Technical Holly carb issue , I think .

Hey all . Been toiling around in my 40 merc and it’s driving me nuts.

when I got her she would barely idle and fall on her face when you would accelerate unless you put your foot right into her.

I drained the tank, replaced both fuel filters and rebuilt the carb.

it’s a holly duel float bowl carb with non adjustable floats and 1 power valve.


Anyways she runs a bit better, the choke makes her stall out, and she idles really low until it’s warmed up.
Still has a bit of a stumble on accel

Over all she runs like crap.

tune up is good.
Fuel system is clean
engine is good

I’m thinking of just taking the holly off and going with an edelbrock , I don’t have much experience with this type of holly , and from what I’ve read they are temperamental.

 

Plugs? I'm sure you did perhaps that would be under tune up you mentioned...

 

This is one of my areas of limited knowledge...points?, out a tooth? Sorry I'm just thinking out loud...

 

Sounds like you've addressed any/the carb issues (which is always the typical "go to" culprit for most..not always justified).
I'm leaning more towards possible vacuum leak, which also may explain the "stumble on accel" contributing to poor vacuum advance performance.

 

Check timing? On my A, I timed with a light, but also by ear. Much better! Small vacuum leak? I have also had to double up on base plate gaskets. After a few heat cycles recheck all bowl screws and base bolts (don’t over tighten). I know it’s basic stuff, but other than dirt in the carb, Holleys are pretty reliable. Let us know, Carp.

 

I've seen this movie a lot on the automotive forums.

"Engine Runs Poorly. Replace Carburetor" is just not listed anywhere in the shop or Tune-Up manuals! I mean sometimes it works, but... Maybe some carburetors are "better" but I'd think just about any serviceable carb within reason could be made to run more than acceptably.

 

Could be overcarbed again the Holleys and all carbs have a rating that should match the engine makeup...

 

Vandenplas, I like Holleys and have worked with them for 30yrs. If you've narrowed it down to the carb,
just to confirm you could put an Edelbrock on it and see if it cures your issues. If you want to keep the
Holley, I would tear it down and give it a good cleaning to start. While inside, I would see what is the number on
power valve, typically they use a number 65. Then see how large the jet sizes are. Typically 65-68 is
a good starting place. Make sure the secondaries are completely closed when adjusted and go from there
Holley offer more things to play with and adjust, which can be good or bad. If you pull it apart, try to use
the blue neoprene gaskets to reassemble as they can be reused several times.

 

He did mention rebuilding it in the OP...not discounting your helpful info...

 

Looking at the photo you need to loosen the pump spring, that will help your off idle stumble. It looks like someone has cranked it all the way down which decreases the pump travel.

 

Vandenplas, older Holley carbs are real good for rupturing the power valve diaphragm. One good backfire through the carb and the power valve is toast. When the valve goes, they run dead rich (like 10 jet sizes too rich) and idle very crappy. Newer Holleys have power valve blow out protection but, the 600 on my 351W has it and still nuked the power valve. My 351 acted just as you described, I like Holleys and have no trouble working on them, but, I would buy a new Edelbrock or Summit carb, the one that resembles the old Autolite 4100. Remember, with your AOD transmission, you have to have the exact right bracket and carb linkage for the TV cable or the transmission will not shift right and eventually burn up. Good luck!
Andy

 

Did you check your fuel pump? Put a fuel pressure gauge or a clear fuel filter on the line and see when you stab the throttle if she is starving for fuel. I hate to say it but our new gasoline stinks and eats gaskets and rubber parts. I had a very similar issue on one of my cars.
Also how are the plugs as they don’t lie and will tell the story if she is fat or Lean and condition of ignition system

 

Have you checked vacuum? That's where I would start. A vacuum leak not only affects the fuel mix but can screw with the timing if running a vacuum advance.

Lots of the Holley's with no external float adjustment we're factory application for something and sometimes needed a special base gasket to seal them up.

 

I bet it still has some kind of float level adjustment? Has to. Might be a pain. Fuel height in the bowl is what is at issue there actually, but that spec is critical to any carburetor.

Holley carburetors have had power valve protection since 1992. It's easy to tell if the power valve circuit is defective, the idle mixture screws will have no effect when turned in all the way. Plus, the spark plugs will be fouled real bad.

 

I look down the carb while running and opening the throttle to see that the pump is kicking in when it's supposed to, that the fuel coming out the venturis happens when it's supposed to, isn't dripping or uneven between the two venturis.

 

I adjusted the pump lever as it was tight to the pump lever
The accel pump worked when I twist the throttle .

the carb was dirty when I took it apart. Real easy to rebuild , pretty sure no issues there.

I looked all over the inter webs and found NO float level adjustments on this carb which really confuses me.

I did find a couple vacuum plugs deteriorated that I replaced.
I does run a bit better once it warms right up.

Im leaning towards a vacuum leak at this point.

I’ve spent the last few days tearing my basement apart. The waterproofing is almost done so I can start drying and repairing the inside.
Hopefully I’ll have an hour or two this week to poke around a bit more.

mist got electronic ignition , I pulled the plugs when I got the car and inspected everything. The plugs where a golden brown and the wires and cap are pretty much new.

the Ford electric ignition is almost fool proof so I don’t think so, but I might just throw some plugs and wires at it anyways .

I want to get rid of those silly yellow wires anyways.

I just don’t want to throw the parts cannon at it and still not fix it, or not know what fixed it.

the car was parked for about 2 years before I got it , just drove around his yard from time to time .

I’ve put gas in the tank twice since I’ve owned it , and I have clear plastic fuel filters on it and they are not dirty, I drained the tank and no real junk came out. It’s definitely not the original tank either . And it looks to be in great shape from the outside.
So again I’m confident in saying it’s not garbage floating around the fuel either.

It’s carb or vacuum leak. I’ll keep poking around and let ya all know.

I’m familiar with edelbrock carbs and factory mustang carbs never screwed around with 4 barrel hollys and all I’ve read it they can be finicky . Only reason I would like to swap it out.

 

I'll send you an edelbrock that needs rebuilt, you send me your Holley, even trade i have one like yours and need another for my tunnel ram project

 

Interesting....lots of advice on what to do to the carb, including suggested jets, and we have one picture that shows part of it, and no LIST number....

first thing I would do is figure out what we're working on.

Second thing I would do is characterize the ignition timing. What is it initial? What is it all in? What rpm does it start advancing, what rpm is it all in? What does vacuum add?

On the float level...you rebuilt the carb, the kit came with instructions, didn't it? That should tell you how to set the float level. If the needle/seat is not the screw adjustable type, then you have to bend a tab on the float, and measure the float level with a ruler, like any other type of carb, right?

 

I know on my Holley carbs you have a screw on the side of the bowl. You unscrew it and fuel should just dribble over. I know Holley used to sell clear screws so you can see float levels

 

All Holley carbs have adjustable floats, but some late model less expensive Holleys require the float bowls to be removed in order to adjust the floats. More expensive versions can be adjusted externally. When you rebuilt the Holley I hope you turned the float bowls upside down and set the floats to slightly below level? There's a tab that sits on the float needle to close off gas, and it gets bent to adjust height.
I'd be looking at the accelerator pump and be sure there's no play between the pump arm and the linkage. Any play will result in stumbling, and lack of response before the pump begins to push gas as you step on the throttle.
I'd hesitate to suggest a jet size without knowing the carb cfm, and all the engine specs. Generally a 600 cfm would be a good choice for a stock SBC 350 of under 300 hp, and I'd want around #64 primary jets, and maybe #68 secondary jets.
As already mentioned you need to be sure the transfer slots aren't over exposed, so no more than .040" is typical. Also want to crank down the air mixture screws and see if they stall the engine. If they wont, then it's likely the throttle plates are too far open and the carb is sucking fuel at idle causing issues.

 

What Holley carburetor are you looking for, I may have one for you.

 

This is what i bought. I want the same one. Probably have to order another one lol

 

Nice, I may have a 600 vacuum but it won't be shiny.

 

https://www.holley.com/blog/post/adjusting_your_carburetor explains dry float settings on carbs without externally adjustable float levels. Every one I've ever rebuilt had external adjustment, but if I set the level dry when assembling the parts, the fuel level in the bowl is close enough when checked wet by removing the sight plugs that it's not going to be a source of problems. Note that if you're using something like a drill bit as a gauge for the dry setting, there's a difference in the measurement at the toe of the float depending on whether you're setting the primary or the secondary side.

Verify that the idle mixture screws have an effect on the idle. IOW, can you crank them in and kill the engine. If not, the primary throttle plates are too far open and exposing too much of the transfer slots which renders the mixture screws ineffective. Should this be the case, the closed position of the secondary plates needs to be adjusted. The carb has to be removed to make this adjustment as the adjusting screw is accessed from the underside of the base plate. If you Google Holley secondary speed adjustment there's a video from Holley that shows how to adjust this.

Google Holley carburetor specifications and it'll bring up a pdf that gives specs on all carbs by list number. This will tell you what the original jet sizes and power valve vacuum ratings were for your carb. I'd assume your carb has a secondary metering plate rather than a metering block, so the jet sizes in the table are referring only to the primaries.

All the above assumes no vacuum leaks, including checking the throttle shafts for looseness which would indicate worn bores in the base plate. That happens, but isn't a common problem except on dirt track cars and similar applications.

FWIW, Holley has probably more tech information online than any other aftermarket equipment manufacturer. A little digging will find the answer to any question you may have. It would be good if other manufacturers did the same instead of the typical 50 pages of nothing but marketing BS.

 

They make a kit to put a power valve protection valve in older Holleys. I have installed several. But like you mentioned it helps prevent blow out but it is not 100% effective.





Bones

 

I will double check my timing , base advance etc.

the rebuild kit did not come with instructions .
It was kind of a universal kit.
The power valve had the same part number as what I removed.
It cam with a new accelerator pump needle and diaphragm.
Did not come with new needle and seats but the old ones looked good , not worn or no ridges.

the idle screws will stall the car when turned in and they effect the idle and power all through there adjustments.

I’ll double check the carb number.
I wanted to order a specific kit from the parts place in town that caters to the roundy round guys so I did get the carb part number.
But he was minimum 2 weeks out so I got a “ universal” kit from Amazon. It was a name brand kit . Came with a bunch of gaskets, o rings etc.

I looked online for float settings a came up nill, I’ll check again this week when I got some more time.
And I’ll bring my time light and tach/Dwell meter from work so I can confirm timing and my tach in the car .and my fuel pressure gauge to see what the pump is putting out.

she runs real good with my foot in her, not so much at lower rpm and idle.

 

Had 10 minutes to play with it when I got home from work, then I pooped the hood on the Merc.

Paying just a little attention, I heard what sounded like a vacuum leak, this whole time I thought it was just air rushing into the carb from the ridiculous oversized air cleaner.
Nope a couple shots of brake cleaner and it’s intake gaskets leaking

bolts are tight, bought this as a running driving car, parked for a year or two. It’s really clean under the hood so I just took it for granted it was junk and dirt in the carb.

oh well gonna order intake gaskets, get rid of those spark plug wires at the same time and clean up a few other things while I’m at it. Maybe even swap out the silly air cleaner !

what air cleaner would look good under the hood ?
I always liked the look of the duel snorkel air cleaners used on ‘85-86 mustangs.
Maybe a Cadillac batwing

not sure!

 

from what you know about the car, could the carb be from around 2011 or 2012?

This is what the needle/seat looks like in there, apparently. No screw adjustment, you have to bend the tab on the float, right?



But yeah, fix the vacuum leak, and you still need to get a timing light on it to see what you have.

 

That’s what I got @squirrel !!

yes after your a few other folks posts I used the old google and found the adjustments I need to do. Kind of crude snd a pain in the butt, I need to pull both ends of the carb off to access the two needle and floats. It is what it is.
driving it around cold is a complete disaster, once warmed up it drives ok if I lean into it, not so much if I’m just cruising.

I’m booked Saturday between fixing the basement and going to my daughters horseback riding championships , but Sunday I should be good to spend a couple hours fiddling

now hopefully I’ll remember my timing light , vacuum gauge and tach/dwell meters to bring home !

 

When you rebuilt the carb, what metering block gasket did you use? There's 2 styles.