NewPunkRKR (5/7/2009)
Thanks Ted. Can you explain a little better the additional vacuum hookup? Drilling the carb makes me nervious but if it's pretty straight forward I might be willing to try. The car definately runs better without the dist. vac advance hooked up, I don't know if that makes sense or not. I think I'm going to have to pull my msd distributor and revisit the curve / total advance that I have set. I was messing with timing the other day (w/ my timing control,) troubleshooting and I had the car running really well at idle / WOT. However then the car had a really hard time turning over / starting. Could be the problem all along?
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Although I’ve modified several Demon carbs for an improved ported vacuum signal, this is something that’s not done lightly and without experience with carbs. For myself, it’s about an hour job and I’m considered pretty quick on these types of things. Although I have no pictures of that particular modification handy, the pictures at the following link will give a rough idea of the ideal hole placement. The fifth picture down in that thread shows the ported vacuum hole to which I refer.
http://forums.y-blocksforever.com/Topic23772-3-1.aspx
Once the hole is drilled in the appropriate location, a variety of methods can be employed to get the vacuum path to the outside of the carb where a hose can be hooked up to it.
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But I have to ask first what is your initial timing set on and what curve attributes do you have in the MSD distributor? What spring combination and what color advance stop bushings are you using? A good starting point are the two light blue springs and the blue bushing. Your description sounds like an excess of initial igntion advance.
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And the next question is which port on the carb are you hooking the distributor to? On the Demon Jr., there are two closely spaced nipples on the passenger side of the carb with one of them being direct vacuum and the other being ported vacuum. If memory serves me correctly, the most forward nipple is for the ported vacuum signal; this is easily verified with the carb off of the vehicle and tracing the circuitry. But in your case, I’d suggest hooking a vacuum gauge to each port with the engine at idle and the carb connection that has no vacuum signal will be ported vacuum. If both nipples have vacuum, then the throttle blades are too far open at idle and that’s a symptom of some other issues taking place if the engine is not idling too fast.