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Another idle / choke problem


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my 77 620 with l20b auto idles very high. I don't know how to set the electric choke. I've tried and still idles at 2k. With the choke flap open it's idling even higher. Isn't it suppose to have a lower idle with the choke flap open? When I step on the pedal the flap does close, sometimes all the way some times it stays open a bit. I haven't checked if I have 12v at the choke yet. My idle screw is backed out to the point that is does nothing anymore. I used the search function and saw the posts about the fast idle thing ivory part that has steps sticking. Mine is metal and not plastic, or really dirty making it look like a metal piece. It seems to be moving too. I'm not sure what to do next?? It runs hella rich, it starts to burn your eyes in a minute. I'll try and make a video tomorrow showing everything

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Lets assume the choke with it's fast idle is working just for now.



For the idle to be too high there has to be a extra amount of gas and air getting in. Here are a couple of other causes ...


1/  BCDD (boost controlled deceleration device) This is a very small 'carburetor within a carburetor' that adds extra air and gas to increase the amount available when the throttle is closed and you are slowing down from high speed. It is supposed to shut off long before you get to idle. The setting could be off. It's that round thing on the driver's side of the carb and has a rubber plug on it.




Under the plug is and adjustment screw. Turn counter clockwise to decrease the sensitivity of the BCDD. This will allow it to shhut off sooner.



2/  The secondary barrel is stuck slightly open. Could be dirt or rust in the throttle plate, piece of gasket from the air filter. Look down the secondary side with a flashlight. The throttle plate must be fully closed. Try pushing it closed with a pencil or with the linkage on the vacuum actuator on the rear of the carb.


3/  Vacuum or mechanical advance on distributor has stuck in the advance position. Try wiggling the rotor and see if it releases.  

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So today it ran at 1200 rpm right at startup but the idle screw is still pretty much unscrewed to the point that it does nothing. Might have to recheck as I was only there for a second. Nothing stuck in secondary throttle plate and it's closed. Forgot to check the BCDD (it definitely idles and stays at higher rpm for a while when throttle is applied). And I forgot to check distributor -_-. Still really rich but since it wasn't running at 2k I was able to breathe lol. here's the quick little video I got before my phone died

Photobucket troubles : please stand by p


Also: i recently changed the alt to a Mitsubishi Galant alt from a 4g63t. The fit was perfect and it was an IR alt. Mike I've seen you say that after 77, they started to have IR alts. The alt that was in my 620 was an IR alt with the S and L in the T connector, but i have the external reg mounted on the passenger side still. my charge light is lit but with a volt meter I'm charging at 15.5 at idle with nothing on :/ (lights, radio)


Also also: my horn relay was never hooked up till today. It clicks like crazy making the horns go off so I took the wires off the horns. I noticed it clicks and basically works when you turn the steering wheel or actually press the horn button. It clicks while turning even with the horn buttons taken off. Does that mean it's shorting somewhere ? It's grounded pretty good on the bracket in the engine bay.

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You need to disconnect the horn relay till you find the problem Horns work without the key on, so the relay may be on all weekend and kill the battery.


After 20 min check the choke is fully off by taking the top off the air filter and looking. Now look at the plastic fast idle cam. If the throttle closing on it??? or is it lifted up and out of the way???

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  • 2 weeks later...

Took steering wheel off and found a screw all the way out that held a copper piece that touched the back of the steering wheel. Screwed it in tight and voila , horn is good!

The dam video keeps getting deleted every time I upload it to photobucket. How else could I stream this 20 second video??


Another question:

These red and black wires are disconnected on both sides of my headlights. Anyone know what they're for ?


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