Emissions and carb question

[LenRobertson]

I'm lost when it comes to actual numbers on jets and such. Does that Dime Quarterly article give any sizes? I wonder if the non-running is actually wrong size parts, or plugged passage or missing parts. Is this the carb that ran, but never ran very well? Or never could get it to run?

 

Len

[p11g20t]

its the original that was in pieces when i got the car. i swapped all the parts over and cleaned it out. it only idles very rough if choke and throttle are wide open, so its getting way too much fuel, and not enough air. even with the idle circuit closed off. which doesnt make much sense because it doesnt look like its really getting too much fuel... idk im confused.

[LenRobertson]

Like most people, I struggle with carbs. I keep messing until something finally works - or at least it runs. Maybe finding the answer on repairing the stripped screw and using that body is what you will have to do, but I'm sure you are getting tired of going back and forth. I did a search for carb stripped screw repair, and found a whole lot of info on door hinge screws and the like. I'm not good at searching obviously. Another thought - study this page http://www.olddatsuns.com/data/Hitachi_Carb_DCH_DCP_DRJ340.pdf and see if you can find any pieces missing from your good carb. Numbers 50, 59, and 60 are the kind of thing I'm thinking about. But there may be minor differences in Hitachi 340s, so keep that in mind.

 

Len

[p11g20t]

thanks for the link! i had the exploded view of it this whole time but it was one that was not labeled from carburetor factory or whatever... that one helps a LOT!

im gonna pull off the top for now and see what i can see. its in the car, so im gonna start with stuff i can find without removing it AGAIN haha

[datzenmike]

If it's one of the screws that holds the top of the carb on I wouldn't worry too much about it. It doesn't really seal anything just holds the top on.

 

The primary and secondary barrels and all jets and bleeds should not be being used at idle. This is why there is an idle circuit to provide fuel. On the L20B carb it has to pass an open idle cut solenoid (must be energized) to get to the idle mixture screw. The idle mix screw adjusts the fuel quantity mixed with how much air is passing the throttle plate. If the idle is set too high the throttle plate will be open too far and not provide enough vacuum at the idle mixture screw opening. Additionally if open enough it will suck fuel through the primary circuit. A non functioning idle cut will result in the idle speed screw turned in so far that the primary is needed to provide fuel and an idle above 1400 rpms.

 

Maybe take the idle cut solenoid out and blow air in to clear the idle circuit. Maybe remove the idle mix screw as well to allow any crap out. A can or WD-40 with the red straw is also good for this plus the WD liquid is a solvent and will dissolve any varnish deposits.

 

I think getting the idle sorted is first before tackling further running issues.

[p11g20t]

yeah the idle circuit is working now i finally got that going, the issue was that when id step on the gas it would bog some and get too much air. so id have to close the choke partway. it wasnt sealing along where the top meets the body.

so now i have it swapped with a new body, and its idling extremely rich so that it wont keep running even. im not sure how, the needle is in all the way.

i noticed the ball at the bottom of the accel pump is kinda stuck, would that cause it to dump fuel through there?

[LenRobertson]

datzenmike - I'm glad you posted. You always can explain things better than I can, even the few things I know. I believe the ball at the bottom of the accelerator pump is the gas inlet for the pump. When the pump goes up into normal position, it sucks the ball open and lets gas into the pump chamber. When the accel pump does it's down stroke, the ball is push closed so the gas goes into the carb throat. Not a very good explanation, but yeah, it shouldn't be sticky. I use spray carb cleaner with the applicator tube, but WD40 may be fine. Wrap a rag around the wand so the cleaner doesn't blow back in your eye (learned that one the hard way!). If you are bogging on acceleration, sounds like a malfunctioning accel pump. The pump itself may be fine, but if it isn't getting enough gas, it won't work right. There should be a little spring or clip on top of the ball I think.

 

There is at least one other ball down under some other part, but I can't remember what it is for. But it is no doubt necessary, and no doubt could be gone if someone has been into the carb before.

 

Len

[p11g20t]

ok i figured out whats happening finally. i didnt have a light to see.

 

the main jet is absolutely dumping fuel in when its running.

the float is set perfect at the dot, its actually at the bottom of the dot.

 

as im writing this i remember something. im an idiot i think... i dont think the little funnel screw thing inside one of the drains is in place.

wow

ill report back in a second.... lol

[datzenmike]

Good enough explanation Len. Under the pump piston is a spring that holds the ball bearing in place loosely. There is a second ball bearing on the discharge side of the pump. It opens under pressure to let the squirt of gas out but closes on the up swing of the accelerator pump piston so that air isn't drawn in and only sucks gas from the float chamber. Either one stuck open/closed will foul the working of the accelerator pump.

 

With engine off work the throttle with air filter off. Look down the primary and you should see a very strong squirt of gas on every pump. This is essential to help transition from the idle circuit to the primary operation. Specially if the gas is stepped on suddenly. The engine will take a huge gulp of air. The idle circuit is not enough fuel and the air hasn't built up enough speed to draw fuel in through the primary venturi. The accelerator pump manually richens up that gulp of air and help get things going.

[LenRobertson]

i dont think the little funnel screw thing inside one of the drains is in place.

 

I'm not sure what this is, but it probably is important. Leftover parts from a carb overhaul usually isn't a good thing. LOL

 

I think the only thing worse than trying to run a cold engine without a choke is trying to run any engine without an accelerator pump. It is possible to get the car to move, but what a pain.

 

Len

[datzenmike]

Be aware that many of the internal jets will inter change. Generally the secondary is larger than the primary.

[p11g20t]

unfortunately the dch340 carb came in two styles i guess. one for the pickup, one for the 200sx. both for the l20b

 

the primary and secondary jets on the pickup come out by two screws inside the barrel. the air bleeds come with them. the 200sx has a single screw for each on the outside that goes through. and the air bleeds are separate.

 

i have three carbs, but the body im using is the 200sx one now, so parts from the other two dont quite fit right.

the pickup has a two part air bleed. the top funnel part, and the tube with the holes. on the 200sx thats all one piece (number 55 and 56 here: http://www.olddatsuns.com/data/Hitachi_Carb_DCH_DCP_DRJ340.pdf)

 

the two piece one fits in the 200sx still, just wont come out easily with the jets like they would in the pickup.

 

hard to explain without pics.

 

at any rate, its running decent, idling well. when i step on it decently hard, it lags power at first, and then you can feel it pickup a bit. it doesnt fully hesitate, just doesnt give it much power. its not just because its a small motor, i can feel that its a air/fuel issue. idk what to adjust though. the accel pump was on the highest setting, i put it on the middle one (of 3), but that would give it less gas. idk if it needs less or more...

[LenRobertson]

It sounds like you are making progress. On your way to being a carb expert. As datzenmike said, with the engine off, look down the carb throat with a good light, operate the throttle linkage by hand, and see what sort of output the accelerator pump is giving. It should be a pretty good squirt, not a spit, spit. If it doesn't look very good, you can take out the pump, spring, and ball, and try more carb cleaner and compressed air. Might help, might not. You can also try the different pump adjustment settings, and watch the stream with the engine off. But any of the settings should give a stream, just not as large for the lowest setting.

 

Len

[p11g20t]

well, i drove her some today, wasnt perfect, still feels like some mixture issues. but i dunno how to figure out which way to go on that. all i can really adjust is the idle mixture and the choke, and the accel pump on the three dif levels.

i was having an issue with the fast idle cam not spinning out of the way, so i swapped another one on, and it still wasnt springy enough the way it came. luckily i was able to twist the spring around one extra loop and gave it a bit of extra spring action. im guessing over the last.... 22 years, it lost its original spring. itll be nice to not drive around and idle sometimes at 1400 and sometimes at 1000 lol

 

the shaking has me really thinking its drivetrain related. what might i check for that? driveshaft mount, tranny mount... suspension is super soft and blown, could that cause it?