#21  
Old 04-01-2019, 06:00 PM
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dlloyd dlloyd is offline
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Thanks guys for the help. Can one of you send me a picture showing which holes I should open up to .052.
How can I tell if my power valve spring has been trimmed by 5 coils?
Thanks for your help

  #22  
Old 04-01-2019, 06:23 PM
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Dick Boneske Dick Boneske is offline
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Power valve first--Stock spring pressure on the power valve actuating rod is 200-250 grams. With a lumpy cam, that should be lowered to about 180 grams, which normally is about 5 turns of the spring. I measure this with a postal scale graduated in ounces and grams. Just remove the carb top and place the bottom of the power valve rod on the scale and see how many grams it takes to see it begin to retract into the carb top.

Second, I've attached pictures of the venturi assy. The hole located by the #2 in the first photo is where the idle channel restrictors are located. The other photos show various styles of venturi clusters. As Kenth said, stock for a 389 is about .046", with the 421 larger. I would begin with .050-.052". Try a smaller drill first so you can see the angle of the hole so you don't ruin the cluster. I don't know how you'd remove and replace the brass restrictors.
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Name:	Rochester 2GC Venturi Bottom View_LI.jpg
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Name:	Rochester 2GC Venturi Side View.jpg
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  #23  
Old 04-01-2019, 06:49 PM
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Mike is pretty much a stand-up guy. Why not check with him on any additional modifications he may have made, and what he might suggest for your current engine configuration.

Mike has bought many sets of the weaker springs from us. You can tell if a spring has been cut by looking at the end. You would not know if Mike reduced the tension on the spring the correct way, by changing the spring.

Jon.

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  #24  
Old 04-02-2019, 09:55 AM
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Can someone post a picture of the idle bypass restrictors.

Thanks, Dave

  #25  
Old 04-02-2019, 10:42 AM
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Quote:
Originally Posted by dhcarguy View Post
Can someone post a picture of the idle bypass restrictors.

Thanks, Dave
Look at my last posting (#22) for a picture of where the idle bypass restrictors are located in the venturi cluster.

Read the post carefully if you want to drill the restrictors. Check for the proper angle with a smaller drill (about .036") so you know how to aim the larger drill.

For most replacement cams larger than stock, a good starting point is about .049"-.052".

Brass idle tubes about .038-.042".

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  #26  
Old 04-04-2019, 11:09 PM
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Thanks Dick

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