When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
1969 F100 360 2 Barrel Runs Good Then Immediately Runs Bad
1969 F100 360 2 barrel 3 speed on the column. Engine was rebuilt by a quality shop years ago and ran fine until recently. Truck runs good then when you rev it up while it is idling in neutral and the idle comes back down, it runs terriblle. Cant figure it out.
I have replaced :
Plugs
Plug wires (double checked firing order)
Rebuilt carb
Both carb base gaskets (2)
Fuel fiters (2) inline aftermarket and stock canister type.
Tank has been removed and cleaned.
Rubber 5/16 fuel lines replaced
Tried a new condenser-didnt help
Still waiting on a new cap,rotor and points but have doubts they will help.
Runs the same with the rubber vacuum line from carb to distributor connected or disconnected.
Any advice appreciated.
Thanks.
Last edited by sixty4chevrolet; May 9, 2026 at 09:36 PM.
Is your idle rpm returning to the same rpm when it comes back down from reving? The reason I ask is if the dash pot is failing it may be dropping the rpm too low.
Check voltages running to the coil. Clean up all electrical connections and grounds.
The idle comes back down lower after revving and makes the engine stumble,
Havent tried a new coil.
Never knew what a dash pot was until reading this. Thanks for the info.
I did notice something unusual when I first started it.
The dash pot had a 1/4 inch or larger gap between it and where it contacts the carb linkage, then I looked again and it was touching the carb linkage ?
Not sure how that dash pot is supposed to perform ?
Another note, This is a 3 speed manual trasmission truck, I researched a little on dash pots and read they were mainly for automatic transmission vehicles, maybe Im wrong.
Also to note, the 2 jets in the bottom of the carb didnt want to come out and I didnt want to force them, but I did blow them out with compressed air, I wonder if that was good enough ?
Thanks.
Last edited by sixty4chevrolet; May 10, 2026 at 03:43 PM.
The main jets on the bottom of the bowl only effects the high speed. The idle circuit is a combination of butterfly position and metering holes/slot in the throats of the carb. So if the throttle is going to a different position every time that a problem that needs to be addressed.
Ethanol or non-ethanol gas? I ask because when my '72 250 set for a while the ethanol gas created a pink goo that wold plug up the idle jets, it was fine at faster RPM's but would actually die at lower RPMs (and I was starting it weekly). I got good at cleaning the carb until I switched to non-ethanol. If it's used frequently probably not relevant.
Ethanol gas. I tested the vacuum advance today with a mightyvac brake bleeder. When I pump the bleeder the arm temporarily pulls in but immediately goes back to its original position and the bleeder doesnt hold the pressure. I ordered a new vacuum advance today. We'll see if it helps. Thanks Again Everyone.
Update, I fixed the issue. I fixed a few things at the same but I think the problem was the rebuild kit for the carb came with multiple gaskets. There is only 1 gasket that is correct to go under the power valve. It is thicker than the other similar gaskets. I think I put a gasket that was too thin under the power valve and the power valve was bottoming out on the carb body without fully sealing. I put the old power valve and gasket in and she runs fine now. However I replaced wires, plugs, condenser, cap and rotor, rebuilt the carb, replaced both carb base gaskets, vacuum advance, fuel lines, fuel filters etc. trying to get to the bottom of the problem. It took me a while but I never paid for a single hour of shop labor.
Last edited by sixty4chevrolet; May 29, 2026 at 05:06 PM.
Great work and a good warning about carb rebuild kits. Now if I only knew just what a power valve is. I've rebuild the Motocraft carb on my '72 250 one or twice but I don't remember that term.
A power valve is an fuel enriching device that is vacuum operated. It come in during WOT or when the manifold vacuum drops below a certain level. It richens the air/fuel mixture to give you more power.
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Slideshow: Called the Fortress, the 850-horsepower pickup combines Raptor underpinnings with military-inspired features, survival equipment, and a starting price of $285,000.
