carb problems

[zr440]

I just switched my tbi to carb. Put on an edelbrock 750 with a performer intake. I have an hei distributor and a bypass fuel pressure regulator. When I fire it up, it sounds like it\'s not running on all cylinders. I can smell a lot of fuel in the exhaust also. This is my first time dealing with carburetors so I\'m a little lost. It has 3 vacuum ports in front and one in back. I connected the vacuum advance to one of the ports on the front of the carb. The other ones I just plugged for now since I don\'t know what I would connect to them. As for the fuel pump I didn\'t do anything with that, just left it to turn on with the key. My next guess was to look at what it has for jets because I bought it used so I don\'t know how it was setup other than it was on a 350.



Thanks,

Josh

[Ryoung68]

I\'m more familiar with Holley carbs, but I\'ve read on here many times that fuel pressure for those carbs need to be around 4-5 psi. Check ther first before changing jets. Good luck! http://www.s10v8.com/images/smilies/icon_wink.gif

[Melonhead]

ZR440, the truck was set up original tbi, that mean about 13psi from the fuel pump. First thing you need is a regulator. Then regulate down to 5-6psi. The float seats can\'t handle more than 6.5psi. Next is vacuum ports. The rear big port is for your brake booster. The two others in the front, the left one is timed vacuum. Thats the one for the distributor. The one on the right is not used, just an extra full vacuum port if need. The last think is a 750 is a bit large if the engine is mild. Edelbrocks normally run rich. I ran a 600 1406 Edelbrock on a stock 350 and had to jet down 6%. http://www.s10v8.com/images/smilies/icon_biggrin.gif

[zr440]

I have a regulator on it set to 5.5 psi. I took it apart and found it had different jets in it, they were like .115 or somewhere around there. I dropped those down to .095. Now it doesn\'t want to run when I try get it timed right. The closer I get to where the timing should be set at it starts stumbling and dies.

[Melonhead]

The two screws on the front are the idle jets. Sense the jetting was so fat, maybe the idle jets are almost turned off. The two thumb screws should be about 1 1/2 to 2 turns out from closed or seated. http://www.s10v8.com/images/smilies/icon_biggrin.gif

[zr440]

I checked the mixture screws and set them to 1 1/2 turns out. Still not running on all cylinders. I\'m thinking it\'s only running on 4. It sounds terrible.

[soopertruper]

you can go to the edelbrock website and download the tuning manual for edelbrock carbs if you need it

[Melonhead]

Vacuum leak??????? http://www.s10v8.com/images/smilies/icon_confused.gif

[Scotty_S-15]

On 2007-05-18 05:04, Melonhead wrote:

Vacuum leak??????? http://www.s10v8.com/images/smilies/icon_confused.gif



Yeah, that\'d sure do it.



Used carbs scare the crap out of me. Unless you personally know where the carb was and how it ran. Too many things a person can do to a carb that could be nearly undetectable without expert scrutiny.

[zr440]

I took the carb apart and gave it a good cleaning. Put it back together with a rebuild kit. Now it runs nice at idle. I realized I was looking at a jet chart for the 1406 carb mine is a 1407. So the jets that were in it are correct for stock. Since the carb is a little bigger than it should be, should I run it with slightly leaner jets? My motor is stock except for the performer intake and an RV cam.