Carb Tuning Help
Posted by Dense-Assistant624@reddit | projectcar | View on Reddit | 23 comments
Just had this YFA carb rebuilt for my 1980 F100 4.9L 300 and having some trouble tuning it. I had to also put a fuel pressure regulator on the line but have not taken a reading of the PSI yet. It now idles at this and has gotten slightly better as it’s running but runs very rough. Will not accelerate easily and begins the aerosolize fuel when reaching full throttle. There is NO vacuum coming off the manifold to the vacuum advance and none from the other port next to the idle set screw. No clue what’s blocking it because it was sonically cleaned. Any help appreciated!
BootPrize_milk@reddit
Check your pushrods I’ve had this exact thing happen to me
Dense-Assistant624@reddit (OP)
I posted again and it looks like the studs came loose and starts to back out
SCAMMERASSASIN007@reddit
Yah id be checking the fireing order again.
Dense-Assistant624@reddit (OP)
Found these issues. I made another post about jt
thedarkonekc@reddit
You need to check your plugs and wires cap on distributor
Gostaverling@reddit
This! This is a dead miss on at least 1 or 2 cylinders.
Dense-Assistant624@reddit (OP)
What’s a way to check?
igobyraymond@reddit
Loosen the bolt for the distributor and with it running, turn it a little bit each way and see if it improves. Sounds like the timing is off to me, especially if pulling wires changed how it ran for each cylinder. Might be worth doing a compression test too. Could have a stuck valve or something
bszern@reddit
I’d double check the firing order, that sounds way off.
Gostaverling@reddit
While running pull a plug wire. If the engine sounds worse that cylinder should s firing correctly. If the engine sound doesn’t change, that sparky ain’t sparkin.
titsmuhgeee@reddit
100%, it's running on four cylinders at most. Start pulling plug wires one at a time to find the dead holes.
Longjumping-Name8541@reddit
Timing sounds off or plugs fouled
Holiday-Witness-4180@reddit
As others have mentioned, check the firing order. Even if it is correct, you should probably reroute some of those wires. That number three wire should not be run like that.
ale624@reddit
you double checked the firing order?
rdm55@reddit
Set the timing and adjust the valves first.
Superlucky1@reddit
Clearly something amiss with the ignition components or an internal engine problem. At the end of the video, some fuel sprays up through the carburetor. This can be due to improper ignition timing, improper ignition dwell, stuck valve or improper firing order. My first guess is that you have two spark plug wires that on the wrong plugs.
hangindawg@reddit
These motors foul plugs pretty easy if they are overloading fuel. Replace the plugs, even if they aren't that old. Autolite coppers are nearly the cheapest plugs out there. It's definitely a misfire. it's wired wrong, or 1 or 2 plugs aren't hitting at all.... Turn the air mixture screw in until you can feel it bottoming out, dont screw it in tight. Just find the bottom. Then turn it back out 2 1/2 turns. Start the engine. It should run. If it's running rough, turn the screw out in 1/4 turn increments, then feather the throttle to see how it idles. It shouldn't take more than another turn to turn and a half to get it idling right. These settings have no bearing once you give it throttle. The mixture screws are only to set idle.
beermaker@reddit
That thing's shaking like a dog shitting a peach pit... Make double sure it's firing on all cylinders.
weelluuuu@reddit
Buy a vacuum gauge.
https://youtube.com/shorts/Vgu058PR3xk?si=dQd706qL9o2-YvaU
DriverXCRX@reddit
Same jets? Electric choke? Do you have a timing light?
Fuel pressure could cause this issue too. You should make sure it's running at the right pressure according to a shop manual before adjusting the carburetor. Otherwise you might have to readjust it.
It does seem like it's running rough. If you have a video of it running smoothly that will help for comparison in order to rule out other potential issues. Additionally, please share all the adjustments available on your carburetor and its make/model.
Onefingertyper@reddit
I'd check that all cylinders are firing first
Intelligent-Major492@reddit
It's perfect 👌
RhubarbIcy9655@reddit
To use the parlance of our time... bruh!