arizonajones Posted August 18, 2013 Report Share Posted August 18, 2013 Hi all, I'm new here and I just bought this 1980 720 2WD King Cab off of Craigslist. This is my first Datsun and will be my first completely DIY vehicle in 13 years. (So forgive me if some of my questions are dumb ones!) I'm not mechanically un-inclined, though, I come from a VW-building family and I'm a DIY bicycle mechanic. Here's a shot of her-- It drives okay, but I've got a growing list of priorities to dive into... The biggest thing I would love some advice on, though, is the idle/mixture/choke/carb. --The guy I bought it from said it would randomly idle too slow, fast, or just right. Sometimes it dies when you come to a stop, sometimes not. --I adjusted the choke back to its center mark (it was just floating in space with no tension) and that helped a bit but still didn't solve it. --I've cleaned it inside and out with carb cleaner --I've adjusted the idle speed and air mix up and down and had no solid results. It seems like it is solved with a higher idle and a richer mix, but then I get a couple blocks down the road and it sputters out when I slow down at the stop sign. I'm wondering if this is just is just a temperamental old carb, or a symptom of something bigger? The rest of my list- -Check (and possibly add) gear oil to transmission (but the the bolt is stuuuuck) -Add air pump back into system (There isn't one, currently) -Add new muffler and last section of exhaust (that's not there either) -Replace driveshaft support bearing (the rubber boot is falling apart) -Tighten connection of sideview mirrors (rusted loose) -New and/or re-upholster seats -Body/Paint/wheels It would be much appreciated if anyone could recommend some good new or used parts sources near Portland, OR. And if anyone local feels up to drinking a beer in my driveway and enlightening me, let me know (I'll buy good beer...) Thanks! 1 Quote Link to comment
wayno Posted August 18, 2013 Report Share Posted August 18, 2013 Welcome B) Good first post. :thumbup: A lot of the parts you might need can be found at the wrecking yards, just go there and look till you find good parts, you might have to buy the whole driveline to get the part you need(rubber part), but that is a DIY option. You sometimes need a really big wrench to loosen that side plug on the transmission. You also can likely find a good exhaust system from the muffler back at the wrecking yard also. Seats are also a wrecking yard option, I know the Plymouth/Dodge neon seats will almost bolt right in, but they put you a couple inches higher than normal, there are others that members here use, but I cannot recall what they are, one of them might be Rodeo seats. Air pump would also be a wrecking yard part. I know nothing about down draft carbs, there are others on here that might be able to help you with that, I live across the river in Vancouver, but I have sorta moved away from 720s, but I still have a couple of them ATM, a 1980 datsun 720 dually diesel, and a 1982 720 diesel that is likely going to be for sale in the next couple weeks. I just noticed that your 720 is a 1980 with an L20b, a weber carb might be an option, you will likely get more HP with one also. 1 Quote Link to comment
datzenmike Posted August 19, 2013 Report Share Posted August 19, 2013 As these settings are unknown... 1/ Check and set your valve lash. An over tight valve will play havoc on your idle and can eventually burn a valve. Set on a hot motor. 2/ Check and set your ignition timing, check/clean your plugs inspect the wiring cap and rotor. 3/ Now after 1/ and 2/ you can adjust your idle speed and mixture. 3/ remove the EGR valve and wire brush it clean. The EGR valve should be closed at idle but years of exhaust deposits can prevent it closing and ruin the idle. 4/ look around for mystery hoses that are not connected or broken/cracked. Quote Link to comment
arizonajones Posted August 19, 2013 Author Report Share Posted August 19, 2013 Thanks guys. This really helps me organize my to-do list. Semi-related question: Does it make a substantial difference in performance or my ability to pass emissions if I don't have the air pump assembly intact? Quote Link to comment
wayno Posted August 19, 2013 Report Share Posted August 19, 2013 Thanks guys. This really helps me organize my to-do list. Semi-related question: Does it make a substantial difference in performance or my ability to pass emissions if I don't have the air pump assembly intact? If they lift the hood in Oregon, your likely going to need the pump even if it passes, but I don't know the laws over their. :mellow: Quote Link to comment
arizonajones Posted August 24, 2013 Author Report Share Posted August 24, 2013 Quick update: --Still need to check & set valve lash. This video is great for anyone who hasn't done it: --I am currently shifting priorities, dealing with a non-functioning clutch. see separate post about clutch forks, master/slave in the 720 section. --Found out my EGR valve is shot. It was covered completely by crud, but even after a thorough cleaning, it's still immobile. Quote Link to comment
datzenmike Posted August 24, 2013 Report Share Posted August 24, 2013 Unless you need a smog test who cares? Better it not work that be stuck part open. How do you know it doesn't work? You would have to ride along under the hood and watch it, as there is no EGR at idle, full throttle or if the motor is cold Quote Link to comment
arizonajones Posted August 25, 2013 Author Report Share Posted August 25, 2013 Unless you need a smog test who cares? Better it not work that be stuck part open. How do you know it doesn't work? You would have to ride along under the hood and watch it, as there is no EGR at idle, full throttle or if the motor is cold Unfortunately I will need to smog it. It seemed like it was stuck open, although, you're right I don't know that for sure without watching it. But it is stiff and rust damaged, so I thought that, if it is stuck open, it might correspond to an overly-lean mixture (even though the carb is adjusted very rich.) Sound plausible? Quote Link to comment
datzenmike Posted August 25, 2013 Report Share Posted August 25, 2013 There is no EGR at idle because the inert exhaust gasses would dilute the fuel and air to the point it wouldn't idle, or idle very poorly. Take it off and clean thoroughly with a wire brush. Maybe WD-40 or penetrating oil the moving parts. Suck on the small tube and the plintle inside should lift up. Quote Link to comment
arizonajones Posted September 22, 2013 Author Report Share Posted September 22, 2013 I'm doing a carb rebuild = Hitachi DCH 340. The truck's idle is very inconsistent and many times i have to side-foot the gas and break when I'm slowing down so it doesn't die. I found that the carb is missing the coasting jet & the coasting air bleed jet. .. just an empty hole where they're supposed to be... This is probably a good reason for crapping out while coasting to a stop, right? Also, I've contacted http://www.carburetorfactory.com to see if they'll sell me those 2 things, but I'd welcome any suggestions if there are better places to buy tiny carb parts. Quote Link to comment
slemers Posted September 23, 2013 Report Share Posted September 23, 2013 I have a Hitachi DCH 340 carb I removed from my 82 720. Good for parts but needs a rebuild. It was running when I removed it but I paid thirty bucks for it before I bit the bullet and bought a Weber. Shoot me a pm if you need/want it for parts or to rebulid. Parts are available but pricey if NOS. Slemers Camas,WA 1 Quote Link to comment
arizonajones Posted October 7, 2013 Author Report Share Posted October 7, 2013 UPDATE: I rebuilt the carb. All of its pieces are in place. I've re-installed it and it still idles like crapola, except now then it first starts, it idles way fast and when I tap the gas it dies. The main idle screw is backed out most of the way - btw. It's also very sputtery sounding - it was before, but I had hoped a carb rebuild might help. The sputter lessens and the RPMs lower if I put my finger over the hose with the suction that connects onto the air filter housing. Also, realized that there is no dash pot installed. I'm hoping someone can suggest where to focus first... Thanks. Quote Link to comment
datzenmike Posted October 7, 2013 Report Share Posted October 7, 2013 Only automatics had dash pots. A standard does not need them. The vacuum line to the air filter housing shouldn't leak. If putting your finger over it seals it then it's leaking.. find out why or where. For now seal it. There is a idle speed screw near the throttle cable. Adjust in to raise idle, out to lower it. Slightly to the front of the idle speed screw is the idle mixture screw. Before adjusting the mixture screw be sure that the valve lash is correct and set. Be sure the timing is set at 12 degrees BTDC. Engine thoroughly warmed up. Idle Mixture Setting. Turn in... idle may get worse or it may improve. If it gets worse turn out until it improves and speeds up and smooths out. Turn the idle speed back down. Turn mixture screw in until the idle gets worse, then out until it gets worse. Pick a spot about in the middle where the idle is the smoothest and fastest. Turn idle speed back down again. Repeat the in and out adjustment of the mixture screw until you cannot improve the idle and the speed is about 750 RPMs. Quote Link to comment
arizonajones Posted October 27, 2013 Author Report Share Posted October 27, 2013 Update: -Did valve lash (several were too tight) -Did timing - off by a couple degrees -Been in an ongoing process of setting idle. Runs good in cold, dies more often in warm weather. I have the choke set a little rich (it is really finicky with a leaner mix) -Found thermostat had died (gauge stayed in over C forever, & no heat from heater) -Replaced thermostat and also found the little straw that sucks coolant out of the overflow reservoir was missing (no coolant could get out.) Replaced the little straw and the whole thing got sucked up. Now that the thermostat is new, the gauge moves to the middle, heater works, idle seems less temperamental (need to do more driving tho). I'm starting to put pieces together -wondering - bad thermostat - allowing overcooling, engine never getting warmed up enough to open the choke fully. Sound like a reasonable guess? Or am I linking problems that don't relate? Quote Link to comment
slemers Posted October 28, 2013 Report Share Posted October 28, 2013 My Z-22 runs much better after the thermostat is open. But I would think that the choke would open fully even if the engine didn't get to full operating temp. Glad to hear it's up and running and things are improving. Sounds like changing the t-stat helped :) Did you figure out all of your vacuum line routing? Your carb rebuild sounds like it worked out well too. slemers Quote Link to comment
datzenmike Posted October 28, 2013 Report Share Posted October 28, 2013 . Update: -Did valve lash (several were too tight) -Did timing - off by a couple degrees -Been in an ongoing process of setting idle. Runs good in cold, dies more often in warm weather. I have the choke set a little rich (it is really finicky with a leaner mix) -Found thermostat had died (gauge stayed in over C forever, & no heat from heater) -Replaced thermostat and also found the little straw that sucks coolant out of the overflow reservoir was missing (no coolant could get out.) Replaced the little straw and the whole thing got sucked up. Now that the thermostat is new, the gauge moves to the middle, heater works, idle seems less temperamental (need to do more driving tho). I'm starting to put pieces together -wondering - bad thermostat - allowing overcooling, engine never getting warmed up enough to open the choke fully. Sound like a reasonable guess? Or am I linking problems that don't relate? The engine is designed to work at just under boiling 180-190 or so. The gas is not fully evaporated in the intake and is simply a foggy mist of droplets that absorb heat from the intake, hot cylinder and piston tops. In effect cooling the plug and the valves by evaporation. So if the thermostat is open, you may be running 130-160 and perhaps even less when very cold. It's understandable that the motor will seem under-powered and balky because you are not burning all the gas. The engine will act lean, and may even backfire out the carb. This is why a choke is used to force the intake air to evaporate as much gas as possible by dumping in lots of it.. If you have an electric choke it will be open. It's heated electrically and timed to open at about the time the motor is fully warmed up. Always run a good ($10+) thermostat and as high a range as required. If your cooling system is working properly you should be able to run in the Arizona desert in summer with a 190 and the air on. It's the rad's job to get rid of any excess heat. Running a 160 thermostat because it over heats in the summer is not really fixing the problem and the rest of the time your motor is running inefficient and cold. Quote Link to comment
arizonajones Posted December 17, 2013 Author Report Share Posted December 17, 2013 Hey guys, I'm throwing a bit more into this old thread.... Many thanks to Wayno for selling me a 720 stock tach! Now that I can really see the RPMs while I'm driving it's got me focusing on the old idle problems again... Here's the deal: --When its cold, it fires up and runs great at 1500 rpms and warms up in about 10 minutes, lowers to 1100rpms (still running great) --After about 30 minutes, when the choke opens most of the way, it craps out. Anytime it gets lower than 1000rpms at this point, it dies unless I keep my heel on the gas pedal. --I have the choke set pretty rich, which keeps it idling better for longer, but I'm getting 14.5 miles to the gallon, which is much worse than I've done in the past. So, I've rebuilt the carb, done valve lash, spark plugs, timing (although I need to check again). It's got a new fuel pump, fuel filter, and thermostat. At this point, I'm wondering if I need to rebuild the carb again or focus my attention on changing out every vaccum line and trying to figure out if EGR or anything like that needs replacing... Does anybody know if a Weber would pass emissions? (I have to pass them here in about a year.) Thanks. Quote Link to comment
arizonajones Posted April 2, 2014 Author Report Share Posted April 2, 2014 Hey! I know this thread is totally old news, but in the interest of closure I'm posting the end of the story: ---I replaced all of the vacuum lines and found a cracked one on the AB valve. Replaced a gummed out PCV valve. Replaced the idle-cut solenoid, which was shorting on and off at random. After I finished these last three things, it runs like a damn dream! Thanks to everybody for offering advice along the way. 2 Quote Link to comment
slemers Posted April 10, 2014 Report Share Posted April 10, 2014 What kind of mileage are you getting now? Hopefully it's in the 20's slemers 1 Quote Link to comment
arizonajones Posted April 23, 2014 Author Report Share Posted April 23, 2014 What kind of mileage are you getting now? Hopefully it's in the 20's slemers Finally in the 20s! After the last fill up it was 20.65mpg of only in-town driving. I'm hoping to get it higher if I can, but I'll take it for now. 1 Quote Link to comment
Charlie69 Posted January 8, 2015 Report Share Posted January 8, 2015 I totally missed this post. What a beautiful first generation 720. Please post more on this truck and please add lots of pictures. 1 Quote Link to comment
denmarkboy Posted January 8, 2015 Report Share Posted January 8, 2015 More pictures ! 1 Quote Link to comment
arizonajones Posted January 8, 2015 Author Report Share Posted January 8, 2015 cool. will do. I never started a proper build thread so I'll do that soon. I gotta get my pictures uploaded! :) -I'm actually getting ready to do the headgasket and paint the valve cover, so I'll start documenting! 2 Quote Link to comment
denmarkboy Posted January 9, 2015 Report Share Posted January 9, 2015 Now your cookin with gas , I searched for a while the other day trying to find your build thread .And now i know why i didnt find one . and what a perfect time to start, right before a repair , perfect ! 1 Quote Link to comment
Charlie69 Posted January 9, 2015 Report Share Posted January 9, 2015 AZjones just make this your project thread. We finally found this one! LOL I you have a word processing program on your computer Just star a daily or weekly journal on your computer and the picture names and or numbers as you go. When you have your pictures uploaded star a post and copy and paste your journal into the new post I leave a blank line between each picture for view-ability. Just a suggestion. Quote Link to comment
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