No idle for minutes after starting, hot or cold.

[hooptylife]

Hello! I'm trying to get a feel for this carburetor adjusting business and coming up short. I've read all the hitachi tuning threads i can find, but not after a few hours of fiddling still can't get my '79 620 to idle right after I start it. This has been an on-going problem for quite some time.

Every time I fire it up, whether its first thing in the morning or after an hour of interstate driving, for the first 2-5 minutes the engine refuses to idle by itself. I have to keep pumping the gas to get it started and to keep it running during that time.

 

With high expectations i adjusted the idle mixture and idle speed screws on the hitachi this morning, in accord with datzem mike's instructions. After struggling thru those first couple minutes just to keep the truck running, i was able to make the adjustments and the idle is smooth and quiet now.

But the start-up problem remains.

 

I played with the choke just to see how it worked, but that can't be my problem since it still dies even after the engine is warm/choke opemed up fully. At leadt that's my thinking.

 

Any ideas for me to try? I've got a long weekend and would really like to be able to solve this issue to make it easier to drive.

[datzenmike]

On a cold engine take the top off the air filter and look down.

 

You should see this, below. This is the choke trying to be closed. Work the throttle and it will snap closed...

 

 

... like this, below. The closed position forces a rich condition and also engages the fast idle system to speed the warmup.

 

 

After about 8 min of warm up the choke should be fully open like this, below...

[TDCTDI]

After just rebuilding one of those ornery bitches I can tell you that unless you've had & worked on it through its life, it's probably been "adjusted" & "tweaked" into an absolute mess. No amount of adjustments can beat starting from ground zero as a lot of the adjustments are made by bending the stop tabs. Get a rebuild kit & remove each jet, emulsion tube, & plug one at a time & clean all passages & then reassemble. I followed the given charts for each factory specified setting & after putting it back on, she fired up & ran perfectly after the pump filled the carb.

 

My carb had been sitting for 25 years so it absolutely needed to be cleaned out but none of the adjustments on mine were correct & probably would have been impossible to get running correctly even if it hadn't been clogged up.

[racerx]

if possible, buy a 32/36 weber. you set it and forget it.

[TDCTDI]

if possible, buy a 32/36 weber. you set it and forget it.

I disagree, while the Weber is a much simpler design & the common go to when someone is having issues with or doesn't understand their carb, they are much more tempermental when it comes to elevation, temperature, & barometric pressure changes. While the stock carb is more complicated, it is designed to be less affected by environmental variations. Save the money & learn about how yours works.

[kelowg]

Had this same thing, did compressor test to find two burnt/leaking exhaust valves.

[datzenmike]

Two sides.

 

Hitachi is hands down the best carb for a Datsun. Combining perfect fit, reliability, fuel economy, low emissions, good mileage, performance and what I like to call drive-ability. To agree with all the above, it is necessarily more complicated. Being more complicated it can be easier to have problems and have things go wrong. Dirt getting in is the biggest problem as it clogs the very small ports, jets, orifices and air bleeds, easily solved by changing the filters regularly and not letting the car sit so what passes for the fuel of today evaporates inside.

 

The Weber can approach but not better all of the above except performance. Being a larger CFM it has a slight performance edge but the secondary is progressive and does come in at about 2/3 throttle weather you want it or not. The Hitachi is vacuum operated and comes in only on engine demand. The Weber doesn't fit without a sometimes problematic adapter plate and gaskets, does not fit the stock air filter, so has a smaller filter, no ATC to prevent carb icing and no cold air system. There is no provision for ported vacuum signal for EGR (this is not the end of the world but won't pass an emissions check)  The Datsun air filter can be modified to fit by cutting to fix all but the EGR above. 

[hooptylife]

Thanks for all the help and education, i'll be ordering in the carb repair kit and giving it a go soon.

 

Also, I've been wanting to check the valves so it sounds like that'll be up next.

[banzai510(hainz)]

rev the shit out of the motor then put a rag over it and maybe and debris might get sucked thru the carb when rag is placed over it.(Mexican tune up)  or  you suck the dirt out of the rag

[hooptylife]

Crap. Things escalated quickly here.

 

Jumped in after work to go pick up my girl this evening and truck warmed up slowly but surely with lots of pumping the gas pedal.

BUT as i accelerated down the road I lost all power. It sounded to me like my dad's mower when a spark plug went out (new plugs and wires on the truck, though). The engine idles roughly now and just wheezes and misses when i try to accelerate. It'll move, and even sound moderately normal when i rev it. But there's no power behind the pedal once i put it in gear.

 

Not sure how to describe this better.

 

Would this be caused by a bad exhaust valve, kelowg? Could you point me towards where I can learn to check/replace those?

 

Any other ideas?

 

Man, such a down when something breaks after a weekend of "improving" this ole thing... thanks in advance to anyone who shares some knowledge.

[hooptylife]

Update: compression is good on all cylinders.

 

1 thru 3 read between 140-145.

 

Cylinder 4 read a bit over 150.

 

 

Tomorrow night I'll try adjusting the valves. Anything else i can check then?

[banzai510(hainz)]

put a timming light on there.

[datzenmike]

See post two. Check that this is how it is running. Costs nothing just a look. If not and we move on I'll assume it was fine.

 

Get the valve lash checked so that is eliminated.

 

Check the timing also so it is eliminated.

[hooptylife]

Alright, no access to a timing light tonight, but i did adjust all the valves. All of the exhaust valves were too tight, and a couple of the injection valves too.

 

datzenmike: the choke appears to be working just like you described.

 

banzai510(hainz): i tried the mexican tune up a few times in a row, no luck.

 

With no timing light my options are pretty limited right now. Any way to get it close without a light?

 

The truck still starts ok, but i have to pump the gas - if i just step on it it dies. Idle is rough too. Definitely something still going on in there...

What's my next step to narrow this problem down? I'll do my best to borrow a timing light tomorrow.

[racerx]

ignition valves?

[hooptylife]

*Injection valves.

[Roadster-ka]

Check cam timing!

[datzenmike]

Possibly.... but the cam doesn't adjust itself. Someone would have had to mess with it. For now, might be better to check a few more obvious things that do do out, like timing and carb adjustments.

 

 

Hoopy adjust the timing by ear. Loosen adjustment screw on distributor and turn clockwise to advance and counter clockwise to retard. When engine pings under load (full throttle) it's too advance... so retard it till it goes away.

[banzai510(hainz)]

injection valaves?  you mean intake.. the exaust is the usual ones that get tight when the valve seats wear to one they you wont be able to adjust them but by 79 I think they used harder seats

 

to me when you push on the gas and tries to stall out it the accel pump on the carb. See if it squirts gas in the main barrel when you cycle the gas. If squrtsgoo I say its ok. but should be a strong squirt.

 

next is the distributor can be out of adjustment.  timming or worn bushing(wiggle)

 

if points ignition the condensore might need be replaced or ck for loose wire/ground

[racerx]

Timing lights are fairly cheap.  Go on Craigslist.  See them all day for like $20 or borrow one from neighbors or friends.  If you do buy one, get the one with the dial on the back so you can easily do total advance timing.  You don't need those expensive ones like Snap On or digital ones but if you see them are garage sales or on Craigs list buy it for cheap. Good tool to have specially for ol skool cars like ours.

[hooptylife]

Alrighty, got some updates but no real progress.

datzenmike: i tried adjusting the timing per your recommendation Friday morning before work. When i was pumping the throttle to get it revved up (and listening for that ping you mentioned), the truck backfired really hard. I mean REALLY hard. So hard that it caused a recall of all personnel in this area of the military base where i live/work (because someone thought it was a gunshot).

 

Needless to say, got a timing light at harbor freight; one with the total advance knob like you recommended racerx.

 

Then tonight i discovered all my tools had been stolen over the weekend. Great.

 

Still wanted to try my new timing light, but i couldn't even get the truck to idle on its own. It kinda surges when i start it then dies in a few seconds if i don't pump the gas constantly.

^^This is new. It would idle on its own (roughly) on Friday.

 

Also, i had the thought that this might be something electrical, maybe a sensor of some sort, since the truck ran fine the day before all this started. Maybe?

 

Tomorrow i plan to remove the carb and clean it up as much as possible.

 

Oh, and banzai510(hainz) i get a strong squirt of gas into the carb when i blip the throttle. Looks like its getting fuel fine, i changed the fuel filter tonight just to make sure it wasn't that little thing. What exactly should i check in the dist. for wiggle? I'll check it out tomorrow too.

 

Any thoughts or suggestions will be considered heavily here, thanks again for your time.

 

 

Damn i miss my tool bag..

[racerx]

messed up about ur tools...

[datzenmike]

I did say 'ping under load' not revving it up by hand. I meant climbing a hill or accelerating. Sorry if confusing. Engine should also be warmed up.

 

You can probably set it close enough while someone cranks the engine over. Then get running at proper idle speed and check it. 

 

A back fire? Out the exhaust? would be a poor ignition. Badly worn points or a loose wire in the ignition power circuit. Out the carb? Over lean condition from revving it up specially if cold. 

[hooptylife]

The Backfire was definitely out the tailpipe.

Alright, thanks for explaining that datzenmike. I will set the timing like that today with the light.

So if this is pointing towards an ignition problem, I'm going to hold off on the carb work and look at the distributor, ignition coil, and wires in between. Any ideas what exactly i should be looking for? I've got a test light, multimeter, and some time..

[racerx]

set base timing first, check ur spark plug wires and make sure they are good, check dist. cap and rotor, if u have one, once these have been checked off then check carb. one of the first thing i would check is of the carb has a vacuum leak. after warm up, spray brake cleaner around base of carb, intake and hoses. listen for rpm going up. if it does then u have a vacuum leak. you can also download a manual for ur truck on this site under general discussion for specifications. good luck.