I have a 1970 Mav. with I-6 200 ci engine. It’s pretty clean - it was a one owner vehicle with 52000 original miles on it when I bought it just over a year ago. I’ve put about 2000 miles on it. Six weeks ago, while driving home one night, it began stalling every time I came to a stop and got progressively worse until, finally, it wouldn’t start again. I had to get a tow home. Turned out that three out of four screws holding the carb (a Carter YF) together had loosened, and one had come out entirely, apparently lost on the road. Besides all of the vacuum and fuel leaks caused by the loose screws, fuel was also leaking through the seal around the accelerating pump lifter link. Rather than mess with it, I replaced the carb with a rebuilt and everything was hunky-dory until the two nights ago. After coming to a stop at an intersection I pressed on the accelerator to move-on and the engine stumbled. I thought it was going to stall but it didn't - I gave it a couple of pumps and it responded hesitatingly. As I rolled forward and gained rpm's it smoothed out and began to accelerate normally. (At the prior intersection everything had been fine). From then on it exhibited this behavior at every stop - and eventually got a little more pronounced to where I had to brake with my left foot, keeping the idle up with my right. Later, I stopped and adjusted the idle speed up to a fairly ridiculous level which allowed me to drive the rest of the way home. Today I inspected the carb, vacuum lines, & etc. The fuel filter and pcv are new (with the carburetor)... everything seems up to snuff. I readjusted the idle and backed off on the choke spring adjustment by two index marks. I also experimented with the idle mixture but eventually left it at its original setting. Then I noticed, sitting in a depression on the exhaust manifold below the carburetor, a small familiar looking disk about 1/2 inch in diameter. After a moment I remembered seeing it on the carburetor before I installed it. It had come from the underside of the choke piston shaft. I reached under and put my finger over the opening and the engine speed increased. Also, that hissing sound went away. Leaving the shaft open, I test drove the car (with new choke adj. setting), stopping and going, and while there’s still a little hesitation it’s better than it was. I don’t understand the function of the choke piston. The information I have doesn’t elaborate. Nor do I get the hissing sound or why there’s any vacuum present inside the thermostatic coil housing. Could this little disk be the problem - it looks like a soft plug and does not look like it’s meant to act as a sealed closure to the piston shaft (which by the way is still “open”). I can see no way to reinstall the disk where it will effectively and permanently seal the shaft... for that matter, why is the shaft even open on the bottom? I’d like to fully understand what’s going on here so I can solve the issue and be comfortable that it’s done correctly. Any help will be appreciated!
I would have put a Carter RBS on it with manual choke.. YF's are junk. The folks over at Ford Six don't really think highly of them either.
Yes there is vacuum inside the choke housing. The piston is a vacuum operated choke pull off. I have had several of the disks fall out of the choke pull off housing. You need to put it back in there with the curved side facing outward and just tap it with a drift and hammer to lock it in place. If you wish you could put some epoxy over it to keep it in place but if it is installed proprely you should ot have to do that. You should be fine after the re-install of the plug. Normaly they will not come out unless you have a backfire of some kind. Maybe it was just not seated from the factory. Good luck Don
I considered manual... I’d rather not go in that direction, though it is the ultimate in “simplification,” which is a good thing. Thanks Don. I guess the plug wasn’t properly seated. It has a depression in the center where, I guess, it was “set,” as you say with a drift hammer My engine has a vibration - that probably helped to knock it loose (probably contributed to the screws loosening on the original carb, too). I like the epoxy idea, or maybe a bead of Permatex or something like it... Wonder why they didn’t use a more positive plug, like something with threads... Thanks! Kevin
