455 with a fresh rebuild, it seemed to start and run fine during cam break-in. QFT carb was leaking from the secondary accelerator pump and I replaced diaphragm and reinstalled carb. Both primary and secondary pumps squirt well. Its running smoothly at idle but will barely run above idle. It starts to hesitate and buck. It doesn't stall out but no power and seems like it's missing badly. It will pull me down the street and back to house but barely. I assumed vacuum leak since I have been messing with all that on the engine install but I can't find one. That is what it is acting like though. It seems to run better when I advance timing but I have 18 degrees in and anymore and it's tough to start. Much less than 16 and it dies. MSD ignition is just a couple years old but I though maybe coil? Pulling spark plug wires one at a time seems to slow the engine so I don't find a miss.

I'm at a loss and appreciate anything you guys can suggest I test.

Thank you in advance.

 

Check fuel supply but it sounds like ignition to me. Could have a bad MSD box. It happens.

 

a vacuum gauge is a good tuning tool, also if a valve job was done you may require adjustable rocker arms, there may be a youtube video for tuning your qtf carb. good luck

 

I have a good auto meter vacuum gauge hooked up, it pulls about 20 at idle and nothing I do with timing seems to change it much.

I do have roller rockers, you think they need to be adjusted after absolutely up 40 mins of run time?

 

Look down inside the carb and raise the rpm with the throttle and see if its spitting a bunch of fuel intermittently. Does it smell rich? What do the plugs look like?

 

sometimes it's best to start at the beginning, compression test, ignition components, battery voltage, wiring, grounds. A look at the throttle blades from underneath can tell you somethings wrong. Good luck

 

He said it idles fine, can't see how idle circuit/throttle blades are his problem.

 

Ok so I've done some more messing. The plugs do look like it's running rich and it smells rich too. Looking don the carb I did see one drop of fuel that did not seem atomized. I have messed with the idle adjustment screws and they have an affect on the RPM but don't seem to have much effect on the hesitation The initial setting on this carb is 1 1/4 turns out however this one runs much better with them turned in. At 1 1/4 turns it will idle with the idle screw all the way out. The float level looks spot on both sides.

so I guess I have to assume this is running rich now. So I guess changing Jets is my only option?

 

I posted a short YouTube video of this thing trying to run.

 

It seems from the video that the primary accelerator pump is not moving, almost like there is no plastic cam?

 

Yup.

 

I posted another video. It pumps but not right off throttle. I have never adjusted it and it was fine before rebuild so I would not think this would be an issue.

 

The accelerator pump should move immediately with no delay period or it will hesitate.

How to adjust:

The first adjustment to check is the clearance between the pump operating lever and the pump diaphragm cover’s arm, at wide open throttle. This clearance should be around .015". The purpose for this clearance is to assure that the pump diaphragm is never stretched to its maximum limit at wide open throttle. This will cause premature pump failure. Once this clearance has been set take a good look at the pump linkage and work the throttle. Make sure that the accelerator pump arm is being activated the moment that the throttle begins to move. This will assure that pump response will be instantaneous to the movement of the throttle. These adjustments can be made by turning the accelerator pump adjusting screw that is located on the accelerator pump arm together with the pump override spring and lock nut.

 

Thank You! I'll try it tomorrow. I really appreciate your and everyone else's knowledge. This is a great forum!

 

If it’s a 45* block with C heads then the pushrod holes would’ve most likely had to be drilled for the different angle. You may want to remove a rocker or two to check that.