High RPM after WOT

W30post · 11-24-2007, 05:59 PM

Guys,
I have changed intake gaskets on my car recently and it has the best idle I can ask for since I started driving it. The question I have is why do I have a high idle after a short wide open throttle run? If I go through all of second gear and let off, it takes a while for it to settle down. Is this the ported/ manifold vacuum switch on the intake causing the timing to be held high? What else could cause this?

Carb has been completely gone through and has no binding. The throttle shafts have been drilled and bronze guides installed for good consistent sealing. The distributor is a new unit and the mechanical advance is not sticking. I cannot say if the vacuum advance is sticking as I have not checked.

Any guesses?

Oldsmaniac · 11-24-2007, 07:44 PM

Here is a guess from me....possibly float level too high in carb or too much fuel pressure if ya have an electric fuel pump.....I would say that its not a vacuum advance problem. Are you sure your throttle return spring is stiff enough??....I would lean heavily on a fuel problem....just too much gas or throttle plates not closing on the carb.....just my 2 cents....

joe_padavano · 11-25-2007, 08:49 AM

Quote:

Originally Posted by W30post

Carb has been completely gone through and has no binding. The throttle shafts have been drilled and bronze guides installed for good consistent sealing. The distributor is a new unit and the mechanical advance is not sticking. I cannot say if the vacuum advance is sticking as I have not checked.

Any guesses?

Are you completely sure the carb throttle plates are closing correctly? I've had a similar situation and the problem ended up being the gasket between the float bowl and the throttle body on the Qjet. The gasket was just a little ragged in the throttle openings and the throttle plates would sometimes hang up slightly. Be particularly careful in checking the secondaries. Assuming this is a Qjet, be sure the link that forces the secondaries closed is adjusted properly.

kevinkpk · 11-25-2007, 11:45 AM

Sounds kinda like the fast idle screw is not set right, or sticking.

Redog · 11-26-2007, 04:57 PM

Yeah I had the carb stick on my old 307 motor. It's amazing how loud a car can be a 3500 RPM's with stock exhaust.

It stuck another time, but just like I learned in driving school, I floored it and it was fine after that, didn't stick again in the remaining 4 months that motor lived

W30post · 11-29-2007, 06:39 AM

I actually hadn't thought about that gasket but the base plate gasket could be causing drag also.

This is a Q-jet. The throttle plates move very easily when off the car and seat very nicely. Again the bores for the throttle shafts have been bronzed so I feel confident this is not a vacuum leak at the throttle shafts.

The return spring is healthy enough but has the placement at the carb linkage moved from the factory return placement. I like it to pull directly from the same spot as the pedal so the force vestor is equaled out.

I have checked the primary side when this condition happens to make sure it is returning to the set screw but I didn't pay attention to the secondaries. I will check that.

The fuel pump is the factory style mechanical and the float has been set and checked twice with a new float so I'm pretty confident in this setting.

The car does run slightly rich at idle all the time but I thought that was because of the cam choice.

I have a 67 Chevy truck and I just realized it doesn't do what the Cutlass does so I started asking. Let me get through these suggestions and I will get back with probably more questions.

Jim's rare 80 · 11-30-2007, 02:46 AM

My two cents,

check to make sure the return spring you moved isn't catching on anything. Just a thought.

11-24-2007, 05:59 PM	#1 (permalink)
W30post Member Join Date: Oct 2007 Posts: 33	High RPM after WOT Guys, I have changed intake gaskets on my car recently and it has the best idle I can ask for since I started driving it. The question I have is why do I have a high idle after a short wide open throttle run? If I go through all of second gear and let off, it takes a while for it to settle down. Is this the ported/ manifold vacuum switch on the intake causing the timing to be held high? What else could cause this? Carb has been completely gone through and has no binding. The throttle shafts have been drilled and bronze guides installed for good consistent sealing. The distributor is a new unit and the mechanical advance is not sticking. I cannot say if the vacuum advance is sticking as I have not checked. Any guesses?

11-24-2007, 07:44 PM	#2 (permalink)
Oldsmaniac Senior Member Join Date: Oct 2005 Location: NJ Posts: 369	Here is a guess from me....possibly float level too high in carb or too much fuel pressure if ya have an electric fuel pump.....I would say that its not a vacuum advance problem. Are you sure your throttle return spring is stiff enough??....I would lean heavily on a fuel problem....just too much gas or throttle plates not closing on the carb.....just my 2 cents.... __________________ OCA Member 2587 '59 98 conv. '66 Starfire '66 Delta Fact.4spd '66 Delta conv. times 2 '67 442 conv. '68 Cutlass conv. '70 Rallye 350 '92 Custom Cruiser

11-30-2007, 02:46 AM	#7 (permalink)
Jim's rare 80 Senior Member Join Date: Feb 2007 Posts: 210	My two cents, check to make sure the return spring you moved isn't catching on anything. Just a thought. __________________

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11-25-2007, 11:45 AM	#4 (permalink)
kevinkpk Senior Member Join Date: Oct 2007 Location: west Posts: 212	Sounds kinda like the fast idle screw is not set right, or sticking.

11-26-2007, 04:57 PM	#5 (permalink)
Redog Alero Chapter Secretary Join Date: Aug 2006 Location: Newtown, PA Posts: 679	Yeah I had the carb stick on my old 307 motor. It's amazing how loud a car can be a 3500 RPM's with stock exhaust. It stuck another time, but just like I learned in driving school, I floored it and it was fine after that, didn't stick again in the remaining 4 months that motor lived

11-29-2007, 06:39 AM	#6 (permalink)
W30post Member Join Date: Oct 2007 Posts: 33	I actually hadn't thought about that gasket but the base plate gasket could be causing drag also. This is a Q-jet. The throttle plates move very easily when off the car and seat very nicely. Again the bores for the throttle shafts have been bronzed so I feel confident this is not a vacuum leak at the throttle shafts. The return spring is healthy enough but has the placement at the carb linkage moved from the factory return placement. I like it to pull directly from the same spot as the pedal so the force vestor is equaled out. I have checked the primary side when this condition happens to make sure it is returning to the set screw but I didn't pay attention to the secondaries. I will check that. The fuel pump is the factory style mechanical and the float has been set and checked twice with a new float so I'm pretty confident in this setting. The car does run slightly rich at idle all the time but I thought that was because of the cam choice. I have a 67 Chevy truck and I just realized it doesn't do what the Cutlass does so I started asking. Let me get through these suggestions and I will get back with probably more questions.