Hard Starting Hot

[Rich72C10]

This morning, my hard start came back with the Carburetor. She would turn over, get up to Fast Idle and die. This cycle continued about 5 times.

Luckily I bought a little check valve and had it on standby. It plugs into the inlet of the filter of the Quadrajet. Though it does restrict fuel flow but hopefully that isn't a issue for a stock-ish truck engine.

Though my understand is this should have correct any flow back: "removed the clip on the needle/seat to let it set when fuel is not flowing to prevent backflow". I that the case, then the check valve will not make a difference when I start her up tomorrow morning. So that begs the question, where is the fuel going (if that is actually the problem, no fuel in the bowl).

[Steeveedee]

Could be the choke break adjustment. Do you have a vacuum pump? With the choke set, apply vacuum to the choke pull off assembly and measure how far the choke opens. Check that against the spec. If it is in spec, maybe be even then the opening can be adjusted slightly smaller so that the truck keeps running.

[Rich72C10]

Yes, I have a vacuum pump.

But I am not sure what you mean. You saying my Choke plate is closing to much or not closing enough? Neither are the case, I have the Choke plate set just like on the Carburetor that I removed and the opening of it is just like it too as the engine warms up. I have a upgraded electric divorced choke installed.

Granted, 100% worth double checking.

[Carl Spangler]

Originally Posted by Rich72C10

I got the returned carburetor installed this morning. I have to say, it's much easier to get her to run down the road without her falling flat on her face. I think I got her dial in okay, though on Tuesday I'll have my shop take a look (she is going in to relook at my rear end leak). The difference is night and day but it is apparent I am no carburetor tuner. This is even with my fancy timing light (to watch for max idle) and vacuum gauge (to watch for max vacuum)!

With that said, I still have these problems:

1. Can't get the anti dieseling solenoid to do its job, still idles ~500 RPMs when solenoid is disengaged.
2. The above is with the throttle closed, of course, and the high pitched whistling is still there. The whistling goes away once I adjust above 600~650 RPMs.
3. The left (passenger) adjustment screw is still really loose, lots of wiggling. The right (driver) seems okay, especially compared to the left. I haven't any idea what issue this could cause, if anything - other than perhaps being able to fine turn the mixture on that side of the carburetor.

Seems the "whistling" would be a air leak, which in turn allows the engine to still idle, even though the throttle is fully closed.

Edit:

From Mark @QuadraJet Power


I am a bit disappointed that it seems they haven't any clue as to the operation of the GM Stop Solenoid / Anti-Dieseling Solenoid.

FWIW, I always assumed the anti-dieseling solenoid was ONLY intended to stop dieseling when the ignition is off. The solenoid wasn't intended (when off) to kill the engine when the ignition is ON.

That said, I feel your carb pain! If it makes you feel any better, I think I've had my 1 barrel Rochester apart at least 20 times in my quest (finally achieved) to get my truck to run sweet.

[body bolt]

I've had similar problems. On my truck, the carburetor fuel inlet is ~34 inches which is approximately the same as the fuel level in a full tank so I know there is fuel in the line. I see fuel stains on top of the carburetor which leads me to believe the fuel is boiling out after shutdown. I've also found if I run cool water over the stock fuel pump my idle becomes more steady. Turn the water off, wait a few minutes, the idle gets more lumpy and engine speed slowly decreases until it dies. I repeated this a few times. And this is with the hood open.

Originally Posted by Rich72C10

This morning, my hard start came back with the Carburetor. She would turn over, get up to Fast Idle and die. This cycle continued about 5 times.

Luckily I bought a little check valve and had it on standby. It plugs into the inlet of the filter of the Quadrajet. Though it does restrict fuel flow but hopefully that isn't a issue for a stock-ish truck engine.

Though my understand is this should have correct any flow back: "removed the clip on the needle/seat to let it set when fuel is not flowing to prevent backflow". I that the case, then the check valve will not make a difference when I start her up tomorrow morning. So that begs the question, where is the fuel going (if that is actually the problem, no fuel in the bowl).

[Rich72C10]

Originally Posted by Carl Spangler

FWIW, I always assumed the anti-dieseling solenoid was ONLY intended to stop dieseling when the ignition is off. The solenoid wasn't intended (when off) to kill the engine when the ignition is ON.

That said, I feel your carb pain! If it makes you feel any better, I think I've had my 1 barrel Rochester apart at least 20 times in my quest (finally achieved) to get my truck to run sweet.

That is correct on the Stop Solenoid. But I can remove the idle screw and turn back the Solenoid screw all the way back and it idles 500 rpms. On my old Carb she plan dies. My assumption, which could be wrong, if the carb doesn't die (staved of air/fuel?) - it can still diesel. On the visor instructions, it stays to hold the gas pedal a bit when warm to get it started - which makes sense as the solenoid isn't strong enough to push up the throttle.

I think @Steeveedee was correct. I just used a good bit of "Can of Air" on the choke coil to freeze it (can upside down while spraying the coil). It looks like I was letting the choke plate close way to much, which points to me being sloppy on the adjustment yesterday. As for the vacuum thingy, it's working like a charm.

[Rich72C10]

Okay, I think I understand between the Choke coil (closes choke plate/engages fast idle) and the vacuum pull thingy.

So when cold and you tap/push your pedal, this should allow the plate to close or almost completely closed. While you are turning over your engine it stays closed for max fuel/flow air. Then as soon as the engine fires over, the vacuum canister should get vacuum and allows the choke plate to open, cause now we need air. At this point we are in fast idle and the secondards are also disabled. Then as the coil warms up, the plate opens more and more. Then when you end up touching the gas pedal, you come out of fast idle, which also disables the vacuum canister thingy and enables the secondaries. Now you can Zoom, Zoom down the road.

So, if (I assume) I have my choke coil adjustment to tight or the vacuum canister isn't working, the choke plate will remain closed - which in turn means no air and engine will die. Which is pretty much what was happening this morning. Pretty darn sure it was misadjustment of my choke coil.

So I only have so much "Air in a Can" so I now have reverted to bags of ice around the choke coil and waiting. Kind of hard to test this stuff when its 95 outside, though there might be some other way to do this test. It is a bit of a PITA.

[Steeveedee]

What I meant was that the choke pull off might be opening the choke too far on cold start. Given that there is some sort of thing going on with that carburetor, not getting it to die with the screws all the way in, I would think that it is getting more air than it should for the choke pull off setting. But if it is 95 degrees out, the choke is of minimal use, anyway.

[Rich72C10]

Ah, I see what you mean Steeveedee. My bag of ice trick at least allowed me to see what is going on between all the outer hardware.

I can say that I can get it into of fast idle and the choke closes pretty good. Then as I am starting it, I see it flutter then just a bit open once the engine starts. During fast idle stays there, slightly cracked (I have the power lead off the coil so it doesn't move the choke plate). Then when I connect the choke coil power lead, the choke plate moves open, I tap the throttle, fast idle disengages and the choke plate is 100% open.

So it seems the mechanics seem to be working like they should or at least the way that I think I understand it.

Now... how will this play out tomorrow morning at 6am I don't know. What I need to do is get my remote push starter on & working but I haven't ever connected it, I am kind of scared to connect it - like I'll blow up my starter or something LOL

[Rich72C10]

Well, after a few days I can't seem to figure it out. So I created a video and sent the link to Quadrajet Power (Mark).

This is with their clip needle thingy removal and I have installed a check valve into the filter.

Truck has set ~10 hours and inside the garage it is 80 degrees. While I gave it two solid pumps in this video for this carburetor, my previous carburetor I only needed to tap it so the choke would close and fast idle would engage.

So what have I fudged up? If you are bored give the video a watch, its just under 2 minutes. At the beginning the carb is still as it was when I had shut it down 10 hours before. The video ends when I tap the pedal to come out of fast idle.


https://drive.google.com/file/d/1ws5...ew?usp=sharing

[body bolt]

It acts like it starts and runs off of the initial squirt when you're setting the fast idle. It's like that runs out before the idle circuits kick in, as if there is no fuel in the bowl. The accelerator pump has its on check ball to hang on to its fuel supply even if the bowl goes dry. Will it start and keep running without touching the accelerator?

[geezer#99]

On cold start your choke plate is opening too far.
Likely half that opening would work.

[Rich72C10]

I did that yesterday (or the day before). I did my normal "one pump" and it started up and then died. I then started again (not touching the pedal) and just keep cranking not letting off the key. After a number of seconds she started up and kept running.

Not sure if that answers your question or not... but at least you are thinking what I am thinking - like there isn't any fuel in the bowl. But where did it go is what I need Quadrajet Power to tell me!

[Rich72C10]

Originally Posted by geezer#99

On cold start your choke plate is opening too far.
Likely half that opening would work.

You mean when when the vacuum canister kicks in? So that is causing it to die right after it starts up?

[pjmoreland]

It looks like the choke opens slightly less after the second start than on the first start.

[Rich72C10]

that would be that vacuum thingy, once the engine starts the vacuum canister gets vacuum and opens the plate - this is where geezer#99 thinks this needs to be open about 1/2 that space.

I am researching how to make that adjustment....

[geezer#99]

Originally Posted by Rich72C10

You mean when when the vacuum canister kicks in? So that is causing it to die right after it starts up?

Yup!
If it’s set right the choke plate shouldn’t move until it starts.
Yours does.

[Carl Spangler]

From the vid: IMO, the choke plate is opening way too much for a "cold" start.

Also, crank the engine (with throttle closed) for ~2 seconds to fill the float bowl with fuel. Then do 1-2 medium pumps and start the engine. The choke plate should be ~1/2 open after initial start when "cold".

[Rich72C10]

Well, working with the vacuum canister is a right pain, starting with getting the hose off to connect to my vacuum pump. Then for my carb you bend the brackets - which seem to be made of titanium and don't want to bend much, if at all.

For the record, I haven't this issue at all with my carb that this one replaced. No extra turning of the key and only one pump of the pedal. Zoom, she will start.

My understanding is when the engine starts, the vacuum canister is suppose to open the choke plate. The plate starts closed before starting and after warming up it slowly opens. So at least I think I have my Electric Choke coil adjusted in the right area.

I just need to get some slack on the vacuum canisters bracket so it doesn't move the plate to soon and not as opened once full vacuum is applied. If only it would adjust without it feeling like I am about to snap something!

[Steeveedee]

You can reduce the opening of the choke by partly straightening out the link from the pull-off diaphragm to the choke lever. That's what I was talking about yesterday. That choke plate should only open about .1", which you can check with a drill bit.

[body bolt]

At 75F the choke on my '71 is wide open and I can start it without doing anything but turning the key. That's how it should work.

[Rich72C10]

Yep Steeveedee, I do get that but getting it to bend straighter appears hard for me but I think I might be getting it. I thought I broke something or flooded it real bad because the truck wouldn't start. But then figured out I just didn't have it in Park all the way and the safety switch had me locked out from starting Doh!

[Carl Spangler]

Originally Posted by Rich72C10

Yep Steeveedee, I do get that but getting it to bend straighter appears hard for me but I think I might be getting it. I thought I broke something or flooded it real bad because the truck wouldn't start. But then figured out I just didn't have it in Park all the way and the safety switch had me locked out from starting Doh!

A pair of pipe pliers is what I use to bend the choke rod.

[Steeveedee]

Originally Posted by body bolt

At 75F the choke on my '71 is wide open and I can start it without doing anything but turning the key. That's how it should work.

I absolutely agree! I think that the whistling issue is a vacuum leak and is giving him grief with the A/F mixture.

Originally Posted by Carl Spangler

A pair of pipe pliers is what I use to bend the choke rod.

Yup, just smash the bend a little flatter. I've done that probably a hundred times, as a mechanic.

[Rich72C10]

When the truck choke is opened (and warm outside) I can turn the key, hardly a half rotation of the engine. What I am talking about is only "cold" starting - after the truck has sat 10+ hours and overnight where it has "cooled" off.

Anyways, my scheduled shop appointment to have my rear end looked at is today (it still has a very, very little leak) - so I decided to punt to my shop. I explained all that I have seen and learned here. Either they can get it right or I am calling this carburator a loss (which is 100s of dollars between the core and the work at QuadraJet Power).