Tuning help! - Team Camaro Tech
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post #1 of 8 (permalink) Old Feb 3rd, 05, 03:17 PM Thread Starter
 
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Ok heres the deal guys,

I got my new engine running a few weeks ago (vortec heads, edelbrock rpm intake, demon 750, and I cant seem to track down the type of cam it is a comp cams hydraulic that is fairly agressive, and msd pro billet dist 6a box and coil)

I had it running well enough to drive it out of the shop and thats about all my auto teacher cared about so rigfht now I am on my own, and I have no damn clue how to tune an engine...

To adjust the timing do I remove the vaccum line to the advance in the dist? Also with it on it idles with almost full advance.

I don't know where to begin with the carb, aside from the idle screw I am as knoweledgeble as most cave men with carbs.

Right now the car is very tough to start also it has to be totally warmed up otherwise it dies when put in gear, also up until 2000 rpm it hesitates very bad and spits back every once and a while.

I am doing the interior so Im not in much of a time constraint with getting this thing to run right.

If one of you guys are from the bay area and think that you could get this thing to run right I'll buy you some lunch, I figure we would take my camaro and if it makes it there its a good enough job haha

I do have everything that I think will be needed to do this (Timing light, vaccum gauge, and basic tools) so if I can be walked through it i'm sure I could do everything myself.

Thanks again
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post #2 of 8 (permalink) Old Feb 3rd, 05, 06:42 PM
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Christopher
 
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I have had a very similar problem so I did some research talked to some people and have solved it. I am still looking for optimum power with my combination though.

to time you do need to unplug the vacuum from the carb and plug the line. This will allow you to adjust initial advance. If you have a big cam you should be 10-12* initial advance and then anytime you have the vacuum attached you should get that advance as well. On my Hei the vacuum is an additional 12* that comes in at 7" of vacuum, so just off idle for me until Wide Open Throttle (WOT). I am unclear on the perfect timing, but in my experience lower initial timing helps spin the tires at lower rpm but you lose some top end power and vice versa.

look at the first article for step by step instructions on how to time, and the second for how it works. one thing to do is play with it see where you like it. Also I am not sure of your altitude, these numbers are for sea level, add 1* of initial timing for every 1000 feet of altitude.

http://www.chevyhiperformance.com/ho...673/index.html

http://www.chevyhiperformance.com/ho...438/index.html

make sure you do not have too much fuel pressure to pass through the needles of the carb should be about 6 psi, if you have an elec fp just flip it on without the engine running and look down the carb and see if you have fuel going in the engine if there is you need to adjust your fp. if not need a fp gauge.

next you need to adjust your float settings. this is either internal (holley 3310) or can be done from the outside (holley 4150/4160) if the external then unscrew the sight plug and adjust so that just a little fuel comes out of the hole with a lopey idle. Adjust by loosening the screw on the top of the float bowl and turning the nut to increase or decrease the level.

As for the carburator adjust this after you have the timing set. You want your car to idle without the vacuum advance in if you can but keep the dist attached because this is how your motor will run. Put your vacuum gauge on the carb. On my Holley 4150 I have a vacuum port on the front that I can plug into. You want to adjust for the most vacuum at idle. The general starting point is one and a half turns out, in will lean it out, out will richen the mixture at idle. I have a four corner idle circuit so to adjust you begin in pass primary then to driver primary then pass secondary then driver secondary.

look at these articles on carbs

http://chevyhiperformance.com/techar..._0503_trouble/

http://www.chevyhiperformance.com/ho...498/index.html

http://auto.howstuffworks.com/question377.htm

http://www.chevyhiperformance.com/ho...638/index.html

(the last one is really comprehensive)

Chris
68 camaro, sbc 385 (going together), holley 4150 750cfm, 4 spd, gm HEI, performer RPM intake
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post #3 of 8 (permalink) Old Feb 4th, 05, 02:27 AM
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You want your car to idle without the vacuum advance in if you can but keep the dist attached because this is how your motor will run.

Actually, you would want the vacum advance operable at idle to increase the VE, smooth the idle and reduce the chances of run-on. Ported vacuum was a crutch developed in the early days of smog controls as a method of reducing certain emissions at idle.
The most common problem modofied engines have with vacuum advance is that folks try to use a stock can that doesn't operate correctly in the vacuum range of the engine. You want to select a vacuum can that will be fully engaged at idle. GM offered various low vacuum cans on the early like these:

VC1810 B28 1965 409 High Perf. 3-5" to start, 8° @ 5.75-8"
1965 327 High Perf.
1966 327 High Perf.
1964-67 Corvette High Perf. FI

VC1809 B27 5-7 9 @ 10-12

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post #4 of 8 (permalink) Old Feb 4th, 05, 06:07 PM
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Jim
 
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Several aftermarket manufactururs make vacuam cans that can be adjusted by stiking an allen wrench in the vacuam tube and turning a screw. This can be helpful, too. The trick with the vacuam is to have lots of advance under low load, but to have it fall off quick when you get into the throttle to avoid part throttle pinging.

https://www.camaros.net/cgi-bin/forum.../9/13143.html?
About halfway down the first page of this post, I went thru the basics of seting timing and mixture with a vacuam guage and timing light. Hope it helps





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post #5 of 8 (permalink) Old Feb 5th, 05, 06:50 AM Thread Starter
 
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One thing i think might be a problem is what should I use as my vaccum source for my dist ported or manifold?

I did not know demons had ported and manifold(they are right next to each other at the same level.

[ 02-05-2005, 07:39 PM: Message edited by: jackalope ]
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post #6 of 8 (permalink) Old Feb 5th, 05, 04:17 PM
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Brandon
 
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Go with the manifold vacuum. save the ported for your auto tranny if thats what your using.
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post #7 of 8 (permalink) Old Feb 6th, 05, 05:00 PM Thread Starter
 
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okay, got the timing where it should be 12* initial (with advance off) 32* total

just one problem, with the vaccum advance hooked up i have all my advance in at idle... JimM was saying its there for whan under high load so i could just be waay out of line here. Also the distributor is a fairly new msd pro-billet so would it have an adjustable can? Any tips on what to do would be awesome.

Also what should be the way to trobleshoot valve noise, I am using the same valvetrain and heads as my old engine and they never made any noise so I doubt anythig is broken, I was planning on loosening and reinstalling the rockers.
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post #8 of 8 (permalink) Old Feb 7th, 05, 03:28 PM
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Jim
 
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nonono u read it backwards or I wrote it backwards.

The vac can will give max advance under high vacuam (no load or low load) conditions. When you get in the throttle, the vacuam advance should drop. Kinda hard to test, you'd have to keep the rpm steady while dropping the vacuam, only way to do that is kinda dangerous.

I wouldn't worry too much about the vac advance unless you are getting a part throttle ping.

You probably need to adjust your rockers again. Best way is running, but it's messy. pull a cover, (engine all ready warmed up) fire it, and run em down as fast as you can. Loosen til it goes clack clack clack, then tighten till it stops. I can do a side in 45 seconds or so, still gets really messy...





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