460 timing issue
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From: mid-MO
460 timing issue
Trying to get the timing on my 460 dialed in. With the truck idling (about 700 rpm) I can throw the timing light on it and it sits at 10* BTC. If I disconnect the vacuum line from the distributor and plug it with a golf tee, the engine sputters and dies before I can even get the light on it. Shouldn't the motor run ok without the vacuum line attached? Should I try to advance timing with the distributor? Whats a good place to set it at? Thanks
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From: BC Cana'duh
For ported vacuum,you need to plug into a port on the metering block.The port should be above the throttle plate or baseplate.At 700 RPM,there shouldn't be any drop at idle when the vac line is unplugged.With a Comp Cams 270H(34-239-4)I set my initial at 10 deg. with a 800 RPM idle.I also have approx. 10-1 comp. ratio.Increasing initial timing results in a NO start when hot.
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From: mid-MO
Well I am pretty sure the vac line is above the throttle plate. Its just a stock port off the carb (Edelbrock 600cfm). Its the same setup that the 390 had before I put the 460 in. So since the motor sputters and dies when I disconnect it, what does that mean? What does your motor time at idle WITH your vac line hooked up and idling? Mine is at 10*BTDC WITH the vac line hooked up. Do you think I need to advance it more?
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From: BC Cana'duh
I'm not familiar with Eddy carbs,but like Monsterbaby said,you're likely close to or fully advanced at idle.I agree that you're probably on full manifold vacuum.Find a port on the carb without any vac at idle.Give some throttle with your finger over the port and if vac is present,then that's your ported vac source.Also check the Edelbrock website for ported vac on the model carb in question.
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Ok, guys, you are good. I went home last night and looked at the Edelbrock owner's manual and it clearly shows the port I am running off of is the manifold vac port and not the ported vac source. I have the ported source plugged. Ha ha. I was reading last night a big block rebuild book and it talked about the difference in distributor advance diaphrams. It said after about 68 or maybe 78, they went to a dual diaphram. Would this make any difference, or do you think its just that I am hooked to manifold port and it should be the ported vac source?
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From: iowa
unless you have 2 nipples on the vacuum pot, you should be hooked up to ported vac. Advance your timing enough to keep it running and then plug in the other port and reset the timing.
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From: mid-MO
Ok, so saturday I worked on the truck and unhooked the vac line going to the distributor and plugged it. I set the timing with a timing light to 10 deg before top dead and then tried to re-hook the vac line and the engine immediately died. I unhooked the vac line, started the engine and this time put my finger over the vac line and had suction. The port that I was plugged into was off of the carb and in my Edelbrock owner's manual it says that this one is a ported vac source. So at idle I should have absolutely no vac pressure, right? Does this mean I have something wrong with my carb? What could it be?
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From: BC Cana'duh
Try a different port.Also too high an idle will cause vac to a port source.That's how a ported vac source works.As the throttle is opened,the ported source"opens" or is exposed to the incoming air causing the vacuum suction or draw.It's possible the carb is at fault.What's the part number?If you're at 10 deg and you hook to a vacuum port(full vac) you're timing should advance into the 30+ degree range and engine speed will increase.Verify TDC is 0 deg on the balancer or try a different timing light.
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From: mid-MO
Finally figured out the problem after talking with a Edelbrock tech guy. I had to advance my base timing (with the vac line unhooked and plugged) which raises the rpms, then back off the idle speed screw until there was hardly any vacuum being pulled. Apparently the butterflies were open due to me cranking in the idle speed screw and that was the reason I had so much vac pressure at idle. Good to know. Thanks for all the help
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