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LS2 Runs On

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Old 05-04-2012, 02:29 AM   #1
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Default LS2 Runs On

I recently got my LS2 Crate fired up for the first time. I have plumbed the steam line into the top hose because I am running a Speed Demon carb on an Edelbrock intake and an MSD ignition box. If I run the engine for a while, then shut the car off, it tries to run on for a bit. Very diesel sounding. Just for a couple of seconds, but enough to sound worrying. I am concerned that the top of the engine isn't cooling properly. Any suggestions or previous similar experience would help.
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Old 05-04-2012, 02:39 AM   #2
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Here is a shot of the engine.
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LS2 Runs On-corvette-engine-march-2012-017.jpg  
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Old 05-04-2012, 07:45 PM   #3
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Nice ride! That's an acceptable routing for the steam vent. What octane fuel can you get over there? I'd be looking at that and timing...
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Old 05-04-2012, 07:59 PM   #4
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Whats the idle at? If i let mine (carb ls2 also) idle at 1k it will run on for a second. If i knock it down to even 900 it wont. With the cam i have it wants to be up there though so i usually throw the fan or blower motor on right before i kill it and it shuts right off
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Old 05-04-2012, 08:49 PM   #5
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Yea dads with a carb on it did that last year tried a bunch of stuff best thing I found was to kick the AC on when pulling in somewhere and then shut it off.

With EFI it dosn't do it.

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Old 05-05-2012, 05:49 AM   #6
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I have run the engine a couple more times. I have the idle screw on the Speed Demon backed right out and I cannot get below 1100 rpm. I find that if I blip the throttle and shut the ignition off before the engine gets back to idle, it doesn't do it.

There is no A/C on this car. It is not worth it for the 2 weeks of summer we get in this country, and we already had them in March.

When I finally get it on the road, I will experiment with fuel quality.
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Old 05-05-2012, 08:57 PM   #7
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Quote:
Originally Posted by Alienlefty View Post
I have run the engine a couple more times. I have the idle screw on the Speed Demon backed right out and I cannot get below 1100 rpm. I find that if I blip the throttle and shut the ignition off before the engine gets back to idle, it doesn't do it.

There is no A/C on this car. It is not worth it for the 2 weeks of summer we get in this country, and we already had them in March.

When I finally get it on the road, I will experiment with fuel quality.
Tuning issues for sure. Don't those carbs have a secondary air bleed under the air cleaner stud? If so, it's open too much. You really need to get the primary throttle blades more on the closed side, as you're pulling fuel from the main jets instead of the idle transfer slots.
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Old 05-07-2012, 12:44 PM   #8
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Quote:
Originally Posted by S10xGN View Post
You really need to get the primary throttle blades more on the closed side, as you're pulling fuel from the main jets instead of the idle transfer slots.
Demon tuning guide says to adjust the throttle blades so the idle transfer slots on both primaries and secondaries appear as a "square" below the blades. How far off are you from this baseline?

Do you have a PCV valve somewhere? I see you have a fresh air hose going to nowhere on the driver's valvecover and I'm guessing you're pulling PCV from the valley cover back to the carb. If you don't have a PCV valve between the carb and the valley cover (or built into the valley cover), it will act like a vacuum leak. Try pinching off the PCV line going to the carb and see if your idle comes down.

Click the image to open in full size.
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Old 05-08-2012, 11:33 AM   #9
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Thanks for the suggestions. I will try this stuff out and report back. I read somewhere that there is a pcv valve under the valve cover on these engines???
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Old 05-08-2012, 12:40 PM   #10
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Did a little searching and it looks like it may be integrated into the valley cover.
LS2 - PCV System

High idle speed indicates a potential vacuum leak to me, which is why I suggested looking a the PCV system, but you should check all the vacuum connections on the carb & intake.

Sorry I didn't mention it before, but it looks like a very well done swap. Very clean install. do you have any shots of the whole car?
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Old 05-11-2012, 11:35 AM   #11
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Any luck figuring this out?
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