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Thread: Vacuum Advance question.
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EricRyan
Revvin Up
Posts: 61
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posted July 09, 2010 03:42 PM |
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Vacuum Advance question.
Hey guys, I've been having vacuum advance plugged ever since I got the truck and I would like to get it going to make the first few gears a little easier to get through. I've got an RB IM and Dellorto carb, so there are only 4 vacuum nipples to "T" off of, I'm also hesitant to drill & tap the carb so I would prefer any other option first.
Brake booster and oil filler neck seem to use manifold vacuum so that wouldn't be an option. But what about the 2 nipples for OMP, which are still in use? I know I need venturi vacuum for this to work properly, so would making 2 separate "T" fittings off of each OMP vacuum lines work? Would there be any negative side effects?
Thanks in advance.
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Klaus42
Rotorhead
Posts: 1877
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posted July 10, 2010 07:59 PM |
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I wouldn't do anything that could possibly compromise or interfere with metering oil delivery, and I think I'd want to try to get the 'right' person on the phone/email at Racing Beat regarding their recommendations for the Dellorto, including running the vacuum advance.
Brad might have some good info. for you as well.
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sparky
Redlining
Posts: 299
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posted July 10, 2010 09:19 PM |
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This is what i did on my series 4 engine with weber carb that also had the vacuum check valves for oil metering injection.
What i did was go with the 2 oil injection points into the rotor housings. Installed an oil metering pump with 2 outlets rather than the 4 that was on the series 4 front cover.
On the lower intake manifold i tapped and brazed some steel tubing into the brake booster tap and connected the vacuum lines the check valves.
Hope this is helpful.
____________
'77 REPU
Stock 6-port
T-2 tranny
Weber IDA 48
Alum Flywheel
3rd gen Torsen in rear end.
DLDFIS ignition
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EricRyan
Revvin Up
Posts: 61
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posted July 11, 2010 10:09 PM |
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My motor is an '83 so I already have only 2 OMP lines. So what you're saying is that I could T off of my existing brake booster line? As long as I use a one-way check valve, would this give the advance the proper vacuum it needs?
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sparky
Redlining
Posts: 299
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posted July 12, 2010 07:56 AM |
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If i rememver right, i don't think you should use vacuum advance with weber and dellorto carbs???
____________
'77 REPU
Stock 6-port
T-2 tranny
Weber IDA 48
Alum Flywheel
3rd gen Torsen in rear end.
DLDFIS ignition
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ericryan
Revvin Up
Posts: 61
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posted July 12, 2010 09:33 AM |
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What's the reasoning behind that though? Is it a problem with fuel delivery?
I think I read somewhere Weber's instructions call for you to remove and cap the advance nipples, but I had no idea about Dellorto. I'm still new to carb's so you'll have to forgive me, but I really am trying to get my head around all of it.
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Klaus42
Rotorhead
Posts: 1877
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posted July 12, 2010 09:34 AM |
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quote:
If i rememver right, i don't think you should use vacuum advance with weber and dellorto carbs???
If it has a vacuum diaphragm, it must have been meant to be used... (Lol!)
Now, where is that special tool that's required to adjust the compression?
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Brad
Rotorhead
Posts: 1672
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posted July 12, 2010 01:53 PM |
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The 2 nipples on the Dellorto for OMP should be used for OMP. They are a ways upstream of the throttle butterflys. To properly do a ported vacuum advance you want the vacuum port to be right above, upstream of the butterflys. Don't premix when you have a perfectly good OMP system in place. Premixing is overrated in street cars and the smell *horrible*.
If you try using the OMP nipples on the carb with T fittings, definately use a check valve so oil won't creep into the vacuum hose for distributor. I wouldn't do this.
Much easier to use Manifold Vacuum for timing. The Weber IDF has a vacuum port for ported vacuum. Find a pic of that for reference if you choose to drill the Dellorto.
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-brad-
74 REPU Lawn Green
81 Rx-7 racecar. 12a J-
Bridge
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EricRyan
Revvin Up
Posts: 61
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posted July 12, 2010 03:55 PM |
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quote:
The 2 nipples on the Dellorto for OMP should be used for OMP. They are a ways upstream of the throttle butterflys. To properly do a ported vacuum advance you want the vacuum port to be right above, upstream of the butterflys. Don't premix when you have a perfectly good OMP system in place. Premixing is overrated in street cars and the smell *horrible*.
If you try using the OMP nipples on the carb with T fittings, definately use a check valve so oil won't creep into the vacuum hose for distributor. I wouldn't do this.
Much easier to use Manifold Vacuum for timing. The Weber IDF has a vacuum port for ported vacuum. Find a pic of that for reference if you choose to drill the Dellorto.
Good answer. I spent some time with a long PDF file on venturi vs. ported vs. manifold vacuum and I have a much better understanding of where I need to drill and tap, and why. Was planning on using a one-way check valve if I had done the OMP idea, but if it's not even the right type of vacuum AND could possibly compromise the oiling system, what's the point?
Gonna go outside and take a look at what I'll be tackling tomorrow. Thanks for all the rays of light guys, really appreciate it.
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