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So today I was going to adjust the carb and set the timing just to check and see if all is correct since the truck is new to me. It's a 79 f100 with 351m and auto. Manual brakes. There is a port on drivers side of carb in front next to adjusting screw, there is a port on the pass side near the choke. Both of those lines and others including the vac advance are all connected to a "tree" that comes off the thermostat housing. Is this correct? I hooked my vac gauge to the drivers side front port, adjusted screws to highest vac and when I hooked the hose back up, the idle shot up pretty good. I have not adjusted the timing yet but shouldnt the vac advance be a dedicated hose? And is it hooked to the right port?
No id tag on carb but have some pictures.
Since I'm sure your curve is set up for ported vacuum it should be hooked to the fitting by the choke if you want to bypass the tree. all other vacuum sources will be manifold vacuum.
Hard to say how much of your smog crap is still there or functional so who knows what's the best answer to that. that's a whole can of worms I always threw away as soon as they got home .
Since I'm sure your curve is set up for ported vacuum it should be hooked to the fitting by the choke if you want to bypass the tree. all other vacuum sources will be manifold vacuum.
Hard to say how much of your smog crap is still there or functional so who knows what's the best answer to that. that's a whole can of worms I always threw away as soon as they got home .
The more I search and read, the purpose of the "tree" if it works correctly, it let's the vac advance work off ported until the engine reaches a certain temp, then the manifold will kick in. This purpose is to idle the engine up which will help the engine cool quicker. I'm gonna say that as high as my idle went up when I hooked the hose up, the switch may not be working.
So if I dedicate the ported to the vac advance then I can plug off the manifold port. Other than the hose to the transmission, what else do I need vac for? I should be able to plug the rest off.
I think you're correct on the tree but I'm not sure if about switching to manifold vacuum. nobody has done that since the 60's. but I can't say for sure.
I'd put a dial back on it and see. if your curve is decent run with it.
I think you're correct on the tree but I'm not sure if about switching to manifold vacuum. nobody has done that since the 60's. but I can't say for sure.
I'd put a dial back on it and see. if your curve is decent run with it.
As far as I can tell, the ported is on the pass side and the manifold is in the front. I think it depends on which model carb you have. I am not sure but the pass side has 0 on the gauge at idle, front has vacuum.
So after my last post, I went and got some vac hose to connect direct from carb to vac advance. Threw the gauge on it again and adjusted carb again. Best I can get is 14 on the gauge. I was finally able to hear a faint whistle, sprayed some brake cleaner at the tree in the rear where it screws in to the intake and the truck idled up some. Think I found my culprit. I'll need to take it loose anyway as my temp gauge doesnt work. I havent tried grounding out the plug to see if the gauge works but it's on the to fix list as well. I'll thread tape it when it goes back in. I did check timing and its holding steady at 8 degrees, no jumping. Carb may need some attention as well but will fix the leak first and go from there.
Thanks for all the input.
Ported should be zero at idle and pick up as the throttle opens. if you have any vac at idle it's manifold vacuum. normally the ported is on the RH side as you say, but that can vary I'm sure.
You can probably stand more initial timing , and that will raise your vacuum reading. but if it kicks the starter or pings under load back it off.
Ported should be zero at idle and pick up as the throttle opens. if you have any vac at idle it's manifold vacuum. normally the ported is on the RH side as you say, but that can vary I'm sure.
You can probably stand more initial timing , and that will raise your vacuum reading. but if it kicks the starter or pings under load back it off.
I was going to play with the timing and see what I can get out of it but...distributor is froze in place at the moment. Letting it soak in some wd40 overnight and see if that helps.
Distributor advance hooks to the ported vacuum port below the choke; carb may have an S on it to indicate the proper port.
Manifold vac is used for A/T, brake booster, A/C/heater line, PCV, and all the rest of the emissions controls (everything else is one way or another part of the emissions controls... carbon canister, gas tank venting, all the little vacuum operated flaps etc.) Some of them are actually beneficial, and do not affect performance, so just blindly disconnecting everything is not a good idea.
If you still have the paper labels on your valve covers showing the emissions scheme (usually a 6 place alpha-numeric combination), referring that number in a Chiltons shows how the vacuum is supposed to be hooked up. You can then eliminate items that don't matter to you.
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