|11-23-2010 07:35 AM|
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.
|11-22-2010 08:57 PM|
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!
|11-22-2010 07:35 AM|
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.
|11-19-2010 06:39 PM|
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!
|11-19-2010 12:38 PM|
|kc8oye||What he said. lol I can't really argue with his advice either.|
|11-19-2010 07:08 AM|
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.
|11-18-2010 11:17 PM|
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..
|11-18-2010 10:10 PM|
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,
|11-17-2010 09:28 PM|
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!
|11-17-2010 08:50 PM|
thanks tbucket, we checked the battery wire to the dist, it seemed to stay at a constant 12.3?? something volts all the time, and i dont belive the exhaust is plugged with anything, but i suppose its possible, no cats just long tubes into chambered mufflers, but i suppose something could have climbed in and died haha, and i have no idea why when i plug up the vac advance it climbs so high in advance, but the good thing is, hopefully, we have a new hei distributor to put in, in the morning...and i should have bought the cheapy mister gasket fuel pressure guage adapter today at advance but didnt do it, we will probably have to go there in the morning anyways so may have to pick it up, but i appreciate the help and ill let you know how the new distributor works out, it needs one anyways.
|11-17-2010 05:46 PM|
A few things to check,
Have you looked at the exhaust to be sure there are no restrictions. This
can kill power.
Check the fuel pressure with a gauge
You say the vacuum advance brought it from 17* to 50* at idle, this is not
I would expect to see more vacuum at idle with that setup, a leak or a
plugged exhaust or late timing will cause low vacuum readings.
Check the voltage at the HEI, it should be battery voltage. That car
originally had a resistor wire feeding the coil and the running voltage would
only be 9-10 volts. This will reak havoc on an HEI.
|11-17-2010 02:16 PM|
heck yea man thanks for the advice, your stuff sounds like a bummer man, especially since you have started throwing parts at it, although the intake gaskets sounds like a good fix , the low compression #8 cylinder on your motor, my buddies, old time chebby heads, said when you do a compression test and one cylinder or adjacent cylinders come up lower than the others to squirt some oil into the plug hole and then see if it comes back up to pressure, if it does its ok, if it doesnt then theres something else the matter, i dunno if i remembered that right but you might give that a shot, but you can only trust shade tree stuff to a certain degree haha, i take it you did check the #8 intake valve to see if it was hanging too, i know a PIA to check but maybe you have an exhaust valve not closing all the way on the #8 but i suppose you would have to pull of the headers or manifold and contort yourself to look in the exhaust port with the ole maglite to see about that one, this crap is enough to drive you crazy.
, i put a glass fuel filter on it this after noon to see what the fuel is like and its pretty clear and is filling the tube, didnt break down for a fuel pressure guage yet though, however i was playing the the linkage to the accelerator pump, and had it in the last hole towards the bottom on the arm towards the engine block, and it made things way worse, backfiring through the carb at the slightist throttle play and ran even worse, so i moved it all the way to the first hole closest to the carb and it ran alot better, actually was able to break a tire loose a little bit, but you still cant use the throttle more than about 1/8 or 1/4 or it starts to choke out, so either to much or little fuel, or its still the ignition, wich he ordered a new dizzy so we are going to put that in in the morning, and replace this wonder plug wires that are on it currently, they are in sad shape, especially the number 5 wire, anyways, i appreiate your input, and hopefully we both can fix our issues and we can swap stories about makingn the pavement scream!
take it easy,
|11-17-2010 10:14 AM|
you sound like what I am going through. However mine has a few other issues that I have taken care of with the same results. i replaced my intake gaskets since they were rotted. i have a distinct misfire on my #6 cylinder. it backfire and pops through the carb. I put a brand new carb on and a Accel HEI Dizzy. i took the intake off adn found the intake vavle on #6 doesnt close all the way and allowing everything to come through the intake. A compression tast was run on it a few years back and it was steady with the others at 120. The #8 was about 90. So it is trickling through the head it seems. So I am in the same boat you and your friend are in right now.
As for plugs. i am running Accel shorty plugs on my 350. part #8199. they run about $30 for all 8. U-grooved. I have gone through a ton of plugs only to have them either foul out or the wires burn up from the headers. I also run accel 8mm HEI wires. I buy the custom set so you can run them how you want. You get great spark if you run them together. Hopefully that helps a little
|11-17-2010 09:07 AM|
thanks 454 thats a good read, i printed it out and kept it for reference, im going to try and work on this thing today at some point, its windy as crap here today so its not going to be fun, ill let you know how it turns out, do you have any recomendations for plug wires for an hei system? also have you used short plugs to avoid spark plug boot burning on long tube headers?
|11-16-2010 06:54 AM|
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