I just aquired a used holley 650 double pumper. When turning the throttle shaft, the primary and secondary throttle plates do not open all the way to 90 degrees. I would say they open to about 70 degrees. Is this normal?
I also have a 750 double pumper and with that one, the throttle plates open fully to 90 degrees. Hoping someone here with a 650 double pumper can verify this.

Thank You

 

They should open all the way to 90 degrees.

 

I found the problem, the brackets on either side of the base plate were bent pretty badly, probably from shipping or being dropped before it was sent to me. You just never know when buying used. My base plate on the 750 double pumper is in really good shape and looks exactly like the one on the 650, even the bores and plates are the same size. Will I run into any problems if I use the base plate from my 750 on the 650?

 

They should be the same.

 

I just stumbled on this post and figured I'd add my observations. I also have a 650DP with a 750 throttle plate with a secondary that doesn't open all the way. How exactly did you bend the brackets to get it to open all the way? It does not look possible on mine.

 

I simply bend them back into original shape using pliers, they were completely bend out of shape as the carb was being shipped. Seems to be working good now and opens as it should. If its only the secondaries that are not opening all the way in you carb, they are mechanically connected to the primaries with a 'C' type bracket, which you can bend a little so that the secondaries will open fully at wide open throttle. Work on you primaries first. It could be that your throttle cable might need adjustment if you are testing the openings of you plates using the throttle pedal.

 

Like yours, my primaries open 90* straight but the secondaries are about 80*. Enough that the throttle shaft is hidden by the plate. When I get home tonight I will look at the bracket geometry. Thanks for the feedback. I just got done removing the choke horn, casting flash, slimming the throttle shafts, and smoothing the venturi. This is for my 89 camaro with a 454.

Have you considered blending the venturi to the larger 750 throttle plate? I'm trying to figure out why not to.

 

After some more research I am against the 750 throttle plate on the 650. I can see a part throttle lean condition occuring as the throttle opens. The top of the throttle blade will be covered by the smaller bore main body up to almost 40% throttle. This could explain my part throttle stumble and would most definetely show up on a dyno.

 

Here you can see what happens when you put a 750 throttle plate on a 650 main body. Not good.

 

I thought the 650-750 used the same base plate anyways? So i'm not sure you will find a 650 specific baseplate that wont be any different than a 750 one.

 

I checked both my baseplates, and the 650 and 750 use the same exact size baseplate. Its the 650 main body that differs from the 750 main body, but the baseplae is the same and it lines up flush on both, therefore no blending to the venturis should be required.

 

What numbers are on the throttle blades? Mine has 172 and 173 with 70645 on the plate.