Engine won't idle....

Old 09-19-2008, 09:28 AM
  #1  
prostreet1972
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Default Engine won't idle....

I have a sbc 350 stock bore and bottom end in my 72 chevelle. Double hump heads ported to match the team G intake. 750DP. Lunati bracket master II solid lift cam (part #00013). It's .500/.515. lift and 256/270 duration @.050. I had to up the jets quite a bit 80/86 with 4.5 powervalve. I have an air/fuel ratio gauge and still says a little on the lean side. I know my fuel pressure is right.

I cannot get this thing to idle below 1200rpm and my total timing is almost 50 advance. If I retard the timing at all it starts backfiring out the carb like crazy. my vacumm is about 5in at idle. With timing like this, it seems to run great, great throttle response and sounds really healthy. This is with no load, I haven't been able to get to the track to test it out.

I have checked for vacumm leaks, none found. Could it be leaking between the intake ports or into the lifter valley? The wall between the intake ports are pretty thin, and I didn't like the way the gaskets were sitting when I put the intake on. Motor doesn't smoke.

I installed the cam straight up (atleast the best I could). I am using a gear drive and it didn't seem like I could get the dots on the gears perfectly inline. Could the cam be installed incorrectly and throw off my timing?

I don't feel that it is a carb. problem, but I am open to any suggestions. I am honestly out of ideas...

Thanks,

Travis
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Old 09-19-2008, 09:40 AM
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gimmemud
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You need to degree the cam in, dont trust the dots. You are flirting with disaster there. It also could be an ignition issue, but since you didnt degree the cam in be sure to do that first.
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Old 09-19-2008, 10:30 AM
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zipper06
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I agree with gimmemud,
go back and degree the cam in, especially since you're useing a gear drive with idlers. Some of those gear drive are off the mark, especially the foriegn made ones. They also have 2/3 degrees backlash in them and if you're running dangerously close on valve clearance they can be a problem.
Also leaking into the intake valley will not alway produce smoke in the exhaust system at idle. It will at higher RPM when the oil starts flying around and you start building up pressure in the oil pan.

JMO

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Old 09-19-2008, 11:57 AM
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curtisreed
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Have you verified the timing pointer to top dead center?

Curtis
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Old 09-19-2008, 01:16 PM
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prostreet1972
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yes, i did find TDC. I have stock flattop pistons with 4 valve reliefs. 1.94/1.5 valves. Like I said it doesn't smoke, so it must be the cam.

So if i degree it in correctly my problems should be solved? I am going to switch to a double roller also.

Thanks,

Travis
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Old 09-19-2008, 01:55 PM
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gimmemud
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That may not be your problem at all, but since you didnt degree it and only relied on the dots on the gears, you really need to degree it to be safe. It could very well be the problem, could be something else, but the cam definatley needs degreeing.

The problem you are experiencing could be ignition related or could be an internal vacuum leak. What ignition are you running?
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Old 09-19-2008, 02:28 PM
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fla1976
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Default Won't idle.

How did you check for vacuum leaks? Did you try partially closing the choke if it has one. If you decrease the amount of air going through the carb and the idle picks up, you have a vacuum leak or a very lean mix. If you have one then the fun begins trying to isolate it. Hope this will help.
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Old 09-21-2008, 11:07 AM
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Tod74
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vaccume leak as stated above, but I would make sure the cam was right anyway. I would not run 50 deg of timing.
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Old 09-21-2008, 01:06 PM
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prostreet1972
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I am running a old MSD 7A with a fixed curve msd timing computer and locked out msd billet distributor, and msd 8.5 wires.

I am running a 750DP with proform body so it doesn't have a choke. I tried cupping my hands around the carb, but doesn't seem to affect the idle. 2 corner idle mixture and 30cc pumps. air bleeds are whatever comes in the proform main body. fuel pressure is 7.5 psi.

I put some gas into a spray bottle and sprayed around the base of the carb and all around the intake and nothing affected the idle. That's what make me think it may be leaking between the intake ports or into the valley pan. It doesn't smoke at any rpm. If i back the timing off at all it leans it out alot.

Once again, thanks for all your input. I appreciate it all
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Old 09-21-2008, 01:45 PM
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dparker
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Check your compression to see if its low. You might have a broke cam pin. The slack in the 3 bolts on the cam will give you around 10 degrees of retard, making you have to advance the ignition timing to compensate the difference. If the cam pin is broke your compression will be down 30 to 40 psi. I heard that some gear drives are subseptable to breaking pins. I know it sounds far out there but check it out.
take care
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