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Carter yfa (7299s i believe) previous owner gutted the vacuum system and capped a lot of the vacuum tree and some ports on carb. Problem im hoping to solve is after letting off throttle engine backfires through carb and spits gasoline all over the windshield with the hood open. Thinking maybe some vacuum ports being open or hooked up incorreectly could contribute? Im also working on finding a timing light to verify the timing, but the engine idles smoothly and revs pretty hard so it cant be that far off.
i have the 300 with the YFA as well and it had a similar problem.First is the carb correctly hooked up to the vacuum advance or is it mechanical? mine used to do that when i put it under a large load. if your idle speed is incredibly low with a very high mixture it maybe idle fine and accelerate fine but when you go to close the throttle the gas builds up in the carb and then it spits all this build up all over your wind shield. If your idle is too high with a low mixture it will idle fine but will bog at mid throttle and sound like retarded timing. my vacuum system was a mess and plugging everything didn't do anything bad. it made it run far better because of the simplicity, you might try checking the throttle plate clearance to see if it is too open and adjust it until it is just starting to close. then adjust the mixture all the way in then out until the engine stops bouncing and sputtering. that's about all that i can think of as far as carb. if your vac advance diaphragm has a leak... it could seal when you accelerate advancing the timing but when you let off it could be retarding your timing too fast or too slow depending on how bad the leak is.
Sooooo check vac. adv. connection at carb. check timing. and check throttle plate clearance. replace vac. adv if bad.
Thanks for the reply, attached is a video of it idling, has modified exhaust but maybe you can hear if it’s idling too low or etc. I don’t have any tach to connect to ignition coil. Dist has vacuum advance. Part of my problem is I don’t know which vacuum lines go where on the carb. Hoping this is an easy fix, I want to drive this truck so bad (18 yr old kid here) I’ll buy some caps to start plugging holes. Additional question, I need a new hot air line for the choke, old one crumbles in my hands. How do you go about getting/making one?
Understood im 16 and took me 3 years on my 78. it sound like its running a little rough. Is there a very strong gas smell or more of a strong sweet smell coming from the exhaust? this can tell you aprox. how rich its running.
this is a diagram. on my 300 my vac adv is connected to the port about halfway up the carb near to the choke and it should run no vacume at idle.. also look down the carb and see how open the throttle is to see it its too open.
the YFA is kinda touchy about adjustment so make sure you have no vac leaks.
you can get one possibly at oriellys or you can buy 1/4 inch pipe and a bender. then crimp the ends smaller so it fits tight in both the holes
also sounds like its idling too high but that wont cause your problem
The problem you'll run into, over the years different folks work on it with different ideas about how to perform a tuneup. Two things that are super easy to bugger up - ignition timing, and carburetor - because any idiot with the "golden screwdriver" can make adjustments.
Never mind the fact that a carburetor once tuned rarely needs much adjustment, and initial ignition timing won't change - people still mess with it, when something else is going on. Say a vacuum hose or a plug splits and there's a big ole air leak. Instead of isolating the fault and repairing it, they try to "tune around it" and compensate for the original fault. So 40 years go by, anything and everything can be horked by now.
Your job then, is to first determine exactly what it is you have to work with, hopefully in good shape, and then get all those different parameters, settings, and adjustments back according to Hoyle, to spec so it will start and run good. Get the Shop Manual Ford put out for your truck. You need this.
That means performing a cylinder compression test. This way if there's a hole burned in a piston or whatever you haven't already gone out and wasted $$$ and bought a bunch of tune-up parts. First things first. Make sure the engine is internally mechanically sound, verify first that it is a good candidate to spend further $$$ on.
Hell, make sure the plug wires are installed in correct firing order. You'd be amazed at how often stupid tijuu like that happens! Check everything, because, no matter how stupid - somebody somewhere has done it.
Oftentimes a light dingleball hone and some new rings will bring an engine back to life, maybe some new crank bearings, re-work on the valve/ heads etc etc. Not everything has to be a high buck restoration but it has to brought back into line or it will be a lot of frustration and it will never run right.
i very much agree with tedster9 over years things get messed with and temporarily fixed and people try to fix a problems by changing something else. when i got my 78 the vac advance was hooked to a place on the carb where it got 5 hg of vacuum at idle because the timing was retarded. this made a part idle bog and causes problems. A vacuum gauge will be good. compression test as tedster said a timing light and just a general look over of the ignition system.
Carter yfa (7299s i believe) previous owner gutted the vacuum system and capped a lot of the vacuum tree and some ports on carb. Problem im hoping to solve is after letting off throttle engine backfires through carb and spits gasoline all over the windshield with the hood open. Thinking maybe some vacuum ports being open or hooked up incorreectly could contribute? Im also working on finding a timing light to verify the timing, but the engine idles smoothly and revs pretty hard so it cant be that far off.
Hey guys thanks for the great info, after playing with distributor and carb settings it has quit spitting and backfiring and has smoothed out considerably
... after playing with distributor and carb settings it has quit spitting and backfiring and has smoothed out considerably
OK.. but you still need to put a light on the damper and see where the timing is at. It can be running smooth as silk (by ear) at idle but the timing could be way, way off and might not even be driveable.
01-23-2018, 07:46 AM
(18 yr old kid here) I’ll buy some caps to start plugging holes. Additional question, I need a new hot air line for the choke, old one crumbles in my hands. How do you go about getting/making one? 
