YF, AARG...

[Anonymous]

Put kit in YF and no change from before.
Idles nicely and gentle acceleration of throttle for 1/4-3/8" causes no issues, but if you hit it there is a huge flat spot then lots of sputtering...
Big thing I did notice: no "shot" into venturi from accel pump.
(old and new pump diapraghms were fine)
Q: No shot would cause a huge flat spot, correct?

I took the top off the carb and watched the accel pump action.
Fuel shot comes up the vertical passage in float bowl wall past the "needle valve" to the top of bowl where it is sealed by gasket.
I put my finger on top of the passage to act as the gasket seal, and the pump shot bleeds back into the float bowl and nothing goes into the venturi! There is what looks like a nozzle into the venturi right at top of the "pump passage" where the bleed port into the float bowl is.
Q: Is this "nozzle" where the "shot" enters the venturi?

If that is the nozzle, it is blocked somehow.
I twisted about 8-10 threads of wire together and tried to push them through, they "hit" something and bent. What could be in there?

 

[grocery getter]

I don't know about your YF but on most carbs there is a ball bearing that is a check valve. if it's missing (or stuck) it could cause your problem.

 

[falcon60]

Yes,that's the place the accel shot enters the venturi. The nozzle can and does plug with debris or corrosion from years of use.You may need a very small drill bit like a torch tip cleaner uses-or a very stiff single strand wire,but you need to open that nozzle to fix the flat spot.
You can plug the return-to-bowl side if you want....it will give you a better accel pump shot if you do. Sometimes beneficial in a high-perf situation.

Terry

 

[Anonymous]

Yes,that's the place the accel shot enters the venturi. The nozzle can and does plug with debris or corrosion from years of use.You may need a very small drill bit like a torch tip cleaner uses-or a very stiff single strand wire,but you need to open that nozzle to fix the flat spot.
You can plug the return-to-bowl side if you want....it will give you a better accel pump shot if you do. Sometimes beneficial in a high-perf situation.

Terry

Cool. Terry, thanks for that verification.
I wanted to confirm my suspicion before I attacked it.

grocery getter, thanks, mine has a needle seat-check valve and it's working.

 

[Anonymous]

The nozzle can and does plug with debris or corrosion from years of use.You may need a very small drill bit like a torch tip cleaner uses-or a very stiff single strand wire,but you need to open that nozzle to fix the flat spot.

I plucked two "hairs" from a wire brush, and used the ever handy hemostats worked great! Now runs properly, wahoo.
Finally able to drive it onto ramps and take look underneath, not too bad just really greasy from old VC leak.
Best part was found out it has an actual flowmaster and 2" exhaust from where the headpipe goes horizontal all the way back

I bet the 300 I pulled the carb from is probably a runner... HMMMM

The correct information when I need it= priceless
This forum rocks!!! :thanks:

 

[falcon60]

Cool! Amazing how that little pump shot makes all the diff,huh? Mine worked perfectly for three months then one day just plugged solid with some old white corrosion that broke loose from a drilled passage....reamed the crud out with a wire-sized drill and all was well.Usually a nozzle like that doesn't suddenly plug so solidly but on the YF the hole is pretty small. On the plus side I am having excellent results with this carb on my 200....can't imagine a better match for power and mileage. I was originally planning on a two barrel swap but this carb is just too nice to change. I believe it's originally from a '75 big six in a pickup.

Terry (last tank full netted 26 mpg and it hauls butt!)

 

[Anonymous]

On the plus side I am having excellent results with this carb on my 200....can't imagine a better match for power and mileage.
(last tank full netted 26 mpg and it hauls butt!)

:wow:

I like the sounds of that, I'll be happy with 20 mpg with the C4.
I bet that 5 speed is a blast!

 

[Anonymous]

HELP! Carb still has issues:
Idles nice and light throttle is ok, progressive acceleration is ugly: hesitation, major sputter/total loss of power.(like it lost fuel supply).
I can stomp it off the line and it pulls ok but not smoothly.
I adjusted the metering rod set screw from standard setting to bottomed out at WOT (per search info) and it got worse. (I put it back to standard) I'm not sure what to do at the moment...
Timing: 10*BTDC, Vacuum: 20" @ idle, Idle speed: by ear(no tach), Vacuum advance(dizzy) is connected to manifold vacuum.

Metering rod, does it "meter" the pump shot?

Could this be an ignition problem?

Thanks! Bill[/b]

 

[mustang6]

The metering rod is part of the main fuel circuit, not the accelerator pump circuit, but it does come into play under full throttle. The metering rod slides into the main jet to create a smaller effective jet size under part throttle. Under heavy throttle the metering rod is pulled partially out of the jet, leaving only a narrower part of the rod in the jet- increasing the volume for fuel to flow through the jet- ie. richening the mixture. Some metering rods are "2 step" and some are "3 step".

The metering rod is a different way of accomplishing the same thing that a power valve does in other carburetor designs. If a metering rod mechanism fails the engine will typically run extremely lean (rod won't pull out of jet), if a power valve is blown out an engine will run extremely rich (valve leaks raw fuel into engine).

 

[Anonymous]

Scott, thanks for the specific explanation!

If I understand it correctly :roll:, the accelerator pump provides a temporary boost to transition between light throttle/low speed cruise=metering rod seated in jet and heavier throttle/acceleration, high speed cruise=when the metering rod should be pulled progressively higher out of the jet to allow more fuel flow to sustain continued acceleration or higher cruise speed?

If that is correct then my problem is the metering jet, because I can feel the little "boost" when I press the pedal to accelerate, but the engine gets starved for fuel immediately after that.
Is it be possible that the metering jet was overtighened in the past and screwed too deep into the seat, limiting maximum flow?
I don't know what else to suspect? I'm trying to only pull out the gray hair.

Thats whats nice about the old engines, when they run like camel excrement its either in the ignition, or fuel system. And theres only 4 things in each system

(couldn't resist, borrowed it from another thread) :rolflmao:

I totally dis-assembled the carb again last night, then blew out all passages with carb cleaner and an air hose so I know for certain that is not an issue. I have adjusted the metering rod from one extreme to the other, while watching it move up and down, but it only makes a very marginal difference in how the engine performs.
That's why I'm convinced the jet is the problem.
Bill

 

[Anonymous]

I removed all extra items from the diagram that aren't on my carb.

#31 (right center) is the metering rod.
#43 (left center) is the metering jet- that has to be my problem!
#42 (next to 43) is the low speed jet- how does fuel flow through that?

 

[Anonymous]

I was aggravated with the carb , so I decided to modify slightly and see what happens... IMPROVEMENT!!

I used an emery board on the metering rod to smooth the surfaces (also shortened the tip due to gouge) and drilled out the .120 jet to .125
Now has only tiny hesitation and will pull(although not strongly) through all acceleration positions with no apparent sputter

I'm thinking about enlarging the jet one more step, but even 1/64th bigger drill bit is .015"
First step was .005" and that made a noticeable difference.
Is .015" too much of a step up?