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Quick question for you guys. 1978 with the inline 6. After fixing a couple vacuum leaks, I am definitely running rich. Smoke on a cold start, and it’s almost like my carb floods itself unless I keep the RPMs a little higher until it warms up a little. All those issues go away but I can still smell that I’m running rich. Yesterday I got the truck warmed up, backed in the mixture screw until she wanted to die, then backed it off 1.5 turns. Upon doing this, I sprung a couple fuel leaks. I circled where it was coming from. All my screws are tight and it’s not coming from the carb/manifold gasket. I already have a new carb that I’m picking up after work. When I tune it with a vacuum gauge, do I put it in the port where the vacuum line from my brake booster connects?
You could but any of the lines off the vacuum tree would work. Just look for a nipple corresponding in size to your vacuum gauge hose. The port you do NOT want to use is the vacuum port at the base of the carb (portedf vacuum) - you want manifold vacuum.
You could but any of the lines off the vacuum tree would work. Just look for a nipple corresponding in size to your vacuum gauge hose. The port you do NOT want to use is the vacuum port at the base of the carb (portedf vacuum) - you want manifold vacuum.
Much appreciated, thank you! I know you can do it by ear, but I figured since I am finally replacing the carb, I want to go the extra step to make sure I have it as dialed in as possible.
Yep I believe you are correct. I think the carb I have on there is pretty much done for too. Besides the mixture screw exposing some leaks, the idle screw doesn't do too much anymore. I can really bump it up, but it doesn't respond too much even when I fully back it out.
Much appreciated, thank you! I know you can do it by ear, but I figured since I am finally replacing the carb, I want to go the extra step to make sure I have it as dialed in as possible.
What you can try is tuning it by ear then use the vacuum gauge to see how close you were to nailing it.
Originally Posted by Peter41
Yep I believe you are correct. I think the carb I have on there is pretty much done for too. Besides the mixture screw exposing some leaks, the idle screw doesn't do too much anymore. I can really bump it up, but it doesn't respond too much even when I fully back it out.
You might be right on the carb being done for but .....
The first picture is that the throttle shaft at the body that was leaking gas?
Before you pull it off get it up to temp and at idle using carb clean spray that area and see if the idle speed changes.
If it dose then yes the carb is done for. There is wear at the shaft & body causing a vacuum leak and this can not be fixed with a rebuild kit we can get.
The carb would need to be pulled apart the throttle blades pulled out (if not put back right can cause issues) and then pull the shaft.
Shaft would need to be turned down and the body bored and bushings fitted before being put back together.
Again not something most of us can do.
Dave ----
What you can try is tuning it by ear then use the vacuum gauge to see how close you were to nailing it.
You might be right on the carb being done for but .....
The first picture is that the throttle shaft at the body that was leaking gas?
Before you pull it off get it up to temp and at idle using carb clean spray that area and see if the idle speed changes.
If it dose then yes the carb is done for. There is wear at the shaft & body causing a vacuum leak and this can not be fixed with a rebuild kit we can get.
The carb would need to be pulled apart the throttle blades pulled out (if not put back right can cause issues) and then pull the shaft.
Shaft would need to be turned down and the body bored and bushings fitted before being put back together.
Again not something most of us can do.
Dave ----
Yessir that’s where one of the leaks was coming from. She was up to temp, all the screws were tightened, and there was a steady drip coming out of there. My next question is the studs to mount the carb to the intake manifold. Realized one was snapped off at the top, but enough to still barely thread a nut on. I’m going to replace those, but nobody has them in stock so I need to wait. Everything I looked up said 5/16 but these are definitely 3/8. Does that sound accurate?
... etc ... Yesterday I got the truck warmed up, backed in the mixture screw until she wanted to die, then backed it off 1.5 turns. Upon doing this, ... etc ...
Sounds rich to me. I adjust in lightly till it falters, then back out to my highest idle rpm, then readjust my idle speed screw, then set the other side idle mix screw using the same method, then finally I adjust my idle rpm again. If doing just one idle screw, same deal but just once. I don't count turns except on initial bench setting from seated lightly.
They are typically 5/16" . maybe someone stripped yours and tapped it out.
Thats what I’m thinking. I checked the thread in the fittings aisle of Orielly and it was for sure 3/8. But just to be sure, I’m going to stop by Ace after work, and grab 5/16 and 3/8 and see which fits. My 20 minute carb swap has definitely turned into a little project.
They are typically 5/16" . maybe someone stripped yours and tapped it out.
Just coming back to this for a little positive reinforcement. I went by Ace with the stud I pulled out, and a 5/16 nut wouldn't thread onto it. Grabbed a couple 3/8 studs, 3/8 nuts, and that threaded onto mine. So I am guessing it was drilled out to a 3/8 at some point or am I missing something? I had to get a fine thread nut but everything is telling me it is 3/8.
Sounds rich to me. I adjust in lightly till it falters, then back out to my highest idle rpm, then readjust my idle speed screw, then set the other side idle mix screw using the same method, then finally I adjust my idle rpm again. If doing just one idle screw, same deal but just once. I don't count turns except on initial bench setting from seated lightly.
It was definitely rich. The screw was backed out a decent amount to account for the vacuum leaks I didn't know I had. So once I got those addressed is when I went back to adjust my mix screw, and that's when I started hemorrhaging fuel. So maybe it was dumping enough fuel in that it bypassed the leaks, but once I restricted that they all got exposed. Is there any logic to that?
After you get the new carburetor installed and working properly, you probably could, in your spare time, rebuild the old one and keep it for a spare.
I thought about that, but I am actually in the process of selling the truck. Another reason this carb problem popping up is less than ideal. But should have it all buttoned up today, just need to vice grip an old broken stud out.
On studs like that I use threaded rod and cut to the size I need.
Before cutting thread a nut or 2 on, make your cut, file or run the ends of the stud on a bench grinder and wire wheel and the nut that was put on before the cut should just unscrew off. If not more filing or bench wheel so it will unscrew.
Now if you want fine thread up top then bought studs is the only way to go.
Good luck on the carb swap & sale.
Dave ----
