Quarterwave Posted January 2, 2019 Share Posted January 2, 2019 Hi everyone, When I picked up my F150 from the "mechanic" that I used to put on my heads/intake/carburetor, he mentioned that the trans was shifting hard. That was never the case before he started working on it. The engine however, was idling smooth (aside from the cam) and no smoke. Before I go on, I will mention that the truck has a C6 with an Edelbrock AVS2 carb and a Performer RPM Air-Gap intake manifold. That being said, the mechanic had the PVC vacuum port at the rear of the carburetor (1/4" hose) running into the 3-way vacuum hose connector located on the firewall. After looking at some Edelbrock videos, it was stated that the hard-shifting issue was caused by the incorrect vacuum port being used. So, I ordered the necessary hoses, plugged the rear PVC vacuum port and ran the hose from the full vacuum port, which is located on the front of the carburetor. When I started the truck, it was running WAY too rich - smoke and stinking of fuel. Before I go and start adjusting the idle mixture screws, have I got the hoses hooked up correctly? Or should I switch the hose to the other port? NOTE - the brake booster is getting vacuum from the intake manifold... Any help is appreciated and apologies in advance to any commenters - I'm learning as I go and are used to working on my Mercruiser 5.7! Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 2, 2019 Share Posted January 2, 2019 If it is now running way too rich, and I'm assuming you mean at idle, then you must have had a large vacuum leak before and the idle mix screws were turned way out to compensate for the extra air coming in. In that case, you will need to adjust the idle air mix screws. But, you also need to figure out where all the air was coming from and if what you did was appropriate. Have you checked to see that the hose to the transmission is connected on the side of the transmission? That would cause a fairly large vacuum leak that you wouldn't hear, and I think it will make the transmission shift hard. Another possibility is a blown vacuum modulator on the tranny. Pull the hose off at the modulator and see if fluid runs out. If the modulator is blown fluid can get past it and into vacuum line and then into the carb, and cause the exhaust to smoke. And, it will change the shifting. As for the vacuum ports on the front and rear, I think both of those are full manifold vacuum. In other words, they aren't "PVC ports". But either can be used as a PVC port. Or, one can be used for vacuum to the firewall-mounted manifold. Does that help? Link to comment Share on other sites More sharing options...
Rembrant Posted January 2, 2019 Share Posted January 2, 2019 I'm not much help as I have a Holley 4160 on my 302 (and a manual trans), but it appears to be basically the same configuration as the Edelbrock with regards to vacuum ports. Mine has a barb straight out the back for the brake booster, and then PCV barb sticking out the front of the carb. Edelbrock below appears to be the same. Then there are the two small barbs...one for ported advance, and one for full manifold vacuum. Link to comment Share on other sites More sharing options...
Quarterwave Posted January 2, 2019 Author Share Posted January 2, 2019 I'm not much help as I have a Holley 4160 on my 302 (and a manual trans), but it appears to be basically the same configuration as the Edelbrock with regards to vacuum ports. Mine has a barb straight out the back for the brake booster, and then PCV barb sticking out the front of the carb. Edelbrock below appears to be the same. Then there are the two small barbs...one for ported advance, and one for full manifold vacuum. Hi Rembrandt, Happy New Year! Re yr message - correct. The rear PVC port was hooked up to what I believe(d) is the vacuum tree for the transmission. I unbolted the fitting and blocked it with a 1/4" NPT plug. While I was there, I wanted to make sure that the brake booster was getting vacuum and followed the hose from the booster to a fitting that had been installed towards the rear of the manifold. I've been thinking about plugging that manifold hole and then re-running the line from the back of the carb.... I then hooked up the full vacuum port (lower right port when looking at the carb front-on) and connected that with a fitting into the 1/4" vacuum hose (I forget the size hose/connector - I think it was 3/16th). Since then, it's been running rough whereas before it was fine. That's what led me to asking - do I have the wrong port at the front of the carb? Should I be hooked up to the timed port? Everything that I've been able to read on this topic tells me that I have the correct port... and if so, that leads me to think that I now need to adjust the screws on the carburetor... or that something else is amiss. I bought some more 1/4" hose and will also hook it up the way it was previously, to find out if that was the issue, but I'd still like to solve the trans-shifting issue. Link to comment Share on other sites More sharing options...
grumpin Posted January 3, 2019 Share Posted January 3, 2019 Hi Rembrandt, Happy New Year! Re yr message - correct. The rear PVC port was hooked up to what I believe(d) is the vacuum tree for the transmission. I unbolted the fitting and blocked it with a 1/4" NPT plug. While I was there, I wanted to make sure that the brake booster was getting vacuum and followed the hose from the booster to a fitting that had been installed towards the rear of the manifold. I've been thinking about plugging that manifold hole and then re-running the line from the back of the carb.... I then hooked up the full vacuum port (lower right port when looking at the carb front-on) and connected that with a fitting into the 1/4" vacuum hose (I forget the size hose/connector - I think it was 3/16th). Since then, it's been running rough whereas before it was fine. That's what led me to asking - do I have the wrong port at the front of the carb? Should I be hooked up to the timed port? Everything that I've been able to read on this topic tells me that I have the correct port... and if so, that leads me to think that I now need to adjust the screws on the carburetor... or that something else is amiss. I bought some more 1/4" hose and will also hook it up the way it was previously, to find out if that was the issue, but I'd still like to solve the trans-shifting issue. I don't know if there is a difference between the 302 and 460, but my vacuum line comes directly off the manifold to a "vacuum distribution block", then to the transmission. Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 3, 2019 Share Posted January 3, 2019 Hi Rembrandt, Happy New Year! Re yr message - correct. The rear PVC port was hooked up to what I believe(d) is the vacuum tree for the transmission. I unbolted the fitting and blocked it with a 1/4" NPT plug. While I was there, I wanted to make sure that the brake booster was getting vacuum and followed the hose from the booster to a fitting that had been installed towards the rear of the manifold. I've been thinking about plugging that manifold hole and then re-running the line from the back of the carb.... I then hooked up the full vacuum port (lower right port when looking at the carb front-on) and connected that with a fitting into the 1/4" vacuum hose (I forget the size hose/connector - I think it was 3/16th). Since then, it's been running rough whereas before it was fine. That's what led me to asking - do I have the wrong port at the front of the carb? Should I be hooked up to the timed port? Everything that I've been able to read on this topic tells me that I have the correct port... and if so, that leads me to think that I now need to adjust the screws on the carburetor... or that something else is amiss. I bought some more 1/4" hose and will also hook it up the way it was previously, to find out if that was the issue, but I'd still like to solve the trans-shifting issue. The timed port is typically used for vacuum advance, and rarely anything else unless it is for some emissions system. Everything else gets full, manifold vacuum. So, if your transmission was originally hooked up via the manifold on the firewall, which was fed from the big port on the rear of the carb, then that was hooked up correctly. But somehow something you've done has made the engine seem like it is really rich. If it were me I'd put things back and see if that fixes it. Then, if I wanted to make changes, I'd do them one at a time and find out which one causes the problem and understand why. You can see here how I like to run things: http://www.garysgaragemahal.com/vacuum-systems.html. Link to comment Share on other sites More sharing options...
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