Emissions and carb question

[p11g20t]

Can someone point me in the direction of that? It makes perfect sense. The accel pump seems to be the only way I'm getting fuel. If I hold the pedal down it acts like I'm doing nothing

[datsunaholic]

The 2 hex bolts at the bottom of the carb bowl. Under the sight glass, they face down at an angle. Those are the jet caps. Since they're at the bottom of the bowl any sediment in the carb ends up there, and plugs up the jets. Same with water, it pools down there.

[p11g20t]

I'm going to hope its not normal for a carb to get plugged every 5 minutes. Clean it out or let it blow out, then 5 minutes later plugged again.

 

It's a new fuel filter from the guy before me, said it was cheap, can it be that bad though?

[datsunaholic]

Well, first i wouldn't trust the prior owner's filter, it could still be bad, or just plugged up really fast and started bypassing.

 

Second, a lot of times the junk is in the lines after the filter. They were open to air for a while, probably started rusting, or bits of hose particles got in there. Any junk loosened up by cleaning the carb could be getting in the jets too.

[p11g20t]

so what should i do then? i cant drive it more than a mile or two without it plugging up again

[deadmonkey]

so in other photos it appears these dont even need to be capped off? doesnt make much sense unless theres a one way valve inside that plugs them off.

 

That jobber is just a vacuum switch like I said before...triggered by heat. It doesn't HAVE to be covered, but it is just good practice to do stuff like that so you don't get stuff inside it. I had wasps, put mud in almost every open hole they could find. I have to get a new vacuum hose now because the last owner didn't cap stuff.

 

You can easily test for vacuum leaks by squirting some brake cleaner on joints, etc and see of the engine races. If you think you may have a fuel delivery issue, see if the filter looks full of fuel. Start at the carb and work your way back.

 

I had a clogged electric fuel pump once with similarish symptoms. barely enough fuel getting to carbs to do anything but idle on fumes.

 

Other than that Perhaps now is a good time to rebuild the carb?

===

- Also, this is a perfect example of what not to do

- That spark plug is being used to cap the engine crankcase breather tube. Don't do that. Your engine can't breath like that. The fumes stay trapped in the crank and can build up pressure. There is nowhere for it to go but out a seal, most likely the oilpan.

http://community.ratsun.net/topic/25127-emissions-and-carb-question/page__view__findpost__p__359808

[p11g20t]

That's not my car lol. In mine I put the PVC valve back in at the end and it vents to open air.

The car is gettin fuel to the window of the carb just fine. And it's full even when it gets fussy, so the issue should be past that it seems. I have tried starting fluid to test for leaks and found none. When it acts up, it seems that the accel pump gets it fuel just the main isn't.

If I step on the gas and hold it in it accelerates for just a second then acts like I'm not holding it in at all, and wants to die having no fuel. I just used my air compressor to really blow things out some. Hopefully it will have helped. My old carb If I undid the jet at the top, theres a long perforated tube that comes out with it. In this carb from the truck that tube doesn't come out. So I cant check it at all

[p11g20t]

On another note I got a new nifty fuel filter by Mr Gasket that is just a clear glass casing so you can see it filter, and then you can just replace the filter inside the casing when needed. Casing and filter plus 3 replacement filters for 11 bucks!

[LenRobertson]

I'm wondering if you have old dried gas varnishing the inside of the float chamber and the lines back to the filter. As this flakes off, it plugs the jets. Really don't know, but it would be fairly easy to check/fix. Take the side cover off the float chamber - the cover with the window in it. There is a tiny spacer on the shaft the float hangs from. Pull it and the float off the shaft. Spray carb cleaner into the float chamber, let it soak a couple of minutes, then wipe it out and see if you are getting goo of some sort. Take the plugs out from under the jets and carb cleaner/blow through the jets. The fitting on top of the carb where the supply line from the pump goes in - if you take out the large bolt holding that fitting, there may be a fine mesh screen under it. More carb cleaner if there is crap on it. Take the line loose from the pump to carb and blow cleaner & compressed air through the line in case there is anything in there. And try to see if you are getting flakes of anything or goo the cleaner has dissolved. If everything looks good and clean, then I've wasted your time, but you have to check to know for sure.

 

Another thought - it has been years since I had water in the gas tank, but I seem to remember it being a come and go thing. I don't know if water can even get through a fuel filter. But a can of gas dry in the tank would be cheap and easy to try. I don't know if the SX has a drain plug on the bottom of the tank. It would be nice to drain the tank and see if there is any crap in it, but it doesn't seem like any of this would get through the filter.

 

I'll have to look for one of those see-through filters. I bought a box of ten filters off eBay when I first started with Datsuns a few years ago. I've nearly used them up, so I'll try the kind you mentioned.

 

Len

[p11g20t]

hmmm, i will pick up some cleaner here in the next day and try, some cleaning. wont using cleaner just break stuff loose and clog it more? it seems like it would clean it but you cant wash it out afterwards. is there a trick to this?

as far as the gas, i dont know how long it sat frankly, it was driven a lot before, then it was garaged for the sitting period, which i dont think was super long... the fuel ive seen so far looks normal, but if cleaning doesnt work i may try an additive. its getting frustrating because if the car sits, then it runs fine and ill think ive fixed it then a few miles later it acts up again.

 

this doesnt sound like a vacuum or needle problem does it? i dont know how all that works, and if theres something that kicks on or off sometimes that could cause this... although when it acts up i can keep it running by hand under the hood, so im controlling the air, and its still doing it...

other theories?

 

just to once again sum up the issue - which comes and goes very suddenly

when i push the gas down, it revs normal for a second then cuts out like im not pushing the gas anymore. i assume this is because the accel pump sends fuel at first, then the main pump is no longer sending fuel to keep it going. it also at this point will not idle until the issue disappears. often if i turn the car off for a minute then back one, it idles okay, then as soon as i get to second gear it starts again.

[LenRobertson]

The idea with the carb cleaner is to dissolve any old dried gas and wipe it/blow it out, so it doesn't gradually come off in pieces. When the side is off the float chamber, the interior of the chamber is exposed enough to wipe out pretty well. I mentioned the fine mesh screen in where the line from the pump goes into the top of the carb. This may have been damaged and thrown away long ago. If you can't find it, it is gone. I don't know if you took the plugs off the jets and blew through them, but do try that, too.

 

Another thought - maybe you have a weak fuel pump, partially blocked line, or junk in the tank blocking the fuel outlet. Enough gas gets to the carb to fill the float chamber at idle/low speed, but as soon as the engine needs more gas, it can't get it. When I brought my 510 back from the dead, it was starving for fuel due to dried gas in the line from the tank to the filter. I had to take the rubber line off at both ends, spray carb cleaner in and let it soak in the line, then blow through with compressed air. I used a long piece of fuel line routed into a glass jar to catch the dissolved junk when I blew through, so it wouldn't get all over the car, and I could see what I was cleaning out. I did several repetitions of carb cleaner/compressed air to get the line cleaned. You will need to drain or siphon the gas out of your tank if you do this.

 

Actually your SX sounds a bit like what my F10 is doing. It would start, get up to 50 MPH, go about 1/2 mile, then die out. The float chamber would be out of gas. I could put gas in the chamber, restart, it would run fine until I got up to speed, the die again. I'm still working on getting it going right, but have been concentrating on my 510. I have the carb off the F10 to rebuild, just haven't got to it.

 

I don't know the cost of a new fuel pump. But you might have dried gas in yours causing problems, and replacing the pump is needed. A lot of figuring out what to do is guess work - and spending money, sometimes on the wrong parts. Just keep trying things and asking questions. It will be a great feeling when you get it fixed.

 

Len

[p11g20t]

Thank you for continuing to help!

I had already checked the wondow a few times and noticed that When its having it's problem, the float tank is staying full, that's why I assume the issue was after that.

[datsunaholic]

I still say it's just junk getting in the jets. I had a tank vent hose disintegrate and end up in the tank, which caused no end of plugging. The filter caught some of it, but there was so much the filters would tear and stuff would get past. I had to change filters every 20 miles for a couple months before I finally removed and cleaned out the fuel tank, blew all the lines clear, and replaced every fuel hose, vent hose, and filler hose in the car. Then it only took 2 years for the debris to finally be clear of the system so I could get maybe a couple hunderd miles between carb cleanings. It still occasionally plugs up though.

 

The issue is the jets in a DCH340 draw fuel upward. Carb vacuum draws fuel through the jet, but the jet holders are below the float chamber, so anything and everything settles right in front of the jets. Carb vacuum pulls fuel through the jets, but it also pulls anything else up into the jets too. Small stuff will go through the jet, or get stuck in the jet, bigger stuff just blocks the jet. When the engine dies, the stuff that was blocking the jet sinks back to the bottom, and the car will run again. That is, until the debris gets sucked up into the jet again. This will happen forever unless every single piece of debris (some of which is almost impossible to see with the unaided eye) is out of the carb and all the fuel lines. And if you have a hose disintegrating or lines/tank rusting, it's generating more debris every day.

[p11g20t]

So would a can of seafoam In the tank maybe help to clean the lines out a bit, and the float tank too?

[datzenmike]

 

The issue is the jets in a DCH340 draw fuel upward. Carb vacuum draws fuel through the jet, but the jet holders are below the float chamber, so anything and everything settles right in front of the jets. Carb vacuum pulls fuel through the jets, but it also pulls anything else up into the jets too. Small stuff will go through the jet, or get stuck in the jet, bigger stuff just blocks the jet. When the engine dies, the stuff that was blocking the jet sinks back to the bottom, and the car will run again. That is, until the debris gets sucked up into the jet again. This will happen forever unless every single piece of debris (some of which is almost impossible to see with the unaided eye) is out of the carb and all the fuel lines. And if you have a hose disintegrating or lines/tank rusting, it's generating more debris every day.

 

This is so true. Carb cleaners and gas treatment won't dissolve rust flakes, dirt, rubber or filter particles. They have to be removed by taking it apart. I have removed the hex cap that covers the main jet but it's not easy, I shortened and ground down a wide blade screw driver to fit up and loosen the jet to remove it. My problem was a casting flake of aluminum that would get sucked up and be held against the jet when driving with a heavy foot or if I hit a big off road bump. Nothing you could do but shut off for 10 seconds let it settle and re start.

 

Best to remove the carb to better get at it.

[p11g20t]

ive taken the 12 mm bolt out and the carb completely off, and blew compressed air in backwards, forwards, together, taken apart from the fuel feed, and the drain. didnt change the problem at all. that was a few days ago. i hate to take the cover of the float chamber off again. i had issues with the seal leaking last time when i put it back on. i had pulled it once thinking the float maybe needed adjusting because it sat a little low. but a little low is still okay right? i mean just a tiny bit

[p11g20t]

i have a question.

so the fuel hardlines have a send from pump to carb and split back to a return. im wondering if instead of the return coming before the carb, i ran a line off the drain below the main jet, through a filter, as a return instead. would that not let anything that got sucked up into the jet, and then dropped when i shut the car off, get pulled into the filter? otherwise now it sits on that drain bolt and gets sucked back up again.

[datsunaholic]

Won't work, and all that will do is drain the carb when sitting so that it's very hard to start. There's no pressure inside the float chamber to run it through the filter anyway, it'd just gravity drain.

 

The return line has to be BEFORE the float valve- that way it keeps fuel circulating even when the float valve shuts. If you put a microfilter between the splitter and the carb it might work a little better, but you need to keep checking that filter.

[p11g20t]

Ok so I'm fighting an idle problem. It idles at 1400 fine but anything below, it dies when the clutch is pushed in. Its also very jerky on acceleration.

I've adjusted the choke to barely close. And this is hope it leaves it when it's warmed up. It doesn't change much... It doesn't seem to be getting caught. If I open it by hand more it bogs down.

What's going on?

also, the needle right above the vacuum advance connection on the base of the carb, that doesnt do anything at all.

and im reading no oil pressure, not sure if its a gauge problem...

 

[LenRobertson]

I'm probably not the right person to answer an idle problem question, since I ran my SX at an "idle" speed of about 1800 for several years. I finally thought I would recheck my anti-dieseling solenoid (which I was sure I'd tested and was fine). In the process of checking it, I lost the needle to it, and now I have a much lower idle, although erratic. It seems the solenoid wasn't working. However, from your pics, it looks like your carb is old enough it may not have this solenoid. What I'm referring to is a hex shaped thingy (17mm wrench fits it I think) sticking out of the left rear of the carb, with a single wire coming from it. I have seen carbs with the wire broken off, too. Anything like this on your carb?

 

Other ideas - plugged idle jet. Don't recall exactly where this is located, so I'm not sure where to try to blow through. Did you get the link to the Dime Quarterly carb article? http://dimequarterly.tierranet.com/ Go to Tech Dept, Engine, Downdraft Tuning Guide. It seems like there is an idle emulsion tube or something that is part of the idle the circuit. I think the DQ article will give you some ideas. Also a setting for the idle mixture screw at the base of the carb. As I recall, if the engine is running fast, adjusting this screw doesn't seem to do much.

 

Finally, on your oil pressure, is the wire connected well going into the pressure sender down on the passenger side of the block? Maybe clean the connection. I believe the fuse for the oil pressure gauge fuses other instruments. If only the oil is dead, probably not a fuse. I'll keep thinking on this one. There may be a test where you jump the sender wire to ground, but I can't recall exactly. Maybe someone else remembers this procedure?

 

Len

[p11g20t]

Would have been the perfect person to answer it! I found a plugged spot in the idle circuit. I also found that the washer going between the anti dieseling solenoid and the carb was not big enough, so even opened, it was plugging the passage. I spaced it out more and it idles now.

And the wire somehow got bumped loose for the oil pressure gauge.

 

Now my issue is next to the fuel inlet, the bolt that holds the top of the carb down, the female side in the carb casting is stripped. It's leaking air in because it's not tightened down. Idk my best option for fixing this. Helacoil?

[LenRobertson]

Wow, not one, but two of my ideas worked? I'm not sure that has ever happened before. Maybe I should retire on that record!

 

I don't know the fix for a stripped carb screw. Are Helicoils made small enough for this app.? No doubt there is a website giving sizes for them. I suspect what most guys do when these screws strip is just swap the carb body with a good one, since there are so many old Hitachis floating around. But that is a bunch of work I know you don't want to face if there is an easier fix. Again, hoping someone who has dealt with stripped carb screw will join in here. Sooner or later, I'll probably strip one myself and need to know.

 

Len

[p11g20t]

I have a few of these carb bodies Now. But I just put so much time and effort into getting this one cleaned up and going, were talking weeks... And I'd have to swap linkage and everything over, I'd rather not if i can avoid it :/

 

And actually all three of your ideas were correct before!

[LenRobertson]

I have a few of these carb bodies Now. But I just put so much time and effort into getting this one cleaned up and going, were talking weeks... And I'd have to swap linkage and everything over, I'd rather not if i can avoid it :/

 

And actually all three of your ideas were correct before!

 

I figured the last thing you want to do is swap bodies. I think you should post the stripped carb screw question as a new topic over in the Engine section here on Ratsun where more people will see it and respond. Maybe tapping it out to an oversize screw is possible, but that might be a disaster in actual practice. It would be good to get a reply from someone who has done a successful fix.

 

Len

[p11g20t]

Well yesterday i actually swapped bodies. Now it won't run. I'm really frustrated. This carb body (actually is the original one) and the one from the pickup (which was stripped out) are slightly different the jet style is a little different and a few things.

Both are from the l20b, but the main jet air bleed seems to be much smaller on this original, assuming I put the right one in? It had a 10 or a 106 or something on it. The truck one that actually ran had s 50 or something on it...