73 - 4300D Gremlins....

[7173Vert]

I’m chasing a stubborn flooding problem on my original 4300D carburetor. After having it a part a couple times to check for obvious signs of possible issues, I’m still having the problem, Basically, the car fires right up and as it is warming up, the carb is generally operating fine. About two minutes in, it starts to stumble and I see fuel oozing out of the accelerator pump (top) and if I hit the accelerator, it shoots out of the available vents.... It is dumping into the engine based on the black carbon build up on the new plugs. I’ve changed out the needle assembly and whatever else I could that comes in the standard rebuild kit. I’ve set the float to 13/16ths as per spec. This carb also has the auxiliary fuel bowl inlet that is located just before the main inlet.It is also controlled by the main float operation.  It appears to be set up properly also. Based on known flooding concerns with these carbs,  I’ve read that it may be advisable to eliminate this by either soldering the inlet shut or purchasing a capped screw to replace it with. With respect to the float itself, it appears to be in good shape, apparently the only test you can do on this is to weigh it against factory specs. I don’t think this is the problem, yet. The fuel pump is the factory original installed unit and clearly is pumping fuel to the carb)).
 

I’m curious if there is a knowledgeable 4300D guru on here that can offer me some pointers, If need be,  I am looking at possibly sending it out for a professional rebuild, but have not yet found a place. If someone has a proven recommendation, that would be helpful. I am also looking to buy an already rebuilt unit known to be in good ready to go operation. Again, if someone has a source, please let me know. I spent the past three months working on this car to get it ready for the summer and now I am stuck with it on the scissor lift until I can correct this last carb issue.

The good news is I did get the valve seals changed, the heater core that had been previously capped off is in fact in good working order today. Completed required maintenance of  the cooling system, retained the dual point set up, all of the original emissions are cleaned up and back in place, complete new brakes all round, shocks replaced, suspension serviced, changed out all the fluids, etc. Just down to this stubborn carb issue...

Anyone have good experience with theses 4300’s?

 

[Don C]

I would check the fuel pressure between the pump and carburetor.

 

[7173Vert]

I would check the fuel pressure between the pump and carburetor.

I plan on it, but, apparently it has been fine for 48 years. It is the original fuel pump. The only thing I changed between the pump and carb was the fuel filter. It was an old Motorcraft filter and I put on an aftermarket. However, thinking about it more, this is also when I blew out the aluminum cap at the front of the fuel inlet on the carb when I first started the engine after completing the work on the car over the winter. Have to wonder if this plug issue plus the fact the carb is now flooding has to do with some unknown issue with the fuel pump now pushing harder then it ever has... What is the factory setting on the fuel pump, 4-5psi? I will also look to replacing the pump with a spare and see what happens. Thx.

 

[c9zx]

I am not a 4300D guru. I have worked on several and rebuilt a few. Getting the float tabs bent exactly right to properly operate the primary and auxiliary needle and seat is real challenge. Some class racers eliminate the auxiliary needle and seat and change the primary to a high flow ball style needs and seat. I would disable the auxiliary with a set screw and se if it solves the problem. The "power valve" is also a known problem, opening too soon and fluttering. The 4300 series of carbs are some of the worst design I've seen. Right up there with the old Holley "tea pot" carbs from the 1950s. Chuck

 

[7173Vert]

I am not a 4300D guru. I have worked on several and rebuilt a few. Getting the float tabs bent exactly right to properly operate the primary and auxiliary needle and seat is real challenge. Some class racers eliminate the auxiliary needle and seat and change the primary to a high flow ball style needs and seat. I would disable the auxiliary with a set screw and se if it solves the problem. The "power valve" is also a known problem, opening too soon and fluttering. The 4300 series of carbs are some of the worst design I've seen. Right up there with the old Holley "tea pot" carbs from the 1950s. Chuck

Well that’s inspiring, lol. I’ve heard about the concerns with these carbs, what can you do when you are trying to keep it original. I was pretty careful when measuring the float tabs. The main inlet required a 1/16th adjustment and the auxiliary was fine. I personally do not see the need for the auxiliary, especially on a street car. I’ll look at the power valve a little closer as well. I actually find the carb easy to work on compared to the Q-Jet on my Vert. Thx.

 

[Don C]

The 4300 series of carbs are some of the worst design I've seen. Right up there with the old Holley "tea pot" carbs from the 1950s. Chuck

The 4300s look like a real carburetor on the outside, a POS in carburetor clothing. Just looking at the tea pots make you wonder how they could work, they were trying to reduce the overall size of the 4-barrels so dual carburetors would fit on smaller engines. Another major fiasco were the variable venturi carburetors, the description of them sounds good, operation of them wasn't. And, talking about carburetor tuning, anyone ever try to tune a carburetor in the late 70s using the procedure in the shop manual and injecting propane into the air steam flowing into the carburetor? 

 

[c9zx]

Don, Funny you bring up the VV carbs. I still have the tech manual for the carb, it is 38 pages long. Absolute junk, I worked on some in 1978/79 at the LM dealership I worked at. Most ended up being replaced under warranty. I never did the propane thing, it sounded like a really bad idea to me. Chuck

 

[7173Vert]

Ok... However, not willing to throw it in the garbage because some don’t like this carb. I’ll keep at it and hopefully find a way to bring it back to life. Process of elimination. Once you put another carb on it, the originality is gone... Thought I would try here to see others experiences in keeping them running. A couple good comments to consider...

 

[c9zx]

I'm not suggesting you throw it away. I am saying they are very problematic carbs. The flooding almost has to be caused by the needle and seat(s), the float and tab adjustment, or the pivot for the float. I understand your desire for originality, but if the choice becomes it is original but you can't drive it, or use another carb that allows you to drive it.......The choice is obviously yours to make. I hope you get it sorted out and keep us updated. Chuck

 

[Don C]

If I had one I wouldn't give up on it, either, it would become a challenge. When you work on it make sure everything is spotless, and make sure every hole is open and doing what it's supposed to. I like squirting carburetor cleaner through the little tube into each one and make sure it comes out where it's supposed to, and then blow them dry. Check it over very closely for any porosities in the castings, I encountered a few carburetors with porous castings from this era.

 

[midlife]

What's strange to me is that everyone complains about the poor design of the 4300 carb, yet the earlier version, the 4100 (from circa 62-67) was considered one of the best carbs ever designed and built.  The new Summit carb is based on the 4100. 

Has anyone thrown a 4100 on a Cleveland?  Did it work?

 

[Hemikiller]

What's strange to me is that everyone complains about the poor design of the 4300 carb, yet the earlier version, the 4100 (from circa 62-67) was considered one of the best carbs ever designed and built.  The new Summit carb is based on the 4100. 

Has anyone thrown a 4100 on a Cleveland?  Did it work?

The 4300 / 4300D has about zero in common with the 4100. 4100 is an incredibly simple and reliable carb. The Summit M8006 is simply a Holley 4010/4011 series that flopped in the 80's.,mainly because it didn't "look" like a Holley I have a 4010 600DP on my 71 right now and it's a very good carb.

I gave a 4300 my best shot on my 71 M-code Cougar and after a month of tinkering with it constantly, two rebuilds and 7 mpg, I bolted on my trusty 800DP with a 1/2" spacer and never looked back. 

 

[7173Vert]

The 4300 / 4300D has about zero in common with the 4100. 4100 is an incredibly simple and reliable carb. The Summit M8006 is simply a Holley 4010/4011 series that flopped in the 80's.,mainly because it didn't "look" like a Holley I have a 4010 600DP on my 71 right now and it's a very good carb.

I gave a 4300 my best shot on my 71 M-code Cougar and after a month of tinkering with it constantly, two rebuilds and 7 mpg, I bolted on my trusty 800DP with a 1/2" spacer and never looked back. 

All the tech guys here that have walked away from the 4300... Interesting. I would think that the carb on my car must have been reliable having been on the car for 48 years before finally giving out. It would have been swapped out years ago by previous owners if they had the problems that some have encountered here. I guess they were one of the lucky one’s. I am somewhat surprised at the poor status given these carbs by this group. I’m not really hearing about specific issues with the carb, more so about not being able to set it up properly. Maybe it’s justified, I will find out one way or the other. In the meantime I will search out a second 4300D carb to keep the car on the road and original.  I’ll then keep tinkering, researching and learning on this carb in all forums until I can come to my own conclusion. I’ll let you know the end result...

 

[Hemikiller]

The maladies of the 43XX series carbs are well documented, and Ford with all their engineering resources couldn't get them right either. 

 

[7173Vert]

So it can be fixed. Good.

 

[clevelandcoupe]

Ken,
I know you will not get discouraged about this carb thing.... After all the issues you had with the quadrajet on the 429, you will get this and will be an expert for the 4300 also. Go get it, I'm sure there is a lot of available knowledge on the web and other forums.
Thanks, Jay

 

[bdennis]

Guys,
Just digging up an old thread and thought I would share what I found.

I have been chasing an intermitant issue with my Motorcraft 4300 (square bore) for a few months now.

It would start up fine and run with no issues. Then I head out on the highway and after a number of K's down the road (I'm in Australia so no miles here lol) I would back off and the thing would run very rich (I have a O2 sensor on one bank of the exhaust). Normally it runs lean heading down the highway but when it starts ti play up, it would run very rich and start to miss fire and blow smoke and at idle all be it a very rough idle.

I know the carby is fine as I purchased it fully restored and rebuilt (by a carby expert).
I also doble checked the float adjustment and found it to be correct.
My car is a 351C H code that I converted from 2V to 4V using a local "small port" 4v inlet manifold (sourced locally as our Falcons ran 4 barrel carbs using the 2v heads - we call them small port heads) to match the 2v heads.

I also rebuilt the distributor as its vacuum advance was sticking.

In doing some research I found a few video's talking about the secondary inlet valve on these carbs is known to be a problem as it is only held by gravity. Also they are prone to issues when fuel pumps are feeding at a higher pressure than the base 5 or 6psi. Last year I replaced my original 1972 factory one with a stock replacement so I suspect it is pushing a little more than 6psi.

I found this video that talks about the secondary inlet. See from about the 5:30 min mark.

- https://l.facebook.com/l.php?u=https://www.youtube.com/watch?v=cxN1OxF9858&t=479s&fbclid=IwAR2Xl1T23Yt8s-rg64Fb5DqbfB8utdzyy5C_MQxTpnHbFjc33Lom1QxgHPg&h=AT0uys9ymYRmHxCM5NlAPybp6JYfnaih9OlkEoqavKL4cxSgg-Mz_OYc0M-ZUtz24bVze1GQMlMrCcpHMMkM2QqC_jjaa33PMYZxwjgBzcJJsBuW7-2N_DHuqLsW5Cta7nSfHQ

As the car is a driver and not a drag racer (stock FMX trans, 2.75 diff etc), I felt that if I follow the advance then I wound have any issues as I am unlikely to be driving the card hard enough for the fuel in the bowl to run out!

Basically the advice was to either replace the secondary inlet valve with a bung or block up the factory one.

From https://www.carburetor-parts.com/75-45 (Mikes Carburetor Parts)


I opted to modify mine my removing the needle and soldered up the hole.
To do this I found a small screw that fit in side the valve snugly and then proceeded to add solder.
As the valve is brass the solder adhears to the brass nicly and a standard soldering iron with a fine tip did the job.

I then reinstalled into the carb and reinstalled back into the car.

I have now been on 2 drives trying to make the engine play up as it was before the change and thankfully, it no longer seems to have the issue.

Of note, when I parked the car after a drive before the change, the garage would always smell of fuel. Now it does not.

I suspect a combination of a slightly higher pressure new fuel pump (stock off the shelf type) plus the gravity design of the needle in the secondary value was the cause of the issue.

I can now comfortably drive it on long runs with out the concern of it failing and or playing up.