carb help for my 620

[datsunaholic]

Just because the idle screw isn't touching the throttle linkage doesn't mean the throttle is closed all the way. There's 2 idle screws, the fast idle that hits the "cams" on the throttle linkage, and the main idle that is only supposed to work when the choke is fully open (warmed up).

 

Anyway, I'm not sure where you are at this point...

 

1) Is the float chamber still flooding?

 

2) Is the float chamber still draining when you shut it off, and how much?

 

If the float chamber is still flooding, is your fuel return system still working? All electric pumps put out too much pressure for the float valve, and most L20B mechanical ones are really close. Hence why the return line is there. I've had mine plug up and cause flooding.

 

If the carb is draining, it almost sounds like one of the main jets is missing. Other than an external leak, there's no where else for the fuel to go.

[Braden]

the float is working fine, i re adjusted it, now it fills up to the dot and none over and stays full, also the fast idle i didnt mess with, its how it was when i took the carb off so it didnt get out of adjustment, and yes the throttle blades are closed because i took the carb off 4 times and verified it

[bonvo]

hmmm interesting problem i have a question did any of the screws that hold the thing together have issues?

 

i have a stock hitachi... it has issues the center section has a broken screw in it but if you helicoil it it works just fine when it stayed together it worked fine i understand the broke thing but if you could send me the cash to ship it you can have the thing maybe use parts from it and yours to make a good carb

[Braden]

see thats the thing my carb worked untill i decided to rebuild it it needed an acclerator pump and a good cleaning, when i took the banjo bolt off the little screen was full of gunk, take a look at the pics its spotless now, when i took it apart i layed out all the jets in perfect order so that when i re-installed them they would be right, maybe i just fucked it all up, im about to smash the thing, no screws are broken there in the same spot and as tight as they were when i took it apart, i tried my best and ive done this sort of thing before, normally when i rebuild a carb it fires right up, do a little adjusting and 5 min later your good, never had a problem like this before.

 

hmmm interesting problem i have a question did any of the screws that hold the thing together have issues?

 

i have a stock hitachi... it has issues the center section has a broken screw in it but if you helicoil it it works just fine when it stayed together it worked fine i understand the broke thing but if you could send me the cash to ship it you can have the thing maybe use parts from it and yours to make a good carb

[LenRobertson]

ghettobraden - I guess I'm going to have to tell you something I would rather not admit in public, but may make you feel a little better. I've been driving my 200SX (L20b, stock Hitachi) for several years now without a low idle. The lowest it ever goes is about 1800 rpm warm and about 2500 rpm cold. Yeah, it probably burns more gas without a low idle, but not as much as the F250 4wd that is my backup vehicle until I get another Datsun running. I haven't bothered to fix it because it is still running, I'm afraid of screwing it up so it doesn't run, I did a lot of reading and poking trying to find out what is wrong and nothing worked, and I'm lazy. So it may be you can drive your rig for awhile with the high idle problem and continue to work on it in your spare time, although it sounds like yours idles even higher than mine, so maybe not.

 

I'm going to try some of the ideas in this thread on my carb and see if anything helps. I really wonder if both our carbs may have the same problem. I've suspected the BCDD, so I'll try datzenmike's suggestions on mine. Could a power valve malfunction cause too much gas flowing into the primary? I was running mine last night at over 2000 rpm looking down the primary. It looked like quite a lot of gas flowing from the nozzle in the small venturi, but I don't know what a normal flow looks like at this engine speed. My secondary was closed, and from what I could see, the primary was open just a little bit.

 

Funny thing is, I just got a rebuild kit Friday for one of my dead 32/36 Webers, and planned to dump the Hitachi. But if I can get the Hitachi to idle slower, I'll save the Weber for my 510.

 

Len

[Buzzbomb]

I had this problem a few times, and yours is more than likely A)hung up secondary, or B)malfunctioning anti-diesel solenoid. I'd bet your problem is one of the two I listed since you never stated you took the carb apart. When I was searching for answers, these two were the most common listed. Both are super easy to test..Grab the main throttle a little, and move it open, while at the same time pushing DOWN on the secondary linkage on the carb to make sure it's shut, and that might solve your problem. When the secondary is hung open, it LOOKS closed, at least in my case.

 

I would bet the Datsun power circuit is much more robust than the older Holleys, where a "blown power valve" is sometimes blamed for tons of problems.

 

The reason why you guys are seeing so much gas flowing into the carb at a 2000 RPM idle is that you are OUT of the idle circuit. If you eliminate the BCDD as a problem, how else could all that gas and air be getting in the intake to be burned, as Datzenmike said eariler? It just doesn't make sense.

 

ghettobraden, to see where all the gas is going, you could idle it up on the truck, make sure it's full, take off and plug the lines, be careful so no gas escapes, and put it on the bench over a piece of cardboard or something to try to see the drip trail. If you aren't getting an external leak, I don't see how that truck is using that volume of gas with throttle bladeS that aren't cracked open.

[Braden]

it doesnt make sense to me either, i have had the carb off several times to inspect the throttle plates, the secondary is fully close unless i push on the linkage to open it, up, im betting that when started the primary goes wide open somehow, im getting ready to go back out there and do more testing, i will report back shortly

 

I had this problem a few times, and yours is more than likely A)hung up secondary, or B)malfunctioning anti-diesel solenoid. I'd bet your problem is one of the two I listed since you never stated you took the carb apart. When I was searching for answers, these two were the most common listed. Both are super easy to test..Grab the main throttle a little, and move it open, while at the same time pushing DOWN on the secondary linkage on the carb to make sure it's shut, and that might solve your problem. When the secondary is hung open, it LOOKS closed, at least in my case.

 

I would bet the Datsun power circuit is much more robust than the older Holleys, where a "blown power valve" is sometimes blamed for tons of problems.

 

The reason why you guys are seeing so much gas flowing into the carb at a 2000 RPM idle is that you are OUT of the idle circuit. If you eliminate the BCDD as a problem, how else could all that gas and air be getting in the intake to be burned, as Datzenmike said eariler? It just doesn't make sense.

 

ghettobraden, to see where all the gas is going, you could idle it up on the truck, make sure it's full, take off and plug the lines, be careful so no gas escapes, and put it on the bench over a piece of cardboard or something to try to see the drip trail. If you aren't getting an external leak, I don't see how that truck is using that volume of gas with throttle bladeS that aren't cracked open.

[Braden]

took apart bcdd, cleaned and inspected, re installed, what do ya know !!!! high idle from hell still!!!!!!!

im not doing this shit all day AGAIN

i applied 12 volts to the solenoid, blocked off the vacumm, bla bla bla, both throttle plates are closed on startup, completely colsed, and what do ya know 4 grand all day long, this is beginning to really piss me off

[Braden]

ok guys i have the carb completely disassembled, any suggestions while im down this far? i double checked all the jets, they are all clear, and in the right position, throttle plates are workign correctly everything seems to be in order, if i have a leak in my gaskets below the carb, inbetween the carb and intake could that sucki excessive air and cause such high revving? a fast response would make my day!!!!

[moparvwfreak]

somewhere you got a massive vac leak. thats all it could be. and the carb is trying to compensate for it. popped intake gasket? disconnected lines?? god forbid a cracked manifold? something is letting it get to much air and the carb is trying to make it right. dont know how or why but thats what it sounds like. i had a small vac leak on my yota, and it would idle at 2000+ rpm when warm. plugged the leak and it now idles at 1000 all day long.

[izzo]

i have 3 dollars cash and 20 dollars in change, try a suggestion that doesnt require the use of money, lol, im probably the poorest guy on the forum

 

http://forum.ratsun.net/showthread.php?t=14566

 

If you can afford to pay for shipping on a bunch of items, then save it up and get a good carb. Itll be a good upgrade :D

 

 

Ill keep my eyes peeled man, if i see one sitting around ill snag it up for you and get something worked out

[Braden]

ok guys heres the scoop PLEASE RESPOND WITH ANY HELP YOU CAN GIVE, when the linkage is sitting on the fast idle cams my throttle cable is very loose and i have no pedal, when i get it off the cams and let the throttle plate close then it allows the linkage to turn down and tighten up my cable then i get my pedal back, when the linkage is sitting on the fast idle it revs super high but when i back it off of the cams it wont run right at all backfiring alot then revving up unless you give it gas, i took the carb apart cleaned it again and verified that all the parts were in the right place, with the linkage off the cams and the truck not revving high i have tried adjusting the idle screw, nothing, it is infact moving moving the throttle blade but it has no effect, all of my intake manifold gaskets are sealing and no leaks, i guess what i need to do is get the fast idle to sit on the lowest cam somehow (correct me if im wrong) and go from there? PLEASEPLEASE RESPOND SOON, i need a vehicle to get to college

[Braden]

also could someone help me with putting my choke on correctly and setting it correct?

[Buzzbomb]

Have you tried running the truck with NO throttle cable on to see what your idle does? If it solves your problem, its the throttle cable. You need to adjust the cable if you have that much slack in it. Adjust it to where you have WOT with the foot to the floor. Start it up, warm it up, rev it to kick it off the fast idle, and see where the idle is- by hand.

 

You need to get the fast idle cam totally OFF the linkage when warmed up- not on the first cam, not on the last- OFF.

 

Fast idle in a nutshel...Fast idle cracks open the throttle blades so the engine can get more air because it is getting more gas. Top step, highest RPM, when choke is basically closed. Bottom step, almost warmed up. OFF the linkage, the IDLE SPEED SCREW takes over.

 

Did you check the carb to see if it is leaking from somewhere? All that gas has to be going somewhere. IIRC, and thinking of my carb, that choke has an index mark that it needs to be at to function right. Line the lines up, you'll see them, that carb is really clean.

[Braden]

with the linkage on the steps, the cable has about an inch or 2 of slop in it, when its off the steps it tightens up the cable but the cable is NOT preventing the primary throttle plate from closing, im honestly about to give up

[datsunaholic]

The backfiring could be a symptom of the same problem.

 

Going back, I realized I had a truck that wouldn't idle at all below 1600RPM. If I cut it below that, the engine died as if I turned the key off. Now, I had lots of carbs to mess with and swapped 2 KNOWN good carbs (as they worked fine on another car) and the problem persisted.

 

I was missing something, but couldn't figure it out.

 

What I plain forgot to think of was the fact that I had changed the intake manifold to get rid of the SU carbs, which worked fine but wouldn't pass smog, to put a stock carb on it. What I didn't realize was that the L18 manifold I used was actually cracked. It was cracked because I pulled it off a wrecked truck, wrecked so bad the air cleaner was pounded flat and the carb's top ring was broken. So I had one MASSIVE vacuum leak, that only got worse when it warmed up. From the amount of hissing it was making, I should have easily seen that.

[Braden]

well guys heres what im going to do, everything i can tell is in working order, everyhting is in the right place, ive checked double checked and triple checked and adjusted everyhting i could find, every jet, every passageway, linkage, choke, anti dieseling solenoid, everything, im gonna remove the bcdd and take it off, i have a very early version of this hitachi on an old l20 and it has a block off plate where the bcdd should be, im gonna block it off and try it and then maybe buy a new solenoid, if that doesnt work i will have a free hitachi carb if anyone wants it, and i guess i will park my truck and let it rot, i know thats not funny at all, thats the truth, i cant afford to fix it so it will rot in my yard untill we move and then it will rot in our new yard, lol or i guess once i pay off my 600$ debt i could try and save for a weber, or for parts enough to use my mikunis

[Buzzbomb]

then maybe buy a new solenoid

 

Why spend money if you don't have to? Did you check the solenoid to see if works? IIRC, you can test this by leaving the ignition in the on position, unplug the connector on the solenoid, the reconnect it and see if it clicks. If it clicks, it's fine.

 

WHy don't you try the old carb on your truck and see if it works better?

 

Lots of good tips in this thread, anyway..Good Luck

[Braden]

wait a minute, if i adjust the fast idle srew down a bit shouldnt it idle it down, then after i get that working good the engine will warm up causing the choke to turn off and the linkage to come off fast idle, then i can try adjusting my idle again, but if my motor was warmed up then why wouldnt my truck run when i took the choke off, and adjusted my idle screw?

[Cuts metal like mad]

with it idling so high, theres no way to tell if your 'base' settings are correct, I'd return everything back to a 'base' setting the way you had when you set this thing on. From there its obviously still gonna do what its doing, but its running on the secondary jet... SO, stick 'something', I use my hand for this but a back fire through the carb at this point could be painful :D The motor should idle normally, or rough, or a 'little' high... but not as high as it was. Then go through your normal tuning process. This is not going to fix your problem, but if the carbs runs normally with the secondary barrel blocked... you have narrowed down your possibilities, like ANYTHING idle related (fast idle cam included), is now off the table.

 

Maybe I'm wrong... but thats where I'd go.

[Braden]

well guys im officially done working on this carb unless someone, has some really good advice, here is what i have determined about my carb, its clean, all of the passages are clear, all of the jets and parts are in the correct spot, both throttle blades are completely closed when engine is off, choke works, on startup both throttle blades are still closed, all gaskets are sealing, bcdd is now removed/blocked off to eliminate its part in the equation, linkage is in correct configurement, and i still cant figure out why my throttle cable came out of adjustment, when i took my carb off the very first time to rebuild it my cable had no slop on the linkage, now that i put it back on and its sitting on the fast idle cam it has about 2 inches of slop? what the hell? anyways im going to make a short video and post it up to show you what is going on, see if you can spot anything that i missed.:mad::mad::mad::mad::confused:

[Braden]

ok so i went outside and stuffed a sock down in the secondary, now the BASTARD JUST ABOUT IDLES BUT IT SMOKES LIKE A FREIGHT TRAIN, is my mixture too rich? when i got it to idle FINALLY!!!!!!!!!!! i noticed gasoline around the intake/exhaust manifold gasket, started it back up and saw bubbles aroud the gasket, so that means i need a new one, but could that have been the root of all of my problems? but if i stuck the sock down in the secondary could that mean i was getting excess air through there? or normally does a small amount of air travel through the secondary constantly? and by me blocking off the secondary acted like me plugging the leak in my gasket causing it to run better? when i change the gasket i will remove all of the egr shit, i know that rail above the intake can go but what else goes? the air pump is already gone, so is the diaphram and the canister.

[Braden]

 

 

[moparvwfreak]

as i said, it sounded like an intake leak. replace the gasket and tune it afterwards. it should run better

[Braden]

ok ordered my new intake gasket and decided to swap out my manifolds for egr free ones, instead of my old heat riser u67 stuff i am swapping over to older riser free u60 manifolds, and i am also deleting my bcdd valve off of my carb, heres some pics, and i want to thank everybody for helping me out on this project, i couldnt do it without my ratsun family lol :):)