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  #46 (permalink)  
Old 04-14-2010, 12:29 AM
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Quote:
Originally Posted by eric32
I need to now tune this thing to run on full manifold vacuum wich will help me with a nicer cleaner idle and that will have a effect on my plugs as well.
The idle speed will increase when you hook the vacuum advance up to a manifold vac, source. Counter that by lowering the curb idle setting.

You only want about an additional 10-12 added by the vacuum advance can. You can check yours w/the timing light by doing a "with" and "without" back-to-back comparison to see how much timing it's adding.

Using manifold vacuum for the vacuum advance will also require the idle mixture screws to be readjusted- set the idle mixture screws to give the highest vacuum/best idle speed just like you've always done. Keep the curb idle speed below where the centrifugal advance starts in.

You want the mechanical (springs and weights) advance to be all in by 2500 RPM or so. No need to delay it too long or to a point the engine will not be able to use it under normal conditions.

Quote:
on the choke part is your motor running richer at 1500 rpm then with the choke cable pulled then when you just hold your gas pedal down at 1500 rpm then?
The fuel/air mixture is richer (more fuel) when the choke is on and the idle is 1500 RPM, than if you do not use the choke and throttle the engine w/the accelerator pedal to hold it to 1500 RPM.

Quote:
How do I know if I have a adjustable vacuum advance?
By whether or not there's an adjustable orifice in the port of the vacuum advance canister. Non adjustable canisters do not have a provision for an allen wrench/screw slot, etc.

Quote:
I also got a msd street fire ignition box will that help me out as well?
It will give multiple "hits" at lower revs, I don't think it'll make alot more power over what you had, but it's a good unit for what it is, IMHO and should help starting, a clean idle and at the RPM range where it's doing the multiple discharge (under 4K RPM, IIRC).

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  #47 (permalink)  
Old 04-14-2010, 06:21 AM
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eric,
I want you to read the vac adv timing added at high rpms/high Hg because you only have 14Hg at idle....

many vac units don't reach full degrees added till well past 17+Hg is present so just plugging into manifold at 14Hg idle can give you a false/wrong 3200 total timing with high Hg where your at cruise miss is happening....

(lol,,,dang crs!!!)
forgot to post above when you read the total timing have your vac gauge plugged in and read/post the Hg at 3500-4000 along with the total timing...

do one more quicky test with the vac gauge while the vac plugged in and the motor is warmed up and post results:
open the linkage with your thumb to about 4k...
now just drop/release the linkage quickly so it immediately goes back to idle due to the spring tension...
observe the vac gauge reading as the rpms come down...
a excellent sealing chambers rotating assembly (rings/valves/walls/etc) will show darn close to 25Hg or more and the needle will be "very" steady as the rpms fall to idle...
the test gives you a reference point for the overall current condition of the low miles motor for future test comparison after many many wear miles...
(for this thread I just want to confirm the motor is basically "healthy")

questions:
can you better describe the miss frequency...
repeated/frequent? interment/regular intervals? comes and goes over minutes or every 30 seconds? single miss or multiple per event?

what brand and model dist is on the motor???

Bill,
first welcome to HR!!!
just a comment:
yup, many do need to grasp the fundamentals first but most then have no problem understanding the very technical....
these threads do stay on the server forever to help members with varying abilities in the future all over the world (and are accessed very often by people all over the world on gooogle)...
so it definitely can be best to have thread posts with both the simplest/basic info possible (me) along with complex info....
LOL,,,darn American English is a nightmare,,,often you will see the same info re-posted by another member with just different wording!!!!
I enjoy posting because it is a trip down memory lane,,,so much of the good info for carbed motors has been lost over the years....

autobreath,
I do agree we should be testing the electrical first to find the miss...
he did ask for learning help in his first post...
his posts tell me he needs to first learn to "always" follow rule #1: "ASSUME NOTHING" at the start point...
LOL,,,learning "how to" "logically only" think can be the toughtest hurdle/lesson of all...
(but it serves you for a lifetime with whatever you are working on and doing)
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  #48 (permalink)  
Old 04-14-2010, 07:41 AM
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Testing

I have a hand help induction device from Mac tools that allows the user to determine what the firing voltage is for each specific cylinder while it's running. It had a cup that you rest an ignition wire in and it tells you what's being used in the cylinder. If there all he same then it's not a secondary ignition fault but you can easily find a bad plug wire or basically any secondary ign problem. I just checked and there still available but with more bells and whistles and of course expense. A person might find one on the net for a reduced price but again it eliminates an amount of guessing. The last 3-4 years of my career Iran the apprenticeship program for the co. I worked with. I got people that had completed an educational program with ASE certs and they needed a lot of help in learning how to apply what had been taught. Diagnosis and repair of automobiles is actually quite difficult as they employ most all physical sciences. Electric, electronic, laws of combustion, thermal expansion, alignment as to directional changes made on a moving object, fluid dynamics....... crap I'm getting a head ache. Anyway my point is that many can apply information after being instructed in what to do but there is so much involved in the dynamics of an automobile it takes a lot of time to master the ability to properly diagnose and repair most systems. For what it's worth I still learn every day, that's why I get involved in these boards.
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  #49 (permalink)  
Old 04-14-2010, 09:34 AM
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Bill,
just fyi:
this is a truly comprehensive/in depth total car information site between the threads "search" capability and knowledge base and wiki articles links...
(the problem is there is too much information for people to find answers easy!!!!)

here's a random pick "basics" example link from the engine section of the hot rod wiki encyclopedia:

http://www.crankshaftcoalition.com/w...o_choose_a_cam

because it is the same 100+ questions over and over again in each forum like "what cam to use",,,the plan/goal is to be able to have a: read this info (appropriate) link as a first reply,,,to then answer what is not clear....

Jon,,, the board administrator,,, especially wants help improving/expanding/adding to the hot rod wiki articles sections (which you can edit/add/change existing ones or write/submit new subject ones)

my point is it takes anyone/everyone awhile to figure out what this site is all about (I'm still learning!)

PS:
my "side note" comment to autobreath was just to let him know I for one will get to electrical testing posts ASAP to solve the miss...
(LOL,,,if we can keep eric from bringing up every topic possible)

I'll shut up now,,,this discussion belongs in a Lounge forum thread...
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  #50 (permalink)  
Old 04-15-2010, 10:14 AM
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Ok guys here's my update. Still had the miss at idle during warm up but it was not as bad today since its warmer out. I took my allen wrench and turned my vacuum advance all the way clockwise till it stopped. Hooked it up and warmed up my truck till operating temp. Idle went up about 300 to 400 rpm and man did this help smooth the thing out. I was able to turn my main idle screw 3/4 of a turn to bring it back down to 900 rpm.

Took my truck out for a nice cruise up hill country and had rpm's between 2000 all the way to over 4000 and no pinging issues so far and even got on it at half throttle and no issues as well. I then got it back home and hooked up the vacuum gauge and now man I am so excited I now got 16 to 17 inches of steady vacuum at idle and it has smoothed out quite a bit I still have the slight lope but the cam seems much tamer now.

I took about 3/4 of a turn of my vacuum advacne just to be safe. But full manifold vacuum at idle has helped me out quite a bit. After I replace my plug wires hopefully the miss will go away at start up. Gauge was steady once again but would only drop when the engine just had a miss here and there but it's nothing bad or really noticable. The miss at say 3200 rpm or so might be an exhaust note as someone stated after all I am running cherry bombs. Well take care guys and thanks again for your help. It must just be something with the way the plug wires are arranged on the cap cause of the chevy firing order. I had this same problem on my old 350 vortec motor that used to be in my truck but it was not this bad.

Thanks
Eric
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  #51 (permalink)  
Old 04-15-2010, 12:30 PM
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LOL,,,now I do understand F-birds response "tone"!!!

eric,
I wish you well but you are on your own from here as far as I'm concerned...
you couldn't take the two minutes to post what the total timing was set too for advice on what to do next...

adios amigo...

drive safe!!!
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  #52 (permalink)  
Old 04-15-2010, 01:20 PM
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Quote:
Originally Posted by eric32
I took my allen wrench and turned my vacuum advance all the way clockwise till it stopped.
Was it adjustable or did you have to go get an adjustable vacuum advance?

Quote:
Hooked it up and warmed up my truck till operating temp. Idle went up about 300 to 400 rpm and man did this help smooth the thing out. I was able to turn my main idle screw 3/4 of a turn to bring it back down to 900 rpm.
This is what you'd hope for- and why it's often recommended for low-vacuum cams; it allows the transfer slot to be covered more when the curb idle is adjusted lower. IIRC, you already had good idle mixture control with your idle mixture screws, but if you didn't, you would likely have control now.

Quote:
got 16 to 17 inches of steady vacuum at idle and it has smoothed out quite a bit I still have the slight lope but the cam seems much tamer now.
The cam is going to have some 'lope', but it sounds like you've gotten a handle on things- good for persevering (wasn't easy) !

Hopefully, the rest will be easier.
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Old 04-15-2010, 03:16 PM
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Well guys thanks for all your help but red65mustang please be easy here. I have had to go back over some posts cause there have been a lot here. My timing is as such. I have 16 degrees at idle with no vacuum advance and I have medium set of springs on my distributor and my timing light says I have about 34 degrees total by 3000 rpm so that is my specs there. I tried other spring combos but this setup gave me the best results.

That is where I have my distributor set at. Now as far as vacuum advance goes I found out my distributor does have one as stated earlier.

You will have to bear with me here but its hard to get the exact reading on my balancer cause my timing tab sticks out a little far and I have to put marks on my balancer with white out to be able to see it correct. I made marks at 16 degrees and also at 34 so I can get my timing right on as needed.

I have not yet put on my timing light too see how much my vacuum canister is giving me at idle but it is right now minus 3/4 of a turn maximum amount it will give me at idle. I hope that is what you was expecting me to post.

I finally got my new wires on but will have to wait till another day for a cold start to see how it goes. But for now is working really good except either my throttle is sticking slightly which I doubt it is cause I did not have that issue before but the idle does not want to stay right where I set it at. I set it at 900 and after driving it and pulling back up into my driveway it will be 1100 etc. I then just bearly have to turn the idle screw ot put it back down. Then if I go to start it again later on it might be a little too low.

I am wondering now if my secondary's being open just a hair is allowing too much air at idle and I now need to close them some. Problem is I have to take the carburetor off to do so unless someone can give me a clue on how to custome make a tiny screwdriver to adjust them with out taking it off.

Ok also on the pcv part will get a good quality one and hook it back up. As far as the baffles go on my covers they are welded ones and they run down hill towards the side of the cover with the cylinder head angle and they are completly closed of with only a square hole for vaport to get through but some how oil gets up over the hole and just enough to pcv to suck some up. Looking at it wise it seems like a good baffle.
Thanks again everyone for help and adivce.
Eric

Last edited by eric32; 04-15-2010 at 03:26 PM.
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  #54 (permalink)  
Old 04-15-2010, 04:48 PM
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eric,
you don't just set a adjustable vac adv at a random pick number of screw rotations...

you first test to determine what it is scaled too per screw rotation over the whole scale....

because of what you did,,,no surprise the idle is going whacko!!!
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  #55 (permalink)  
Old 04-15-2010, 04:53 PM
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When you set the idle mixture screws, the engine is FULLY warmed up, right? Like after a drive, not just run for a few minutes just sitting still- it needs to be fully at normal operating temp.

Next time you drive it and you get back w/the idle speed higher than when you left, shut it off w/o touching the gas pedal. That way you can check the carb to see if the linkage is sitting on the curb idle screw like it should. If it IS as it should be, check to see if you can manually close the secondaries any. If the secondaries are OK too- closed against the stop, w/o any "play" when you try to close it- suspect the mechanical advance is hanging up some.

You could (while still warmed up) crank it back up w/o touching the gas and check the timing while the engine is idled up to see if it's advanced more than it should be.

If it's too advanced than it should be, the faster idle speed could be caused by the idle speed being right at the point where the mechanical advance tips in. Your timing light will tell you that by watching where the advance starts. BUT- I'd have thought that two "medium" springs that delayed full advance until 3000 RPM would be stiff enough to keep the advance from starting at 900-950 RPM, though.

So, be sure the mechanical advance mechanism is butter-smooth and returns easily when worked by hand with the cap off.

It wouldn't hurt to close the secondaries to where they were stock. Just compensate w/the curb idle screw if the idle drops, you have plenty to use there w/o having too much transfer slot exposed.

All the rest you have down AFA what all you still need to do, so I'll leave it at that.

Good luck.
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  #56 (permalink)  
Old 04-15-2010, 05:03 PM
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Ok Cobalt, dumb question here. Why would someone increase the secondary base flap position? I worked with Mercedes Benz for 40 yrs in a technical capacity and the only time there were issues with secondaries not closing the car had idle control issues. I'm curious as to why one would modify idle characteristics in a non mixture adjustable circuit.
Bill
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Old 04-15-2010, 05:35 PM
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Ok here goes. I turned the allen wrench on the vacuum canister clockwise till it stopped. That would give me the most amount of vacuum the canister will give at idle. I took it out for a drive to see how it would work and checked for pinging and had none. When I got back home I took my allen wrench and went back into the canister and turned it counter clockwise about 3/4 of a full turn to take away just a hair of vacuum advance so as not to have too much.

And yes my engine is warmed up and taken out for a drive and all warmed up really good before I make any adjustments on the idle screws or idle mixture screws. I know carburetors have to be good and warm and not just like ten minutes warm to get things really good and going to properly tune them.

I will check the linkage like you said and try to see how much advance my vacuum canister is giving me at idle. Should I only be looking for maybe 12 inches at the most if happens te be giving me more? Will get back this weekend. I have to work the next couple of days and might not have time to get the light hooked up. By Saturday should be able to give you an idea.

And to answer the one guys question reason I have the secondaries opened up just a little is to allow more air cause of the bigger size cam I am running. That is a whole other story and tech article about cams and overlap etc to get into. Also the mechanical advance on my distributor is buttery smooth like you said. I have checked it before and I don't get any mechanical advance till after 1500 rpm.

Eric

Last edited by eric32; 04-15-2010 at 05:44 PM.
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Old 04-15-2010, 05:51 PM
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Ooh and on redmustang65 I adjusted the vacuum advance per the instructions I found at jegs. They said to turn the screw too get the maximum amout of advance and take it out for a drive and listen for any ping and it you have some take out some advance by turning the allen wrench one turn at a time then test drive again then after its gone your done. This is my first time here so give me a break. Sorry if I am coming off as rude but I am new to a lot of things and working my way around

Have a good one

Eric
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Old 04-15-2010, 07:40 PM
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Quote:
Originally Posted by eric32
Should I only be looking for maybe 12 inches at the most if happens te be giving me more?
That is correct- around 10-12 added by the vacuum advance is usually adaquate as a starting place, at least.

Quote:
Will get back this weekend. I have to work the next couple of days and might not have time to get the light hooked up. By Saturday should be able to give you an idea.
See you when you get back.
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Old 04-15-2010, 07:52 PM
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Quote:
Originally Posted by Bill Adkins
Why would someone increase the secondary base flap position?
With non 4-corner idle Holley carbs, the secondary side still has an idle circuit. If the primary side needs to be opened so far to get an idle (due to a low vacuum cam) that the transfer slot is "over exposed", the off idle tip in suffers, as does the idle quality, etc.

One way this is countered is by using manifold vacuum for the vacuum advance canister to increase the idle speed, as well as provide more advance for the usually overly lean idle air/fuel mixture. This allows the primary blades to be closed some, in turn exposing less transfer slot- often enough to regain idle mixture control using the idle mixture screws, which is often lost when the slot's over exposed.

The other thing that's sometimes done is the secondary butterflies are tipped open a slight amount, so the primary side can be closed a like amount, if the vacuum advance at idle isn't enough. This is preferred by many to drilling holes in the primary blades- an unnecessary modification in probably 95% of the times that it's done, IMHO.

BG carbs use "Idle Eze" to accomplish about the same thing w/o using the secondaries.

There are many others here better versed than I am, perhaps they'll chime in on the subject as well.

Last edited by cobalt327; 04-15-2010 at 08:07 PM.
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