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  #16 (permalink)  
Old 11-17-2010, 10:28 PM
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I'm willing to point the finger at that edelbrock carb.. Edelbrock makes great intakes.. but their carbs suck ***. i've heard similar complaints from a lot of edelbrock carb owners.


something else to consider is your valve lash.. how did you set it?
if the valves are lashed too tight and the lifters are holding the valves open, that will do the same thing.. I made this mistake once.. the engine couldn't even make enough power to climb the trailer ramps.. but it sure idled nice!

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  #17 (permalink)  
Old 11-18-2010, 11:10 PM
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kc, im leaning more towards the carb being the issue too, we put the new hei dizzy in today, getting more power, fixed on plug wire that was totally dead, and it managed to get sideways today, but totally bogged out and popped throught the carb the more you push the throttle, but once the car got up to speed and you can open the secondaries, it came back to life a little bit, so im thinking maybe its flooding out, but the wires are still and issue, and im not postive theres not a vacuum leak that we can find either,

also with the new dizzy, we cant run the vac advance or it pulls all the way up to 60* thats the end of the marks on the timing tape, but without the vac advance, the timing curve is smooth and steady, and sitting at about 14 initial and tops out at 34 total at around 3500 give or take, it doesnt jump around like the old distributor, next we have a fuel pressure guage to install and then the new wires, maybe the pressure will indicate something, if not then its either the carb loading up, or a vac leak, by the way will running the vac hose to the pcv valve on the drivers side valve cover and using a breather filter on the oposite valve cover affect vacuum?

and the valves are adjusted about a half turn past zero lash, and recheck when running, we backed them off till they clicked and adjusted accordingly to half turn, in quarter turn increments, tighten a quarter, let lifter pump back up then tighten another quarter, so that should be ok. and sometimes when its running some smoke/steam stuff is coming out of the breather on the valve cover, just because im not use to carb motors, is that normal?


thank you kc and everyone else for you help so far, we really appreciated, slowly but surely we are coming along, if i get some spare time, ill try to take a video of what its doing and put it up for you guys to take a look at maybe,

thanks

matt
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Old 11-19-2010, 12:17 AM
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are you running a PCV valve? if you are, smoke/steam out of the valve cover is not good. if you aren't, it's normal.

60 with vac. advance is normal.. that's what it does. it adds even more timing ontop of your 'total'

60 sounds a touch high, but you have to run it and see. that advance is only there when you are 'cruising' and maintaining a fairly high intake vacuum. the extra timing lowers engine temps, improves emissions, and improves throttle response when you stab it.

I don't know how to tune and eddelbrock carb, but it sounds like you really need the secondaries to open much later. This is a common mistake people make with qjets, the assumption is made that if the secondaries open sooner, you get power sooner.. but if they open TOO soon, you get that nasty bog until the engine is actually ready for that extra air.

I did a lot of track tuning on my holley and I found that since I'm using a fairly small carb (650cfm) I could have the secondaries come in rather quickly with a light spring. when I borrowed a 750, I found I needed a much heavier to spring because it was too much air too soon..
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Old 11-19-2010, 08:08 AM
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you can make a little stopper plate that will fit in the distributor to reduce the amount from the vacuum advance.

A simple plate bolted to the vacuum advance to reduce the amount of travel in the slot.

a trial and error deal, but reducing the amount of vacuum advance by 1/2 would be a good start.

I would use a little more timing, try 36 total.
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Old 11-19-2010, 01:38 PM
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What he said. lol I can't really argue with his advice either.
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Old 11-19-2010, 07:39 PM
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Hmm yea I've read a bunnch about making limiter plates for the, just haven't thought about making one, if I can get a smooth. Timing curve coming in by 3k and getting a total timing of 36 all without the vac advance, wil there still be a need for the vac advance? I know I read the link provided earlier about advance 101 but what I gather was that aslong as the curve is smooth and timing is all in by 3 to 3.5k it doesn't matter what combination of vacuum and mechanical advance you use, as long as the end result is the same, or did I just get that all wrong lol

Also when the vac guage is.hooke to the manifold vac port on the carb for testing, when throttle increases vac increases as well from the 15 or so to almost 25, isn't vacuum suppose to drop at higher rpms? If you blip the throttle it goes to zero then recovers, I'm not sure how much valve overlap is with this cam as I understand that has an affect on the vacuum as well, all things considered I feel the cam is relatively mild/small compared to stock, so I didn't figure it would change the vacuum to much?

When we get a chance we will play some more with the dizzy and see if we can get that extra 2 or so degrees total timing out of it without the vac advance hooked up. I appologize I kinda feel like I'm getting to the point of beating a dead horse here, or a dead bowtie, lol bad joke, anyways thanks for the advice guys, much appreciated!

Thanks
Matt
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Old 11-22-2010, 08:35 AM
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You need vacuum advance if you want to get good/better gas mileage. I would say the highway mileage will drop by 2 or 3 and city by 1 mpg without the vacuum advance. (maybe more).

I use manifold vacuum on my vacuum advance. I like a bunch of timing at idle so I can run a very lean idle mixture (a lot less smelly).

At wide open throttle (wot) vacuum advance has no effect. so if you plan to drag race everywhere you go, then you don't need vacuum advance.

revving up the engine in the driveway is not a load on the engine so it is not a good way to test the advance system.

when the vacuum is high it means there is not load on the engine so it adds more timing. If the vacuum is low (under 8-9 inhg), it means there is a load on the engine so it takes the extra timing out.

Chevy vacuum advance canisters typically start to add timing at 8 inhg and are fully engaged by 9 inhg.
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Old 11-22-2010, 09:57 PM
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so after some more tinkering and such, we were able to get some more power out it, with more timing and a new dizzy, then i kept thinking about the vacuum being so low and started searching for leaks...checked the usual places capped of stuff and such....as it turns out, all four corners of the intake are leaking, where they meet the heads, and im pretty sure its because we used the front and rear gaskets, wich i knew better, but hopefully the intake isnt warped now, but back to disassembling it and hopefully this will fix the issue,
so i figure this is causing the choking out issue and it running better with more and more advanced timing thrown in it to help burn the lean mixture? \ it seems to be sucking air into the front and rear intake runners, but the middle ones look pretty sealed off so who knows, i feel like an idiot but i swear i checked that the last time on the vacuum leak search, but crap happens... so we will see where this goes, hopefully hopefully this will fix this bad boy. by the way klm performance on ebay sells a bad *** hei aluminum dizzy for around 35 bucks, the best i can figure is that its a pro comp unit, judging by the part number, just figured i would pass that along if anyone needs a cheap replacement, solid unit too, complete from gear to coil. anyways thanks for you guys help and ill keep you posted on the results when this is fixed!
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Old 11-23-2010, 08:35 AM
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make sure the mechanical and vacuum advance is adjustable on the distributor you buy.

A thick line of RTV as the rear and front seals is best for a chevy.
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