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Old 08-07-2019, 04:26 PM   #1
JayChicago
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Default Carburator problem, I think

Built flathead, Holly four barrel, electric fuel pump. After a drive at highway speed, suddenly engine will not idle at all. I can keep it running by continuously pumping the accelerator, or holding throttle open to keep RPMs up. My thought is something got lodged in the carb's idle circuit. But before going to a carb rebuild, I am looking for other opinions. Is there something else that could produce that symptom? Is there something on the carb I can easily check? Let me know if I need to provide more info. Thanks.
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Old 08-07-2019, 04:44 PM   #2
Seth Swoboda
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Default Re: Carburator problem, I think

I suppose you could start by pulling one plug wire at a time to see if/what cylinders are getting fuel and aren't. It's a start. If it is idling rough and you you pull a plug wire and no change or you pull a plug wire and the engine dies you'll have identified if it is a fuel issue and what cylinders it is affecting. You might have a jet that is clogged with dirt.
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Old 08-07-2019, 05:01 PM   #3
19Fordy
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Default Re: Carburator problem, I think

Time to rebuild the carb. It's easy to do so buy a rebuild kit and a can of carb cleaner.
Here's the kit I use.
https://www.speedwaymotors.com/Holle...CFM,33864.html

I also replaced the secondary adjustment screw shown in this video so that it could be adjusted while carb is on the engine. This really affected running at idle.
https://www.youtube.com/watch?v=b8ROjrGAH2I

Also adjusted the idle mixture screws while using a vacuum gauge to obtain the highest reading possible at idle. Ended up with a reading of 18.

Last edited by 19Fordy; 08-07-2019 at 05:21 PM.
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Old 08-07-2019, 05:19 PM   #4
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Default Re: Carburator problem, I think

Is it really easy for an amateur like me to rebuild a carb properly? I can spray some carb cleaner and let it soak, and install the kit parts. But how will I know all the tiny narrow passages in the carb are clean and clear? How about the details and weak-points of a Holley that a pro re-builder knows to check, that I have no clue about?
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Old 08-07-2019, 05:49 PM   #5
19Fordy
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Default Re: Carburator problem, I think

Jay, Here's what you do.
1. Build a little wooden stand with 4 protruding bolts that will allow you to mount the carb on the stand just like it was on the intake. That stand will make it very easy to work on the carb,remove the various parts,and reassemble. I can email you a photo if needed.
2. Buy carb cleaner that has a plastic tube so you can spray into all openings.
3. Take close up photos of each piece of the carb before you remove it and also it's position for proper reinstall. Take plenty of photos.
4. As you remove each piece lay it out on a big clean piece of cloth in it's proper position for reassembly. Pay special attention to o rings.
5.Then clean each piece with carb cleaner based on what replacement parts are included in your kit. (WEAR SAFETY GOGGLES)
6. Reassemble using a drop of oil on the rubber parts. Do not over tighten the bolts that attach the fuel bowls as they are tightened in inch pounds only.

If you have never done it before, go slow, follow the directions in the kit and don't take anything apart that you think you won't be able to reassemble. This will change as your confidence grows. There is an excellent book HOW TO REBUILD THE HOLLEY 4150 AND 4160 390 CARBURETOR that will really be a big help. You must buy this book as it is a gold mine of excellent info.
https://www.alibris.com/search/books...E&gclsrc=aw.ds

I felt the same as you at first but,kept at it until I got it right. If others could do it, I figured I could also. So can you.

Last edited by 19Fordy; 08-07-2019 at 06:47 PM.
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Old 08-07-2019, 06:08 PM   #6
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Default Re: Carburator problem, I think

OK, thanks for the vote of confidence and all the info. I will order a kit and follow your advice. I have rebuilt carbs before, but I always felt unsure if I was able to get all the tiny passages clean.
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Old 08-07-2019, 06:50 PM   #7
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Default Re: Carburator problem, I think

Book also available on Ebay. it's a book you read a little at a time so as to digest the info in a meaningful manner.
https://www.ebay.com/sch/i.html?_fro...LH_TitleDesc=0
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Old 08-07-2019, 07:31 PM   #8
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Default Re: Carburator problem, I think

Thanks. Already ordered the book from the Alibris.com site you suggested. A used book, with shipping, under $10. Can't beat that.
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Old 08-08-2019, 07:38 AM   #9
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Default Re: Carburator problem, I think

I use a camera with an SD card when i work on something with a lot of parts. That way you can take pictures in steps as you take it apart and also refer back to what you did at a later date. Sometimes you can get interrupted and may not be able to get back to it for a couple of days.
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Old 08-08-2019, 07:52 AM   #10
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Default Re: Carburator problem, I think

I had that problem on mine several times over the years. Found it was the inlet needle assembly. Seems like the fuel caused it to become sticky,. New inlet needle assembly, end of problem. I always try to use non-ethanol fuel.
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Old 08-08-2019, 09:07 AM   #11
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Default Re: Carburator problem, I think

Try this.. Hold RPM up high.. 3000 or so. Now choke the carb and go wide open. Make sure you are choking the carb enough to where it wants to kill the engine. Don`t let the engine die.. Release choke and let rpm come back up. Might take 2 or 3 tries but this puts a huge vacuum on the carb and usually will clear an obstructed passage.
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Old 08-08-2019, 11:26 AM   #12
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Default Re: Carburator problem, I think

Thanks for the advice, guys. I will try sucking out an obstruction with high vacuum. And if it doesn't clear, will take pics and replace the inlet valve during the rebuild.
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Old 08-08-2019, 12:13 PM   #13
Seth Swoboda
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Default Re: Carburator problem, I think

Quote:
Originally Posted by 37 Cab View Post
Try this.. Hold RPM up high.. 3000 or so. Now choke the carb and go wide open. Make sure you are choking the carb enough to where it wants to kill the engine. Don`t let the engine die.. Release choke and let rpm come back up. Might take 2 or 3 tries but this puts a huge vacuum on the carb and usually will clear an obstructed passage.

I have done this with success on a Ford/Holley 94 carburetor.
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Old 08-08-2019, 02:30 PM   #14
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Default Re: Carburator problem, I think

Quote:
Originally Posted by JayChicago View Post
Thanks for the advice, guys. I will try sucking out an obstruction with high vacuum. And if it doesn't clear, will take pics and replace the inlet valve during the rebuild.
Save yourself some work, replace the inlet.
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Old 08-08-2019, 02:46 PM   #15
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Default Re: Carburator problem, I think

How does an inlet valve cause an engine to not idle, but runs when more throttle is applied ?


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Old 08-08-2019, 03:00 PM   #16
flatjack9
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Default Re: Carburator problem, I think

Simple, at low speeds there is not much fuel needed. At more throttle there is more flow and tends to keep the needle open. Trust me, I have experienced this twice on my car. The car acted exactly like the OP stated. You can use whatever theory, you like, but this is the way it happened. The first time was going to an event in Indianapolis. Stopped to get gas and the car would hardly run. On the highway it was perfect. Stayed overnight, got up in the morning and it ran great. By the time I got to the show, it was acting up again. Took me a while to figure it out, but the cure was putting in a new needle and seat.
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Old 08-08-2019, 04:43 PM   #17
scicala
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Default Re: Carburator problem, I think

Thanks for the explanation. Strange stuff does happen. Just never experienced that situation.


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Old 08-09-2019, 06:19 PM   #18
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Default Re: Carburator problem, I think

Usually when a needle valve is leaking the car will be flooded when trying to restart due to fuel pressure pushing fuel in when the engine is off.
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Old 08-09-2019, 09:26 PM   #19
flatjack9
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Default Re: Carburator problem, I think

The needle valve wasn't leaking, it was sticking.
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Old 08-09-2019, 10:41 PM   #20
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Default Re: Carburator problem, I think

Quote:
Originally Posted by flatjack9 View Post
The needle valve wasn't leaking, it was sticking.
In that case, it wouldn't run at higher speeds. Doesn't make sense either way. Suspect the idle circuit clogged. How about linkage sticking like a bad return spring.
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