77 620 hitachi carb adjustments...I need Help!

[eliandzekespapa]

Actually I really need step by step instruction with pictures... I need to tune my carb starting with the re-build adjustments. What are the rebuild adjustment settings? I have a little experience with adjusting the twin S/U carbs on a 64 volvo 122 but i'm lost with this one... mainly because I cant see clearly what I'm adjusting. Can anyone give me a picture of the fuel/air screw so I can at least verify I'm adjustng the right one!?! 

[eliandzekespapa]

PEOPLE......I HAVE A BOOK ON ITS WAY FOR ALL OTHER TECH ISSUES, I NEED HELP ON A STARTING POINT NOW. THE BOOK WILL BE HERE NEXT WEEK AND I NEED THE TRUCK NOW. THE ONLY ISSUE I CAN SEE WITH THIS TRUCK IS THAT THE CARB IS WAY OUT OF ADJUSTMENT. SO I NEED A STARTING POINT(THE CARB WAS SUPPOSEDLY REBUILT SO...A REBUILD SETTINGS FOR THE IDLE/AIR SCREW), A PROCESS FOR FINE TUNING THE IDLE /AIR SCREW AND SOME PICTURES OF THE IDLE/AIR SCREW. ALSO...TO SET THE IDLE AT A CERTAIN SPEED...DO I USE THE THROTTLE STOP SCREW OR WHAT?

[datzenmike]

No need to capitalize, my ears hurt.

 

The idle mixture screw is the one on the base of the carb with the spring on it. Turning out increases the fuel mixture. The idle speed screw, also with a spring, is over to the left and partly hidden by a vertical linkage. Turning out reduces the idle speed .

 

The hex shaped unit with the red wire is the idle cut solenoid. With the ignition on you should hear a click sound if it is working. When on, the idle cut solenoid allows fuel down to the idle mixture mixture screw. If there is no power to the idle cut solenoid there can be no fuel for idling and it won't run.

 

With the motor warmed up and running and idle turned as low as you can, turn the idle mixture screw in until the idle quality drops. It may already be bad and if so turn out. Find a place where the idle increases and improves. Keep turning out until the idle quality drops. Back up to find a place about half way between. Usual;ly there is about a turn and a half where it runs well just pick a position in the middle. Likely the idle speed has picked up, so reduce the  RPMs by turning the idle speed screw out. Go back to the idle mixture screw and turn in till it stumbles, then out till it stumbles and set about half way between where it idles the smoothest and reduce the idle with the idle speed screw. Continue adjusting as many times as needed until you cannot improve the idle quality and idling smoothly around 750-850. This adjustment only affects idle and has NO effect on anything above that.

 

 

 

 

 

The large round black object is the electric choke heater. When cold the coiled spring inside holds the choke plate closed to provide a rich mixture to aid in starting. The electric heater warms the choke spring and it expands and uncoils slowly, opening the choke plate as the motor warms up. If you look carefully the choke heater wire is usually blue. Power is only on when the motor is running and not to be confused with the idle cut which is on when the key is on.

 

 

 

With the motor cold, depress the gas peddle once. The choke plate should snap closed over the primary barrel as in the picture above. When the motor is started the choke linkage also engages a fast idle cam to rev the motor to speed the warm up. As the motor warms up (about 8 minutes)  the choke plate will rotate open fully. If only part open check for power on the blue wire to the choke heater. Depressing the gas will disengage the fast idle.

[Hyspeedz]

Excellent post, as usual, Datzenmike!

[datzenmike]

Well I didn't want to write a book... :lol:  but that should get you closer and if there are any questions... ask.

[eliandzekespapa]

Thank you, very much datzenmike. You helped confirm that what I was doing was correct. Now I think that I have a vacum leak and some other issue.

 

I have a mechanic freind that is helping me with most of what I do to this truck and the basics are covered. The specifics of what direction to turn the screw to acheive which effect and which screw is what was much needed and very appreciated! Once again thank you. Until my book arrives... I'm gonna ask you! 

 

 

Oh and sorry about the caps...

[UkieDime]

Saved again by the Ratsun Forum and Datsunmike in particular. Just swapped my 620 cylinder head, intake and exhaust manifolds and carburetor only to STILL have a surging idle.

So I read this post this morning, came home and hooked up my idle cut solenoid which I thought was an anti dieseling valve.....3 minutes later my truck idles like new after 2 1/2 months.

Granted I did have a nasty intake vacuum leak along the way but sage  advice from this site again is.............priceless!

One high point of all my trouble was swapping my A87 head to my L20B in my dime-nice and less prone to pinging as advertised.

 

Thanks again, Nestor

[datzenmike]

So I read this post this morning, came home and hooked up my idle cut solenoid which I thought was an anti dieseling valve.....3 minutes later my truck idles

They are basically the same thing. Dieseling is just that. The heat of compression explodes the idle fuel and the motor keeps running with the ignition off. The idle cut solenoid shuts the fuel to the idle circuit when the ignition is turned off. NO FUEL... NO DIESELING

[Project Bandwagon]

Fantastic post Datzenmike! Thank you

[DanielC]

Make sure the valves are adjusted, the timing is set, and the engine is warm before adjusting the carb.

Getting a vacuum gauge, and hooking it to manifold vacuum will also help you adjust the carb.  Tune the idle mixture screw to highewst vacuum, while maintaining the idle speed.

[Project Bandwagon]

Just to be sure I understand correctly. Let's say you've got a "freshly rebuilt" carb according to the previous owner, it looks clean but the truck is running pig rich, so rich that you can't stand to be in the garage as soon as it's running.

I should have the idle mixture screw as far out as possible?
and the idle speed in the middleish?

It starts and runs, but it lopes really bad and is so fuel rich. also with the engine completely cool, I can't get the choke plate to stay open, i'd guess based on the threads ive been reading i should be looking at the high idle 

[datzenmike]

Forget the idle mixture for now. It can only be set properly once it runs properly.

 

The electric choke should warm up and shut the choke off in under 10 min. If carb was rebuilt it probably needs adjusting.

 

 

The round black thing is the choke and electric heater in one. Loosen the three screws and try turning it to the lean or clockwise direction When engine is warm. It should open the choke plate.

 

You might also check that there is 12 volts on that wire, but only when engine running. Without 12 volts the heater will not warm up and the choke will remain on.

[Project Bandwagon]

I think my main problem is someone didn't put this cam back right. Can I get a detailed shot of how it goes and which way the spring should have tension?

[datzenmike]

 

A choke linkage moves it into position when cold and depending on how cold and how much choke the throttle closes on higher and higher steps to increase the fast idle.

[5t341tH]

This guy knows everything!

I have a question for you datzenmike.

My L20 runs great once its warmed up but when it's still cold, stepping on the gas causes it to stumble and die/almost die every time. What I usually do to warm it up is tap on the gas pedal once and then start the car and let it warm up that way. Revs around 1K for maybe 3-5 minutes. After that it runs great. Can I adjust the electric choke somehow so that I don't have this hesitation problem?

[datzenmike]

A cold engine will run almost as well as a warm one, lacking power mostly. My L18 starts cold and can be immediately placed in drive and driven.... as it should from the factory. The gas 'mixed' with the air in a cold engine does not have a nice warm intake and combustion chamber to fully evaporate the fuel droplets and it will run poorly. The choke increases the richness of the air fuel mixture so that the engine does get a mixture close enough to 14 to 1 to actually run on. The rest just carbons up the exhaust pipe. In addition the choke at the same time operates a fast idle cam that revs the engine and speeds the warm up.

 

Your electric choke may be set a little lean but it can be adjusted. 

 

 

 

Take the air filter off when the engine is cold. Pump the gas peddle once and you should see the choke plate snap closed. (choke on) At the same time the fast idle cam will drop down and hold the throttle open on one of those steps. (ring finger below)

 

 

If that linkage is not free to drop down, the fast idle won't work properly, so pull the choke plate back to off and open throttle slightly to release the fast idle cam and check it again. WD-40 or carb cleaner can be sprayed over all the moving linkage parts to clean and lubricate them. Move linkages by hand to loosen.

 

 

To adjust the choke, loosen the three screws and rotate the black choke heater housing counter clockwise slightly to make richer. You may notice that the choke plate closes even further.  Once set the choke should automatically increase itself when it gets colder and decrease when it's summer.

 

 

This is the heart of the electric choke. There is a bi metallic coil that expands and unwinds when warmed, contracts when cooled. Behind it is an electric heater that warms it at a predictable rate and turns the choke off without you having to remember. That 'J' shaped hook at the end of the coil must engage the choke shaft in order to move it properly on and off. If for some reason you remove it, be sure you engage it before setting.

 

 

Setting the choke may require several tries over several days when it's cold. I just leave those three screws just loose enough to hold the choke adjustment but easily twisted by hand. Tighten it when you get it just right.

 

Fast idle should be 1,500 to 2,200 RPMs so don't be alarmed if it seems a bit high. If you have an automatic, lightly tap the gas to reduce the fast idle before placing in gear. The choke heater takes about 8 or so minutes to warm and shut off the choke (more or less) by then the engine should run and idle by itself.