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

You set the timing per l-jet instructions?

The Cap'n

Yes

One question though, when I set the timing I set it to 900 rpm after the vacuum advance lines are removed and plugged correct or set it while they are connected and then remove?

with thee lines plugged should the idle change as the distributor is rotated? If so rotate it till it is 7.5 degrees BTDC and then lower the idle with the idle adjustment screw?

What are the rest of the engine specs?
You may find drilling a 1/8" hole in the throttle plate will help. There are times when the engine moves more air at idle than the stock idle bypass screw will allow for.

2.0 Heads were done by Len Hoffman
CR 8.56:1
Full Raby valve train kit
Stock L-jet throttle body, air cleaner, and intake runners
stock 2.0 heat exchangers
pertronix ignition

Anything else that I am not listing?

Would this be a induced by the better cam?

Sounds like you are doing the timing properly.

With L-jet, the idle speed lowers if there is a vacuum leak, and the car will not start at all if there is a leak to large.

With D-jet, the idle speed will increase with an air leak, same as with carbs.

Before you go and modify things, check everywhere for leaks, again.
It amazes me how I miss leaks the first five times I look for them....

Typically I find all the leaks the last time I look for them.

The entire engine combination. Thats what its all about, moving more air! Its doing its job.

Jake hopefully you'll see this and and offer some advice.

I have a AF ratio meter with wide band O2 sensor hooked up now.
I still didn't drill the hole in the throttle plate but i am wondering if the symptoms are pointing that way.
here's where I am at:
L-jet 2056 9590 cam
No vacuum leaks that I can find, plenum removed and pressurized to check for leaks
All other hoses are new

Idle is somewhere between 300 and 500 rpm with AF reading 26-28
If I crack the throttle and bring the rpms up to 900 I get numbers closer to 16-17 (this was just a first glance) which lead me back to the 1/8" hole in the throttle plate.


Does this point to needing that hole so I can even get the idle up to where the AF is giving relevant logical readings?

If its that lean, there has to be a leak...if you add a hole, that will just add air...is your idle stop screw set right?

Valve adjustment will make a big impact to the idle...ask me how I know...

What is the right setting for the idle screw? Is I back it out all the way it doesn't really change the idle much.

I took an extra TB and drilled an 1/8" hole and had noticeable improvement. I could actually get the idle to change a little with the screw, particularly after it was warmed up.

I guess I can always go back and check the valve adjustment just to see if it makes a difference.

on the other hand, if it works.......

Have you read up on how to tune L-jet?
Are you familiar with the bypass screw on the air flow meter?
Have you tried adjusting it?
Its doubtful that drilling a hole in the throttle plate will improve the function of your system.
The idle is so low because there isn't enough fuel for the amount of air getting in the engine.

I disagree.




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.

hmmm.. this would explain why I have to use the throttle stop to get the idle I want...the bypass screws don't do much if anything.

I don't pull a very large vacuum at idle..but can get a pretty decent 800 rpm..

Exactly.




You can't have vacuum without chamber filling. You can't have chamber filling without intake volume.

got it! thanks!

I read the article online about tuning L-jet which has been very helpful.

I richened the mixture up all the way and the engine still would not idle. So I tried the hole in the throttle plate and I am much closer to getting numbers that are more in line with where the mixture should be.

The article stated to move the static mixture till you got idle close I couldn't even get close. the mixture screw on the meter is only supposed to be used to fine to mixture at idle

right now my numbers are:
Accel - 12.4-13.7
WOT - 12.1-12.7
Cruise - 12.6-13 Too rich I know
Idle 12-14 I am still having some fluctuation in the idle and it not coming down after driving

So do I lean it out more to bring the cruise mixture down and then richen up the dynamic to keep the other numbers where they are?

Jake,

I have the timing set at 7.5 BTDC@800rpm now

you mentioned timing in your last post, Is there more I need to do with this?

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.

I drilled mine in the center just to one side of the shaft. not sure if that was the best location or not.

I drilled mine in the center just to one side of the shaft. not sure if that was the best location or not.

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.

Thanks Jake

would full advance be around 3500 rpm?

Yes, but the actual RPM that the distributor reaches full advance will vary.

Ok I went back and set the timing at full advance 28 degrees BTDC

I am still fighting the idle.

When first started it idles low
As it warms up it rises to 800 rpm
Once it is reved it idles at 1800 rpm
If I turn the bypass screw in I can lower it but as soon as I rev the engine it climbs back to 1800 rpm

If I try to pull it down by placing a load on the engine it will drop but as soon as the load is gone it climbs right back up.

Acts as if the vacuum retard isn't working. I checked the diaphragm and it was good.

Idle mixture @ 800 rpm is 19.6 - 20.7
when it idles at 1800 rpm mixture is 13.1-14

any more ideas of what to look for?

Have you drilled the throttle plate yet?

You'll probably find that AFTER the throttle plate is drilled (leaning the engine out by adding air) that you'll need to richen the fuel mixture. What helps with this is adding fuel pressure for better atomization at lower engine speeds.

Yes I drilled the throttle plate and it is much better but now the idle behaves as mentioned in the last post. What is making it keep going to 1800 rpm?

My mixture numbers are running like this:

Idle 1800 rpm 13.1 - 14
Idle 800 rpm 19.6 - 20.7

Accel. 13.1 - 13.7

WOT 12.3 - 12.7

Cruise 13.1 - 13.8

From what I have read the accel. and WOT are pretty close to the correct range, Cruise is way too rich

Any suggestions (Richen the Static and lean out the Dynamic?)

Can you get a an adjustable fuel pressure regulator for L-Jet? Can one form D-jet with the adjustable screw be used?

It is now climbing to 1800 RPM because the additional air leaned out the idle. Lean engines idle high and won't settle when you toss them a rev.

An AFR meter is fairly worthless at idle, because the exhaust pulses are too slow and because of reversion in the exhaust system. Make the engine happy at idle, give it what it wants- it probably wants to be a lot fatter than it is now.

ok so I finally had a chance to get back to working on the car.

I richened the L-jet by moving the static mixture adjustment 1 tooth richer and leaned out the dynamic mixture by 3 teeth.

The idle is starting to come down but everything else is too rich so i tried 3 more teeth leaner on the dynamic. I believe this is inducing another problem by relieving spring tension on the barn door it is allowing the wiper to swing past the potentiometer and then the engine cuts out till it comes back onto the potentiometer.
Also the accel. and WOT numbers are still too rich.

So I seem to be stuck by not being able to get the idle mixture rich enough without making all the mixture too rich. The idle mixture screw on the meter does help a little but not enough to get it where ti needs to be.

Is there something else I can do?

Will changing the advance on the timing have an effect on mixture? particularly at WOT and accel.?

Is there any benefit at looking into changing fuel pressure and or adding a resistor to the CHT circuit(or is that only applicable on D-jet)? to change the mixture