'74 Maverick 302 - Low vacuum / Carb / A/C issues

Please bare with me as I'm very new to working on cars, trying to help my grandfather (of 82yrs) work on a Maverick he recently bought. It's been sitting on a carport for the last 30 yrs unused and has ~60k miles on it.

He's taken it to a shop a few times where they put on one (motorcraft) carburetor and returned it running rougher than before. He took it back and they changed it out again. Still not running good he took it to a second shop where they got it running ok but not great.

Thinking it was good enough we decided to try to figure out why the A/C vent selector is not working. I checked the various positions of the control unit (from the Ford 5 vol shop manual) to see if the hoses to the vacuum motors were getting vacuum (OTC 5613 Vacuum Gauge). No vacuum. I checked Vacuum line going to the control unit and the gauge is hunting around 13-14 inHg. So I'm wondering if it's not enough vacuum or the vacuum selector switch doesn't work. Throttling the car, the vacuum builds to around 17 but still doesn't get vacuum to any of the vent vacuum motors.

I then hooked the vacuum gauge to the engine on driver side where a fitting comes out with two vacuum lines off at 90 (one thruough the firewall for the a/c) and a cap straight up. Taking the cap off and plugging in there I get the same reading. We then tried to adjust the idle to see if we could get more vacuum. Ran two idle mixture screws in all the way, then two full turns out and adjusting from there. But I notice that the adj screws, esp on the driver side, are extremely loose. At two turns out, they move if I barely touch them.

The place that put on the carbs, also did some adj to the timing, but I don't know yet what adj was made. I assume we probably need to double check that, but I need to get timing light and tach, I guess, to make sure idle is set right.

I've learned most of what I know in the last couple weeks. My grandfather was a jet engine mechanic in National Guard and at one time or another has rebuild engines from weed eaters to cars to helicopter and planes, but at 82 he's forgot a lot and is out of practice. There is a lot to take in at once for me. I'm hoping for some ideas on where best to start. I assume I need to work out the idling and low vacuum before I can get any confident diagnosis of the A/C?

I'd greatly appreciate any advice. Thanks.

 

I don't think those idle adj. screws should be loose - don't believe you will get it to idle properly w/ air coming anywhere in the carb., other than thru venturi's . There are several folks on this forum in the Atlanta area -- perhaps some of them can help w/ ur problem.

 

You can use the vacuum gauge to adjust the carb. The timing must be correct an make sure if you have points they are set at factory settings. You should be between 19 and 21 hgs. Ac would be last . Can you give anymore details on the car?

 

If you need anything I can help. jamesrschroensr@yahoo.com

 

After setting so long , did anyone clean the fuel line from the tank to the fuel pump.?

 

Yeah, I don't trust those screws at all. We tried taking one off today to see if we could do something with the spring, but it's too loose. I'll try to check around tomorrow and find some replacements if they can be bought separately.

 

It does not have points; it's electronic ignition. We tried adjusting the carb using the vacuum gauge but never got above about 15-16. Learning from YouTube University, we hooked up gauge. Run both screws in all the way, then backed them out about 2 full turns. We started up the eng, and continued backing them out till we got about 4.5 turns out. There was negligible improvement, maybe 1-2 inHg. But the screws were so loose, even after a couple turns.

I'll work on checking the timing next. I think my grandfather has an old timing light we can use to check.

What other details would be useful to list?

Before I started helping him on it, he had pulled the fuel tank and had in lined because it was in rough shape. He replaced the fuel filter and lines forward from the filter. They had problems with trash somehow getting through and one of the mechanics that worked on it installed another fuel filter under the hood, on the passenger side of the carb. I'm not sure I'm comfortable with that, but that's where we are. I haven't until now thought about checking in to that further.

I appreciate the replies. I guess I've been working from the tail end backwards starting at A/C. Looks like we need to go all the way back to square 1. I guess that means 1) checking the timing and adjusting to spec, 2) finding replacement adj screws for the idle mixture and adjusting that out, 3) ... Not sure yet. Do I need to check fuel pressure to make sure the fuel supply is good?

Edit: Fuel pump was also replaced.

 

1. I don't know of any source that sells just the mixture screws/springs.

2. Mixture screws should be adjusted out 1 1/2 turns...and VERY LITTLE after that. 4.5 turns is WAY too much.

3. The vacuum canister on the passenger side probably has a leak, which is why the AC switch in the dash is not working. It looks like a tin can behind the passenger side shock tower. A bead of silicone around where the hose nipple is attached to the "tin can" will fix that.

 

If the engine still runs after you turn the mixture screws all the way in...You have a vacuum leak somewhere. Vacuum can as craig stated is a common culprit as well as bad vacuum hoses or a bad carb base gasket. It sounds like you have a vacuum leak to me. Lack of response to mixture screw adjustment also tells me ...vacuum leak...Take a squirt bottle full of water and spray the base of the carb...If the engine stumbles/stalls, (spray everything that has or distributes vacuum) you found your leak. Once you are certain you have no vacuum leaks...Adjust timing using your vacuum guage. You want to reach highest possible vacuum reading with the timing adjustment. Then adjust carb...Same thing with the mixture screws. Try to attain highest vacuum reading. You will have to fine tune from there...But this will give you a good baseline to start from. Go to the shop that did the carb and see if they still have the old carb (Probably not since there are core charges on em) and get the mixture screws from that one if possible. Make sure they replaced the carb base gasket. Have seen people try to use the old gaskets. ( never a good idea) I am guessing your car has an EGR valve. That as well as the base plate its on (Sandwiches between the carb base and intake manifold) Are prone to leaking (Vacuum) and the base plate is prone to cracking (These will cause a vacuum leak ) as well...Good luck! Hope this helps you out.

PS: Do not use any thing flammable to test for vacuum leaks!!! IE: starting fluid...If you have a bad (leaking plug wire) you will find out the hard way...

 

Agreed, even two turns is to much for these carbs....

To troubleshoot your engine vac issue plug off at least the feeds to the cannister & A/C controls... Maybe even PCV valve, a wrong/bad valve can cause issues... If it's plumbed into the #7 cylinder intake runner you can just about count on issues...

 

It wouldn't hurt to do a compression test too. Another quick and easy check for a vacuum leak is to close of the air horn of the carb when it's running. Once it's warm push the choke closed, if the engine speed momentarily increases you have a leak.

 

like some have already said.. strip ALL the vac connections away, PCV included, and cap them off to better isolate the issues you're seeing here. Can also eliminate fuel system variables by bypassing the entire rear fuel section and running the fuel line directly into a can of fresh gas.

IMHO, you'd also be much better off to run the distributors vacuum advance pots hose to a FULL manifold vacuum source rather than the factory's ported/timed connection. This added ignition lead at idle WILL increase manifold vacuum and help you dial in those mixture screws closer to where they should be. Aside from reductions on nOX emmisions, there is absolutely nothing to be gained from running retarded timing at idle(ported vacuum) and ending up with richer mixtures then the motor is capable of efficiently burning.

Also very easy to test the distributors vac advance pot by sucking on the hose connected to it. If it holds vacuum against the tip of your tongue?.. it's all good. You can also swap the vac advance hose around between ported/timed and full manifold sources to get a feel for what the engine likes best. Ported sources only help lighter throttle cruising.. full manifold sources helps idle AND cruise because it's always available full time during part throttle conditions.

 

I had a similar issue getting my original 6 to run smooth. When I pulled it out and started stripping the engine bay, I found the vacuum accumulator (tin can) that was mounted on the passenger side down low near the firewall, was rusted through on the bottom, even though it looked perfectly good from above. Just one more thing to check out.

So far, that has been the only rust I have found on my car....hmm wonder how it got enough moisture in there to rust it out, must have pulled moisture back through the vacuum system. And with it being about the lowest point, it must have also acted as a water accumulator.

 

...

with a vac. leak you will never get the carb adjusted correctly. if you screw the idle screws in all the way and it still runs, you have a vac leak.
check all the plastic nipples to see if any are cracked.
may we have a pics of the engine bay?
what side of Atl. are you on?

 

Isn't a PCV valve just a great big manifold leak?

When doing basic troubleshooting, I usually prefer to cap ALL the leaks off.