TheGeneral Posted January 9, 2022 Author Share Posted January 9, 2022 I see. Yeah the valve cover sticker was long gone when I got the truck. Distributor is new, carb is original but I am unsure if it still has a tag. I'll go check. So, what does the metal painted tag above the engine refer to, then? Useless gibberish to my untrained eye haha! no carb tab either, but there is a number on the base below adjuster screws = 7655S, and 8603 and a 111 over by the throttle position sensor. I am guessing those are just for the base components? Link to comment Share on other sites More sharing options...
mat in tn Posted January 9, 2022 Share Posted January 9, 2022 That is a "buck" tag and was used on several pieces to bring them together on the assembly line. Beds, cabs, and some radiator supports had them. And I don't know how to decode them. Tomorrow I'll scan in the other 6 of the pages and post them so you can compare the vacuum diagrams to yours. You should find a match. I'm very glad that all of the doc's are available and the help is there to get it sorted out correctly. but is anyone thinking through the diagnosis? it runs and has power but idles very rough is what i understood. i certainly hope it's a simple confusion of vac lines. still let's back up to step one. it runs so i would start by capping every vac line and be a simple engine. fuel, fire, and compression. start it and verify timing. how does it run in this condition? Cap even the brake booster port. it is entirely possible for a vacuum leak to be in a vacuum controlled device nowhere near the engine. the hvac vacuum switch for one, brake booster for another. just two examples. Link to comment Share on other sites More sharing options...
85lebaront2 Posted January 9, 2022 Share Posted January 9, 2022 I see. Yeah the valve cover sticker was long gone when I got the truck. Distributor is new, carb is original but I am unsure if it still has a tag. I'll go check. So, what does the metal painted tag above the engine refer to, then? Useless gibberish to my untrained eye haha! Here's what I have show as "all" for 1985 300 engines. Link to comment Share on other sites More sharing options...
85lebaront2 Posted January 9, 2022 Share Posted January 9, 2022 no carb tab either, but there is a number on the base below adjuster screws = 7655S, and 8603 and a 111 over by the throttle position sensor. I am guessing those are just for the base components? 7655S is the Carter model number for the carburetor. Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 10, 2022 Share Posted January 10, 2022 I'm very glad that all of the doc's are available and the help is there to get it sorted out correctly. but is anyone thinking through the diagnosis? it runs and has power but idles very rough is what i understood. i certainly hope it's a simple confusion of vac lines. still let's back up to step one. it runs so i would start by capping every vac line and be a simple engine. fuel, fire, and compression. start it and verify timing. how does it run in this condition? Cap even the brake booster port. it is entirely possible for a vacuum leak to be in a vacuum controlled device nowhere near the engine. the hvac vacuum switch for one, brake booster for another. just two examples. Matt - You are right, just knowing the proper vacuum routing is not necessarily going to fix it. And your approach of capping everything would probably get it running correctly. But, then he'll need to know how to connect things back, and that's where the documentation comes into play. Link to comment Share on other sites More sharing options...
FuzzFace2 Posted January 10, 2022 Share Posted January 10, 2022 Matt - You are right, just knowing the proper vacuum routing is not necessarily going to fix it. And your approach of capping everything would probably get it running correctly. But, then he'll need to know how to connect things back, and that's where the documentation comes into play. If he has the vacuum line routing as shown on his sticker Then why cant he follow it? Even if the colors are faded he should still be able to follow where they go and make sure they are hooked to the right places no? Dave ---- Link to comment Share on other sites More sharing options...
85lebaront2 Posted January 10, 2022 Share Posted January 10, 2022 I'm very glad that all of the doc's are available and the help is there to get it sorted out correctly. but is anyone thinking through the diagnosis? it runs and has power but idles very rough is what i understood. i certainly hope it's a simple confusion of vac lines. still let's back up to step one. it runs so i would start by capping every vac line and be a simple engine. fuel, fire, and compression. start it and verify timing. how does it run in this condition? Cap even the brake booster port. it is entirely possible for a vacuum leak to be in a vacuum controlled device nowhere near the engine. the hvac vacuum switch for one, brake booster for another. just two examples. Actually, Matt, my first thing to look at on a rough running 300 is the actual carburetor as the harmonic vibrations on these will shake the carburetor apart. Start with the bottom joint in that Carter YFA as if it gets loose you get an air leak into the idle circuit and loss of the vacuum signal to the metering rod diaphragm. Link to comment Share on other sites More sharing options...
TheGeneral Posted January 10, 2022 Author Share Posted January 10, 2022 If he has the vacuum line routing as shown on his sticker Then why cant he follow it? Even if the colors are faded he should still be able to follow where they go and make sure they are hooked to the right places no? Dave ---- 1.) Because I am only about 85% certain that I am reading it correctly.... 2.) "she" lol 3.) based on Model Application code info page I believe my calibration code is F150 - - 2/W/D—M/T—Calif. 4-51S-R02 392 (1985 4.9, 2WD, Manual transmission, California) 4.) Matt in Tn, you are right, a more thorough troubleshooting diagnosis would be helpful but I am not going to make things worse for myself by unplugging everything at once. Now, it is possible that an unseen line crack developed somewhere as a result of taking it apart etc, but the reason I think it is likely a mistake on my part is that if the manifold leak(s) are now gone (they are) and nothing else has changed, then it should be running better, not worse.  Link to comment Share on other sites More sharing options...
TheGeneral Posted January 10, 2022 Author Share Posted January 10, 2022 Actually, Matt, my first thing to look at on a rough running 300 is the actual carburetor as the harmonic vibrations on these will shake the carburetor apart. Start with the bottom joint in that Carter YFA as if it gets loose you get an air leak into the idle circuit and loss of the vacuum signal to the metering rod diaphragm. I have double checked the carb flange, new gasket, it's tight and the base below is tight too. Although the carb is hissing like a snake out the top, also a new development. I am in far Northern CA, on the coast, only an hour from the Oregon border. If anyone has a shop recommendation within a couple hundred miles I would jump on it. Link to comment Share on other sites More sharing options...
mat in tn Posted January 10, 2022 Share Posted January 10, 2022 I have double checked the carb flange, new gasket, it's tight and the base below is tight too. Although the carb is hissing like a snake out the top, also a new development. I am in far Northern CA, on the coast, only an hour from the Oregon border. If anyone has a shop recommendation within a couple hundred miles I would jump on it. hissing like a snake! awesome. that's a good sign. do you have a vacuum gauge? hooking that to an intake vacuum port will give you intake vacuum and then you can possibly tune the carb with that info. if you have no vacuum leaks you should see 17-21in of mercury (hg) on the vacuum gauge. hissing strongly tells me that there is likely no vacuum leaks at the work you have already done. you are making positive steps. hissing strongly also tells me that it is now a little rich as there is enough fuel to make a good fire, throttle response is probably good too. if the carb had been attempted to be tuned to a previously existing vacuum leak that is what i would expect. Link to comment Share on other sites More sharing options...
Recommended Posts