620 dying when driving

[Radiant-Designer]

Oh Ratsun, where were you in my hour of need???? first thing i wanted to do when my 620 was giving me issues was come on here and it was down....

 

 

Ok so last Wed i jumped in the truck and started her up. Put it in reverse and a few seconds and about 5 feet later it died... ok.... tried starting it again and it wouldnt start.... after a little bit I popped the air cleaner sprayed starting fluid in and it started and ran for a few seconds and died.... Ok so it must be getting spark, not fuel... the fuel filter is full.... I pop the fuel line off the carb and put it in a glass vase and use starting fluid again and start it a few time.... no fuel, so it must be the fuel pump. Call up a few auto parts stores and none have one in stock so I order it, will take about 5 days.

 

In the mean time I go and get an low PSI electric pump (not as cheap as I remember, it was about $46!) and mount it in the engine bay (I know thye tell you not to, but I didnt have time to try mounting it under the bed or anything) and nothing.... i read more and see its a "pusher not a puller" and all this... I hear it running, so to trouble shoot that I put a 1 ft fuel line from the intake on that to a gallon of gas and the other end into the vase, stll no gas, so it wont get gas from a foot.... yes i primed it... so the pump was junk. I take it back and of course they dont have another so I move up to the higher PSI model (I had a fuel regulator on the line anyway) mount it in the same location and TADA! started up and ran.

 

I drove it all the way to portsmouth, about 45 minutes away, getting up to about 50 mph at some parts. have dinner up there, go to the homebrew club meeting, and start headed home, I get 10 minutes away and it starts acting up. Chugging a little, bucking, and if I didnt put it in neutrual it would die. I could restart it and go a little further, but then it would ahppen again, mostly when I got into 3rd gear. Finally I called AAA and got it towed.

 

A few days later the mechanical pump was in and it took 10 minutes to put in. But the problem is still there, it seems to be intermittent. To me it seems like its not getting enough gas. I could start it and if I rev the engine in place no issues, I could keep the RPMS up for a while. and even drove it down the road, I got a mile away no problem till i jumped on the main st through the area and tried getting up to 45 or so, it seemed that even if I kept pressing the gas pedal it wouldnt do anything and then bucked and died. I pop started it and nursed it home.

 

Its a 77, with a weber carb. I do have a pressure regulator on it. Now the mechanical pump is back on.

 

I started going through it last night, replaced the fuel pressure gauge just in case and started putting a better fuel pressure regulator on it. One thing that I noticed when looking at the carb itself is that it seemed to rock, so I took it all off and the mounting plates the allen bolts that were on it, it seems that the lock tite didnt hold so well because a few of them were loose and it may be that it was causeing a vaccume leak. Would that be a possibility of the reason for my symptomes?

[datzenmike]

First, replace the fuel filter. It's cheap and easy. Being full of fuel means nothing, it could still be plugged or restrictive. If you haven't replaced it in the last 6 months, do so.

 

Plugged fuel line? Get a can of gas and strap it down good under the hood and run a line to the mechanical pump... see if that fixes it. Use all caution with gasoline.

[Radiant-Designer]

Thanks Mike, I did replace the fuel filter about 6-8 months ago, but for the $2-3 it would be easy enough to replace again. My next resort was to use a gallon of gas on the passanger floor. I already have neoprene fuel line throught he firewall for this, going to attach it to the fuel filter and then the pump. This way I will know if it may be something in the tank (which would b odd since it ran fine up until this point)

 

I forgot that when I was replacing the fuel line from the hard line to the bottom of the fuel filter (figure it hadnt been replaced in how long, maybe it is collapsing under sucksion) we did take the air comresser and blow back into the tank to make sure the line wasnt clogged or something. At least that was the thought.

 

I had the gas cap unscrewed slightly and could hear the air come out through the gas cap.

[datzenmike]

Don't carry gas inside the cab. Under the hood or in the back is bad eough but inside with you is very bad.

[Suspect]

I did the gas in cab before, ran the fuel line threw the rust hole in the floor to the fuel pump... figured it was a bad idea.

 

I have a similar problem with my 73 620. It runs good for a couple weeks, then one day it just wont get gas. When I was driving it daily, this was real frustrating. I found that forcing air (air compressor) from the fuel line before the fuel pump towards the tank would help. It must have a fuel hose collapsing or constricting because after you force the air one way, then it will be fine for a couple weeks.

[Radiant-Designer]

I figured if it was on the pass floor I coul dkeep an eye on it better. I have a nice heacy metal can that wouldnt tip over or anything, and I could always put another gauge on it to see if the preassure is dropping or something. Under the hood I can not see a good way to mount it securely. I may just go to the bed of the truck and tie it down.

[datzenmike]

Always look at worse case scenario. You might have your eye on it but what about some dipshit texting who runs you off the road? Or T bones you? Rear ends you? You do not want to take a gasoline bath in a closed cab while moving down the road. We want you around here for a long time.

[Radiant-Designer]

Always look at worse case scenario. You might have your eye on it but what about some dipshit texting who runs you off the road? Or T bones you? Rear ends you? You do not want to take a gasoline bath in a closed cab while moving down the road. We want you around here for a long time.

 

Awe mike, i think im blushing ;)

 

 

good point. I would have taken it down my street and around the roads here, where there is no traffic. but you are right, I dont kno whow many times I have though, "I would be smart if I did this... oh what could happen" and sure enough that one thing happened.

[moparvwfreak]

try replacing the gas cap. i had a cap once that wouldn't vent right and basically caused a massive vacuum in the tank and would not allow fuel to teh rest of the system. stupid later model plastic tanks...... also a stock pump is all thats needed for a weber, i knwo i have 2 weberd L20bs with stock pumps. they run fine. you should get rid of the regulator. its not needed.

[ggzilla]

that truck caught fire here, they had a gas can inside to feed the engine ... crikey. It was all over the news.

 

 

It's likely to be the regulator -- get rid of that thing. The stock pump is good for twice the HP of the stock engine. Stock Datsun pumps are excellent.

[Radiant-Designer]

Ok update, I didnt even need to bypas the gas tank. I replaced the regulator, the fuel filter, and when I was playing with the carb I noticed that it was a little loose, apparently the locktite that I used when I originally installed wasnt enough, or didnt cure all the way or something, I tookt he carb completely off , along with the mounting plates and re did all of them. The truck ran like crap, but it ran, took it out and if the RPMs were up it evened out....it died a few times on my way to town and back but only when I was coming to a stop.... looked it over againa nd took out some starting fluid and traced down a vacuume leak that was hidden (under another line, I had capped it but apparently in the investigation and so on it must have came off somehow), Now it runs MUCH better.

 

Aside from the obiouse fuel pump being dead, I believe it was the regulator. I noticed with the original one on there if i reved it up the PSI gauge dropped from 3.5 to almost 0..... so it must have been malfunctioning. I replaced it with a Holley I had from a VW project and i think that was the ticket.

 

As for those that say get rid of the regulator all together, I dont have an OEM fuel pump, the only one i could get was an aftermarket and I honestly dont know how many PSI it runs. I know the Webers need to be under 3.5 but I cant say for sure what the pump puts out, any ideas?

[ggzilla]

First, great work tracking it down.

 

You can meaure your fuel pressure. It's built into most vacuum gauges, or you can buy one for $10. The regulator is bound to go bad sooner or later, and the less parts the more reliable your car will be.