idle drop back down

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Carb tuning. Centrifugal advance weights in the dist. either sticking or the springs are a little too light. Vacuum leak. Just to name a few
 
fishy68 said:
Carb tuning. Centrifugal advance weights in the dist. either sticking or the springs are a little too light. Vacuum leak. Just to name a few
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Does not change with the tuning of the carb as far as the dizzy not sure no vacuum leaks I know of.

I think it may be the valve springs. I am using stock 340 j head springs with this .506 cam.
 
1973dusterkid said:
Does not change with the tuning of the carb as far as the dizzy not sure no vacuum leaks I know of.

I think it may be the valve springs. I am using stock 340 j head springs with this .506 cam.
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Valve springs will limit your max RPM's, but is not going to be the idle problem.
Sounds like distributor weights to me.
What RPM's is your idle set at currently?
 
What size carb?Carb too big can cause low port velocity. Takes a bit for the motor to burn off fuel droplets not suspended in the intake plenum.
 
The valve springs may not be the right springs for the cam but they won't affect idle like your describing. The only possible way a valve spring would ever affect idle is if it's totally shot and letting the valve hang open at idle causing the cylinder to misfire which would cause a slow rough idle.

One other thought is do you have the vacuum advance hooked up and if so where do you have it hooked up? If you have it hooked up to direct manifold vacuum it's possible it's pulling in when you rev the engine due to the vacuum going up enough to activate it then when you let off the throttle the manifold vacuum drops low enough that the vacuum advance slowly drops out. If you have the vacuum advance hooked up make sure it's hooked to the ported port on the carb.
 
Try just unhooking the vac advance temporarily and see if it quits doin it.
Easy information could come from this.
 
You need to cap off the port on the carb for that test to stop the vacuum leak
 
1973dusterkid said:
Passanger side block
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Ok, that's the correct place

1973dusterkid said:
If I unhook the advance the idle rises.
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If the idle rises when you unhook it that means it's pulling vacuum there and the reason the idle rises is you've created a vacuum leak by unhooking the hose. It also means you have the primary idle speed set so high it's exposing that port to vacuum which should not be. That port should never have vacuum at idle. I'd back off the primary idle speed screw and adjust the secondary idle speed screw in 1/2~5/8 turn. It's the one located on the bottom side of the base plate on the pass side and you have to access it with a small screwdriver. You may have to take the carb off to get to it because some manifolds cover it up when the carb is bolted down. If you do that and find it helps but it still needs more you may have to drill some small holes in the butterflies to let more air in at idle so you can lower the front idle speed more to get it in the proper relation to the idle feeds slots.
 
fishy68 said:
Ok, that's the correct place



If the idle rises when you unhook it that means it's pulling vacuum there and the reason the idle rises is you've created a vacuum leak by unhooking the hose. It also means you have the primary idle speed set so high it's exposing that port to vacuum which should not be. That port should never have vacuum at idle. I'd back off the primary idle speed screw and adjust the secondary idle speed screw in 1/2~5/8 turn. It's the one located on the bottom side of the base plate on the pass side and you have to access it with a small screwdriver. You may have to take the carb off to get to it because some manifolds cover it up when the carb is bolted down. If you do that and find it helps but it still needs more you may have to drill some small holes in the butterflies to let more air in at idle so you can lower the front idle speed more to get it in the proper relation to the idle feeds slots.
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Ok I will check and do that. Its raining so I can't really do much.
 
you should remove the rotor and spray a light weight oil on top of the shaft, then put rotor back on and turn it and check for tightness of rotor and if it returned to the same spot each time its ok I also had same problem it turned out to be the light weight springs.
 
1973dusterkid said:
Plugged the line the idle did not accelerate, But the idle is still slow to decrease.
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That is what I was wondering, thank you.
Sorry about not mentioning to plug the port when you disconnected it.
I assumed. :)
 
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