online170

Heres a little background of what ive done recently.
https://www.thirdgen.org/forums/tech...g-new-cam.html

Just read towards the end. I had a little bit of an accident a couple weeks back where my distributor was in free floating timing, and i got a backfire through the carb, and a VERY VIOLENT backfire out the tail pipe.

Long story short, before the car backfired and stuff, i had it set at mechanically locked out timing at 36*, plus an additional 12-15* of vacuum advance set with my Accel vaccum adjust.

The car ran like a bat out of hell, ive never had it so easily spin the tires at such high speed, it was definately the fastest its EVER been.

After the back fire, (i shouldnt have had to adjust the vacuum advance) but i had played with the base timing a bit to get it to limp home. So after the backfire i set it back to 36* base, and should have been the same vacuum as before, and now it runs like crap.

When im at WOT, it seems to run similar to before, but its not as quick. There doesnt seem to be any knocking though. At part throttle, and offidle, its very very bad. It hesitates, and feels "lean" on the primaries. Like if youve ever driven with a lean carb, your revs will climb, but the car wont seem to have any power or acceleration. (the carb hasnt been changed, it shouldnt be lean all of a sudden).

The idle is the same as before, but its constantly misfiring or missing. The "misses" are not in any pattern, they are completely random. Meaning its not any 1 given cylinder doing it.

Could a backfire through the carb blow the vacuum advance canister???

When i was fiddling with the vacuum advance to start it showed somewhat similar symptoms, but not nearly as bad as they are now. So i think my vacuum advance is the culprit. Ill play around with it tommorow, but i need to know if a backfire could have damaged the canister? Could someone explain how the vacuum advance works? Meaning, what triggers it? And is it always advanced and then retards when triggered, or vise of versa?

Its attached to the "timed port" on a holley 4150 series carb.

impaled

backfire through carb is a lean issue, through exhaust is a rich issue.

if a solid backfire occured through the carb, there is the potential that you blew the power valve, as many people have experianced.

me, personally have had a few backfires through the carb, panicked, pulled the bowl and metering block and the PV was fine.

there is an easy way you can tell if the power valve is blown. if you let it idle, turn the idle mixture screws all the way in and see what happens.
1. engine dies = PV is fine
2. engine doesnt die = PV is blown

at least try that and see what you get.

online170

I was worrying about the power valve as well, but it shouldnt cause a miss or a missfire. I did the check, and its still fine. The carb was bought new 2 years ago, so it has the "check valve".

As for the misfire, it was the vacuum advance. However, i was able to fiddle with it and have the misfire go away. But its still not running 100%.

I dont understand why that went out of adjustment, but anways. A little more fiddling and i should have it running decent.

impaled

what is your exact ignition setup?

Sonix

iTrader: (1)

can you tell if it's misfiring at idle?

if so, hook up a timing light to each different wire and see if any plugs are misfiring.
---- HAVE YOU PULLED ANY PLUGS YET?!?!
Remember they are your window to your engines soul... i'd want to look at those if it was me

impaled

definitely pull the plugs. and while you are at it, do a compression test. the plugs may be a window to the engine's soul, but the compression is the car's blood pressure... lol.

online170

It doesnt seem to be misfiring at idle. But im getting frustrated with this adjustable vacuum advance canister. I think i need to go buy a new one. WHen i got it, i couldnt get it to go fully counter clockwise, so it may be defective.

I have been procrastinating taking the plugs out, because i dont think i can get to all of them with the headers, but ill get at them this weekend.

I got my freind to drive the car to get a second opinion, and we both agree, the misfire doesnt come in till about 2000+ rpm, when held under a steady load.

He said he doesnt think its mifiring, because the vacuum gauge stays pinned to the same value, and the tach does not fluctuate what so ever. But you feel the slightest 'bog' for a split second.

As for the timing, its an HEI distributor, with a super accel coil on top. The mechanical weights have been taken out, and the mechanism is fully advanced and locked. In this manner, and with the vacuum advance plugged, the timing was set to 36* and the adjustable vacuum canister turned clockwise 3.25 turns. (chart says 4 turns is 15* advanced for a car with 14* base timing and it changes when this curve is changed).

Before the "bang" this 36* "initial" and 3.25 turns made the car run like a top. No knocking or misfiring or anything.

Let me put on my holley 750 next weekend, and get a new vacuum advance canister, and ill report back. The 650 has always given me wierd off idle characteristics, so maybe my 750 will remedy that.

online170

I think i know what the problem is. I have a feeling i installed the vacuum canister wrong.

Its the Accel Canister.

I just swapped it out with the old canister, but the only thing i can adjust on it is with the allen key. Aparently there is supposed to be a "plate" that controls the AMOUNT of advance? and the Allen key adjust just controls the rate of advance? Is that right?

I dont think mine came with a disc....

Ill also be checking my plugs when i get a spare moment. probably on friday.

Sonix

iTrader: (1)

yes, that sounds right. That's how the Crane canister works.

online170

So i installed it right? But how does turning the allen key adjust the amount AND rate of advance?

Also:

Any ideas for removing spark plugs? I cant seem to get the socket on with my headers. BUt i have enough room to remove all of them.

I was thinking of buying a header spark plug socket, from SLP or something. They are shorter and you turn them with a wrench......

Sonix

iTrader: (1)

No the allen key adjusts how much vacuum it takes to add a certain amount of advance. The "rate" I guess.
The amount is controlled by the plate. It preloads the can. So lets say you have 20* of advance in the can, you use the plate to preload it 10* (so that adds 10* to base, so you back it off 10* to re-correct) then your canister only adds 10* more.

Get a 5/8" wrench and break 'em loose. Plugs on an SBC (headers or not) are supremely easy.
Most spark plug sockets have an end on it so you can turn it with a 3/4" wrench if you want.

online170

Yea, but the accel canister didnt come with a plate. SO how does IT control the amount of advance? Unless i installed it wrong. The instructions were pretty awful.

As for the wrench..... 69 heads, with 13/16ths plugs..... I have to probably buy a wrench.

Sonix

iTrader: (1)

you have this one?
http://store.summitracing.com/partde...w=1&N=700+150+

you need one of these
http://store.summitracing.com/partde...rt=CRN-99619-1

to limit the amount

ah, perhaps customize a stubby wrench or something.

online170

NICE!

I didnt know i could get the cam plate on its own. Ill have to pick that up this week. I was getting ready to cough up anouth $50 or so for a crane set.

Sonix

iTrader: (1)

you got a local source for small parts like this?

I'm driving up to summit at Tallmadge tomorrow night (i'm in Mt Vernon OH right now in a training course) to buy a bunch of stuff. Let me know if you can't get it locally, and I can bring one up to Canada for ya, then just send it over to you in an envelope. Easier than paying duty, $9 order fee, etc for a $5 part...
if it comes to that.

online170

thats a nice offer, but i think ill be ok. Theres a speedshop like 4 mins from my house, and they get their stuff from keystone. Its usually the price on summit. Ill let you know if i cant get it.

online170

Ok whoever built my headers was clearly thinking of plugs, they did a good job. I was able to just slide the 13/16ths socket on each plug, then i just used an adjustable wrench to break em loose. Worked like a charm. Heres some pix and what i found. My freind has the comp. testor, ill ask him if i can borrow it tommorow.

Heres the result, but for the most part, they looked pretty good.... If not perfect.

PLUG----------->GAP (found)------------>Condition
1--------------->0.043------------------>Sooty everywhere but electrodes
3--------------->0.040------------------>Sooty everywhere but electrodes
7--------------->0.041------------------>Perfect (tan all over, dry)
5--------------->0.041------------------>Sooty everywhere but electrodes
2--------------->0.043------------------>Sooty/ Tan (50/50)
4--------------->0.040------------------>Perfect (tan all over, dry)
6--------------->0.035------------------>Lean? Slightly grey, mostly tan
8--------------->0.043------------------>Sooty, wet with oily residue
Plug 1


Plug 3


Plug 7


Plug 5


Plug 2


Plug 4


Plug 6


Plug 8


All plugs regapped to 0.043 thou.

The "bang" happened aprox. a week ago. The car was doing the whole misfiring thing all week. I played with the vacuum advance a bit on sunday. Drove 30 mins to a freinds house, 30 more mins to the race track. Made 5 WOT passes, drove 30 mins back to freinds, 30 mins back home. Seemed alot smoother on the way back, but still not 100%.



Pix were taken as soon as the plug came out. The "sooty" deposits you see in the pix, smells exactly like the stuff the PCV is supposed to suck up. I was running breathers for a while, so thats probably why. I cleaned them off for now.

online170

Checked the compression.

I could only get at 4 cylinders. The testor wont fit in the others. Ill try again in a bit, but i doubt ill get anywhere. The ones i didnt check, had very good plugs so im not worried.

CYL-------->Pressure (PSI-g)
1------------->168
3------------->158
2------------->168
8------------->142--------This is the cyl with the foul plug, and has alot of blowby on this bank that comes up through the breather.

Do i need rings?

five7kid

iTrader: (14)

What kind of heads are you running?

online170

The heads are 69-70 441 casting, with a 76cc chamber when new. I cant say for sure if any port or milling work was done to them, but i would imagine some port work was done to them.

If you care to read up on iit, supervisor and sonix helped me figure out a few things about the engine a while back. https://www.thirdgen.org/forums/tech...tml?highlight=

I dont suspect the valves to be the culprit for low pressure, the vacuum gauge usually stays very "glued" in one spot. No flickering or fluctuation.