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1985 nissan 720 rwd california daily.


Toxicrain

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First post here I have gotten some good information from this site thanks to everyone in the community that comes together to help fellow ratsun owners such as myself.

 

(i will figure out how to get some pictures up here eventually so this makes more sense)

 

I have a 85' 720 st 3spd auto with z24 with 130k engine 180k total(first owner towed it behind rv some of its life) and I bought it roughly 8 months ago. Last owner replaced dist/cap wires plugs etc. and I installed a 32/36 Weber dgev around 3 months (2000) miles ago. Since ive had the truck I have had a fun time with it intermittently stalling and cutting out and random mishaps..It would run great for a week then it would cut out / stall and wouldn't restart for 10-15 min (thought it was a tank sock problem so replaced the whole tank) never gotten it towed luckily so far only pushed back to the driveway a couple times..

Replaced the fuel pump and filter 4 times each(after 2 decided to switch carbs and after the 3rd one did the tank). I did use stock pumps and they would run me around 2-3 months at a time until they would just *tick* louder and eventually no fuel in bowl..

Replaced the fuel tank and ran pump through the original line and ive also ran rubber fuel line that still connects with a tee to the carb and the return line has a valve to adjust fuel going back into return line.( opened and closed it during my process of diagnostics just to restrict the flow to go to the carb and not back into the tank)

I bought a carter #4070 pump suggested by many Weber owners and they had no complaints at all. I replaced the FPR and installed a 0-5 psi gauge. just deleted everything but egr until i get a plate.. Im pretty sure i have plugged all the intake ports with proper plugs and seal tape.and I have put the filter before the fpr, before the fuel pump(by the tank).

No matter what It reads 4.5 psi. no matter where i move the FPR dial or where i move the filter. (moved it in front of pump to see if it would restrict flow. unsuccessful..) I am out of options and have concluded to hoping that someone here can help me out. The truck will idle, gas is coming out of exhaust (I have muffler off because its shot going to glasspack it or straight pipe from cat-back.) I have not driven it yet because i dont want it to stall out on me again (drove out driveway got up to 3krpm in first gear and shifted, it leaned out and got pushed back.. I have carb cleaned the carb 3-4 times in between different starts and it idles fine and i do get the solid squirt so i know the acc pump functions so its not the carb itself. all im trying to do is get the pressure down to 3 ti tune it and hopefully get her back on the road again so i can begin doing the front suspension...

 

Really missing my $10 a day in gas rather than $20-25 driving the dads tundra.

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What type of fuel pressure regulator do you have?

And actually in what order do you have things?

The way I read what your saying is from tank, you have the filter, then the regulator? Then the pump?

 

The regulator should be after the pump..

I used a Holley low pressure regulator recommended by someone here and it works really nice... I think they are around $25... but I also read you have a return line... there are also regulators for that application too...

 

I am running the carter 4070 pump also and it was flooding my weber at 6.5 psi before I installed the holley regulator.... I think i have mine set at 3.5 now...

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The stock fuel line has a restriction in it just after he carb on the return line. It comes up from under the intake to the carb and turns around and goes back down as the return line. The restriction is very small so that pressure will build on the carb inlet side and can push into the carb. If the restriction hole is too large, gas would by pass the carb and simply go back to the tank over working the pump. The pump is self regulating at 2.5 to 3.5 PSI and will shut off between pumps or run slower. The small restriction hole simply allows gas that is heated near the engine to be returned and replaced by cold fuel from the tank nothing more.

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I got the mr.gasket 0.5-5 dial fpr and replaced it when I got the carter pump to eliminate that possibility. Sorry for the confusion the way its setup is tank/pump/filter/regulator/gauge/carb. Never ran anything before the pump other than filter to see if it would restrict the pressure.. no luck. Removed the stock rubber lines that ran from the frame rail to the underside of the intake/carb because they were made all kinked up with a lot of bends and I thought that was causing my original problem of no pressure at all(yet it was another stock fuel pump)

 

off the 2 framerail lines I built a tee with a needle valve on the return line and have it set it closed or half turn to allow the fuel to the carb and not back into the tank. I have tried running it without the gas cap and it doesnt make a difference. I did remove the gas canistervaccum hoses were already diss. all over the place so I cleaned it up and I put a breather on the end of the evap tube.

 

I did also try with my added rubber line from the pump ziptied through the bottom of the frame along the original framerail lines to the filter/reg/gauge/carb without my tee/ return line and it refused to run at all and it looked like it it was pressurizing with air by looking at the filter (only 1/4 full barely reaches the bottom hole using the spectre glass one) probably becausethe line was filled with air lol. when I hooked the line up to the tee it was having the same problem from when the original line was hooked up.

 

I haven't tried running without regulator some people have had it run just fine with the carter pump with the same carb so i might try that and just hope that the $50 gauge i got is accurate. 

 

I never knew that the pumps shut off /skip when they reach a certain psi. Im thinking i have to try a different regulator as people have said the mr.gasket stuff isn't that great.

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I never knew that the pumps shut off /skip when they reach a certain psi. Im thinking i have to try a different regulator as people have said the mr.gasket stuff isn't that great.

 

I don't think the carter shutoff but they circulate internally till the demand is there....

And yes the Mr gasket regulators are kind of junk... also those glass spectra filters are kind of junk too... the in/out seem to have very small internal diameter....

 

Try a wix filter not sure what size line you have so cant help with part number.

The wixs had the largest opening compared to hose size...

And the Holley 12-804 is a 1 to 4 psi regualtor, you need to get npt fitting to match your hose size too...

 

I use to have both the spectra and Mr gasket before and never did get my carb to run right....

 

Using the Holley and carter my pressure gauge holds at 3.5psi and at wide open it only drops to 3... weber is very happy ..

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using 5/16 line and i have access to fittings as I work in a hardware store.. looks like im going to have to settle and get the holley fpr and hope for the best. 

 

I have been using a 0-5 psi gauge but it was never specified if it is fuel safe... so as a backup i bought a 0-15 mr.gasket (only one i could find at o'reily and autozone) and I might switch it out and see if the gauge was bad or not meant for fuel or whatever..

 

Back when the truck was running right before it decided to have problems it stalled out on me twice and i took the filter off (was placed after pump back by the tank) and the truck would start right up and drive off... I know this is a bad idea as it can send crap straight into the carb but it got me home both times and I would just put it back on and the next morning it would take me to work with no problems for the most part...

 

Another problem is in the mornings it would drive perfectly fine and by the afternoon when i get off on hot days (85' and up) it will start up. idle, and about 50ft down the street it would lean out and not restart for 10-15min...And when I got it started I would get maybe a mile before the issue of leaning out no restarts I would just park and wait for the outside temp to cool down thinking its the fuel boiling or turning into vapor before the carb... worth a shot to see if anyone has an idea because Im at a loss on that one..

 

Havn't gotten her to run down the street and back correctly  since I put in the tank and got it to run it leans out like the previous statement.. pushed it back into the driveway twice now.. Im thinking its a vapor lock issue which I have no idea how to diagnose with the truck not running so I will come back and ask that later..

 

Local mechanic that I talk to has finally said that I should just dump it and get a yota LOL. Been through 10k miles of intermittent problems and so many hours of messing with this truck that I want to get it running for my own sanity and so it will be worth more than $500 to someone that sees it as parts or a project even though ive replaced almost everything but the engine/tranny itself.. almost a fully restored 720 at this point..

 

ill try to reupload the images through a different app so you guys can get a better understanding of the process that ive been going through.

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Unless you have a air fuel ratio gauge how are you determining that it 'leans out'? Could just as well be flooding making the restart difficult. You need about 3PSI on a Weber (you could always try less) and the return line is not going to regulate it at that.

 

The stock inline fuel pump should also have a filter in the bottom. If running something else it's advisable to have one before the pump to keep trash out.

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Unless you have a air fuel ratio gauge how are you determining that it 'leans out'? Could just as well be flooding making the restart difficult. You need about 3PSI on a Weber (you could always try less) and the return line is not going to regulate it at that.

To be honest I have no idea if it is leaning out or flooding all I know is that on some occasions it would refuse to start / run. I actually had someone install the carb for me and when i was messing around with the tuning on the carb i noticed he had the air/fuel about 5 turns out.... so reset it and havn't gotten any farther than the gauge telling me 4.5 and its running rich and I can tell this because gas is dripping out the exhaust.

 

I will keep the filter before the pump from now on or might add a 2nd one there or something. I'm not going to run a different pump than the carter because I got amazon to send me a 2nd one for free when it took a week after the delivery date for it to come 

 

I have looked at getting an air fuel ratio gauge but the ones im lookin at are like $300 and ive got $800 into it in the last 2 months and havnt been able to drive it 10 miles... unless there are ones that are reasonable. It looks like I have to put it in the spot the o2 sensor goes I read somewhere when looking into this which isnt a problem because ive already screwed off california emissions with a weber and vaccum lines delete.. dont have to smog until aug 2019 and ill probably be out of state by then if the truck still runs or whatever.

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They NEVER need to be out 5 turns your jets are too small. Below 1/2 turn they are too large. Too small won't be the case... it's just set wrong.

 

Read this...

 

https://www.racetep.com/manufacturer/carbs-and-injection/weber/weber-carb-tuning-and-technical-info/jetting-and-tuning-downdraft-and-sidedraft-weber-carbs.html

 

 

Don't assume. Make sure your engine is tuned up, valves set, timing set, no vacuum leaks etc. Follow the suggestions before even starting to set the Weber up.

 

 

 

Just in case...

 

http://redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm

 

http://www.carburetion.com/Weber/adjust.htm

 

.

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There's something to be said for having the stock set up. It's easier to troubleshoot because it's known to work. Adding other components or modifying it throws it into disarray. For example the stock set up does not need a fuel pressure regulator.

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There's something to be said for having the stock set up. It's easier to troubleshoot because it's known to work. Adding other components or modifying it throws it into disarray. For example the stock set up does not need a fuel pressure regulator.

When I had my guy install the carb it was with stock pump and he suggested regulator so I got it to play it safe.. he was able to deliever me my truck and it ran solid for about a month until the issue of no start/stalling. My guess to why he had tuned it so far out was he never finished the job and left some vaccum leaks.. which i'm pretty certain ive tracked them all down but hopefully I can get some pictures up soon so you guys can double check it. I would just have my guy look at it but its stuck in my driveway and i live 45 minutes from him and idk if i honestly want him working on it whenit didn't get setup right the first time around..

 

I will also double check my timing and valves but I don't think it will lead to anything because they wouldn't just fall out of tune after awhile unless im wrong, I have gotten 2000 miles out of the weber and it did drive good when it wanted to other than the WoT issue and the issue when it was hot in the afternoons.

 

I wont have time until Friday to mess it with her so I want to get as many opinions/possibilities to hopefully be able to at least take her down to get a car wash if im lucky. and im going to go ahead and try the holley fpr and if it doesn't fix the issue ill just return it.. Ill look into an air/fuel gauge more as the process continues of trying to find out the main setback of it being over pressurized.

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85 720's are notorious for having intermittent fuel pump relays. If you are still using the stock wiring to power your new fuel pump, it could be the cause.

We were scotch locking the wiring at the relay to diagnose that in 1985!

When the guy was installing my carb he noticed that the power to the fuel pump was coming from some random source he couldn't even find so he tapped into a round harness thing( i will get a picture up eventually to help make more sense) which it runs off the ignition switch so i dont have a mounted push button or anything, and hooked ground up to the frame. Whatever the harness did for the carb is now just being used for the pump and the electric choke so its not using the original wiring to answer that question.

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https://s13.postimg.org/j5nd69kcn/Snapchat-1809636749.jpg

 

Showing my tee setup that I made coming from the frame rail line through filter/reg/gauge and into weber

 

https://s13.postimg.org/cf6vwvf7b/20180115_181838.jpg

 

Showing my canister removal and the evab tube breather filter.

 

https://s13.postimg.org/hteuvhz07/20180112_104212.jpg

 

Showing the replacement that I made from the original line that came up from the frame rail to the carb previously. up by where the return line meets is where I put the tee

 

https://s13.postimg.org/xew6frnwn/20180124_0949.jpg

 

Showing the tee itself that I made. you can tell that the fittings on the right for the return line is smaller and I have been turning it back and forth during the truck idling to see if it would affect the psi and no luck.

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https://s13.postimg.org/j5nd69kcn/Snapchat-1809636749.jpg

 

Showing my tee setup that I made coming from the frame rail line through filter/reg/gauge and into weber

 

https://s13.postimg.org/cf6vwvf7b/20180115_181838.jpg

 

Showing my canister removal and the evab tube breather filter.

 

http://s13.postimg.org/hteuvhz07/20180112_104212.jpg

 

Showing the replacement that I made from the original line that came up from the frame rail to the carb previously. up by where the return line meets is where I put the tee

Use the " hot link for forum button " and the pics will appear...

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20171224_110617.jpg

would be a lot easier if i drew on this one but you can see how the previous fuel line came up and into the filter.. You can also see some vacuum lines which I have then removed and its a lot cleaner but can also see where the electric choke and the fuel pump power as well coming out of the cut round thing properly sautered and heat shrinked so no loose connections there.

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