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8 deg btdc seems retarded


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24 replies to this topic

#1 privateer

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Posted 10 September 2006 - 09:04 AM

When I set timing on my 1984 4wd gl (ea81) to factory setting the engne is slow revving. It runs much better when I set the timing by ear. I was wondering how much advance I can get away with before getting into the danger zone. I don't want to be the cause of engine failure. Does anyone have experiance running higher advancement. My engine has high milage so the compression is probably down a little which should help prevent predetonation.

#2 NorthWet

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Posted 10 September 2006 - 12:11 PM

2 dumb questions (neither of which answer you):

Do you have the vacuum advnce disconnected and plugged while checking/setting advance? (not so important with ported vacuum)

Does the advance advance change with change in engine RPM?

If the distributor's advance mechanisims are not working then the engine will want more advnce than the static 8deg BTDC.

#3 GeneralDisorder

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Posted 10 September 2006 - 03:05 PM

My engine has high milage so the compression is probably down a little which should help prevent predetonation.


Actually on an EA81 that means more carbon build up, so higher compression and usually more pinging. I had one with 360k that I couldn't set over 6 degrees

As NW mentioned - vac can's on these usually don't work by now. The rubber inside rots out. Test it.

8 degrees is plenty if you have things hooked up properly, and about normal for a carbed engine.

GD

#4 privateer

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Posted 10 September 2006 - 07:37 PM

Actually on an EA81 that means more carbon build up, so higher compression and usually more pinging. I had one with 360k that I couldn't set over 6 degrees

As NW mentioned - vac can's on these usually don't work by now. The rubber inside rots out. Test it.

8 degrees is plenty if you have things hooked up properly, and about normal for a carbed engine.

GD

My Vacuum hose was disconnected and plugged while timming. The vacuum hose was plugged into the steel tubing network under the manifold. I noticed that there is no suction from the steel tubing when I pulled the hose off. After I set the timing I connected the Vacuum advance directly into a barb on the top of the passenger side of the intake manifold which did have suction. This did not seem to change the engines performance any. So the Vacuum advance on the distributor may not be working, I'll need to test it. This is not a feedback carb but it still has a ton of vacuum hoses and plumbing much of which is probably connected wrong or parts not working. I wonder if I strip all but the Vacuum for distributor and choke & brake booster what adverse affects it would cause, runs poorly as is now.

#5 mikeshoup

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Posted 10 September 2006 - 08:50 PM

The vacuum source for the disty is ported. There won't be any vacuum in it until the throttle opens. Its supposed to be that way.

Check the vacuum advance by hooking a vacuum tube up to the vacuum advance unit and sucking. Have the disty cap off, and see if the advance unit moves.

#6 GeneralDisorder

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Posted 10 September 2006 - 08:56 PM

Yes - DO NOT connect the vacuum advance to straight manifold vacuum. This will give you full advance at idle, and no advance at WOT. The fact that nothing at all changed points heavily to the unit not working. They can be rebuilt by a distributor shop for about $15 - $20 by installing new rubber in the diaphram.

The unit is designed to accept ported vacuum. That is vacuum from above the throttle plate that increases linearly with engine speed and throttle posistion. If you want to overlook the hard lines, that's fine, but run a vacuum line from the front of the carb directly to the disty.

GD

#7 IdahoJak

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Posted 10 September 2006 - 09:02 PM

Here is an interesting site about checking engines with a vacuum gauge that might be helpful:
http://www.users.big...ergoff/vac1.htm

#8 pyromanic

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Posted 10 September 2006 - 11:17 PM

Yes - DO NOT connect the vacuum advance to straight manifold vacuum. This will give you full advance at idle, and no advance at WOT. The fact that nothing at all changed points heavily to the unit not working. They can be rebuilt by a distributor shop for about $15 - $20 by installing new rubber in the diaphram.

The unit is designed to accept ported vacuum. That is vacuum from above the throttle plate that increases linearly with engine speed and throttle posistion. If you want to overlook the hard lines, that's fine, but run a vacuum line from the front of the carb directly to the disty.

GD


Well, that brings up something regarding my 85 EA 82 wagon. I'm running a very old Weber, it has no vacume barbs anywhere on it, so I've been running the line for the advance straight off the manifold. I didn't know that was bad. Any way I can drill and tap it for a "ported barb"? Any other options? It runs ok, but more gutless that I expected. I bet it's the advance thats causing the problem.

Pyro

#9 GeneralDisorder

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Posted 10 September 2006 - 11:29 PM

Every Weber - even old ones - that I've seen has a port. Look for a brass one on the front possibly blocked off with a small brass threaded insert that can be removed with a small flat bade screwdriver. Should be right under the choke linkages and stuff on the front.

As for drilling - no, you cannot drill anywhere on the carb body without special equipment. The hole needs to be extremely precise, and only a fraction of a mm from the top of the throttle plate so that vacuum is immediately availible off-idle.

GD

#10 Subaru_dude

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Posted 10 September 2006 - 11:39 PM

everything anybody's told me and everything i read says to run it off the manifold off an ea82. is that why my car doesn't ever seem to run right no matter what??

#11 GeneralDisorder

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Posted 11 September 2006 - 12:32 AM

everything anybody's told me and everything i read says to run it off the manifold off an ea82. is that why my car doesn't ever seem to run right no matter what??


Probably why you don't have any power, yes.

GD

#12 Subaru_dude

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Posted 11 September 2006 - 12:47 AM

oooh i've got plenty of power... can smoke the tires if i wanna, just doesn't run very smoothly and sounds like it wants to knock.

#13 pyromanic

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Posted 11 September 2006 - 12:25 PM

Every Weber - even old ones - that I've seen has a port. Look for a brass one on the front possibly blocked off with a small brass threaded insert that can be removed with a small flat bade screwdriver. Should be right under the choke linkages and stuff on the front.

As for drilling - no, you cannot drill anywhere on the carb body without special equipment. The hole needs to be extremely precise, and only a fraction of a mm from the top of the throttle plate so that vacuum is immediately availible off-idle.

GD


Hey GD, thanks for the response. I looked, and I think you probably mean right next to the jet on the front. There is a jet on front, "right of center" a bit, and just to the left of that is a place a hair "left of center" where there is a casting spot as though for a barb, but it's not drilled through, it's blank, or dead or whatever.

It's a raised "collar" so to speak, that if drilled through would exit behind the sleave in the throat (that's a veturi, right? and I think it's removable if you take the top of the carb off), just a bit above the throttle plate. So I guess I got a wierd webber. Bet I could drill it and tap it. But how much difference would that make power wise?

Pyro

#14 GeneralDisorder

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Posted 11 September 2006 - 12:57 PM

Advance needs to increase linearly to engine speed. The faster the piston travels, the sooner the spark needs to occur in order for the flame front and the top of the piston to meet at the optimum point for maximum benefit from the burn - ie: best mileage, and best power.

If the pot is attached to manifold vacuum, there will be only mechanical advance for high speed as the manifold vacuum is almost non-existent with the throttle plate wide open. With it attached to "ported" vacuum above the throttle plate, the venturi inside the carb creates vaccum that is inversely propotional to the manifold vacuum. It's high at high RPM, and zero at idle (throttle plate closed).

This is the design of the subaru distributor. It *could* have been designed to accept manifold vacuum, but was not. Without ported vacuum it will not work correctly, and if attached to manifold vacuum, it will perform opposite of intended, and actually hurt mileage and power more than if not connected at all.

As for drilling that hole - the port inside the carb has to be immediately above the throttle plate, and it's only about the size of a pin head. I'm sure that it's probably part of the casting, but I highly doubt the hole is actually there in the inside of the carb. I think you would probably damage the carb unless you have proper tools for this sort of thing. I am going to reccomend you NOT try that.

GD

#15 robm

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Posted 11 September 2006 - 01:19 PM

Usually, that vacuum port is well below the venturi, right above the throttle plate. Really, it is manifold vacuum you are getting, but it is valved by the throttle. No vacuum when the throttle is closed, and it appears when the throttle is open. That way, the vacuum advance is a function of LOAD, not RPM. Full throttle, low rpm is high load, low vacuum, low advance, no ping. Part throttle, high vacuum, low load, lots of vacuum advance, gives better fuel consumption.

The thing about ported vacuum,is there is no vacuum advance at idle, when the vacuum is high, but there is no load at all.

#16 GeneralDisorder

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Posted 11 September 2006 - 02:15 PM

Usually, that vacuum port is well below the venturi, right above the throttle plate. Really, it is manifold vacuum you are getting, but it is valved by the throttle. No vacuum when the throttle is closed, and it appears when the throttle is open. That way, the vacuum advance is a function of LOAD, not RPM. Full throttle, low rpm is high load, low vacuum, low advance, no ping. Part throttle, high vacuum, low load, lots of vacuum advance, gives better fuel consumption.

The thing about ported vacuum,is there is no vacuum advance at idle, when the vacuum is high, but there is no load at all.


The throttle plate acts like a second venturi in effect - restricting the airflow and causing the incomming air to speed up.

You can check for yourself. The vacuum does drop off some at WOT, but that's taken up by the mechanical advance.

EGR port works the same way, but is only slightly higher so it gets vacuum later than that advance pot. More throttle = more EGR. Pretty simple really.

The SPFI has a simliar port for the EGR, and doesn't even have a "venturi" in the common usage. The throttle plate serves the same purpose for that port.

GD

#17 pyromanic

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Posted 11 September 2006 - 02:35 PM

Advance needs to increase linearly to engine speed. The faster the piston travels, the sooner the spark needs to occur in order for the flame front and the top of the piston to meet at the optimum point for maximum benefit from the burn - ie: best mileage, and best power.

If the pot is attached to manifold vacuum, there will be only mechanical advance for high speed as the manifold vacuum is almost non-existent with the throttle plate wide open. With it attached to "ported" vacuum above the throttle plate, the venturi inside the carb creates vaccum that is inversely propotional to the manifold vacuum. It's high at high RPM, and zero at idle (throttle plate closed).

This is the design of the subaru distributor. It *could* have been designed to accept manifold vacuum, but was not. Without ported vacuum it will not work correctly, and if attached to manifold vacuum, it will perform opposite of intended, and actually hurt mileage and power more than if not connected at all.

As for drilling that hole - the port inside the carb has to be immediately above the throttle plate, and it's only about the size of a pin head. I'm sure that it's probably part of the casting, but I highly doubt the hole is actually there in the inside of the carb. I think you would probably damage the carb unless you have proper tools for this sort of thing. I am going to reccomend you NOT try that.

GD


Wel, I'm pretty sure that I see in the casting where the port SHOULD have been. Why theres nothing there beats me. Your right, the hole is not there. But the little "collar" is there, maybe 1/4 inch diameter, and 3/8 deep. Flat in the bottom. this be easy to tap, then I could drill a TINY hole through. I have a drill press, and tiny drill bits. Seems like it could work. Sure wish I knew the exact spec on that hole. It's just a tiny hole right?

Pyro

#18 daeron

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Posted 11 September 2006 - 03:14 PM

well, to your credit it DOES sound like you might know what youre doing :lol: so maybe some pictures are in order?? it sounds like one of you is adamantly saying the port is there, and the other saying its not but im 99% sure i could drill it in...

one of you i think may be right, but it would take some pictures of the weber that needs the port to be certain. is there any way that you can get a good foto of the part of the carb in question?? maybe you arent seeing what you are looking for because youre not looking in quite the right place?

picture == 1000 words

#19 GeneralDisorder

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Posted 11 September 2006 - 05:15 PM

I think the "jet" you are describing is the vac port. Take the "jet" looking thing out and you will see what I mean. It's just a block off brass bolt in case the port isn't to be used. The other port (that's not drilled on some older models) is for EGR, which didn't used to be common.

On a weber the ONLY jets that can be seen without taking the carb apart is the primary and secondary idle jets, and those are higher, on the same horizontal plane as the choke houseing - one on the front, and the other on the back. They are bigger than a vac port, and are to the right of the throttle bore on the float side.

The idle mixture needle is way down on the base of the carb, and has a spring behind the slotted adjustment head.

Seriously - take that jet looking thing you describe out and you'll probably find that's your vac port.

GD

#20 pyromanic

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Posted 11 September 2006 - 08:08 PM

Thanks for your time on this. I'd really like to get this right, and for sure I don't understand everything I know. I took a pic, and will try now: Yea, ok, picture worked. See the round collar or opening behind the choke cable? Is that where the ported vacume barb should be? And there to the right is the primary idle jet, correct? Thanks for having a look, and I sure do appreciate your expertise on this, I don't know much, but I'm learning.

Pyro



I think the "jet" you are describing is the vac port. Take the "jet" looking thing out and you will see what I mean. It's just a block off brass bolt in case the port isn't to be used. The other port (that's not drilled on some older models) is for EGR, which didn't used to be common.

On a weber the ONLY jets that can be seen without taking the carb apart is the primary and secondary idle jets, and those are higher, on the same horizontal plane as the choke houseing - one on the front, and the other on the back. They are bigger than a vac port, and are to the right of the throttle bore on the float side.

The idle mixture needle is way down on the base of the carb, and has a spring behind the slotted adjustment head.

Seriously - take that jet looking thing you describe out and you'll probably find that's your vac port.

GD

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#21 GeneralDisorder

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Posted 11 September 2006 - 08:59 PM

Hhhmmm - air cleaner looks round.... is that a DFV series?

Although the layout doesn't match any of my DFV's.... looks like a DGV the way things are cast. Ah well - here's what I'm talking about so there's no more confusion:

Posted Image

See what I mean about it being *right* above the throttle plate? The edge of the hole on the inside of the carb actually touches the throttle plate when the throttle is closed. This gives that hole vacuum when the throttle plate is cracked open just a tiny fraction of an inch (known as "ported vacuum"). The EGR is up higher and doesn't get vacuum till the plate is open a little further (EGR is basically an enormous vacuum leak, so the engine has to be turning pretty good to overcome it).

Also notice the block off brass "bolt" used in the EGR port if you are not hooking that one up. It's a factory thing. My NIB Redline weber (not this one) came with one as well, so it's a factory thing now. They used to come without that port drilled, or with it blocked off with a brass inset plug like the middle port in the one pictured above.

GD

#22 pyromanic

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Posted 11 September 2006 - 09:36 PM

Thanks GD. I see now. Oh, mines a DG____something something who knows what 32/36, manual choke. The round air cleaner plate is just an adapter for a wierd double plenum for twin K&Ns.

But I see where the disty port is now, both on yours and on mine. Thing is, mine is blocked off, I can tell. I probed around inside the casting collar where the barb should be, and the probe bottomed out about 1/2 to 3/4 of an inch. I'll have to pull the carb to find out what's actually down at the bottom of the hole, the steering pump leaves no room to see or really get in there and check it out. At least I know where it's supposed to be now, THANKS!!

Oh, and mine doesn't have anything there where y our EGR is.

Pyro

#23 GeneralDisorder

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Posted 11 September 2006 - 09:39 PM

The hole neck's down inside - the barb is the size for a regular vac hose, but the hole into the throttle bore is very tiny - maybe 1/32". Probably why your probing bottomed out.

Yeah - on the EA82's it's a tight fit. I had to put the hose on, and then mount the carb with it attached on the one's I've done.

GD

#24 pyromanic

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Posted 11 September 2006 - 09:52 PM

The hole neck's down inside - the barb is the size for a regular vac hose, but the hole into the throttle bore is very tiny - maybe 1/32". Probably why your probing bottomed out.

Yeah - on the EA82's it's a tight fit. I had to put the hose on, and then mount the carb with it attached on the one's I've done.

GD


Well, ther's no fitting there at all, the the protrusion of the aluminum casting.

If start the engine, will I be able to feel vacume with my finger over the port, (if that is it is actually open through to the inside)

Pyro

PS I guess I have totally hyjacked this thread, and do indeed apolgise. On the other hand, I guess this discussion regards timing, so maybe nobody is too mad, but still------------sorry.

#25 GeneralDisorder

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Posted 11 September 2006 - 10:05 PM

Probably won't feel anything - definately not till the throttle is opened, and then the engine speed is too fast for you to tell. Too much vibration, hot metal, etc. I doubt you would feel anything with the size of the hole anyway. That's weird that it's not fitted with a barb there - must be REALLY old. I have a couple 1980's DGV's and they have both. And I have a holley 5200 with some vac fittings too. But then it came off a Ford in the 70's so that really doesn't surprise me.

Don't worry about the hijack - his question was answered.

GD




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