720World

Little Trucks, Big World

Hey everybody!  I have a 81' king cab 4x4 with a 32/36 carb on it.  Everything is running just fine and I am very pleased overall.  However, being who I am, I always have to mess with stuff. 

 

I am tired of the way my truck acts when the weather is cold.  It starts fine, but since weber only has ONE step on their fast idle cam, when I hit the gas and the choke opens the engine rpms are so low that sometimes it dies.  There is about a 300 - 350 rpm difference in the idle when it is cold and when it is warm.  I've tried turning the idle up a little (900 rpm when warm) but I tend to get run-on when I cut it off.  I was wondering if anybody has installed some kind of idle switch to compensate.  I know that my old ford had a switch on it that would push the throttle a little when the AC was cut on.  If I could wire a switch up like that, I could just turn that on when the engine is cold.  Any thoughts?  Ideas?

 

Thanks,

 

Jared

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ANNOYED!  

First I want to thank everybody for your time and thought on this little annoyance of mine. I have driven it for the past two days and in 5 or 6 times of cutting the engine off it has had run-on once and very close a second time.  I did not mess with anything between the drives either.  Carburetor is set as follows:

Idle mix 1 1/4 turns out

Idle speed 1 1/2 turns ( about 800 rpms when warm and no lights or fan on)

primary idle jet 65

secondary idle jet 65

main 150

secondary 155

I can't remember the air correctors, but I didn't change them out, I think they are 160 and 170

fuel pressure steady at 3 psi

timing was set to 5 deg BTDC but I slightly turned it down so call it 4 deg BTDC

The truck runs wonderful and I get 20mpg around town, but RUN-ON!

The only thing I know to try is changing the gaskets.  Good thing its nothing serious, just a little embarrassing sometimes.  Definitely didn't think it would turn into such a long thread!

One thing I'd like to mention, often times when people put on a Weber, they cap the top of the Thermal Vacuum Valve.  This actually disables it from working, it needs a source of air to create a vacuum "leak" in order to properly work in limiting the venturi vacuum signal to the distributor advance and disabling the EGR valve during warm-up.  It really should be routed to the air cleaner assembly.  Since there's no nipple on a standard Weber carb filter plate, most don't connect it.  You should really install a small adapter by drilling a hole in the underside of the filter housing.  It doesn't have to be anything fancy, just a plastic elbow fitting with the correct sized barb to attach a vacuum hose from the TVV to the air cleaner.

Something like pictured below, and you'd just use a nut on the back side to hold it in place (with a lock washer of course)

OK I found my place! I have an 81 720 22z stick, with Weber 32/36 electric choke conversion. I too am trying to optimize my vacuum and spark advance. My question is in in regard to this drawing: What is the significance of the boost control unit, and the vacuum switch? I disabled them both. Now everything is plugged. All I have going is the vac port on the carb to the spark advance on the distributor, and the top port of the thermal vacuum valve going into the air cleaner. Acceleration is pretty good, but sometimes it doesn't want to start: specifically it cranks a couple times then hangs up- I fear that my timing is too advanced. I turned the distributor back, but I lost acceleration. Is there another way to connect my vac lines to improve my spark advance/acceleration?

I figured I would give another update just in case it helps anybody in the future. 

First of all I want to thank everybody for their input.  I really appreciate it.

I actually called weber and they said the dieseling was from the butterfly being open too far.  They said that you can't have the idle speed screw turned in more than 1 1/2 turns.  Well, I did all this, retuned the idle circuit once again.  I actually had to go back to a leaner idle jet, which is fine.  However, where weber has lost some cool points with me is still on the idle situation.  With the idle speed screw at 1 1/2 turns in, and the timing set at 5 deg BTDC I would only get 650 rpm.  That is with the engine fully warm and no lights or fan on.  The only way to get the idle up was to raise the timing, which I am now at 7 deg BTDC, I also turned the Idle screw in another 1/4 turn.  I have only had 1 case of dieseling in the past 10 days or so probably from the extra 1/4 turn, but I can hear some slight pinging when chugging the engine.  I'm not one to rant and I guess you cant get everything perfect, but Idle cutoff solenoid = total waste of money.  Plus, turn timing up for decent idle?  That is a terrible way to tune your engine.  I mean, how hard could it have been to get another 1/2 turn out of the speed screw?

Try adjusting your valves.When I put my weber on,I did a little adjustment,the idle screw was turned to far out,couldn't get it to set on cam when you first start.Took to a carb. shop,he fine tuned it but I had my wiring wrong,I had  the blue wire going to choke and idle soleniod,ran good but at start up had to pump to get to start,Tiger Racing said I had my wires wrong.I also looked in my 85 Nissan truck repair manual,it has the blue wiring coming from the choke heater relay to choke,red wire going to soleniod,that made my fast idle work.The kicker is,I bought a new remanufactured engine at the same time as my new weber,couldn't get the old motor and new weber to run right,had same problem you had.I also tried turning down idle to 850 rpm,it was starving for gas,not ideling right,so it's set at 1100 rpm and it runs like a buldog in heat from GEORGIA.on my last 2 tanks of gas,I average 17.1 and 17.3 and that's right for a 4x4.Your motor may need replacing,I have 23,000 on my engine and weber and the idle solenoid works great.

You shouldn't be adjusting ignition timing to tune idle speed, this is counter productive.  Do you have an aftermarket cam in this engine?

I'm not understanding why you feel you needed to go leaner on the idle jet?  You're having to open up the throttle plate more in order to get more velocity, which in turn creates more venturi vacuum, and pulls in more fuel.  But by opening the throttle plate you are transitioning to the main fuel circuit, which is why your idle cut off isn't working, it only cuts of fuel in the idle circuit.  If you've opened up the throttle plate past the idle circuit, you're picking up extra fuel that way, so then you have to adjust in your idle mixture screw to compensate...  Go with a bigger idle jet so you can close the throttle plate further, and then your idle adjustment will actually be adjusting the idle fuel, and your fuel cutoff solenoid will work...

You need a idle cut off solenoid,order one from Redline Weber,I use one on mine,idles and cuts off perfect,also check out my Weber conversion video and do your's like mine.On my 85,I run the blue wire to the choke,red wire to the idle cut off solenoid,your 81 wiring is different.

Hi Ya'l;l Weber owners,here's what ya'll are miising on your carbs,will make it idle good and no dieseling,had mine for 7 years,runs like a top.

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