I'm at my wits end!! - Team Camaro Tech
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post #1 of 11 (permalink) Old Jul 24th, 03, 03:59 PM Thread Starter
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Matt Jones
 
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I need your guy's help very badly. I'm getting real tired with the car. I even took a couple weeks off of working on it, and I'm frusterated all over again. Here's the story:

Needed a new oil pan gasket, so I decided to change the cam at the same time. I went from a Crane 266 (210/210 110LSA), to a Isky 270 Megacam (221/221 108LSA). The Crane ran great, had good torque, but not enough top end for my 3.73:1 gears. I can't get the motor to run worth a darn with the new cam. Here's my combo:
-355ci
-180PSI hot cranking pressure
-Cam installed 0* Advanced
-Vortec heads
-Perf. RPM Intake
-Road Demon carb (w/4 corner idle)
-HEI w/ 10* initial, 6* Vacuum, total 16* at idle
-2500 Stall Converter

After the cam break-in, the motor wouldn't idle. Found that valves were too tight, and re-adjusted them and can now idle @ 900RPM in gear. I used some EOS during the break-in, so I hope it's OK.

NOW, to the problem...the darn thing won't idle less than 1200-1300RPM in neutral, and has about 8-9" vacuum at 900RPM (in gear). I've tried several timing figures at idle; 0*, 8*, and 16*. 16 is best, but still runs too fast. Because of this crappy idle, I can't adjust the 4-corner idle (which I can never seem to do anyway, regular 2-corner is a cinch).

I've tried two PCV valves, one high-flow and one normal one, neither affects the idle speed. I can play with the primary and secondary screws all I want, but still wont get lower than 1200RPM. Checked for the throttle binding, and it's OK. I haven't checked for vacuum leaks yet, but it would have to be a pretty big leak to let the motor idle at 1200 with both primary and secondary's closed (speed screws backed out completely). Even tried two different timing lights, and a different balancer to make sure the timing was correct.

Sorry for the long post, but I really need the help. If I can't get this to work, I don't know what I'll do. Thanks...

Matt Jones
Lead Mechanical Engineer
Art Morrison Ent. Inc.
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post #2 of 11 (permalink) Old Jul 24th, 03, 04:19 PM
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John
 
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Hmmmm - let's see, you went to a longer duration cam with less LSA and it won't idle to well - sounds right to me.

The fact that the engine is enjoying the more advance lead you are giving it seems to points to a vacumm leak (I take you you've already checked for that by your post) OR the cam being a little big for your set-up. If the cam truely is 'straight-up' then you could try advancing it @2~4 deg. and see if it will idle better.
If it still won't idle worth a dang, you could go a little smaller on the cam (Comp 264-268 range) and try that.
What ratio rockers are you running? If stock, you could go to larger ratio with a smaller cam and gain a little top end.
Just my .02 as usual.

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post #3 of 11 (permalink) Old Jul 24th, 03, 04:42 PM Thread Starter
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Matt Jones
 
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I understand this cam won't idle like my old one...that's obvious. But 8" of vacuum at idle? That's too low, also considering my compression is high enough to have 180PSI of cylinder pressure.

I didn't degree the cam, so I can't say for sure it is straight up. All I did was set the crank gear for 0* advanced, that's the best I can do right now.

This cam is reletively small, so I'm pretty sure it's not over-cammed. I've driven cars with 235-240 @ .050 (it was a Comp Cams grind in a 350, so at 110LSA), and it idled better than this does by far.

So, because the idle wont go down, I can't adjust the idle mixture, which gives me terrible throttle response, and burns your eyes. Ugh...

Matt Jones
Lead Mechanical Engineer
Art Morrison Ent. Inc.
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post #4 of 11 (permalink) Old Jul 24th, 03, 09:24 PM
 
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hey there,
I had a nearly identical problem not long ago. Rebuilt 350, good cranking pressure, cam checked and rechecked, could not adjust idle properly, would run with mixture screws seated, ran good with rpm, 6" vacuumm. Triple checked valve lash and vacuum leaks. Ended up being an INTERNAL carb leak. Just a thought. Good luck!
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post #5 of 11 (permalink) Old Jul 24th, 03, 10:43 PM
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silver, you should be able to get that cam dialed in easily. the fact that the car won't idle down even with the idle screws backed clear out is definately a problem. that sounds like a massive vacuum leak, or throttle plates hanging open. you should be able to idle it down to the point it dies. i'd start by seriously looking into a vacuum leak first, using propane or carb cleaner or what have you. the road demon is kind of a touchy carb it seems, but it ran before it should run again. the way i dialed in my speed demon when i bought it, was get the fast idle screws so they just come in contact w/ the cam, but no movement, then turn it about 1/2 a turn. both of them the same. then set the 4 corner screws at 1 1/4 turns, again equally. then start the car (another person is nice), and if it won't idle, bump the fast idle screws up a bit, again evenly, untill it will idle. then adjust the four corner, then the fast idle, then the four corner, etc,etc, untill you get it running right. don't set the four corner screws far off from one another, mine runs best with 1 1/4 and 1 1/8, front rear. you'll love the cam when its right, isky cams are great. and by no means advance it any, isky cams routinely start out about 3-4 degrees advanced from the factory, as are other manufacturers. it really is likely a tuning issue, imo. just double check everything, esp. the simple stuff, and look into the possibility of a vacuum leak. good luck with it, you'll get it [img]graemlins/thumbsup.gif[/img]

Sean

1968 rs with an old school 354" SB2.2 pump gas motor.

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post #6 of 11 (permalink) Old Jul 25th, 03, 04:47 AM
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Aka Eugene! Do you remember what was the problem with the carb? Was it a rochester? I think I am having the same problem (all stock L-48 with 14in vac), but can't find it [img]graemlins/angry.gif[/img]

thanks

Kevin


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post #7 of 11 (permalink) Old Jul 25th, 03, 05:44 AM Thread Starter
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Matt Jones
 
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Sounds good guys. I'm going to grab a 6.5 PV to replace the 8.5, and I'll pick up some new gaskets and clean out the carb.

I did pull the Demon off last night, and noticed that the secondary butterflys were open slightly, showing a little more than the usual .020" transfer slot, and this is with the secondary speed screw backed clearly out. I couldn't see any binding issues. I don't know if all Demons are set like this from the factory, or if I have something wrong. I'll go down to the speed shop and look at a new Demon to see if it's the same way.

I'll let you know how things turn out.

Matt Jones
Lead Mechanical Engineer
Art Morrison Ent. Inc.
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post #8 of 11 (permalink) Old Jul 25th, 03, 06:07 AM
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Hi Matt,

Your problems are very common. You might get something from my comments in this thread...

https://www.camaros.net/forum/ultimat...=010074#000002

I advocate going over any new carb to insure the factory set it up to their published spec's. It seems a lot are way off.. Here's more on an Avenger that supports this...

https://www.camaros.net/forum/ultimat...=007150#000001
&
https://www.camaros.net/forum/ultimat...=007221#000000

...Dennis

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post #9 of 11 (permalink) Old Jul 25th, 03, 10:55 AM Thread Starter
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Matt Jones
 
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Thanks for the info, Dennis. The comments made by you and Eric are helpful.

Okay, so here's where I stand now. I changed the PV to a 6.5, and I tore the carb apart and cleaned it up with new gaskets to prevent any internal vacuum leaks. I also used some real thick carb gaskets (about 2x thicker than normal), to make sure things were sealed up good.

I fired it up and adjusted the mixture. It definetely runs better, I now have 10.5-11" in gear (750RPM), and 14" in neutral (1000-1100RPM) and doesn't burns the eyes. The idle isn't lumpy at all with the 108LSA, just makes lower vacuum.

So all is good, right? Well, maybe. Even when I close both primary and secondary idle speed screws, it will only go as low as 900-1000RPM in neutral. So where is this air coming from? The PCV? I even did the propane test around the intake manifold and didn't find any vacuum leaks. I'm baffled, any ideas?

As I was about to take it for a test drive, the engine just flat out quit and wont restart. I think the module or pick-up coil went south...oh well...

Matt Jones
Lead Mechanical Engineer
Art Morrison Ent. Inc.
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post #10 of 11 (permalink) Old Jul 26th, 03, 03:15 PM
 
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hey Kevin and all,
The problem with mine was that after suffering a backfire (from having the dist 180*) some of the passages in the gaskets became linked together. It made low vacuum and would run with the idle mix screws all the way in. After rebuilding it, it continually flooded and leaked out the hole for the acc. pump rod. Ended up that was because the float pivot was bent out of shape and was proping up the gasket causing an internal FUEL leak. After the re-rebuild, it runs great! Yes it was a rochester 4mv.
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post #11 of 11 (permalink) Old Jul 29th, 03, 01:53 PM Thread Starter
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Matt Jones
 
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To give you guys an update:

I re-set the valve lash to 1/4 turn past zero, and this really cleaned up the performance. The Speed-Pro lifters really do not like 1/2 turn at all.

I disassembled the carb, and found little bits of stuff (looked like carbon) on the secondary bore, causing the throttle blades to hang up. I'm now able to set the idle speed to where I want.

By the way, using a 6.5 power valve help alot (vs. 8.5), since the engine would die when put into gear.

Matt Jones
Lead Mechanical Engineer
Art Morrison Ent. Inc.
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