I have a 1985 chevy truck with a 305 and quadrajet that I just rebuilt. After rebuild the truck will only run for 5-10 seconds before shutting off. I know the jets are smaller than the original because I mistakenly bought the wrong size jets. (Stock is 72 I put in 65 jets) IF the choke is closed completely the truck will run but idle very rough and as soon as the choke opens the truck will die immediately. I replaced the float and the needle and seat with the rotary inlet valve in the rebuild kit. Just looking for ideas on this issue. And does anyone have any experience with the rotary inlet valve?

 

I have never heard of a rotary inlet valve in a Quadrajet.

Jets shouldn't affect the idle - you have another problem - possibly a vacuum leak or a stuck open EGR valve.

How many turns out are the idle air/fuel mixture screws???

 

I screwed them all the way in then turned both out 3 turns apiece. I then tried to start the truck and it would run for maybe a second and then cut right back off. I then backed them out one more whole turn and it ran for maybe 3 or 4 seconds. I then backed them out one more full turn and it ran for close to 10 seconds and cut off as well. Thats when I tried to close off the choke and it runs but nit very good. When the weather subsides I am going to take the air horn off and see how much fuel is in the bowl and make sure the rotary valve is working. The rotary inlet valve came in the rebuild kit and replaces the needle and seat.

 

That was the best picture I could find of the rotary inlet valve. In my haynes manual it says that the rotary inlet valve replaces the needle and seat.

 

rotary valve works I've always referred to them as a needle and seat.

With the mixture screws being 2 1/2 - 3 "full" turns out and if everything else was OK it should at least idle - maybe not perfectly smooth but it should idle.

I would look for a bigger vacuum leak - perhaps the base gasket between the carb and intake manifold or possibly a bad diaphragm inside the power brake booster. Generally there is more than one base gasket supplied in the kit and it's critical to use the correct one.

With the choke partially closed - just enough to keep the engine running - maybe set it on the high step of the fast idle cam - spray a small amount of carburetor cleaner around the base of the carb and along the intake to head gaskets. Running that lean it wont take much to affect the idle so look for a big change when the spray finds the air leak.

Did you match up each gasket from the carburetor against the ones that were supplied in the rebuilding kits - they usually have more gaskets than you need.

I hope some of this made sense and helps.

 

Check that bowl to base gasket (there are two different ones) and your float level. You've either got a vacuum leak or are starving for fuel.


Allan

 

It is raining pretty bad outside so I have not had a chance to check anything above. My first thought was the float because I replaced that but actually was in a hurry and forgot to check the float level. I saved the gaskets from the carb and made sure I had the right ones. I should be able to check everything mentioned above before the weekend. I will let you guys know what I find.

 

So I had a chance to take off the air horn today only to find about 1/4 inch of fuel in the bowl. I adjusted the float and shes back to running again. Thanks guys for the help and suggestions.