School me on the electric choke

[XavierBK]

Since it has been cooling down lately I've been having a hell of a problem getting my truck started. I know the choke isn't working right but I don't know why. It seems to "normally" hang open and it DOES NOT snap shut when I press the accelerator to the floor. In fact, if I manually close the choke it will, from tension with the little spring on one of the linkages, slowly open itself back up.

My question is.. should it normally want to open itself? If it doesn't snap shut, what do I check or adjust?

I was thinking maybe there is a problem with the choke relay, is this on the same bracket as the fuel pump relay? If I were to test it, what kind of readings should I be looking for on each pin?

I honestly don't have a lot of experience with carbs, let alone electric chokes so this is all a learning experience for me right now.

Thanks in advance for anyone who can shed some light on my problem.

[Davezilla]

Quick schooling on the electric choke...
If it's functioning correctly it works great, but if it needs an adjustment it can give you some fits... Best advise I can give you is to set it up either with the engine fully warmed up or completely cooled down. Since the mornings are just now starting to cool enough to make your carburated engine difficult to start up, this is a good time to set it up with the engine fully warmed up.
First thing we need to do is loosen the 3 screws that hold the choke thermostat in place loose enough that you can easily turn the thermostat, with the warm engine we want the thermostat to be fully open so let's move it to full open if it's not already, but since you said your engine is getting hard to start I'll assume it's already fully open so let's back off from the open position til you see it start to move to the closed position, then set it to where it's open again and lock it down. If the thermostat is working correctly, when it cools all the way down it should snap shut when you step on the gas or open the throttle from the carb and it's a done deal.
This of course is all that's needed if the thermostat is working properly and there's no binding in the linkage etc...

Now let's say the engine is fully cooled down and hasn't been started yet today, you can adjust the choke to the fully closed position and lock it down, then start it up and it should open to the full open position as the engine warms up and usually in about 5 to 10 minutes. When adjusting it cold you'll want it to snap shut when you step on the gas or open the throttle at the carb and you'll need to hold the throttle open while adjusting it so the lock out mechanisms won't prevent adjusting. You can reset the choke to open the butterfly valve by holding the throttle open and moving the valve to check for range of motion if needed, but the basic adjustment is to get it to fully shut, then lock it down, then open up the throttle while holding the butterfly valve on the choke open and release the throttle, now open the throttle again to make sure it snaps shut and you're done but you'll need to make sure it opens all the way once warmed up.

There's a vacuum operated choke pull off in the system that does exactly that... it pulls the choke open when you step on the gas to take off while the engine is still warming up, if the choke pull off isn't working you'll know because your engine may bog from the choke staying closed when you take off from a stoplight etc... You can test these with a vacuum pump to make sure they pull back under vacuum, but that's all there is to testing them, either they work or they need replaced.

The other part of the system is the fast idle cam which moves with the choke valve which allows the engine to idle at a higher speed during warm up to prevent stalling, this needs to be adjusted with the engine cold and at idle, so be sure you have access to this adjustment screw before starting your engine if it needs to be adjusted. The fast idle is usually set around 1300 rpm but check the manual to be sure.

things that can cause the electric choke to malfunction other than being out of adjustment is usually carbon build up in the linkages which can prevent the linkages to move freely, bent or improperly installed linkage rods, and if the thermostat is just worn out and will no longer move from full closed to full open and vise versa, but this one is a rare occasion since usually another adjustmsnt will fix the problem.

My final note on choke adjustment is that it's always easier to adjust them with a fully warmed up engine since you only need to open it enough to reach the full open position with no extra tension on the choke valve, then it won't matter how cold it is when the engine cools since there will always be enough tension to hold it shut as it warms up, and it'll always reach full open after the engine reaches operating temperature so no further adjustment will be needed. Yes, you can adjust it with a cold engine, but you may need to readjust it after it warms up if it's not opening all the way or not closing all the way on the warmer mornings.

[XavierBK]

Thanks for the info Davezilla, one question though, what do you mean by the choke thermostat? The choke coil? If so, how is it adjusted? I ask because mine is riveted on and doesn't seem like it is adjustable.

[luistone]

Thanks Davezilla for the post helped me to fix my choke.

Yes is the choke coil, the one riveted, mine wasn’t working but was carbon build up in the linkages and dirt that were preventing it to move freely. Got it running yesterday just cleaned the linkages and started to open and close freely, also check vacuum operated choke pull mine wasn’t working just connected the vacuum line and started working, mine is missing fast idle cam so need to accelerate manually.

[XavierBK]

I know the linkages are clean because I just rebuilt mine. I also know the pull-off is working because I tested that when I had the carb off for the rebuild.

[Davezilla]

Ok, I've been busy but here's the answer for the riveted on choke coils... You can drill out the rivets and replace them with the right size screws and nuts, you may need to use a bit of blue or green locktite to keep the screws in place but you'll end up with an adjustable choke coil.
If you're not comfortable drilling the rivets out you can also grind the heads off with a dremel and use a small punch to knock the rivet shanks out. If the rivets are pop rivets, they'll drill out easily with no worries about the bit slipping but the solid rivets require a really steady hand or just grind the heads off.
For the screw size, the M3's should go right in or you can use M4's at the right length but you may need to open up the holes a little bit with a drill. Use the lightest holding locktite you can get on the threads so future adjustments will still be easy to do.

[XavierBK]

Well, I pulled the carb from the truck and drilled out the rivets to check out this choke coil and I believe I found a problem.

First of all, I still don't see how it can be adjusted as there is a notch in the cap and a small bump on the base that the notch covers. You can see this on the base on the upper left side.

Secondly... I imagine the lever that the choke coil is supposed to move against should move somewhat freely, correct? If so, this appears to be my problem as mine is seized in place. I cannot move the lever AT ALL so that even kills the idea of installing a manual choke. The linkage attached to that part of the choke that runs down with the little nub sticking out by the fast idle cam has about an 1/8th inch of movement but that's it. It looked like there had been water inside my choke coil at one time as it was all corroded to hell when I originally popped the cover off.





At this point it's done as I said the hell with this thing and ordered a Weber 32/36. $250 shipped and hopefully no more headaches.

[Davezilla]

See if the lever inside will move at all when you hold the throttle open, if it doesn't move with the throttle open then you have a problem with your linkage binding or something else is preventing it from working properly.

I guess Nissan/ Hitachi doesn't want people to be able to adjust these chokes, but grinding off that little nub that goes into the notch in the choke coil housing would let it rotate and adjust.

But I must say congrats on getting the Weber carb... much more user friendly than the Hitachi not to mention they're a breeze to tune... you'll love it.

[XavierBK]

Nope, the lever doesn't move anywhere. With the throttle open and the fast idle cam clear of the linkages it is still completely locked in place.

[Davezilla]

Definitely something else wrong like a bent linkage arm that can be really hard to detect unless you have a good one to compare to or there's something in the way that prevents it from moving. Pretty much the only way to find the problem is to disassemble the mechanism one piece at a time til you find what's stopping it from moving, but since you got a new Weber on order I really won't go into all that unless you need this to run until your new carb arrives. I do still have my old Hitachi carb and can send pics of the linkage arms and rods as well as what they should look like installed if you really need to fix this one.