Hi all Ever since I purchased my 1973 250 Auto (non AC) it has run rough on idle. I rebuilt the carb and fitted new gaskets which seems to have made matters worse! The problem seems to be that it is running very rich no matter where the mixture screw is set, and this in turn leads to it fowling up the plugs! The previous owner has removed the smog/emissions but im a little concerned that this may be part or all of my issue!?!? The EGR has been blanked off and the recirc pipe has been cut and blocked at both ends. There are two vacuum pipes on the distributor, one connects to the side of the carb and the other to the inlet manifold. There is also a thicker metal vacuum pipe (presume is from the trans modulator) connected to the manifold. the "egr" connection on the carb has been blanked off, as has the one at the very top of the carb. There is a plastic vacuum connector on the firewall, one side disappears into the transmission tunnel and the other end is open! The ignition side of things is all new. Im a mechanic of 35 years and gone through the logical processes, but im not familiar with these old US Fords, so may have overlooked something Any advise would be appreciated Thanks PS. Im in the UK so dont have to worry about the legalities of the emissions that have been removed
Back in day I never worried about emissions, first thing was plug it all off. Start by connecting front vac port on dist to either ported vacuum on carb or direct to manifold. Ford used the ported and mostly I still do. Disconnect the other dist port(retard), if it has vacuum plug off source. Transmission modulator near rear transmission mount requires FULL vacuum. Be sure it's routed properly, plug up everything else. A/C controls also require full vac, but nothing for std heater. If adjusting idle mixture inward doesn't produce a stall, the carb has issues. I don't know enough about 6cyl carbs to make a recommendation.
It doesn't stall if the mixture screw is turned in fully. In fact it doesn't make any difference to the running no matter what position its in! Which is a concern! Its running so rich that its fowling up the plugs in no time at all and there is lots of soot left on the floor after it has been running (and you can physically see it coming out the tailpipe). The carb is just dumping fuel on idle!
The RBS carb used on the 250's is really a pre-emissions carb slapped on so the 250 could clear the Maverick low hood line. Not a bad performer when in good tune. As mentioned, if idle mx screw makes no changes, disconnect all vac sources and test. If still no effect, carb is likely issue since there is no possible intake manifold leak without a head casting crack. Loose worn throttle shafts, warped carb surfaces and internally crusty old carbs are best (sometimes only) tested with a carb swap even if temporarily to localize problems. I keep a nice clean reliable response Maverick 170 Carter YF carb around for inital startups, and test swaps... . A favorite swap for 250 is a commonly available/inexpensive Holley 2300 series 2Bbl though a simple 2 X 1 adapter and with good tune can be a performance upgrade as well. The 2300 is available as 350 peak CFM and 500CFM for modified engines. They say CARBURETOR is French for : "Don't F%$K with it "... H/W 5200 'progressive' 2300 2bbl 'synchronous' . have fun
I have found that with the problems you are having it's probably warped some where in the body . If you can turn the screws in then it's sucking enough fuel to keep the engine running . I would either spray some carb cleaner at the carb while it's running and see if anything changes . Make sure and plug off all your vacuum ports and try and not spray those . It will expand them . You might try even starting fluid . I think your problem is that pcv hose ?
Thats the problem it seems, its drawing fuel from within the carb somewhere, not air (spindle shaft looks good). If I disconnect all the vacuum hoses from the inlet so the idle increases, and then turn the idle screw down then it will idle quite nicely (this is with the mixture screw fully screwed in). Experience from old European Fords tells me the carb is screwed/cracked internally as you guys pointed out. Now im going to have to do some kind of work around so I can continue to use the car through the summer months! Im not wanting to spend a load of money to do a weber conversion or anything like that, as I have recently purchased a 5.0 with AOD which is still in Oakland waiting to be shipped to me. That was my winter project, but something tells me I will be doing it sooner rather than later. I was hoping that I was overlooking something Thanks for the input guys
Problem solved! When I pulled the carb 3 or 4 times to check to see what was going on, I didnt pull the brass caps that cover the diaphram's as they are difficult to get off without damaging them! Anyhow, with nothing to lose, I pulled the cap that covers the "step up" diaphragm and it had shriveled up and had a hole in it! Luckily I had kept the old diaphragm that I pulled a few weeks ago which was undamaged, so replaced that and its all good. Im not sure if its the fuel over here that affected it or its just cheap chinese rubbish (hygrade). I also checked the acc pump diaphragm and that was starting to look a bit suspect as well, so I put the original of those back in! Hopefully it will last long enough for me to get the Five-O fitted later in the year
