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distributor tuning.


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15 replies to this topic

#1 Dirk

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Posted 11 October 2011 - 08:31 PM

Just a quicky. Ill give more details later but.....

I noticed that my engine was running silky smooth at low rpm but getting quite rough at about 3000rpm and then starting to smooth out again after 4000rpm.

I have not done much technical testing but I figured my full advance was coming to too soon and probably too much.

Therefore have fiitted heavier springs and closed up the slots on the timing lever.

Had to re-adjust base timing after fitting heavier springs.

Engine now runs smooth all the way to 6000rpm.

Feels like it may have more power at 3000rpm now but it tails of at 5500rpm.

More fine tuning to do but so far a marked improvement.:clap:

#2 Quidam

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Posted 12 October 2011 - 07:53 PM

Just a quicky. Ill give more details later but.....

I noticed that my engine was running silky smooth at low rpm but getting quite rough at about 3000rpm and then starting to smooth out again after 4000rpm.

I have not done much technical testing but I figured my full advance was coming to too soon and probably too much.

Therefore have fiitted heavier springs and closed up the slots on the timing lever.

Had to re-adjust base timing after fitting heavier springs.

Engine now runs smooth all the way to 6000rpm.

Feels like it may have more power at 3000rpm now but it tails of at 5500rpm.

More fine tuning to do but so far a marked improvement.:clap:


Hey it's me, just some thoughts...and I don't know what you've got to check total timing.

I take my dial back timing light and with the motor running set it to 0. Rev it up and see where it ends up. Newer Subaru with more efficient heads seem to run 25* Total. Some older cars I've known ran thirty two to thirty eight. Just depends on the motor.

On a subaru, no replacement flyweights are available to change the curve itself. This ain't a SBC huh?:)

Generally, timing should be all in around 2500 rpm or so.

Now i'm wondering if I forgot the question. :)

Doug

#3 Dirk

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Posted 14 October 2011 - 12:47 AM

Hey Doug,

Thanks for feed back.

No back dial timing light as of yet but I should be able to borrow one.

I'm chasing my tail a little bit on this until I get the timing light. Also I am suspicious of the secondary barrel on my carb. Need to get this sorted in order to assess performance.

That said I feel like I am on the right track.

Base Timing is set with vacuum gauge and my judgment.

I have a variety of springs and weights from other dizzies so there is plenty potential for fine tuning.

Judging by power, smoothness, sound and how much my gear shift rattles, I think I am close.

Power off the line is good and smooth
Power at 2500-3500rpm is good but maybe a little rough.
Power after 4000rpm is less good but smooth. Also its reluctant to get past about 5000rpm.

This suggests to me that there is not enough advance at this engine speed.

Curious though since timing should be all in by about 2500rpm.

Would be cool to see the Factory advance curve if anyone has this data?

I will post more again when I have timing light.

Dirk.

#4 Quidam

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Posted 14 October 2011 - 05:55 PM

Please do, i'm curious what you see. You've got 10.0 to 1 compression, or there abouts?

Mabie more fuel? Not enough cam for 6K rpm?

One thought. Try lighter springs, as long as it doesn't ping.

On a drag race car you can lock all the timing, except total out. With a start retard.

Doug

#5 Dirk

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Posted 15 October 2011 - 07:33 PM

Managed to borrow timing light.

The results are colourful.

Base timing 20 degrees

Total timing 32 degrees.

Timing pretty much stays at 20 all the way up to 2500rpm then creeps up to 32 degrees at 5000rpm.

Surprisingly this all seems to work quite well.

Engine starts well and idles smooth and cool at 20 degrees. Slight pinging off the line but hardly enough to write home about.

As I have already said, I can feel the engine searching for extra power after about 3000rpm.

Also If I cruise at 3000rpm for long enough the temp gauge creeps up a little but still with in limits. Not got the vac advance connected so this could help that.

A sensible man would try to re-work timing back to normal specs but I am keen to try a slighty lighter spring to get timing to come on sooner (maybe try for 32 degrees at 3200rpm

This will probably get me more advance at 5000rpm since the timing lever is not topping out at the moment.

I can pull back base timing if total timing gets too much.

Edited by Dirk, 15 October 2011 - 07:37 PM.
spelling


#6 Dirk

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Posted 16 October 2011 - 12:20 AM

So........

I have been playing with the base timing and unless the timing light is screwed it really is happiest at 20 degrees btdc. Who am I to argue.

Have put in a lighter spring so now I get 30 degrees at about 2800rpm.

Total timing at 6000 rpm is about 36 degrees.

Have re-connected the vac advance and test driven. All feels good.

Have scored an O2 sensor from a 99 legacy. Going to get the auto electrician to hook it up to a meter for me so I can do more carb tuning.

Stay Tuned!

#7 Quidam

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Posted 09 November 2011 - 01:27 PM

Hey Dirk,

This is a Hitachi distributor from a 1986 EA-82T. I don't have any points type Subaru distributors, and I'm assuming you're working with an Hitachi?
Posted Image
It's possible the "15.5 A" means that's what's built into this one for mechanical advance. With 20* initial, 35.5* would be about right. On this distributor the lower right spring is the main mechanical advance spring. I realize you may know this by now.

The upper left doesn't come into play until the end of the advance curve and actually acts like a "brake"...soft landing for it all, and the last few degrees of advance.

I've got Hitachi 2 wire "small rotor", Hitachi small rotor 4 wire (electronic spark control), Nippon Denso 2 wire electronic, and Hitachi "large rotor" 2 wire. I'm sorting through them.

This is the Hitachi 4 wire small rotor and the vaccum advance cannister can be modified easily. I'll take some pics.

Doug

#8 Quidam

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Posted 09 November 2011 - 08:43 PM

This is an Hitachi "small rotor" 2 wire electronic distributor. I found an adjustment screw for the vaccum can. I screwed it in 9 turns and that "locked" the advance...

I believe the Hitachi and ND vac cans may be interchangeable.
Posted Image
I have an 87 carbed wagon that pings when put under part throttle load on regular fuel. To fix that, I'd just turn the vac can screw in a turn, and see what happened. Or a half turn. Then test it out, go another half turn or whatever until the ping is silenced.

Web moving slow, more later.

Doug

#9 zukiru

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Posted 09 November 2011 - 09:38 PM

finding this interesting.
I had no idea you could do so much to a disty.
subscribed.

#10 Dirk

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Posted 14 November 2011 - 05:11 PM

This is an Hitachi "small rotor" 2 wire electronic distributor. I found an adjustment screw for the vaccum can. I screwed it in 9 turns and that "locked" the advance...

I believe the Hitachi and ND vac cans may be interchangeable.
Posted Image
I have an 87 carbed wagon that pings when put under part throttle load on regular fuel. To fix that, I'd just turn the vac can screw in a turn, and see what happened. Or a half turn. Then test it out, go another half turn or whatever until the ping is silenced.

Web moving slow, more later.

Doug


Up to my eyeballs in work and other stuff at the moment. So no further tuning at this stage.

Yes this is the dizzy I am using (Hall type)

Although I can not see a adjusting screw for the vac can.

Discovered that the dial light I have been using is hoplessly wrong.

Therefore I have no good data untill I can buy or borrow a good one.

Dirk.

#11 Quidam

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Posted 14 November 2011 - 09:42 PM

On this one, I removed some silicone from the end of the vaccum can to get to the screw. It's a very small screw and takes a jewelry type screwdriver.

I have several out for inspection right now and the vaccum cans physically screw on to either type of distributor. The actuator arm is of different length tho.

Doug

#12 alexinvancouver

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Posted 15 November 2011 - 02:29 PM

i've got the same problem with my 86 hatch
launched it a few times 0-60 yesterday and all i get is 22 sec in average
i wonder how does Your car performs?
and was going to buy timing light today anyway (it's not that expencive - $40-50) and play with it

Feels like it may have more power at 3000rpm now but it tails of at 5500rpm.

More fine tuning to do but so far a marked improvement.:clap:



#13 Dirk

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Posted 15 November 2011 - 04:38 PM

i've got the same problem with my 86 hatch
launched it a few times 0-60 yesterday and all i get is 22 sec in average
i wonder how does Your car performs?
and was going to buy timing light today anyway (it's not that expencive - $40-50) and play with it



0-100k in 14seconds average. But then its a light sedan with carpets and other non-essentails ripped out.

Tips the scales at about 850kg with empty tank and no spare wheel.

Dirk

#14 Dirk

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Posted 02 May 2012 - 01:39 AM

Righty ho then.

Since my last post I rebuilt another distributor and swapped it in. This one setup more or less stock.

I had to re set base timing to about 10 degrees for the mech advance to work correctly. Found the screw in the back of the VAC. Set vac advance accordingly.

Since the engine seems to idle better with more advance, I hooked the vac advance up to the manifold to achieve this.

This is essentially a stock setup now with stock curves.

Not sure if I particularly like it that much. Will try the previous setup again to see if it was any better or if its just psychological.

BTW The timing light I was using IS accurate. Will use it again to compile data from both setups.

#15 Señor Brat

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Posted 02 May 2012 - 02:00 PM

Righty ho then.

Since my last post I rebuilt another distributor and swapped it in. This one setup more or less stock.

I had to re set base timing to about 10 degrees for the mech advance to work correctly. Found the screw in the back of the VAC. Set vac advance accordingly.

Since the engine seems to idle better with more advance, I hooked the vac advance up to the manifold to achieve this.

This is essentially a stock setup now with stock curves.

Not sure if I particularly like it that much. Will try the previous setup again to see if it was any better or if its just psychological.

BTW The timing light I was using IS accurate. Will use it again to compile data from both setups.


Keep posting your findings! I'm very interested in your "research"

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#16 Dirk

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Posted 10 October 2012 - 02:49 AM

SSSSUP Kids.

Its been a while but I have not been idle.

I am still chasing the perfect timing/fuel ratio combo.

Until recently the engine was still feeling rough at the 2500 to 3500rpm band.

I partially cured this by throwing fuel at it. For a while I was running a 155 jet in the primary barrel of the carb. This smoothed things out a bit and gave me heaps of power but the plugs started to get quite black. Also fuel economy was pretty bad.

I replaced 155 with a 114 jet (after trying many sizes inbetween). This felt a little lean but not tragically so.

The biggest break through to date is I now have factory specs for timing advance!

They are as follows:

850rpm - 8 to 10 degrees
2400rpm - 12 to 16 degrees
4600rpm - 24 to 28 degrees for pre 1980s engines
4600rpm - 26 to 30 degrees post 1980.

This is interesting to me since I was led to believe that full advance should be at about 2500prm.

I have reset my mechanical advance curve to the following:

900rpm - 10 degrees
2400rpm - 16 degrees
3000rpm - 20 degrees
4600rpm - 30 degrees

So far the results are pleasing. Engine much smoother at 3000rpm but not yet perfect.

I have just replaced the primary jet again. This time to 130. MPG will suffer for this but maybe with VAC advance working the open road MPG will be OK.

Not yet given it a go but will let you know the verdict asap.

Also factory specs for total advance including VAC are:

42 to 52 degrees (pre 1980)
46 to 56 degrees (post 1980)

I have not yet reconnected my VAC advance. Will do this as soon as I am happy with mechanical advance.




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