idle on a 2056 with 9590 cam Options

[jmargush]

I am having trouble getting my new 2056 with a 9590 cam to idle. When I start it is idles around 500rpm or lower and I can't speed it up with the by pass screw.

I am running L-jet injection
I hear a hissing sound when the engine is idling but I cannot find a vacuum leak, plenum couplers are new and all other hoses are in good shape.

I can't find the hissing with a mechanics stethoscope so I was going to try to find a leak with propane but it has been too cold to work on it lately.

The idle does seem to get a little better after it has warmed up a bit I think, it has been several weeks since I have had it out.

One question I had is does the new cam require any change to the mixture? if so how do I go about adjusting the mixture?

Thanks in advance for any input

[Jake Raby]

Its doubtful that drilling a hole in the throttle plate will improve the function of your system.

I disagree.

The idle is so low because there isn't enough fuel for the amount of air getting in the engine.

I disagree. The idle is low because the engine that is now breathing more effectively at idle speed now has a much greater demand for chamber filling. Because of this the air bypass screw becomes extended so far that idle air often fluctuates.

Drilling the throttle plate allows bypass air to occur, thus reducing the amount of air that must pass through the factory idle air bypass circuit. Drilling the throttle plate with this combination is often required, especially at lower elevations, as air density effects the bypass volumes even more.

The other thing that can impact this is initial timing advance, the key to tuning this combination is optimizing initial advance, advance curve and idle air bypass quantity. After these are complete, one can move to enrichment.

Thats my input as the designer of the camshaft profile, and they guy that has not only made it work a couple thousand times; but also made it work the first time.

[Porschef]

I have a 9550 cam, with Ljet. Whereabouts might this hole get drilled? I'm chasing my last (hopefully) vacuum leak this evening, and depending on how that affects things, I may need to try the drill my idle still hunts at temp.

[Jake Raby]

I have a 9550 cam, with Ljet. Whereabouts might this hole get drilled? I'm chasing my last (hopefully) vacuum leak this evening, and depending on how that affects things, I may need to try the drill my idle still hunts at temp.

In my experience I have found that a hole the same size as the VW logo stamped on the butterfly works well... BUT don't go that high straight away. Always start smaller and work your way up.

BTW- Setting timing at idle makes no sense to me, when doing this you are depending on a 40 year old distributor to have the exact same internal specifications that it did when new, and it seldom does. I set timing with vacuum disconnected at 28-32 degrees full advance without the vacuum attached.

There's a reason why we call it "optimized timing", because no two engines or environments are the same. You must apply changes and then listen to the engine and give it what it likes best. Once the engine is happy, it is optimized.

This requires trial and error couple with situational awareness and good old common sense.