removing the smog equipment and rebuilding your carb would be a good weekend project and would certianly help to elimante your problem, if it didnt totally eliminate your problem it would certianly eliminate one huge variable in your equation, if its a 79 with l20b then you have the newer type smog manifolds with heat riser, unless you want to keep the heat riser i would go ahead and get a different manifold while you are removing the smog crap, take into account the exhaust flange is totally different so you will either have to make a new flange and have it welded on or buy one with your manifold and have it welded on as well, as far as emissions you can take basically everything off the right side of the motor and only replace the manifolds and the carb, you need 2 vacumm hoses hooked up to your intake one for your brake booster and one off of your carb for your vacumm advance, everything else either goes or is blocked off, try to elimnate the hoses down to where they connect to metal (plugging hoses with screws or bolts is unacceptable and will most certianly make it run worse) take a few pics of your carb and all that surrounds it, post it and get back with us, i will give you a part nummber for carb kit if you need it, its not hard to rebuild

[Guest kamakazi620]

^^^^^Do everything these dudes said water in the gas is common and will do this^^^^ I forgot 'bout that :blink: :D

[Runslikeapenguin]

What i mean by "something more sinister" is its a smog controlled carb. It took me a good 10 minutes to figure out how to get the top off of the carb to get to the jets ( or at least the ones i could see).

 

Fuel filter is fine, Fuel is clean and fresh.

Car was driven regularly before i got it.

Valves, timing and ignition should all be fine, like i said it was running pretty well before the problems. And it runs well for about a second when it's first started which rules all that out. This is not my first rodeo when it comes to cars. I thought after rebuilding IDF's i could handle any carb, but i guess this monstrosity has proven me wrong.

 

I blew out every jet i could find but i might have missed one. Anyone have a diagram for this carb? and what carb is it BTW? I wasn't able to see any markings.

 

I don't have to have this truck smogged so out with all the BS.

 

Also, if i were to have my friend ship me that Offenhauser manifold with the Weber carb, what exhaust would i need to put that on?

[Guest kamakazi620]

a non smog l20b

[Runslikeapenguin]

a non smog l20b

 

That's it? The exhaust from a non smog L20b would work?

[Guest kamakazi620]

It should,I know some of the L20b's had diferent ports sqaure to round??? someone correct me if i'm wrong,but get one that matches (ports)yer old one

[Runslikeapenguin]

i wish you had come to the oreillys where i worked, i probably could have rebuilt your carb in the time it took you to drink your coffee at the gas station, anyways if your getting fuel and spark, it souds to me like you are getting one hell of a vacumm leak through one of your 400 plus hoses, removing the smog equipment and rebuilding your carb would be a good weekend project and would certianly help to elimante your problem, if it didnt totally eliminate your problem it would certianly eliminate one huge variable in your equation, if its a 79 with l20b then you have the newer type smog manifolds with heat riser, unless you want to keep the heat riser i would go ahead and get a different manifold while you are removing the smog crap, take into account the exhaust flange is totally different so you will either have to make a new flange and have it welded on or buy one with your manifold and have it welded on as well, as far as emissions you can take basically everything off the right side of the motor and only replace the manifolds and the carb, you need 2 vacumm hoses hooked up to your intake one for your brake booster and one off of your carb for your vacumm advance, everything else either goes or is blocked off, try to elimnate the hoses down to where they connect to metal (plugging hoses with screws or bolts is unacceptable and will most certianly make it run worse) take a few pics of your carb and all that surrounds it, post it and get back with us, i will give you a part nummber for carb kit if you need it, its not hard to rebuild

 

I missed this post some how . . . .

 

Thanks for the pointers. One thing i didn't mention was that the truck has a small exhaust leak. Seeing as the intake and exhaust are on the same gasket could this be the problem?

 

When you say flange for the exhaust you mean coming off the manifold to the rest of the exhaust right?

I mentioned i had a Weber carb and an Offenhauser manifold, what would i need to do to get that working? What kind of exhaust modification. That would probably be the easiest thing to do.

[datsunaholic]

No such thing as a non-smog L20B (in stock form). A '79, if stock, has roundport exhaust with the single-opening exhaust manifold, so fairly significant exhaust mods are needed to switch to a non-smog manofold, and even then it's not the RIGHT manifold for the engine (though it'll work).

 

 

For the carb:

 

The main jets aren't located under the top. They're behind plugs under the float bowl, there are 2. They sit low, and the cavities fill up with water easily (as they're the lowest part of the carb) but water won't pass through the jets. Hence, having to run it with the accel pump. If you can drive it a couple blocks (let alone a mile or more) on the accel pump then it's not a fuel supply problem. But you can easily verify that by checking the fuel level in the float chamber.

 

I have had this exact symptom on numerous occasions. It has always been a plugged main jet- either from water or debris (the debris typically being varnish residue from a carb that dried up). Every time it was a fuel delivery problem, the car would kick and sputter but run at low throttle levels (or idle) unless the fuel system totally plugged up, then it wouldn't run at all.

 

When you get a small amount of water in the tank (just below the fuel tank pickup line), a lot of times it will run fine because driving around makes the water slosh around, so it doesn't ingest a huge amount of water all at once. Because the droplets are so small, they just run through the system. But then you take a long drive, and then stop. The water in the float chamber settles to the bottom of the carb, which just happens to be where the main jet fuel inlets are. On the DCH-340 Hitachi it's even more pronounced because the jets are in little subchambers below the float bowl, so they act like little pits to trap water in. So then you go to restart, the car runs briefly on whatever had pooled up in the manifold and whatever squirted in when you pumped the pedal. Then it tries to atomize the water, which doesn't burn, and the thing cuts out. It'll refire off the accel pump and the idle circut until you press the pedal, then it shuts off. Pumping the pedal makes it run because the accel circuit has it's own supply line, and any water will be forcibly ejected, but eventually the idle circuit will plug up too so now it will only run when giving it pedal.

[hang_510]

One thing i didn't mention was that the truck has a small exhaust leak. Seeing as the intake and exhaust are on the same gasket could this be the problem?

likely culprit for a vacuum leak!

make sure all the IN/EX mani hardware is there too. busted studs are common. :angry:

[Braden]

I missed this post some how . . . .

 

Thanks for the pointers. One thing i didn't mention was that the truck has a small exhaust leak. Seeing as the intake and exhaust are on the same gasket could this be the problem?

 

When you say flange for the exhaust you mean coming off the manifold to the rest of the exhaust right?

I mentioned i had a Weber carb and an Offenhauser manifold, what would i need to do to get that working? What kind of exhaust modification. That would probably be the easiest thing to do.

wheni rebuilt my carb the first time i put it back on the truck and it wouldnt idle below 4000 rpm, i foud a small leak on the intake /exhaust manifold gasket that was leaking fuel!!!!! when that happened i decided to change the gasket and remove the smog crap since i had the manifold off anyways, i swapped from a heat riser intake/exhaust to the older non riser manifold, the manifold you are running should go from 4 exhaust into 2 into 1 , the non smog mani goes from 4 to 2 then after the exhaust flange it goes to one straight pipe like this

in one of the pics it shows the heat riser intake next to the non heat riser intake that is to be used in conjunction with the non heat riser exhaust manifold also pictured

[Braden]

on the last picture there you can see the block off plat ethat i used to get rid of the emissions return lines, the plate allows me to still use the positive crankcase ventilation valve to vent ,my block like it is supposed to be

here is a picture of the leak that i was talking about, it seems as though when i removed my carb to rebuild it it loosened the intake/exhaust gasket, i found that it only had liuke half the bolts in it anyways, so i replaced the gasket with the bolts and all was good, removing the emissions crap didnt take but a few hours (i already had the block off plates and only unbolted and then re attached all of my parts) after i removed the emission junk it is so much easier to get under the hood and work, looks clean and i dont have to worry about vacumm leaks!!!!!

 

hope this all helps, if you have any questions let me know

[Runslikeapenguin]

No such thing as a non-smog L20B (in stock form). A '79, if stock, has roundport exhaust with the single-opening exhaust manifold, so fairly significant exhaust mods are needed to switch to a non-smog manofold, and even then it's not the RIGHT manifold for the engine (though it'll work).

 

 

For the carb:

 

The main jets aren't located under the top. They're behind plugs under the float bowl, there are 2. They sit low, and the cavities fill up with water easily (as they're the lowest part of the carb) but water won't pass through the jets. Hence, having to run it with the accel pump. If you can drive it a couple blocks (let alone a mile or more) on the accel pump then it's not a fuel supply problem. But you can easily verify that by checking the fuel level in the float chamber.

 

I have had this exact symptom on numerous occasions. It has always been a plugged main jet- either from water or debris (the debris typically being varnish residue from a carb that dried up). Every time it was a fuel delivery problem, the car would kick and sputter but run at low throttle levels (or idle) unless the fuel system totally plugged up, then it wouldn't run at all.

 

 

This was my original thought and i thought i had ruled it out by blowing out the jets i found. If this turn out to be it I'm going to kick myself.

So i need to take the float cover off to get to them right?

[Runslikeapenguin]

 

ghettobraden thanks for the pictures and the replies. I really hope i can get this running by cleaning the jets, if not then Desmog it is.

 

So basically if i want to use my Offenhauser manifold and the weber, i need to get a completely new exhaust. Are there any aftermarket suppliers out there? If not a friend of mine builds custom headers for American Iron and I'm pretty sure i could get him to fab one up for the datsun. Although it would be pricy and i would feel weird having a TIG welded super high end header on a stock Datsun 620. :lol:

 

[datsunaholic]

No, they're below the cover, on the bottom of the bowl, not inside the bowl. 2 hex-head plugs, supposed to be retained with a clip retainer (most don't have that, and I had one of the plugs fall out because of it). Jets are inside that. It's not real easy to get to them with the carb installed, especially with all the emissions stuff there. And getting the carb OFF with all that smog stuff is a royal pain as well... Pretty much requires a specially bent 12mm wrench to get one of the carb nuts off.

[420n620]

so your leg got tired from having to pump the carb so you could get the trk home.

 

did you check the fuel sight glass to see if the gas was level at the little dot. if so then what you need to do is take the top of the air cleaner off, not the whole aircleaner, and work the throttle by hand at the carb, look down into the carb and see if it squirts gas as you give it full throttle, if it does NOT then your accelerator plunger is shot. Time for a rebult from sitting so long and because of the age of the trk.

 

as for taking off anything smog, leave it on till you figure out the problem first, it was running with all the smog stuff, if you want you can pull that stuff off latter..

[datzenmike]

Why are you replacing the exhaust manifold???? There's nothing wrong with the one that was installed back in '79. Headers are a waste of time and money. Take the carb off and clean it out and it will run good enough till you put the Weber and intake on.

 

When people don't know how the emission equipment works they think they are being cheated out of some power somehow. The only thing that convinces them is to remove it.... and it runs the same. :rolleyes: All that work and nothing. On the 620, the only thing that remotely reduces power (it at all) is the EGR system... and it isn't even working at full throttle or idle. Pull the hose from the EGR and plug it and it's de activated... simple. Otherwise, don't fuck with anything.

[datsunaholic]

Hm, the EGR is one of those arguable components- and it's easily disabled by disconnecting the vacuum line to it. What is a parasitic draw is the air pump, and that's solved by removing the belt. Still, only robs about 5-7 HP at 5600 RPM, and MUCH less at normal speeds. Not enough to notice, unless the thing is failing. The ALTERNATOR actually robs more power. The vacuum tubing is more a tuning issue when its hooked up wrong or the hoses are cracked. It looks like a lot of spaghetti but there's a reason for everything.

 

Removing everything makes it really hard to pass smog if you move to a smog State, or your State changes its rules. States changing the rules happens more frequently than you think- Wisconsin is considering adopting California rules right now. Think what would happen if all of a sudden every 1968-newer car had to be smogged again... could you make it pass? It could happen...

 

And yes, I have vehicles with all that stripped off, and others with it all still there. They run, about the same, power-wise. Fuel economy wise, another story.

[Braden]

not a whole new exhaust just a new flange welded on, that is iff you use a non smog manifold, i bought a flange on here, i got ripped off but other people have them and they are cheaper, just post up a parts wanted add, some one will reply soon