Jwalth02 Posted April 24, 2018 Report Share Posted April 24, 2018 Hello people. I am new to this site but not new to working on trucks. Carbs still elude me so I'm looking for assistance. The best place I have been able to find information for my problem has been this site but still the problem is winning. I have a 1984 Nissan Datsun 720 with the 2.4. I let it sit in my yard for years before finally deciding to chase down the original problem. It was a fuel pump. When I replaced it the truck fired up and ran fine for the little I ran it. I decided to do a tune up wanting to use it for a work ride. I changed spark plugs (both intake and exhaust sides) after verifying the gap, distributor cap, rotor, and plug wires. I have verified the order of the wires to the plugs on the cap the only thing I am not sure on is which coil is the intake and which is the exhaust. Both are working however as I am getting spark on all eight plugs. The problem: now that I completed the tune up, changed gas, added seafoam, and all of the vacuum lines that were bad and verified their routing, the truck refuses to idle. I am hesitant to pull the carb to fully clean it as there are way too many moving parts and I would need a lot more time than I have to spend on it, however I have pulled the fuel cut off switch (which clicks with the key so it should be working) pulled the idle mix screw and shot carb cleaner through the cutoff till it came out the screw hole, pulled the float cover off and cleaned, verified fuel was getting to it, and tried to adjust the speed and mix screws to no avail. The only way to make it idle is to adjust the speed past the point it opens the throttle through the main butterfly. Though even when I do this it will occasionally just shut off (no sputter or nothing just cut out) The choke is working properly, getting plenty of fuel, but it will not idle. What am I missing? Or should I just get the aftermarket carb that I am seeing a lot of? Thanks for reading, I took pictures but I need to figure out how to get them on here. 2 Quote Link to comment
datzenmike Posted April 24, 2018 Report Share Posted April 24, 2018 Well welcome to Ratsun. You haven't mentioned setting the valve lash although you may have done so. Proper clearance (0.012" on all) is good or a strong idle. Ignition timing is also good. The '84 should be set at 3 degrees BTDC with a +- of 2 degrees. Again good timing = good idle. I can't stress enough that NGK plugs are the only ones you should use on Nissans. BPR6ES on the intake side and BPR5ES on the exhaust side. Do you have a round 6 wire connector on the back of the carb? and an O2 sensor in the exhaust manifold? To post your pictures you will have to use a picture hosting site (other than Photobucket) There are lots of them and free. You upload your pictures there and can arrange them in albums if you want too. When you need to post a picture you go there and copy the picture image information and bring it here and click the little green square just below the yellow happy face above your post. Follow the prompts and there you are. 2 Quote Link to comment
Dolomite Posted April 24, 2018 Report Share Posted April 24, 2018 You might try shooting some carb cleaner around any gasket surfaces while a helper keeps it running. If you get a stumble while spraying a specific area, chances are you have a vacuum leak. Recheck all potential sources of leaks, set valve lash and adjust timing, then go from there. Could be gunk in the lines, did you change the fuel filter? I recently had issues with idle and surging on a 510, a new fuel filter, valve and timing adjustment and it idles like a champ. 4 Quote Link to comment
Jwalth02 Posted April 24, 2018 Author Report Share Posted April 24, 2018 Thank you for your prompt responses, King, I have not set the valve lash yet, I didn't even think of that part yet as it ran before I changed plugs and all that. I will do it when I get home though. Is there a how-to on this site as all I have is a manual for an 82 (or is this similar), also the timing not really familiar with that so if there is one for that as well it would help me immensely. As for the spark plugs I made sure to get the exact plugs that were in it, which were the NGK's (which I prefer to run on all my gas stuff) the gap on all was around .3, is this correct? On the back of the carb I only saw one plug with two wires going to the electric choke and to the fuel cutoff valve, I did not notice an 02 sensor anywhere. Dolomite, the only fuel filter that I was aware of was the one inside of the stock pump which is gone and the new Facet pump I installed had the inline filter which I put in. Do these trucks have a secondary filter mounted on the frame that I am missing? I will try to get my pictures uploaded tomorrow so you can see exactly what I am working with and if there are any additional ones I can provide let me know. 1 Quote Link to comment
tr8er Posted April 24, 2018 Report Share Posted April 24, 2018 I've never heard of sea foam causing this symptom, but perhaps try connecting the fuel pump to a spare gas tank to see. At least eliminate the fuel quality as a variable. I'd also question the vacuum advance diaphragm. These commonly disrupt a good idle, but I can't explain why it broke when changing plugs, other than it sat for a time, got brittle, then got used and broke. Maybe. 1 Quote Link to comment
Jwalth02 Posted April 24, 2018 Author Report Share Posted April 24, 2018 tr8er, I pumped all the old fuel out of the tank before filling it with premium ethanol free fuel. I added the seafoam just to help clean out the system. Is that diaphragm on the carb itself? I will look in my book if I don't hear from you. Edit: never mind, vacuum advance is on the side of the distributor. I will check that in the morning with the rest of the stuff. 1 Quote Link to comment
datzenmike Posted April 24, 2018 Report Share Posted April 24, 2018 If the idle speed is set properly there is no vacuum to affect the vacuum advance. The vacuum advance signal is taken from a port on the side of the carb opening just above the throttle plate. It will sense ordinary outside air pressure. When the throttle is opened above idle, the throttle plate lifts to, and above the port and some vacuum is felt there. As it continues to rise, more and more intake vacuum is felt as the entering air pinches by it. At some point maximum vacuum is reached and then begins to drop off. At full or wide open throttle there is almost no vacuum advance. Again, if the idle speed is above normal, some mechanical advance can creep in and affect your base timing of 3 degrees. Idle should be 700 RPM +- 100 The two wire carb is the easiest to trouble shoot so goods news. The stock electric fuel pump has a filter in the bottom. If replaced with something else an in-line filter between it and the tank should be used. 1 Quote Link to comment
captain720 Posted April 24, 2018 Report Share Posted April 24, 2018 I made a you tube video on the valve lash, in the comments there is also a link to the service manual for the valve lash. You should be bale to find the video by simple clicking in my channel in my description here. 1 Quote Link to comment
Jwalth02 Posted April 25, 2018 Author Report Share Posted April 25, 2018 Ok, just got done setting the valve lash. Can't check the timing yet as I don't have access to a timing light. There were a couple of valves out of adjustment but that has been taken care of. Still no idle though. Well the picture thing isn't working. Clicked on the green square and put the html code from the hosting site and it won't let me ok it. What am I doing wrong? 1 Quote Link to comment
Jwalth02 Posted April 25, 2018 Author Report Share Posted April 25, 2018 Best I can do I guess... First that's the coils, which is intake and which is exhaust?Second this is what I'm working onWithout air cleanerSide of the carb with the plug and you can see where I removed the plug.You can kinda see the timing adjustment on the cap hereBetter viewLastly this:Sight glass on carb fuel bowl, is the level supposed to be at that dot? Occasionally it goes up to where it's plum full. Can this cause flooding? Browser was being stupid. Fixed. 1 Quote Link to comment
datzenmike Posted April 25, 2018 Report Share Posted April 25, 2018 The cap is marker I intake and Ex for exhaust. Follow the wires back to the coils. Now this assumes that someone has not mistakenly switched them. It really does not matter as they both do exactly the same thing and fire together at the same time. Yes the idle mixture screws sealed so the owner cannot mess up the setting. What I do is turn in or out till the idle falters then set about half way between where the idle quality is strongest. Now turn the idle speed down and do again, selecting the best strongest idle. Lower the idle speed and keep repeating untill you cannot improve on the idle quality and the idle speed is 700. I would definitely set the timing first but if you need this just to idle to set the timing you can repeat this after. Keep going there are still several things to try. 1 Quote Link to comment
Jwalth02 Posted April 25, 2018 Author Report Share Posted April 25, 2018 Ok, that makes me feel a little better as when I was swapping cables I mistakenly forgot which plug went to which coil and wanted to be sure I didn't screw something simple up, but if it won't affect it I won't worry anymore. 1 Quote Link to comment
DrvnDrvr Posted April 25, 2018 Report Share Posted April 25, 2018 Cool, you got it. 2 Quote Link to comment
captain720 Posted April 25, 2018 Report Share Posted April 25, 2018 As much as I hate to say this..... Just get a harbor freight timing light, it's like 20 bucks and I've had mine for over a year now. It works fine and hasn't broken yet (im honestly surprised). 1 Quote Link to comment
datzenmike Posted April 25, 2018 Report Share Posted April 25, 2018 If it's worth anything I think someone said the coil to the front of the vehicle is the intake. Like I said it really does not matter. Is that the fuel level??? That should really be at the dot on the glass. All the air bleeds and air correctors work best when the fuel level is correct. It probably won't affect the idle circuit but running may be compromised. 1 Quote Link to comment
Jwalth02 Posted April 25, 2018 Author Report Share Posted April 25, 2018 Yes that was the fuel level with it just sitting there not running. When it runs it goes up and down and occasionally fills all the way full. This can be corrected by adjusting the arm above the float correct? 2 Quote Link to comment
datzenmike Posted April 25, 2018 Report Share Posted April 25, 2018 Yes float need to be set lower so it closes the needle valve at a lower level. If it over fills it can easily dribble down into the intake totally messing up the idle mixture making to extremely rich. 1 Quote Link to comment
Jwalth02 Posted April 25, 2018 Author Report Share Posted April 25, 2018 Ok, I will adjust that tomorrow. I will be getting my hands onto a timing light as well so I will get that checked and get back with you for the next step. 3 Quote Link to comment
tr8er Posted April 25, 2018 Report Share Posted April 25, 2018 The float can be flooded as well. At least other carb floats can be. Which leads to flooding reservoirs. Do you still have your old wires? looks like you put in all new wires. I wonder if they are faulty. does it run if you rev it? then just die if you let off? BTW, Thanks Mike, My vacuum av. did fix my idle, but I was at a higher idle with he 38/38. different scenario for sure. I presume you to be right that that is not the issue here. 1 Quote Link to comment
Charlie69 Posted April 25, 2018 Report Share Posted April 25, 2018 He probably pump shit out of the fuel tank when he first started it before the tuneup and fuel change. Before resetting the float take the needle and seat apart and blow compressed air backwards out the inlet. It amazes me with the responses you have gotten. First it ran after changing the pump. This tells you timing, valve adjustment, and all the other things that have been sugested here for you to do is mostlikely not your problem. Change your inline fuel filter by the tank and if the stock carb has an inlet fuel filter inside it change that do as i suggested befor and clean out the bowl. Take the idle mixture screw out and blow through it with compressed air. Clean up the inside of the carb as best as you can. and put the top on it after checking and adjusting the float if necessary. Also try swapping the coil wire positions on the distributor cap. My 86 720 king cab idles rough if I get them wrong. Bad idle is usually vaccuum leak or plugged idle circuit or automatic choke out of adjustment. Try again to start the truck. Besure the truck is to operating temperature before doing any of the sugested fixes from other members. Good Luck I hope this will help! 1 Quote Link to comment
Jwalth02 Posted April 25, 2018 Author Report Share Posted April 25, 2018 tr8er, I do not have any of the old parts anymore... kinda kicked myself for that already. The truck runs great if I hold my foot barely on the pedal but as soon as I lift off it sputters and dies. Charlie, I have not located a secondary fuel filter yet, though the only one I knew of was in the stock pump which went away after I changed it to a new Facet pump which came with a filter that I installed. I have gone through the plug wires multiple times and every time I changed one to verify, it would not run at all. And I did have the engine to temp before I did the valve lash, and that's when I noticed the fuel level issue. I will take care of that later today and report my findings. 1 Quote Link to comment
banzai510(hainz) Posted April 25, 2018 Report Share Posted April 25, 2018 idle jet clogged? 1 Quote Link to comment
KELMO Posted April 25, 2018 Report Share Posted April 25, 2018 This may be out of left field but I am not sure if I read it all correctly. You said you replaced the inline filter that came with the new pump, did you find an inline filter prior to replacing this one? If not, there should be a plastic inline filter in the engine compartment...it will have both inlet and return on the top of the filter and I think it should be in the engine compartment toward the right front. Like I said, this may be left field but I'm not really a 720 guy just adding my $.02 worth. 2 Quote Link to comment
banzai510(hainz) Posted April 25, 2018 Report Share Posted April 25, 2018 MY 521 had a plugged idle jet (No idle but ran fine when I cyled the gas or stay running above 1500 rpm) I clean the jet it ran and not more than a minute it plugged again. Had to get a new filter 1 Quote Link to comment
Charlie69 Posted April 25, 2018 Report Share Posted April 25, 2018 Here is a drawing from the Nissan factory parts book. The fuel filter I am talking about is circled in red. 1 Quote Link to comment
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