X2 what ctubutis said. My truck for example: Summer = 0 pedal pumps; cool temp. = 1 pump; cold temp = 2 pumps...

 

So my father in law started it up yesterday after about 3 hours of sitting and didnt touch the gas. It started up. He let it run 10 min and drove it around. I started it up this morning. It took 3 times to keep it running but it just needed a littke more gas. I let it run 10 min and it idled down on its own, exhaust was running clear. I drove it down to the train and it seemed to run a little rough. Especially when I stopped. I was trying to pay attention to how it was running. As I was driving it felt like there was slight gerks or a slight lunge. Nothing major just hardly noticable. If that makes since? Oh and when I put it in drive the dash lights seemed to flicker. So starting and idling everything seems good now that I have an understanding on the starting. After it goes into drive it acts unusual.

All the hoses and everything all looked to be hooked up correctly based on what you guys said.

Thanks for all your help so far.

 

Glad to know you're becoming one with your carb.

You mention long warm ups but you shouldn't need them. You certainly don't want to go full throttle right away but you should be able to drop it in gear and drive it cold.

Here's a good look at the fast idle cam I mentioned in a previous post. On the left is with the choke closed and on the right with the choke open.

If the fast idle cam is working right, on a cold day, with the choke closed, you might start out idling at 1,400 in park, and for the first few miles you should be idling 800 or 900 RPM in drive. Finally, with the choke fully open, you should be idling 650 in gear.



If you are having drivability issues try to describe them better. Rough idle, slow idle, hesitation off the line, cutting out, missing, stuff like that.

 

So I've been trying different things to try and isolate the issue. Last night I started it (it likes one pump of the gas pedal and one small tap) it starts and idles high or high rpms. I dont have a gage so I dont know exact. After X mins the rpms went down. I let it run for 15 min I put it into reverse and then drive. It held the high rpms and took off. Lol. I hit the gas on the road and got up to 40 mph. I stopped at the gas station and it idled fine in park. I started it back up after about 5 min. It was running but the rpms were real low and it had problems staying running. I dont know how to describe it but it shakes the truck. Just real rough. On the way home whenever I would stop it wanted to die so I would tap the gas and move up a little. From what I've noticed, to me it acts like in drive that the rpms are dropping too low. When I stop its not idling high enough.

Im trying to understand how the truck idles. When the truck starts it idles high to heat up. As it heats up the flap opens due to the spring heating up and the rpms drop. At any point if I touch the gas pedal the rpms drop all the way down to what I would consider the completly warmed up and idling rpms. If I rev the engine when cold shouldnt it go back to the high rpms when i let off the gas since its not heated up yet? Same when I stop at a red light. If its still cold would it idle high like when I start it?

Here is a picture of my carb on that side.

 

The "high idle" position is just that - the speed at which the engine idles when it's cold; it should never try and run at a "normal" idle speed when the engine is cold, where "normal" is defined as, the speed at which it idles when fully warmed up.

If I rev the engine when cold shouldn't it go back to the high rpms No; it should have never left the high-idle speed in the first place... your choke needs adjusting...

 

Ok. So my understanding is correct.

But how do I go about adjusting the choke if its non adjustable? Is there another component besides the spring like the fast idle cam?

 

I'm not the best one to answer that, maybe @85lebaront2 will chime in....
BTW I edited my original response, something is out of whack there....

 

Ok, first item, if you have a voltmeter, check the feed to the choke thermostat, it should be 7 volts with the engine running, it feeds from the alternator stator.

Next item, the diaphragm cover on the front side of the choke housing, this is what is called the vacuum break, it kicks the choke blade open once the engine starts, good quick seat of the pants check, it should only open the choke far enough to drop one step on the fast idle cam. There is an adjustment for that in the center of that cover.

Next, air filter, the factory 460 air filter has two vacuum operated doors, one is thermal controlled on the air inlet horn, the other is on the driver's side and rear in a plastic scoop. It is straight vacuum possibly with a delay valve in the vacuum line (it's been a while, and ArdWrknTrk has mine since I am now EFI) it's function is to let that beast breathe under WOT acceleration. If it isn't closing, you have no preheat. Even with it, you can get carburetor icing, I did. Where I am, we get a lot of low above freezing wet conditions and mine would ice up, stall, then restart fine.

Hot restart, a properly tuned 460 should fire up and run fine with no additional throttle unless your carburetor is leaking internally. It may take a few seconds to smooth out though.

If you need all the adjustment specs for the 4180, I have my 1986 information, and a lot of the 86 and 87s still used 1985 PN carburetors.

 

Ctubutis: yeah it look me a min but I got what you were saying. Lol

I dont have a voltmeter. I will see if I can get one. The choke thermostat would be the black cap with the wire attached? Just to make sure with the voltmeter I put one end to the wire and put the other end to ground?

How do you tell if the fast idle cam is only one step? When I start the truck the choke blade opens. I quickly looked at it but I would say it opened 1/4 inch. I will try to measure this weekend.

I will check the doors on the air filter.

Yeah not touching the gas pedal on hot restart seems to be working. The problem I had yesterday was after it started it was acting like it was about to die. The idle was lower than what it was when I shut it off.

Any info would be helpful. There isnt much info out there and im sure if it is out there im probably not searching using the correct language to find it. Lol

Thanks again for the help from everyone.

 

Check the voltage with the wire connected, just slide it back enough to expose part of the pin. The fast idle cam should have several steps, the initial break should just allow it to drop down 1 step. The fast idle if I remember correctly is 1800 on the next to highest step fully warm. You have to raise the cam up by pushing the choke against the pull off with the engine running. You have to open the throttle a little in order to move the choke.

 

It does sound like your choke could be opening too early.

The choke spring is heated by the wire attached to the choke spring housing. Sounds like it should be 7 volts (according to our esteemed panel of experts) but if somebody hooked 12 volts to it...well that would certainly make it open early.

About the fast idle cam: it actually has 3 steps; high, medium and low. After that it's regular idle.

About the choke. There is a vacuum diaphragm on the choke side called the "unloader" and it's job is to pull open the choke if you rev the motor. Notice how the idle speed kicks down when you rev it? Maybe take it easier when it's cold and see if the choke stays on longer?

I will take the choke spring housing apart on my spare and up loan some pictures over the weekend. Should help you if you decide you want to adjust your choke.

But before adjusting the choke you should a) check that voltage to the choke as previously described and 2) check your vacuum advance.

There is a vacuum line attached to your distributor. With the motor off, disconnect the vacuum line from the distributor, attach about a one foot section of vacuum hose in its place, and suck on it. You should not be able to draw any air through the vacuum line. If you can the vacuum advance is shot and needs to be replaced.

The difference between my vacuum advance working and not working is about 150 RPM at idle. Maybe that's the cause of your low RPM once the fast idle is completely off.

 

Okay, first step is marking the choke spring housing so you will always know the original setting.

 

Step 2 top left. Identify the screws holding the choke cover onto the choke housing. See red circles.

Step 3 top right. The factory used blind, un-slotted screws to hold the choke choke cover onto the choke housing. If you still have the original un-slotted screws it will be necessary to cut a slot into them to remove them. Here I'm using a Dremel tool with a cut-off wheel to cut the slots.

Middle right. Here's a better look at the screw once it's been slotted and removed.

Step 4 bottom left. A look inside once you've got the choke spring cover off. See the red circles, when you put it back together the loop on the choke spring must go over the lever arm. See the green box, you must grind away this tab to be able to rotate the the choke spring cover to adjust the choke.

Bottom right. DO NOT remove the tab that fits into the choke housing. Remove the tab (circled in red) that fits into the choke spring cover.



Step 5 Finally, once you put it all back together, loosen the screws and rotate the choke spring cover counter clockwise to increase the choke function and clockwise to reduce the choke function.

 

Final notes. Cutting the slots into the blind screws may be very difficult with the carb on the vehicle. It is possible to remove the entire choke assembly from the carb with carb on the vehicle but getting it back on correctly might be a challenge. Let me know if you want to see that.

Otherwise, if the problem is low idle, and you've verified the vacuum advance is working, it might just be easier to adjust the idle speed with the idle adjustment screw located on the driver side of the carb. Half a turn clockwise might have the desired effect. Note however adjusting this screw only adjusts the hot idle and will have no effect on cold idle since that is controlled by the fast idle cam.



Good luck!

 

Those are some great instructions. Thanks

I had a busy weekend and didn't have time to play with it much.

On Thursday night I let it heat up for 15 min and drove home. I only touched the gas pedal when I pulled out on the street. I stopped a couple of times and it didn't die. I got home and parked and it sounded like it was idling perfect.

We drove it on sunday and again no issues. Even parked, restarted and drove again. It was also warmer in the 50s I believe.

It sounds like what you said. When its cold outside the choke is opening all the way too fast and it runs perfect when its warm.

I will have to check the voltage to see if its correct.

If I start the truck and it goes to the high idle, then I press the gas and the unloaded opens the choke plate, what would stop the fast idle cam from taking back over and letting it go back to the high idle until its warmed up?

If the vacuum advance was bad would I still have an issue when the truck is warm?

Thanks again.