Help!... I'm ruining my new truck! :/

[mattykrab]

So, apologies if the obvious answers to my questions lie in existing threads. I've been searching here and there and haven't been able to figure out the puzzle that I've created.. haha

 

Short story of the truck:

 

I bought it and it was running fair. It started on a dime after one pedal pump, needed some revving to keep it idling while cold, but when it warmed up, idled perfectly. It had a bit of a hesitation problem where the engine sounded like it wanted to sputter out in what I guess you'd call the bottom end of revving..... and then it would pick up and drive fine after a certain rpm (no tach, dont know specifically). The problem was just from a stop and other than that it ran good, but did feel a bit like it should have more power than it did. I bought it knowing this and figuring it would be a fun problem to figure out how to solve and a definite starting point on learning about automotive work. I learn best from fixing problems!

 

---------

 

Fade to:

 

EXT. LOS ANGELES NEIGHBORHOOD STREET - DAY

 

Matt opens the hood of his 620 Pickup and looks over the deceivingly simple looking l20b motor. He notes what looks like crappy speaker wire coming out of the distributor cap and leading to a small 2-inch squarish box that's been shoddily attached to the driver's side wheel well. He shakes his head...

 

MATT

Whatever, I'll figure out whatever the

hell that is later...

 

He sighs.

MATT

I guess I'll just start by rebuilding

the carb. Maybe that'll fix the

hesitation issue... Then I'll figure

out what the fucked up looking

speaker wire modification is...

 

Matt looks over just in time to see the stray dog finishing up a stream of urination on his passenger side tire. The dog trots off proudly, still dripping a bit as he prances over Matt's small pile of tools on the edge of the sidewalk.

 

MATT

Hmm...awesome...

 

The poor automotive amateur grabs a soiled 12mm wrench and reaches into the engine bay of the Datsun 620. He begins his simple quest: to loosen 4 nuts that hold the Hitachi carburetor down. How much will he learn? What will he completely fuck up? How much longer than he ever expected will it actually take to get off those 4 god damn nuts?? Only time will tell.....

---------------

 

So anyway..... I took the carb off and rebuilt it. Nothing looked out of the ordinary. Pretty clean. no visible clogs. almost every screw head was worn from some guy's undersized screwdriver, so it had obviously been taken apart a bunch. I carb cleaned the living shit out of it, replaced all the gaskets, but I actually kept the old accelerator pump because it looked better than the one in the rebuild kit! the kit looked to be about 20 years old. I scraped the old gasket off of the intake manifold. taking the same care i took when i scraped the old gasket off of the valve cover.....damn these stuck gaskets on this thing. Took a long time... didn't damage the metal too much. I put the carburetor back on.

 

At this point 2 major things have changed.

1) couple carb adjustments....I brought the idle mix screw back to it's rough "starting point" as suggested by most things i read online. 2 turns out from seated. When I rebuilt it, it was about 8 1/2 turns out! The idle speed was changed too. I figured I'd tune it all again from scratch. I adjusted to a great degree all the metal tangs as per the directions in the rebuild guide. Originally the high speed idle steps never lined up with the idle stop screw. Not sure why it was that out of whack but there was no way that i could ever be resting on a high idle step.

2) I stripped out a screw hole when trying to reattach the top portion of the carb to the middle. I cursed a bunch, but then I just decided to get a new sized bolt, re-drilled and re-tapped it and it all seems ok.

 

 

Here's where the fun begins!

 

I put the carb back on, pretty excitedly actually. I've fixed all the previously broken electrical connections for the fuel stop solenoid and the auto choke, and I've wired then back in to where they're supposed to be originally. the previous owner had done something indescribable to them... they didn't work. I attach everything to where it originally was, only having some confusion with the carb springs, but figuring it out eventually. Then I try to start it up and.... hmm.... taking a little bit to get fuel....and......bam! it fires up!..... and then it backfires through the carburetor! and i rev it some more and more backfiring!! I let off the gas and it dies completely. great...

 

some further tinkering doesn't do much of anything. I rebuilt it a second time.. this time blowing out all the passages and soaking the jets in cleaner.

 

It's current state is as follows:

 

I start it up and it idles. My tach multimeter reads between 29 and 33-ish (x10, so 3000 rpm? a bit high right?). It wont stay completely still, which i'm not sure is normal or unnormal, and I cant seem to bring the rpm down to anything close to the factory specified 600rpm without it wanting to die.

 

I'm now unable to start the car in what was previously (before rebuild) the correct dizzy position for timing. now it's rotated ALL the way clockwise and my light shows it dancing around 10-15 BTDC. (my timing mark seems a little more erratic than before). There's no way to make the mark reach 0.... it's either 10 or earlier!

 

it wont idle at all unless the choke is closed slightly. I force it closed by spinning the auto choke housing... about a 4mm gap between the wall and the plate.

 

My vacuum gauge now shows a vacuum around 13 Hg... I'm not sure if this means much though, since the idle speed is much higher than it was originally, but it was around 20 in the green zone before I started taking things apart.

 

SO! I'm at a loss! I keep trying things and keep expecting the answer to suddenly pop up but I'm getting very frustrated :( I hope that someone here has a suggestion or two about what I've messed up or what I can diagnose. It would save my life at this point. I'm enjoying the puzzle and the challenge of all this, but right now I really want to get it running again before street cleaning day!

 

THANKS in advance and sorry for the very lengthy post!

[datzenmike]

Vacuum should be almost 20 so there is a loss here. Adjust the valves. If that doesn't help check the carb base for a leak. Listen for any hissing sounds.

 

Timing should be around 10-12 degrees not 0

[datsun brat pack]

I have a 78 620 king cab i got the truck about a month ago and i stared to work on it and i was having problems with timing also .Come to find out they had the timing out 180 deg .So i reset the timing and in the proses i had to ajust the two pice coller on the disriburtor make sure to ajust that also or you wont be able to rotat the disributor to the right timing mark . Also make sure to pull vacum line from vacum advance befor u set the timing i hope this helps you out.

 

 

[mattykrab]

Hmmm...there's kind of an overall hissing noise that my neighbor attributes to being just the carb in general. I haven't done anything to the valves before or after the This carb rebuild attempt, which seems to have caused all the problems

 

my main question is why would my dizzy position have changed so much? Before the rebuild, 10-12 degrees was more toward the counterclockwise end of the adjustment range and now 10-12 is practically all the way on the clockwise end.

 

Is it normal for the timing mark to jump around a lot? Is that just caused by a changing vacuum from the advance?

[mattykrab]

What do you mean "adjust two piece collar" Datsun brat pack? Maybe I screwed it up by pulling distributor halfway apart and putting it back together wrong? Hmmm...

[banzai510(hainz)]

thats a nice truck you better figure this out

 

olddatsuns.com

 

read up there!!!!!!!!!

[mattykrab]

...you better figure this out...

 

 

Haha thanks. I cant find any leaks with propane or carb cleaner. I may try to reattach the carb sans heat riser to see if it changes anything. I hoping something is going to suddenly become clear :/

[mattykrab]

well I just wasted a bunch of time shortening all of my carb mounting bolts with a grinder only to find out that the carb wont fit flush onto the manifold without the broken spacer because it collides with another part... Oh, the slow learning process :/

 

So now I'm attempting to jb weld the crack in the spacer..hoping that my leak was coming in through there because it is broken after all. I'm really confused about something though. Why did the rebuild kit come with a handful of carb base gaskets, but only ONE actually has a seperate hole for each barrel? The other base gaskets just seal around the outside but not between the barrels. I feel like there should be two (for the top and bottom of the spacer) to seal this area, otherwise there's a gap, which was very evident in the burn marks on that part of the spacer when i pulled it off this last time. Anyone know what I mean? Am I wrong?

 

 

 

[banzai510(hainz)]

if adapter is cracked it will not idle as I had this happen to myself.These are the thin 1/4 adapters. they are famous for cracking cause people over torq the nuts. You dont need much

 

I dont get why you grinded the bolts?????????

 

the base gasket doesnt need a separation between both barrels.yes you need a gasket on base of manifold then on top with the carb. I use the old gasket and make new ones with a sheet gasket material. The grey stuff. it just a little thicker.

 

 

good luck as the later L20 id you have the intake and exhaust that are bolted together are a Mofo to ever take out. if you have to take it out.

 

PS L motor are EZ. just the later ones are full of emmission stuff and it hard to get at the nuts and bolts.

[mattykrab]

Oops.

[mattykrab]

Heh... Well I shortened the carb studs because I wanted to try fitting It one without the spacer. They were too long and the carb wouldn't seat... Didn't end up working. And I just repaired the spacer :/

 

I may have reversed the red and green wires on the ignition! I switched them to test and now it runs without backfiring while revving... Hmmm. I'll have to figure out exactly why made it act that way eventually.

 

I still can't get it to idle slowly. It wants to die at a little less than 3000rpm. And the dizzy is twisted ALL the way clockwise... In any other position it won't run. Vacuum is still lowish around 15"...

 

I drove it around the block a few times to test a steering thig I adjusted and when I parked and popped the hood there was coolant GUSHING out of an overflow tube beneath the cap! Haha. There's no reservoir though because it was a shoddy custom job, but it's the first time I noticed since I bought it. Engine Seemed fairly hot also and the temp gauge on the dash said cold. Hmmm...

[banzai510(hainz)]

My mistake

I thought you had a weber DGV carb on there.

The spacers are fonolic for heat I guess.

 

Once I remove a stock carb I always put a weber on there. So dont have experience with putting a stock carb back on as those gaskets always get struck together and tear.

[mattykrab]

My mistake

I thought you had a weber DGV carb on there.

The spacers are fonolic for heat I guess.

 

Once I remove a stock carb I always put a weber on there. So dont have experience with putting a stock carb back on as those gaskets always get struck together and tear.

 

 

Once I learn a little more about all this I'd love to go to a weber... Although I guess it can't pass emissions without the stock carb can it?

[datzenmike]

Engine Seemed fairly hot also and the temp gauge on the dash said cold. Hmmm...

 

 

The temp sender is on the thermostat housing, a yellow wire I believe. Ground it with the key on and the gauge should read full hot if working. Maybe the wire is off?

[mattykrab]

. Ground it with the key on and the gauge should read full hot if working. Maybe the wire is off?

 

ah good info. I appreciate it, mike! I figured that was the sender... It's attached but I've been unplugging and plugging it a lot lately so maybe the connector is just dirty/bad

[fastdadd]

I still can't get it to idle slowly. It wants to die at a little less than 3000rpm. And the dizzy is twisted ALL the way clockwise... In any other position it won't run. Vacuum is still lowish around 15"...

 

try turning the dizzy to center adjustment the bring the motor to top dead center or 12 degrees even and the take the cap off and see where the rotor is pointing

[banzai510(hainz)]

watch this naked

 

near the end of vid I install a number of dizzys take note. Dizzy should be close in middle of the timming plate range.

 

however if you truck was running ok before I will assume its OK and wasnt from Previous owner selling you soemthing he coulnd fix or assembled wrong.

 

http://www.guba.com/watch/3000024223/Hainz-Datsun-L-Series-Engine-01-Timing-Tare-down-and-Rebuild

[Skib]

watch this naked

 

:blink:

[mattykrab]

try turning the dizzy to center adjustment the bring the motor to top dead center or 12 degrees even and the take the cap off and see where the rotor is pointing

 

 

so with the dizzy in center adjustment it looks like the rotor is JUST about to hit the #1 point. Of course that position doesn't run well... the better sounding position is all the clockwise, which is just more advanced I suppose. not sure if that positioning is normal or not.

 

Guess it's time to take off my pants and watch Hainz's video.... O.o

 

I just got back from driving it around. boy was my first attempt at toe-in alignment a failure! haha

[mattykrab]

http://www.guba.com/...own-and-Rebuild

 

Hey Hainz, I'm curious, whoever owned this truck before me obviously put a matchbox dizzy on, but instead of turning it 180 degrees to clear emissions and exhaust stuff, they pulled the matchbox off, mounted it to the wall, and spliced the cables with what looks like basic black speaker wire. It seems to work I guess but it just looks retarded (dumb, not timing related :P) and there's a open hole in the dizzy all the time. Is this problematic at all?

 

Also I haven't pulled the valve cover off again to check marks. I didn't imagine it was possible to skip a tooth, but it certainly seems like the timing was proper before my carb rebuild, and now it seems like the dizzy rotation is a bit off. Still i'm not educated enough yet to make this guess. :P Back to the web....

 

Thanks for the video link!

[datzenmike]

watch this naked

 

 

:blink:

 

 

[mattykrab]

I really have no idea how to respond to that, Mike. lol

[Guest DatsuNoob]

 

:rofl: :rofl:

 

...so any updates on the truck? I remember backfiring outta the carb on my L20, pretty rad when they blow flames huh? :D

[mattykrab]

...so any updates on the truck? I remember backfiring outta the carb on my L20, pretty rad when they blow flames huh? :D

 

well i switch the red and green wires on the dizzy ignition module and it stopped backfiring. No clue how i managed to reverse them! Now I just cant get it to idle down. Initially it would only run with the choke mostly closed, so i started spinning the idle speed screw in while spinning the autochoke open until it evened out and stayed alive with wide open choke. Unfortunately, the speed is above 2000rpm and anything less will make it sputter out. I replaced the cap, but autozone didn't have a rotor. I still cant find any air leaks :/

 

 

 

[banzai510(hainz)]

2k RPMs your running on the main jet circut. Esp if you have the spedd screw turned in alot.

 

sometimes if carb is rebuilt or messed with the mixture screw at the base of the carb is out of adjustment.

 

I say start w/1.5 out from fully in. do half turn increments. till it idles soem what. If this dont idle the idle jet could be plugged or the 12volt wire fell off the idle cutoff selinoid.