620 won't idle then idles too high (L20B

[MattC280Z]

I have a 78 620 which ran fine. However last weekend I noticed that when I stop at a red light or stop sign it wants to die. For that matter if the clutch is pushed or in neutral. It goes to idle then slowly dies off. Have to tap the gas pedal to keep it from doing so, then after driving around and let it set for about 5 minutes I go to start it again and it starts but then the idle shoots up like its being choked.

 

I've checked the choke plate, when warm is it supposed to be 100% open? Because it's like 70% open, I've also ran seafoam through it here recently. Last week I did take off the Vacuum solenoid that was a part of the AC bolted to the firewall but it wasn't even plugged in so I can't see that affecting anything, also I plugged the vacuum line that went to it.

 

Tried using the idle screw on the carb to fix the idle but it didn't seem to change a thing.

[banzai510(hainz)]

seems like you know what your doing.

I would do the idle mixture and speed screw but sound like you did that.

ck for tightness on carb and manifold

 

I would do a valav lash ck

then run the shit out of it with carb cleaner and put a rag ove it when its reved up to suck any dirt thru the passage(mexican tune up)

 

78 had more emissions so ck the hoses but I dont have a clue after that

 

ck the timming? using a light

 

 

70prcent open might affect the high end performance by chiking the air off. But at idle I think 70% open wouldnt do much

 

I think somtime running seafoam makes things worse. and loosen more junk up to plug things up.

[arizonajones]

check fuses too. I had similar issue with my truck at one time, and it was a cracked vacuum line combined with the 10amp choke fuse being burnt.

[datzenmike]

70% open is a problem, it should be fully open. In the summer engine heat alone will shut the choke off most of the way just like that. Use a $5 test light and see if there is power on the Blue choke heater wire on the back of the carb WHEN ENGINE RUNNING. If not the choke heater relay is possibly not working. This is usually the alternator not charging properly. Do you have charging issues? dim red charge light on? Hard to crank over and start?

 

Easiest fix is to ignore the relay and jumper the Blue choke heater wire to the Red idle cut solenoid wire right beside it. This will power the choke any time the ignition is on. But make sure your alternator is charging first.

[MattC280Z]

No no charging issues at all the alternator that's on it is about 3 months old. I have a test light I'll try that, would the choke RICH/LEAN knob affect anything?

[datzenmike]

Shouldn't. When warmed up it should be full off. Only way to be sure the power is getting there is to use a meter or a test lamp.

 

You could disconnect the choke... disable it, and this would fix some of your problem.... but when the colder weather starts you'll be right back here. It simply needs to be figured out and fixed so it runs right.

[MattC280Z]

Okay been messing around tonight and the idle is now super high. And I close the choke to kill it while I'm under the hood and after I close it there's a white smoke in the barrel under the choke

[datzenmike]

The 'smoke' is just vaporized gasoline... normal.

 

Part of the choke system is a fast idle. Fixing the choke... fixes the fast idle. Check the wire to the choke heater when running. Is there power??? If not, this is all that's needed to get the choke to turn off fully.

[MattC280Z]

I check everything last night, no power coming to the heater, I did check while the engine is running. So that means the relay is bad? I tuned and tweaked all of those screws. And finally got it calm at warm idle, have to check today when I get home on the cold start but since the choke isn't getting power I don't see it being too good. Also, when I tap the gas the plate doesn't close. I tried looking at the mechanism but it seems the connection to the throttle and choke plate is way down low and the actuator for the ABV which I did notice the nipple on it was snapped off and barely hanging on still. I plugged the vacuum line with my finger and it didn't seem to change anything.

[datzenmike]

OK so, we need a 12 volt power source for the choke now. 

 

 

Easiest fix is to ignore the relay and jumper the Blue choke heater wire to the Red idle cut solenoid wire right beside it. This will power the choke any time the ignition is on. But make sure your alternator is charging first.

[MattC280Z]

Okay I'll try that, I'm debating on figuring out a way to put a manual choke on it if that's possible

[datzenmike]

Again easier to fix it.

[MattC280Z]

Okay I had to let it sit overnight to cool off again, but today I noticed when I got hope that tapping the gas pedal doesn't close the choke anymore? What exact link makes this happen? If I close it by Hand then touch the gas it opens but it won't close as it's supposed to normally

[Tolkmod]

 jumper the Blue choke heater wire to the Red idle cut solenoid wire right beside it. This will power the choke any time the ignition is on. 

 

Holy crud d-mike, this is the answer I was looking for on my b210 lol  You just saved the day.

I think this is my idle issue problem, I just checked my choke relay, no power at all.  Might be completely burnt out.  Fuse is good though.

Have I said that you rock lately?  If not... YOU ROCK!  :thumbup:

 

 

sorry bout hijacking your thread OP  :angel:

[banzai510(hainz)]

ohm out fuse.

many look good visually

[MattC280Z]

Any of you guys have a picture of the link on the choke? It feels awfully loose to me but I may be paranoid. Like I said tapping the gas pedal doesn't make it close so I'm lost as to what the issue is

[MattC280Z]

Okay installed a SW tach last night. Looks like idle is at 1400 RPMs and still struggling at cold starts. I've tried to drop the RPMs but 1400 is the lowest I could go with idle/mix screws

[banzai510(hainz)]

idle /mix screw then theres the speed screw also. Unless thats what you meant by idle screw.

 

What about the timming?  maybe distributor needs turning retard.  get timming light.

 

auto choke there is s heated coil the round thing that moves a flat rod to the butterfly. its just c cliped or E cliped in there that why its slopy and loose.

One can loosen the 2 or 3 screws that holds it down and move the choke so it opens sooner or later,but I was never good at this.

 

Not to familiar with the stock carbs myself

 

just make sure vaccum advance goes to carb not the intake manifold as I seen soem people do

[datzenmike]

See posts #4 #6 #8 and #12. A SW tach is not going to fix this!!!!!!

[MattC280Z]

I have the choke heater on the fuel cut off solenoid like you said. The choke heater works now. It's not the choke coming off that's the problem it's that tapping the pedal doesn't close it. And if I close it by hand it won't stay closed.

[datzenmike]

You should up date when you fix things.

 

 

 

Remove the three screws holding the heater element to the choke lever...

 

 

 

In the back you can see the heating element. In front is a bi-metallic coil that unwinds as it warms up. As it unwinds it open the choke.

 

Check that the J shaped part is hooked over the choke lever when you put it back on.  Before tightening the choke heater, turn it counter clockwise (richer) and the choke should close. Leaner and it should open. With the carb completely cold turn until the choke is completely closed and snug the three screws. Pump the gas once and the choke should close. Start the engine. Choke should warm and open in about 5-8 minutes. If not enough choke turn counter clockwise (richer) and try again the next day when completely cold. When very cold weather arrives you may have to adjust even richer.

 

[MattC280Z]

My bad, I've adjusted the choke to where at warm its fully open, I think the arm that connects the fast idle cam to the choke has come unattached. its just hard to see down in there. I used the starting fluid test to see a vacuum leak and the rpms never went up.

[MattC280Z]

Also, and I wouldn't have noticed without the tach, if I put the truck in neutral. The Idle goes to 1400 as stated before, but when I push the brake pedal the RPMs begin to drop and if they hit 900 or so the truck will just die.

[datzenmike]

Well remove the large hose to the brake booster and plug the fitting on the manifold. If this prevents the drop in the idle then the booster is leaking vacuum.

 

My bad, I've adjusted the choke to where at warm its fully open, I think the arm that connects the fast idle cam to the choke has come unattached. its just hard to see down in there. I used the starting fluid test to see a vacuum leak and the rpms never went up.

 

Spray WD-40 around the fast idle cam and work the linkage to the choke up and down while holding the throttle part open.

 

 

 

 

Unexplained high idle can be....
 
Throttle cable too tight and won't let carb close fully.
Secondary barrel stuck just slightly open.
Idle speed screw not adjusted.♦
Choke on slightly or fast idle cam stuck
 
Check the choke is fully off when the engine has warmed up in (about) ten minutes. If the choke is even part on it will engage the fast idle cam. Check that the throttle lever is not closing on this plastic piece with the steps on it...
 

 

 
If choke is fully open and the fast idle cam engaged it may just be stuck. Spray WD-40 all over this area and with the throttle held part open work all the linkages to loosen and lubricate it. It should normally fall back out of the way so the throttle can close fully.
 
 
Now listen near the carb while someone turns the ignition switch on off on off on off (don't start it) You, should hear a soft clicking sound. This is the idle cut solenoid opening and closing to let fuel in to the idle circuit. Without it, you will never get the idle below 1,000 RPMs. If you hear it click at least it is working.
 
 
Unscrew the idle mixture screw carefully, don't loose the spring around it. Count the turns so it can be put back close to the same spot. Now unscrew the idle cut solenoid carefully and spray WD-40 in the hole using the red straw. (these two are connected, so this should dislodge any dirt in the idle circuit) Put the solenoid back. Now spray the mixture screw hole well with WD-40 using the red straw that comes with it. Put mixture screw back.
 
 
Before adjusting the mixture screw the valve lash must be set or confirmed and timing at 3-5Degrees BTDC

[MattC280Z]

Okay I can confirm the click. So the solenoid works, it's brand new the old one had detached from the needle inside and I think the PO adjusted the carb to compensate for that. Will check the cam when I get home, should the threaded part grab the cam when the pedal is tapped?