Carb tuning thread ( start with secondary spring)
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Lead Driver
Joined: Nov 2000
Posts: 6,628
Likes: 345
From: Albuquerque
Carb tuning thread ( start with secondary spring)
I'm running a Street Demon 750 (new) with vacuum secondaries. It comes with the plain steel colored pod spring. I'm trying to decide if the spring opening rates in the link below are based on wide open throttle or if the throttle position doesn't matter.
http://documents.holley.com/lit350rev.pdf
i.e. at low/medium rpm cruise is it going to be open somewhat or wait till I mash on the gas.
http://documents.holley.com/lit350rev.pdf
i.e. at low/medium rpm cruise is it going to be open somewhat or wait till I mash on the gas.
Laughing Gas
Joined: Jul 1999
Posts: 1,048
Likes: 22
From: Lacey, WA
Hi,
I picked up a spring assortment package. It contained around 8 different colored springs.
The secondaries operate based on engine load. In Park/Neutral you can floor the gas and the secondaries will not open as there is no load on the engine. I only bring this up cause some folks don't realize this.
I put a paper clip on the rod coming out of the vacuum canister, up against the canister. Then took the truck for a drive. When the secondary opens it will slide the clip down the rod. After you test drive, pop the hood to see where the clip is.
Play with different springs till you get the opening to occur that provides opportune performance.
If you put to light a spring in,... the secondaries will open to soon and cause a bog.
Take care,
I picked up a spring assortment package. It contained around 8 different colored springs.
The secondaries operate based on engine load. In Park/Neutral you can floor the gas and the secondaries will not open as there is no load on the engine. I only bring this up cause some folks don't realize this.
I put a paper clip on the rod coming out of the vacuum canister, up against the canister. Then took the truck for a drive. When the secondary opens it will slide the clip down the rod. After you test drive, pop the hood to see where the clip is.
Play with different springs till you get the opening to occur that provides opportune performance.
If you put to light a spring in,... the secondaries will open to soon and cause a bog.
Take care,
Thread Starter
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Lead Driver
Joined: Nov 2000
Posts: 6,628
Likes: 345
From: Albuquerque
Good idea, At one time I had a micro switch that wold show me when they stated to open.
I understand the secondaries wont open in nuetral, what I'm not sure of is if their opening rate (as per the chart) is totally dependent on RPM (internal vacuum source) or if the load plays any part. It would seem they need both rpm and load (low manifold vaccum) to open. Of course the are limited by the main throttle opening.
I understand the secondaries wont open in nuetral, what I'm not sure of is if their opening rate (as per the chart) is totally dependent on RPM (internal vacuum source) or if the load plays any part. It would seem they need both rpm and load (low manifold vaccum) to open. Of course the are limited by the main throttle opening.
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