Carb adjusting advice please, see video

[jstone4646]

I am not afraid to admit when I do not know something, and this is one of those moments. I also like to try and learn from those moments. I have been watching youtube and reading up on holley 4 barrells, even downloaded the holley manual for the specific one on the truck. I understand how to do the work, where the idle adjustment is, the mixture screws, where the jets are located, etc....but before I start doing major adjustments I wanted opinions. The truck is at operating temp in the video, high idle as you can hear. I tried adjusting only the idle screw 1/4 turns at a time in both directions and all I could get it to do was increase idle speed instead of lower. When I had the engine off before I started adjusting I went clockwise and counted the turns until it stopped, and then returned it back to where it was after attempting to adjust the idle. I am just carb clueless and need an education! Can any of you veterans tell by listening to it, what needs to be done in order to get the idle down and get her running a bit smoother?

EDIT: I should probably mention that when she is dropped into gear, the idle lowers significantly, to about the level I would imagine it should be while its sitting there warmed up in park or neutral.

link to my video: https://youtu.be/TghLS-rMg6k

[Gary Lewis]

You may have a vacuum leak or have full manifold vacuum going to the advance on the distributor.

Sticking with the latter, I don't like running manifold vacuum to the distributor - especially with an automatic transmission. When the transmission is in neutral the engine is unloaded so runs at high RPM and creates a lot of vacuum, which pulls the advance on and speeds it up even more. And when you drop it in gear it goes in with a bang. Plus, that loads the engine so the RPM comes down, which drops the vacuum, which reduces the advance which lowers the RPM which reduces the vacuum which reduces the advance which lowers the RPM which.....

Instead, I run ported vacuum, which is vacuum that is not present at idle but is as soon as you open the throttle. I'm not familiar with Holleys to tell you which port is the right one, but there is almost always one on the carb - that doesn't have vacuum at idle but does when the throttle opens. Try that to see if the idle comes down.

If that doesn't solve the problem you may have a large vacuum leak. In that case you won't be able to get the idle speed to come down even if you back the idle speed screw out so far that the throttle blades fully close the carb off. So you need to see if you have a leak by checking all the vacuum hoses for cracks, ports that aren't plugged, etc. And if you don't find it then squirt brake cleaner at the base of the carb, the joint between the intake manifold and the heads, and anywhere that air can get into the intake system. If there's a leak the engine will speed up when it sucks the brake cleaner in. And the wrong base gasket under the carb can easily do that. Or the lack of the EGR adapter on a stock manifold.

And, by the way, you can put the Youtube right on here to make it easier for people. Click "Embed", then "Insert Embed Tags, and paste your embed code from saying Share and then Embed on Youtube between the > and the < characters in the string that gets inserted:

[jstone4646]

You may have a vacuum leak or have full manifold vacuum going to the advance on the distributor.

Sticking with the latter, I don't like running manifold vacuum to the distributor - especially with an automatic transmission. When the transmission is in neutral the engine is unloaded so runs at high RPM and creates a lot of vacuum, which pulls the advance on and speeds it up even more. And when you drop it in gear it goes in with a bang. Plus, that loads the engine so the RPM comes down, which drops the vacuum, which reduces the advance which lowers the RPM which reduces the vacuum which reduces the advance which lowers the RPM which.....

Instead, I run ported vacuum, which is vacuum that is not present at idle but is as soon as you open the throttle. I'm not familiar with Holleys to tell you which port is the right one, but there is almost always one on the carb - that doesn't have vacuum at idle but does when the throttle opens. Try that to see if the idle comes down.

If that doesn't solve the problem you may have a large vacuum leak. In that case you won't be able to get the idle speed to come down even if you back the idle speed screw out so far that the throttle blades fully close the carb off. So you need to see if you have a leak by checking all the vacuum hoses for cracks, ports that aren't plugged, etc. And if you don't find it then squirt brake cleaner at the base of the carb, the joint between the intake manifold and the heads, and anywhere that air can get into the intake system. If there's a leak the engine will speed up when it sucks the brake cleaner in. And the wrong base gasket under the carb can easily do that. Or the lack of the EGR adapter on a stock manifold.

And, by the way, you can put the Youtube right on here to make it easier for people. Click "Embed", then "Insert Embed Tags, and paste your embed code from saying Share and then Embed on Youtube between the > and the < characters in the string that gets inserted:

I am guessing you are correct with the latter, when I drop it into reverse or drive from N or P it quite literally jolts the truck into gear. I will read up on the carb and see what I can find out about the vacuum lines. Thanks again!

[Gary Lewis]

I am guessing you are correct with the latter, when I drop it into reverse or drive from N or P it quite literally jolts the truck into gear. I will read up on the carb and see what I can find out about the vacuum lines. Thanks again!

Keep us posted, please. We are still learning, so need to know how things work out. And, we take great joy in solving problems.

[jstone4646]

I am guessing you are correct with the latter, when I drop it into reverse or drive from N or P it quite literally jolts the truck into gear. I will read up on the carb and see what I can find out about the vacuum lines. Thanks again!

Ok a little more research and I found that the truck does not have a vacuum switch installed. It was in the 'parts bin' provided by the previous owner, and I was not sure what it was at the time....just happened to see it while researching vacuum lines and ported vs manifold. So I am thinking tomorrow I will need to really dig in on the vacuum setup and figure out whats what.

[Gary Lewis]

Ok a little more research and I found that the truck does not have a vacuum switch installed. It was in the 'parts bin' provided by the previous owner, and I was not sure what it was at the time....just happened to see it while researching vacuum lines and ported vs manifold. So I am thinking tomorrow I will need to really dig in on the vacuum setup and figure out whats what.

I'm not sure which "vacuum switch" you are talking about, but a simple system doesn't need them. This page explains how simple a system can be.

[jstone4646]

I'm not sure which "vacuum switch" you are talking about, but a simple system doesn't need them. This page explains how simple a system can be.

Great info, thanks! I will give a report on what I find tomorrow afternoon.

[PetesPonies]

Great info, thanks! I will give a report on what I find tomorrow afternoon.

When you close both idle mixture screws .. . and the engine still runs, you have a vacuum leak.

[jstone4646]

When you close both idle mixture screws .. . and the engine still runs, you have a vacuum leak.

So this is where am I at now, I only had about 30 minutes to give it a once over, but I think I covered all the bases of the vacuum system...what little of it there is. Please educate me if there are components I am missing, and keep in mind since I do not have heat or A/C in the truck, I am sure there are several bits missing on that end which are just plugged now.

[Gary Lewis]

So this is where am I at now, I only had about 30 minutes to give it a once over, but I think I covered all the bases of the vacuum system...what little of it there is. Please educate me if there are components I am missing, and keep in mind since I do not have heat or A/C in the truck, I am sure there are several bits missing on that end which are just plugged now.

Ok, this is going to be a long post.

At 26 seconds you show two hoses that go from the carb back to the vacuum fitting on the intake manifold. And I'm pretty sure both of those hoses are connected to the wrong spot. You said you have info on that carb, but check to see if you are supposed to hook manifold vacuum, which is what the fitting on the manifold has, to any of the ports on the carb.

Saying it another way, some of the ports on the carb supply manifold vacuum, but they are not supposed to be hooked to manifold vacuum.

In a way, it is like connecting one electrical outlet in your house to another electrical outlet. Both are supposed to supply electricity, not get electricity. So I think you should pull both of those hoses and cap all four fittings.

The PCV valve is hooked up correctly. However, very few of them have an opening in that top fitting. In fact, I've never seen one of them open, although I know some are. So, if yours is open and you can feel vacuum there then you are right to have capped it.

And the cap on the distributor means there's no vacuum going to the vacuum advance. So, for now forget everything I said about what type of vacuum you should put to the distributor as you don't have any vacuum there. Probably one of the two fittings from which you removed the hoses, as discussed above, is ported and the other is manifold, and we will work that bit out later.

At 1:35 you say "I came over here to the idle adjuster" and then you said you turned it clockwise all the way in. But, if you really were working on the idle stop screw I think turning it clockwise would have sped the idle up dramatically, not slowed it down. I fear that you turned the screw that is vertical and goes to the arm on the accelerator pump. So, can you take a pic and point to the screw you adjusted? Perhaps I misunderstood.

And then you said you screwed the idle air/fuel adjustment screws all the way in and it didn't make a difference. And there, Houston, we do have a problem. Pete said that's an indication of a vacuum leak. But in my experience if you turn the idle air/fuel screws all the way in on any carb that is working correctly the engine will die. That's because you just shut off all the fuel going into the engine.

(Note that I made "in" bold in the previous paragraph. That's because I wanted to call attention to that lie. The problem is that there are some emissions-era carbs in which those screws work backwards. But, this is a relatively new Holley, right? It should not have those weird screws, so forget that.)

Bottom Line: There's something weird going on. However, those two hoses could be sucking fuel through the ports on the carb and into the intake manifold, thereby bypassing the idle air/fuel screws. I'm not sure that it is possible, but maybe. So, let's first disconnect those hoses and cap all four ports and see what happens.