73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: txchainsawgogi on September 02, 2010, 10:43:54 am
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What would cause the engine to run roughly with the vacuum lines connected, specifically to the advance on the distributor.
If I cap off the vacuum advance it starts and idles and runs much smoother.
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Sounds like you are using manifold vacuum. You could switch to a timed vacuum source.
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Where is your timing set, or has it been set? Timed vacuum might help or retard your timing and leave the vacuum alone.
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I haven't set the timing yet... it was doing the same thing with the old distributor. I figured a new one would help, and it did with everything but the vacuum advance.
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I think you need to set your timing before you try to troubleshoot any further, but if you just wanted to play around you could try to retard your timing a little and see if it makes it run as well as it does with the vacuum unhooked.
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I've never timed a truck before...only a few motorcycles. I'm sure I could do it though...
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Nothing to it. Do you have a timing light? Make sure to plug the vac advance hose when you do it.
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Id have to borrow one from autozone or some place. My haynes manual mentions a VECI label with tune up specs that's long gone from the engine compartment.
What do I do?
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The VECI label will give you the factory spec timing baseline, but I would ignore that and set it between 8-12 degrees before TDC. Most labels will say 4 or 6 degrees BTCD. I run mine at 12 BTDC without EGR. If you can get a dial-back timing light and set your total advance and work your way back to initial timing that would be prime.
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Id have to borrow one from autozone or some place. My haynes manual mentions a VECI label with tune up specs that's long gone from the engine compartment.
What do I do?
I've got a timing light (well, 2) and can help if you want, possibly this weekend. :)
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Dang, can't seem to find anyone that loans timing lights. Kind of lame. 454 id take you up on that but my truck isn't street legal(or even in my name yet) and another ticket is the last thing I need.
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Well, where are you? I don't mind taking a drive. 8)
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I think O rileys/kragens does.
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No harm in buying one, too. Good investment IMO.
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Have you checked your vacuum advance on your dist. yet to see if it was operating properly ? Check the most obvious first is my theory.
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I don't know how to check it!
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Alright I've got a light... when I loosen the dist. Clamp and rotate it do I do this with the engine running or what? How do I know what marking to match it up with? 8-12 BTDC?
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sure, move it around while idling....you can get a good idea of what it sounds like in the different positions.
Clip the timing light on the #1 spark plug wire....looking at engine 1st plug wire on right, closest to you.
aim the light at the harmonic balancer. You should get a yellow marker, or white chalk or something to highlight the mark on the harmonic balancer first. Then put a white mark or something on the correct setting on the guage over the harmonic balancer, whether it is 8btdc or whatever. Idle the engine w/ the vacuum advance hose unplugged from distributor and plugged with a golf tee or something. If 87 or newer, unhook the brown or tan wire near master cylinder that controls advance.
turn distributor until the lines match up on balancer. Then tighten up the 9/16" bolt to hold down the distributor and you're set. I tend to not go by the factory settings ---i go w/ what feels good to me.
(http://www.delbridge.net/tab1.jpg)
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Ahh ok. Wasn't sure about moving it while idling...it makes sense but my haynes doesn't mention it. Do I have to keep my hand on it when its loose?
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You're not loosening it that much. Just enough that you can rotate it.
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it won't spin around on you or anything....it may shock you though. I take a rag and put it on the dist.cap and I won't touch the wires while it runs.
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it won't spin around on you or anything....it may shock you though. I take a rag and put it on the dist.cap and I won't touch the wires while it runs.
x2, been there.
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X3 on shocked. Been shocked on my 66 I6 mustang when I converted to the pertronix as well as on my HEI
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Oh yeah...never got around to setting my timing. I checked but don't have timing marks. It runs smoothly and strong but I'm getting crap mileage!
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x4 on being shocked, although I got shocked while the truck was off! the key was on and i was setting the plug wires to firing order. ZZZZZ. Ouch. Haha.
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i need someone to give me a vacuum diagram on a 1983 chevy stepside(inline 6-250 engine) if anyone can, my email is haulinb29@yahoo.com---thanx..