Testing of the carburetor secondary throttle valve (1 Viewer)

[LEO5651]

As the title says - Testing of the carburetor secondary throttle valve - is there a way? Our 1980 FJ40 stock 2F with rebuilt carb does not seem to open up or feel the secondary valve when we step on the gas, not like the 1971 Ford Bronco we have with a 302. We know that the 2F is not a rocket ship engine but it seems flat in response and with out that secound bit of pep or power when the foot is applied. Any suggestions were and what to look at or test.
Note: The carb is pro-rebuilt and presumably set to install without any needs other than the mixture and idle which were done- runs good good
Thanks

 

[1911]

The easy way to test for any movement of the secondary diaphragm is to put a small paper clip on the flatish metal rod that comes out of the diaphragm pot and connects to the secondary valve (butterfly) to open it. Push the paper clip all the way up to the bottom of the diaphragm pot, then go take a drive up a steep hill where you can push the accelerator pedal to the floor and leave it there for a bit. When you get back home, check the position of the paper clip. If it has moved, your secondary diaphragm is functioning. If the paper clip has not moved, it is not functioning.

 

[LEO5651]

So you mean that the paper clip should be at one end rapped around the rod lightly to were it can slide a but then slide it up into the diaphragm housing to were the tip of the paper clip is up against the bottom of the diaphragm itself? Is this just testing the diaphragm its self? Cant this be tested with out the paper clip and driving? Thanks

 

[Pin_Head]

The paper clip tests whether the secondary is opening.

More info:

Aisan Carburetor vacuum operated secondary

 

[LEO5651]

Okay now I am tracking-thanks guys we will give it a go.
If its not moving then the diaphragm has a hole, but I hope not as it should of been replaced when re-built.

 

[LEO5651]

We had time to run to the shop with the 40 (no real hills) with a paper clip on the shaft of the diaphragm as shown and when we returned an looked it had not move but ever so slightly on the arm. Tried it again with a snug cotter pin slipped over the flat shaft with the same out come, no real 12-13mm movement. We checked the rubber membrane in the housing with a bright mini mag behind it to see if any pin holes or tears exist, none. The little seal in also in-place between the carb/diaphragm were the two screws hold it on. The arm at the bottom were it meet's the shaft that runs inside the carb base is good. But not sure about the roller and arm on the right side of the carb, looks as it's not being contacted by the small arm to push it up when I hold the throttle wide open. We will watch the video if there is a part on the secondary adjustments.

 

[Pin_Head]

The way it works is that the mechanical linkage kicks open the secondary a little bit. This is enough to build vacuum inside the secondary venturi. The vacuum sent to the actuator is the lesser of the primary and secondary vacuum levels. As the vacuum builds in the actuator, the more it opens the secondary. You may need to increase the mechanical opening to get enough initial vacuum in the secondary start the opening.

Also note that this only kicks in at wide open throttle (pedal to the metal) for 10 seconds or more, so it never kicks in during normal driving.

 

[LEO5651]

I do appropriate your help on information, we just finished with just a small tweak to the part to bend just enough to give the butterfly about a 4-5mm opening when it just starts to touch, we put a new paper clip on and test drove, unfortunately the clip fell off so we don't know what the readings are, but when we turned into the yard the engine was now running really crappy and low on idle with black smoke coming out of the exhaust (rich). We did nothing but bend the tab a hair and nothing else other than stomp on the gas a few times (to the floorboard). So we leaned it down enough to keep it from dying out. So now we have a new problem, oh well. The only thing we can think of is we put a can of Seafoam in the full gas tank a few days ago but was running fine up until now. I believe the initial setting for a mixture screw is 1.5 turns out from fully seated and it was out around 3.5, so maybe the seafoam did something and cleaned out the carb but as said it in a fairly newly re-built carb (2-3 months). Still working the issue. Got to get it running for hunting.

 

[JAFO2014]

Make sure that the gas level for the float bowl is center in the site glass, aligned with the white dot on the glass.
The idle mixture screw really doesn't affect the secondary much I don't think. It is more for idle. If you get it idling good, then the truck should drive, but have no get up and go under any load without the secondary kicking in. I fought the secondary for a while. My 40 was a dog going up hill.

Remove the secondary diaphragm assembly. Push a short piece of say gas line tight up against the small air hole in the assembly and suck on the tube. The diaphragm should move the rod inwards. If that works then you are not getting suction from the carb. You might have vacuum leaks or such. The port that feeds the diaphragm might be clogged. With the assembly removed shoot some compressed air into that small hole in the carb to try to blow it out. Also make sure you have a good seal between diaphragm assembly and carb and are not blocking that port.

I did the paper clip trick and it works good. I used a large size paper clip. You clip it onto the rod, right up against the bottom of the housing. Then when the rod moves upwards into the housing it slides the clip down the rod. So with the engine stopped after test, if the rod moved the clip is now down the rod from where you initially clipped it.

What I found was some blockage in the air port in the carb and also my secondary butterfly was not adjusted correctly.

 

[LEO5651]

Just cam back from the gas station, the gas gauge we have is needlessly to say unreliable as the wires need some attention. Meaning we were reading near full and really it was at 1/2 tank when we wiggled the wires. So we had one full can of sea foam in a 1/2 tank of full about 6 gallons, no wonder we were running rich. Now we have the tank full of fuel it seems to run and idle much better without blowing black smoke when revved.
Can anyone tell us what a normal setting is on the mixture. We set it to fully closed and backed it out 1.5 turns as the books states, and now it set to about 1 turn out (drop/lean) from fully closed but runs good, but before it was like always around 3.5 turns out, so is now about one full turn from fully seated - okay?
As soon a we validate the mixture setting, we will get back the secondary testing.
JAFO2014 you say a large paper clip maybe thats why we lost ours as it was a small clip. Do you feel the secondary kick in now after you got it all set. Pin-Head says about 10 seconds +/- until it kicks in. Glad you were highlighting the possible blockage in the ports even if its newly re-built doesnt mean its a 100%. If we fail on the clip test fails we will clean the ports as you suggest. I guess it's not like our Bronco as when you are driving and then you punch it and the secondary kicks in fast and away you go. Will post our outcome ASAP.
Thank you

 

[Pin_Head]

Try adjusting the mechanical linkage first. This is a common problem and a common solution that it easier than disassembling the carb.

The screw only adjusts the idle mixture. You adjust the primary and secondary mixture by changing the jets.

 

[LEO5651]

Updated - took the 40 out and it started to run crappy again so not sure what took place but cant check the secondary diaphragm assembly out until I find out what is making the idle crappy. Plugs could be fouled from the seafoam. the strange part is if I turn the mixture in to were its 3/4 from fully seated it runs better but it may be to lean? Was running fine before?

 

[Pin_Head]

Maybe you have a bigger problem than the secondary. If it runs when the idle mix screw is all the way closed, it isn't idling; it is running on the main jet due either to a manifold vacuum leak or a lack of idle fuel.

 

[LEO5651]

Still don't know what changed while testing the secondary diaphragm assembly, as we noted we just removed the diaphragm to check the membrane inside for holes reinstalled, checked the secondary shaft, and drove fast with peddle to the metal a few times.
We will check for manifold for leaks and possibly the notorious crack found in the intakes below the carb and Spark plugs, fuel filter.
Lack of idle fuel is that one of the same with the main jet?
Can you mention what is a normal amount of mixture screw turns from fully seated, normal settings usually on the 40 carbs, just for reference like is it 2.5 turns out or when set or ? Oh just for kicks we checked the timing and it is spot on.

 

[Pin_Head]

Dirt floating around inside your carb can cause intermittent problems. The idle fuel comes from the “slow” jet. Two turns out is a good starting point, but it is set by the “lean drop” method detailed in the FSM. No change in 4 turns means something is wrong. If it runs with the idle screw closed, then it isn’t idling and something is wrong.

 

[LEO5651]

Just heading out to do some chores, I will be able to work on it in a few hours, will check for the leaks as you said, and the others mentioned, may even pull off the top of the carb and look into the bowl and float area. The idle screw seems to be working as we can set the idle up or down its just the mixture is acting goofy. Maybe we dislodged some crap with the combination of the seafome being pretty strong in tank, and the hammering of the throttle while tiring to get the secondary to kick in.
We (family) have a bit of time unlit hunting, so thank you for your interest and help, nice to have a web site like this and folks like you guys.

 

[LEO5651]

My dad is pulling the spark plugs witch was a good place to start, as you can see they are pretty well fouled from what I am guessing the Seafoam being to much concentrated (more Seafoam than gas in the tank) and going out driving and flooring the throttle, blasting all the loose crap in the valves out producing low speed fouling at idle. Seafoam does work.
He is cleaning the plugs and installing soon and we will test run and if all is good with the mixture setting and idle we will proceed to check the secondary with the clip again.

 

[Tancruiser]

I think I would replace those plugs .

 

[LEO5651]

No we have a air driven abrasive spark plug cleaner that made them near new again which it did, re gaped and installed, but we are still getting the same response on the mixture and idle. If we got back to the tail pipe and listen you can hear the missing and stumbling that is a tell-tail sound telling us something went amiss. Before it was smooth and steady in sound.
As I remember if I was to close the mixture screw all the way in the engine should stumble and fail. In this case it will continue to run. We did the soap and water in a spray bottle trick and shot it in all the gasket areas we could find without any noticeable change in RPM, so I believe a vacuum leak is not the problem unless we miss something. The top of the carb was removed and the float and needle was inspected and when running the fuel level is .5 of the window on the bowl. Checked and used a air nozzle to clean out most all the ports, along with the jets, power valve, acc pump, and anything else we could get to to include the Ventur's. Removed the fuel filter and inspected and visually watched fuel moving in it as the engine ran. As mention in one post the timing is spot on but we will put a vacuum gauge on to see positively on the vacuum leak or stuck valve..
I forgot pin head was well versed in the 40 carbs so I feel better with him and you other guiding us a bit. Probably need to start a new posting on "What went Wrong".

 

[LEO5651]

IT'S OVER- we found the problem and as most of the time it's an overlooked item.
Seems as my dad without me knowing bent the adjusting tab a hair up for the contact of the secondary butterfly valve to the lever arm. It was barely noticeable but with a inspection mirror and a flash light from the side it looked okay until I looked in from the top with a flash light at the butterfly, it was hard to see but it was about as wide as a small pin opening, it was not closed tightly as I believe it is suppose to be. I bent the tab back to were we could get a piece of paper between the tab and lever arm. Now the mixture is out about 3-4 (as it use to be) or so turns and not one miss from the engine, smooth as before. I guess pin head or someone can give the reason for this butterfly loss of vacuum but I am just happy that it is done and the other best part is we completed the clip test or my dad did and it moved as he said about 1/2" on the shaft.
So we have it all set and good to go, wow what an ordeal just for a paper clip. Thanks everyone for the help.