Hard start when warm/stalling

[JWray707]

So, I just replaced the carburetor in my 1978 620 L20b and have been trying to tweak the tuning so it's on point. It's idling fine...the issue/s im having is that its not wanting to start when the engine is warm. Starts no problem when it's cold, just cranks when it's hot. This issue was starting to happen before I replaced the carb so it probably wouldn't have anything to do with the new one, right?

The other issue is that when it's running and I lightly press the gas it stumbles and dies. If I punch it, it's OK, only when I lightly press the gas does it have issues. Haven't taken it on a full test drive yet...I don't want to get stuck waiting for it to cool off.

Could this be a symptom of it running lean?

The vacuum lines are all hooked up (as best I could with diagrams) the ones that I couldn't find where they go are plugged.

Any help on this would be awesome!

[datzenmike]

Timing set to 12 degrees?

Valve clearances checked?

 

 

Assume this is an Hitachi carb and not some POS from China???

 

RESTART when hot....

When warmed up check that the choke is fully off or open.

When hot after shut of,f take the air filter off and see if gas is dripping inside carb.

Check the sight glass on the front. Is the fuel level at the mark or over filled.

There should be a fuel line from the tank to the fuel filter and beside it a return line to the tank. Is there?

Is the engine over heating? running hot?

[racerx]

Have u checked ur plugs?

[JWray707]

Timing set to 12 degrees?

Valve clearances checked?

 

 

Assume this is an Hitachi carb and not some POS from China???

 

RESTART when hot....

When warmed up check that the choke is fully off or open.

When hot after shut of,f take the air filter off and see if gas is dripping inside carb.

Check the sight glass on the front. Is the fuel level at the mark or over filled.

There should be a fuel line from the tank to the fuel filter and beside it a return line to the tank. Is there?

Is the engine over heating? running hot?

Yes its a Hatichi.

Haven't checked timing or clearances, have to look into how to do that first off. Hah. Would carb adjustments have changed those two things?

Choke is fully open when warm...closed when cold.

I will have to check float bowl drip tomorrow. There is fuel pumping in there though.

Fuel level in sight glass has been a bit under the mark line.

Yes, both fuel lines are there. I did just install a in line universal fuel filter between in line fuel pump and carb. Would that be effecting fuel distribution into carb?

The engine was running hot for a second before I started tuning the carburetor (high rpms?)

It is running a bit hotter than it was before changing out the carb. Currently staying halfway in between low and high. Used to run even a bit lower than that though.

[JWray707]

Have u checked ur plugs?

Started to, then realized I dont have the right socket. Checked as in...for spark or color or just in general?

[JWray707]

I did drive it around the block earlier up a hill and its definitely struggling on the first press of the gas. It will pick up after the first second of acceleration. Havent really opened it up in gear though so I dont know how it would do at higher speeds. Also been running it intermittently to watch temp and it seems to be staying pretty even.

[JWray707]

Have u checked ur plugs?

I was pulling them to check for color but I guess checking for spark wouldnt hurt either, huh?

[racerx]

You asked if running lean. One way to tell is checking your plugs. Of whitish color then running lean. But you should check your timing first, base line, always.

[JWray707]

Just checked the timing and im not seeing a mark for timing. I do have the timing mark tab, but not sure exactly what im looking for on the wheel. Seems like it should be a notch from what im seeing on other posts...is that right?

[JWray707]

You asked if running lean. One way to tell is checking your plugs. Of whitish color then running lean. But you should check your timing first, base line, always.

Yes, that is why I was going to pull them, checking color. I shall check that tomorrow after I (hopefully) get the timing figured out. Thank you.

Saw something about checking the plugs after driving and not just when idling. Would that make a difference in determining fuel mixture?

[racerx]

Yes, you can check at idle and also after driving for like 10 min. Or so. Be careful, plugs and engine area can be hot. If you are looking for manuals, someone here downloaded a bunch.

[JWray707]

Cool, thanks again!

Downloaded a Haynes online manual, I'll check that out for setting timing procedure. If nothing there I'll check back here for a original manual. Need to buy a physical original manual soon...I know it will come in handy!

[JWray707]

Not finding anything on setting timing. Hoping I don't need any specialized tools...

[Crashtd420]

Checking timing is easy. . You will need a timing light. You Can Rent for free from autoparts stores.. there is a notch on the crank pulley that will line up with that timing mark tab.... I used a small dab of white paint or even white out to make to notch more visible...

[datzenmike]

If it runs then it's getting gas. If getting gas there should be lots in the carb for a restart.

 

 

Check for spark on hot restart. It's remotely possible you coil is over heating and not working. Confirm this first. Just pull any plug wire off and put a plug in the end and lay on a grounded surface. Turn engine over with the starter.... got spark????

 

 

There should be a small notch in the back of the pulley closest the timing scale. You may have to use the timing light flashes to see it.

 

Best to have timing and valves set before setting the idle mixture.

Set you idle mixture while engine is running and warm. There are two controls for this, the idle speed screw which just opens and closes the throttle, and the idle mixture which increases and decreases the gas that gets into the idle circuit. Get the idle stabilized and as low as possible with the idle speed screw. Now turn the idle mixture screw in or out to find the fastest smooth running position. Idle should have gone up so turn idle back down with the idle speed screw. Adjust mixture screw for fastest smooth idle and turn down the speed. Repeat as many times as needed until you cannot improve the idle quality and the idle speed is 750-850.

 

You can 'read' your plugs only by driving it. Plugs should be tan light brown but there is a lot of is a lot of interpretation. Generally if very dark or black you are burning oil or running too rich. Very light or white you are too lean. A part blocked primary jet is the usual cause of running a bit lean. A flooding carb will cause over rich.

[banzai510(hainz)]

get a dam imming light!!!!!!!!!!!!!!!!!

shit just turn the distributor and see if it starts ezer.

 

 

olddatsuns.com tech section

[racerx]

One of tools u will need for our datsuns is a timing light. Real cheap.

[difrangia]

Your profile shows you are probably working with a 78 model 620 pickup. If so, and it has original electricals, it should not have a coil as it will have a remote module electronic ignition system. On that little fellow, the module is inside the cab on the right side kickpanel up beside the glovebox. If you don't have spark after warmup, you might check the module out and the wires going to the module. I had a problem with either the red or green wire but the intermittent break was at the little junction box mounted on top left of radiator. I wound up replacing the original module with a $15 GM unit and haven't looked back. 

[difrangia]

My bad. There is a coil with the electronic system. I should have added,that you might check out the coil. I've had them go bad on my air-cooled VW in that they won't fire when heated up so like Mike added, check out the coil. I had a real time finding that module the first time up under the dash.

[JWray707]

Thanks for the advice everyone.

Turned the distributor and noticed a slight difference in idle, but still having an issue with stumbling on acceleration. Also there's been a slight dieseling when shutting the engine off. Checked the connections for that and there is 12v going to the solenoid. Must be something else.

Have to wait to do the timing with a light, as I don't have a ride to pick one up this weekend.

Will also check the coil and that module and wiring. Thank you.

[JWray707]

There's also one more thing I can't find anything about in diagrams or the manuals. (This is a photo before I replaced the carb.)

 

 

What is that little unit?

I know that T connection is wrong but what is supposed to connect there? I've been putting the vacuum for the AB valve on there.

That large tube is running from the master vac directly into the manifold.

[racerx]

What's your rpm, usually when rpm is too high and U turn off car, it will diesel, around, 800 rpm is good

[JWray707]

Don't have a way to measure rpm. Maybe the timing light will help with that. By ear, it seems fairly low though. It definitely drops when I put it in drive. Should it be more or less in idle than in drive?

[racerx]

If u can buy a timing light with tach or install one. When I start my car, w manual choke, rpm is about 1,300 depending, how much i pull, after a minute or so, it idles about 700-800 range.

[JWray707]

My bad. There is a coil with the electronic system. I should have added,that you might check out the coil. I've had them go bad on my air-cooled VW in that they won't fire when heated up so like Mike added, check out the coil. I had a real time finding that module the first time up under the dash.

I think I found it under the dash. Wiring looks ok, need to test I suppose. Do you know what the coil is for?