Can't get my Holley 390 to idle properly HELP

[19Fordy]

I have a Holley 4160 390CFM 4bbl carb with vacuum secondaries on my
1959 Ford 292 Y Block standard shift vehicle. I started the engine and the engine had it's usual curb idle of about 750 RPM. There is an inline filter at the carb and a filter mounted at the gas tank before the electric fuel pump.

Then, I shut it off and added some antifreeze. Restarted the engine and now the engine
won't idle unless the curb idle is around 1100 RPM. I did not do anything else to the engine and
never touched the carb. I don't think the anti-freeze has any bearing on the problem.

I don't want to start taking the carb apart without first having some idea about what might be causing the problem. The carb is about 10 years old and has always run great both at curb idle and on the road.

Any suggestions and info. are very much appreciated. Thanks.

[40cpe]

I had a problem with an Edelbrock and was looking on line for help. I ran across a suggestion to count the idle mixture screw turns in to stop, remove them, and spay 2-3 shots of carb cleaner into the mixture screw holes using the straw. Then replace the idle screws back to where they were before you removed them. It worked wonders on my carb, but I realize yours is a Holley.

[KULTULZ]

... now the engine
won't idle unless the curb idle is around 1100 RPM.

Is the choke operating correctly and is the fast idle cam falling (gummed linkages).


Throttle linkage operating freely?

[scicala]

What 40 coupe said is a good plan. It sounds like there may be some contamination in the idles circuit, if that's the only place it won't run good (at idle). The idle mixture screws are on the left and right sides of the metering body, which his the section between the front bowl and the main body.


Sal

[cousinjd]

Check the rear barrels of carb for sticking open even slighty.

[darrell]

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if you have air take the idle screws out and shoot a blast through.works every time if nothing else wrong

[19Fordy]

Thank you all for taking time to respond to my question. I will heed advice.

[Flathead Fever]

The only way the idle would go up is if it got both more fuel and air. If it just got extra air the idle would drop. If it just got extra fuel the idle would also drop. That's if the air fuel mixture was correct. Its probably the throttle linkage or choke linkage not letting it close all the way. Remove the linkage and see if it returns to idle or if you can adjust the idle speed screw to bring it back down. Do not start with out a return spring on it.

[scicala]

19Fordy doesn't have an issue with the carb not being able to idle down to a normal idle speed. He has to hold it to at least 1100 RPM for it to idle at all.


Sal

[KULTULZ]

The only way the idle would go up is if it got both more fuel and air.


If it just got extra air the idle would drop.

Sal ... ?

[paul2748]

Check all your vacuum lines. You might have moved one without noticing it.

[scicala]

Read my post #9. That's all I have to say. Done. 19Fordy probably has it fixed by now anyway.


Sal

[KULTULZ]

Originally Posted by scicala

Read my post #9. That's all I have to say. Done. 19Fordy probably has it fixed by now anyway.

Sal

... ok ...

[Flathead Fever]

Originally Posted by scicala

19Fordy doesn't have an issue with the carb not being able to idle down to a normal idle speed. He has to hold it to at least 1100 RPM for it to idle at all.


Sal

I'm in a chatty mood. Lets see if I can redeem myself? I Apparently I can't read anymore. I had a failed cornea transplant and sometimes my eyes and brain don't sync up. Sorry about that. I had answered about a dozen questions between this one snf the flathead site. I was in a hurry to go outside and work on my own projects and I skimmed through this question to fast. Plus my brain is plugged up with cheese. I think I'm loosing it sometimes?

Once upon a time I was a ASE Master Mechanic with 17 certifications. Which means nothing. Anybody van read a book and take a test. Don't I wish when something went wrong it could only be a choice of A,B.C or D to fix it. And A and D were such stupid answers that only left B and C could be the problem. After 40-year's of working on this stuff I always see new problems break in new ways I never thought possible. I worked on all the new computerized stuff. Did smog inspections. Even helped write the exam questions for the State Smog Mechanic certification test. We repaired everything in-house except for engine machine work. 400 phone company vehicles. I never stopped learning how stuffed worked. What I really love is working old Fords.

If your gearhead you need to know how things work otherwise you can't work on them. You can but you are going to waste a lot of time and money. It takes years to learn all this stuff and you will never stop learning. That's what I love about. The mechanics of it all is what interests me along with the history of it all. I like to work on car but I have little interest in driving them. I know what they drive like. I have a '66 GT-350 that's been sitting out in the garage since 1984. I put 50 miles on it since then????? I just want to build cars and put them up on my shelf like I did when I was a kid???

I love teaching people who are truly interested in this stuff. But 99% of them just want to know what part they need to replace. It drives me nuts because cars are their hobby. Why are they not interested in what make them go? I have a neighbor that thinks he's a car expert. He stands there every weekend revving the engine on an El Camino thinking that's going to fix it (it has a definite engine misfire). He has bought every part you can bolt to the outside of that 350 and it still has a misfire. This has gone on for a couple year's. I have told him what to check and he refuses to do it or read up on how an engine actually works. Maybe it has a bad valve, valve spring, flat cam, no compression in a cylinder.... He really thinks he's a "mechanic" but he will not logically try to diagnose it. I'm getting like those old-time mechanics that taught me. I'll point him in the right direction and see what he does with the info. But I'm not going to stand there and do it for him.

Back to your engine. You might have a plugged idle jet, a vacuum leak or maybe a misfunctioning PCV valve or a thousand other things. If it has a PCV valve,make sure its not stuck. It should rattle when you shake it. Also a PCV valve hose can collapse if it gets oil soaked (really rare). I had a PCV fail on my personal Mustang. It ran fine one minute. I shut it off, then started it again and it would not idle at all??? I was young and did have a clue? All I did was open the driver's door, maybe that's the problem? The neighbor worked at Ford, and he dragged raced Mustangs. He was a pretty sharp guy. He walked right over pulled the PCV valve out of the valve cover put his finger over it and the 289 idled. Then he walked away without saying a word. That forced me to get out the '65 Mustang shop manual and read how the PCV valve worked. That's how I learned best I need to have my butt kicked a little and I then will never forget how to fix that problem When I was a garage helper the old-time mechanics at work would watch me struggle with diagnosing something. After a couple hours they would come over, touch something that I had no idea what it was on a smog car and that it would fix it. Then they would walk away. They made me need to stop and think and do a little research on my own. I'm not sure if they were laughing at me struggle or trying to teach me? Whichever it was it worked and I became a decent mechanic. There is no such thing as the guy in the white lab coat with all the answers. Sometimes it takes the village to fix an engine problem.


Believe me coincidences happen. Every once in a while it happened to me at work. I'd pull a truck in for a oil change and then it wouldn't start afterwards because the ignition module died? I was nowhere near the module. I had a water pump let loose right after an oil change. It just let loose and puked out all of the coolant. I had a F800 blow a rear tire while on the hoist with the shop doors closed. I couldn't hear for a week. I had not aired it up or damaged it anyway. There was no load on it, it was off the ground? Why would it blow up because I moved it? I was so glad I worked at a fleet and didn't need to convince a customer it wasn't me that messed this stuff up.

You changed coolant and now it won't idle. Maybe that just happened to be the same time a piece dirt got stuck in your idle jet or the spring in you PCV valve broke. It messes with your head, because 99 times out of hundred it actually was something you touched that screwed it up. That is the first thing I ask people. What did you touch last? Next I look for anything that is not factory, especially the wiring. But every once awhile the Universe just likes to screw with your head. I wonder sometimes if its not one of my dead friends screwing with me? They would do it if they could. Heck, I'd do it to them.

Stick your finger over the PCV valve and see if it will idle. That could be your problem. Then go on line and see how a PCV works. Everything you work you need to find out how it works. If you replace the PCV cut the old one in half and see what living inside. Do that with everything you can gut in half

Next, Try spraying a little starting fluid in the carb while its running and see if it will idle at 600-700 rpm while your lightly spraying. If the idle goes up you will know it has a vacuum leak. The extra air from the vacuum leak, maybe the PCV is stuck open? The extra fuel and will raise the RPM. If it will idle at 700 rpm with the starting fluid then it is starving for fuel and you probably have something stuck in an idle jet. What happening at 1000 rpm is venturi vacuum is starting to pull fuel out of the other systems like the idle transfer port. A little propane bottle works even better for checking the air fuel mixture. That's the other thing. Find out what vacuum is? When it occurs. The difference between manifold vacuum and venturi vacuum. Its really important you know this stuff to diagnose cars. Its all very simple you just need to be interested it and it will all make since. Learn the seven basic circuits of a carburetor. If you treat each circuit separately the carburetor won't be a big mystery.


Make sure the float adjustment is correct by taking out the inspection screw on the side of the bowl.

Screw the mixture screws in while counting the turns so you can put them back where they were if you need to. Pull out the air fuel mixture screws (don't mix them up) and jamb a carb spray can with the straw tip against the hole and see if spray is coming out the idle ports below the throttle plates (while it is not running). You might be able to blow whatever is stuck in there out with the carb spray. Put the screws back and gently seat them. Back them off 1 1/2 turns and then start it. Turn them in evenly 1/4 turn at a time until the idle starts to drop (at the correct idle RPM) Then turn them back them out (evenly) to the highest idle speed, plus another 1/4 turn. Now if it will idle correctly pass the propane bottle over the carb or a small spray of the starting fluid. If the idle goes down you have it set to the rich side and you need to lean it out, maybe an 1/8 turn in on the screws. If it the idle goes up with the propane you have it set to the lean side so you back out the screws out a "little". If the propane hardly has any effect on the rpm you have set pretty darn close. You can turn the screws out an extra I/4 turn for better all around driving. That compensates for temperature changes and atmospheric pressure changes.

Ignition dwell (point gap) is set first. Then the timing at the correct rpm. Then the idle mixture and last the idle speed. That is because dwell changes timing but timing does not change the dwell. Timing can effect the air fuel ratio. The air fuel ratio cannot effect the timing. The last thing is the idle speed screw to get the correct rpm. It has to all be done in this order.