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Trouble with Vacuum Advance Distributor on 2110cc Engine
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thefladge
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PostPosted: Tue Feb 22, 2011 7:42 pm    Post subject: Trouble with Vacuum Advance Distributor on 2110cc Engine Reply with quote

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I just put an Aircooled.net vacuum advance distributor on my 2110cc engine.

The engine has dual Weber 40IDF carbs, an Engle 120 cam and about 8.5:1 compression.

The vacuum hose goes to a T and is attached to each carb.

I don't seem to be getting enough suction from the carbs to move the plate in the distributor. I can see this through the (temporary) clear cap. I rev the engine and there is no movement.

When I remove the hose from the distributor I feel a pulse at the end of the hose, but not much suction.

I have tested the vacuum unit by sucking on the hose and watching the plate move.

Any ideas how to solve this problem?
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earthquake
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PostPosted: Tue Feb 22, 2011 8:00 pm    Post subject: Reply with quote

TF
You might try using a vacuum can reservoir, you can find them in most wrecking yards, they were used for cars with covered head lights, they also had them on some cars to give a stronger vacuum single for the MAP sensor. I had to do this on a friends Scirocco that I put a set of 40mm DCOE's on , the vacuum diaphragm would vibrate and you could hear it.

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PostPosted: Tue Feb 22, 2011 11:42 pm    Post subject: Reply with quote

You need ported vacuum from all 4 cylinders, not 2 which is what you currently have. I see that you care about your linkage, but not the quality of your distributor cap? Confused

Why not go the extra mile and treat your ride to a crank triggered distributorless ignition? That way you could give it whatever curve you want at will from the driver's seat, and you'll never pay for another cap or rotor ever again. Megajolt is what I put on my car, and I'll never look back.
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thefladge
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PostPosted: Wed Feb 23, 2011 6:12 am    Post subject: Reply with quote

miniman82 wrote:
You need ported vacuum from all 4 cylinders, not 2 which is what you currently have. I see that you care about your linkage, but not the quality of your distributor cap? Confused

Why not go the extra mile and treat your ride to a crank triggered distributorless ignition? That way you could give it whatever curve you want at will from the driver's seat, and you'll never pay for another cap or rotor ever again. Megajolt is what I put on my car, and I'll never look back.


The cheapo clear cap is only there so I can see if the points plate is moving or not. I only run Bosch caps otherwise.
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the caveman
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PostPosted: Wed Feb 23, 2011 6:34 am    Post subject: Reply with quote

I'm about to address this same problem on my 2165, dual 44's. I didn't seem to have much of a signal from the vacuum ports either . Talked to john at ACN and he mentioned that i may not see much of a signal by just blipping the throttle, it must be driven and under load in order for there to be enough to pull the vacuum can. I was a little dubious , but after a few miles of driving, my temps went way down.
This happened after i put a small vacuum catch can in the system, although i can't confirm whether it alone made a difference.

"You need ported vacuum from all 4 cylinders, not 2 which is what you currently have. "

This is not what i was told . I will double check, but the 1 vacuum fitting on each carb is exactly there for that purpose. i also asked John about this to make sure.

Engine is going on the dyno next week and will get back with my findings.
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mharney
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PostPosted: Wed Feb 23, 2011 7:19 am    Post subject: Reply with quote

It's a new distributor, and it might just be a little tight on the can and plate. I can say that IDFs don't have nearly the responsive vacuum port that the Dells have, but it should work.

The T is still getting an odd fire signal, since #1 and #4 are consecutive pulses, not evenly spaced like #2 and #4 or #1 and #3 would be.

The old Alfas had a device called an anti-pulse valve that was like a check valve except that it had a slow bleed back in it to keep from fully checking vacuum, so when the signal drops, you don't keep advancing. You can find these from time to time. I think Dellorto.co.uk still sells them. These help a lot with the pulse signal.

Try driving it with and without and see if you can feel a difference. John is right... part of what makes vacuum is going to be driving it under a slight load. Investigation with a vacuum gauge can tell you some stuff too.

The more cam you have, the less intake vacuum you are going to have too, and this can certainly figure in. With that said, I have enough from my FK8 on my 2332 to pull a good signal with my 48 DRLAs. One of the advantages of larger carbs on an engine is that for less plate angle, you get more air flow, and so the duration of the vacuum advance is longer in the range you tend to cruise in. Smaller carbs need more plate angle to flow the same air and so you are more quickly out of the vacuum advance port's functional range. I've often wondered if there would be a benefit from modifying the IDF's vacuum advance ports to get a little more signal. The holes are small, which slows the response time, and the phasing is shorter as well because of the hole size as well.
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wompninja
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PostPosted: Wed Feb 23, 2011 9:30 am    Post subject: Reply with quote

The diaphragm in the SVDA is new so it's going to be a little tight and harder to move probably requiring a little more vacuum. Once it gets worn in it should move a little easier.
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74 Thing
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PostPosted: Wed Feb 23, 2011 10:32 am    Post subject: Reply with quote

I agree with the others-the vacuum diaphram is just tight-run it a while then check it again.
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pdub
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PostPosted: Wed Feb 23, 2011 10:58 am    Post subject: Reply with quote

I have the same set up but 2276 with 9:1 CR and 44 IDFs with 36 mm vents. Mine is broken in and I get 30 deg w/o vac and about 38Deg w/vac at about 3K. This is w/o load in the driveway. Not sure what it does under load. I think the venturi size can affect the vac signal as well. I did send mine back to John to have him "recurve" it for my engine once I upgraded for the 35 PDSITs to Webers. It would be good to slap a vac guage on there and see how much you have and at what RPMs.
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webebuggin
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PostPosted: Wed Feb 23, 2011 3:44 pm    Post subject: Reply with quote

I had/have the same problem on my 2110 with a Mallory Unilite,with vac, running dual 44 idf's with the #1 cyl. and #4 cyl. off of each carb "teed" to the can, does not seem to pull just sitting,but feels like it 's advancing under load...Might just be the internal advance. I do know that i don't have the right can for this set-up..according to John @ aircooled.net, there are like 5 cans for the Unilite,and only one will work with the v.w. it's adjustable thru the port with an allen wrench..and i'm only running an FK-7 with 1;4's and 36 vents...
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thefladge
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PostPosted: Sat Mar 05, 2011 10:12 am    Post subject: Reply with quote

Actually, I bought this distibutor about 6 or 7 years ago. I ran it on the engine for a few hundred miles back then and it worked well.

The engine had to come out because of pushrod / rocker arm issues and it sat for a few years before I made the repairs.

Recently the engine went back in, but I put a 009 on it. I don't remember why I re-installed the engine with the 009 instead of the vacuum advace distributor. Maybe I didn't want to bother with the hoses at the time.

Anyway, the vacumm unit doesn't seem to move the points plate now.

There are some changes to the engine since the first time around: Shorter intake manifolds (Type 3 style) and stock rocker arms instead of 1.25:1 ratio.

Could those changes have an effect on things? Could the points plate be sticking from sitting unused for so long?
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clonebug
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PostPosted: Sat Mar 05, 2011 4:17 pm    Post subject: Reply with quote

Did you remove the little screw plug inside the vacuum port tube??

You might not get enough vacuum to the diaphragm unless you are driving down the road.

Advance works on light load throttle positions.


Clonebug
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thefladge
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PostPosted: Sat Mar 12, 2011 3:09 pm    Post subject: Reply with quote

clonebug wrote:
Did you remove the little screw plug inside the vacuum port tube??

You might not get enough vacuum to the diaphragm unless you are driving down the road.

Advance works on light load throttle positions.


Clonebug


I did remove the screws.

I bought some new hose and a new vacuum T today.

Sucking on the old hose I realised I was getting some air. I'll install the new parts this week and see if it makes a difference. If not, I'll re-install the 009 and forget about it.
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thefladge
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PostPosted: Mon Mar 14, 2011 7:45 pm    Post subject: Reply with quote

Update:

I installed the new hoses and a new T-fitting today. I also advanced the timing a degree or two.

While revving the engine in the garage, I observed some movement of the points plate through the (temporary) clear cap.

I would rev it up to about 3000 RPM and then give it a quick rev up to about 4000 RPM or so to get it to move.

Later this week I will take it out on the road to see what the performance results will be.

The goal is to improve performance and increase gas mileage. Let's hope it works!
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the caveman
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PostPosted: Tue Mar 15, 2011 3:59 pm    Post subject: Reply with quote

Just got back from the shop/dyno. I now believe my vacuum gauge is junk, which would explain more than a few things :D .

At any rate, without the vacuum connected i could only get to about 30 o advance at 3000. with it connected i got 38 o . We were on a time restraint by the time i got to the point of being able to check it all properly, but all that to say that it does have a positive effect.
BTW my 2165 . 40x35 CB 044's and dual 44 webers pulled 140 hp and 157 ft lbs between 3800 and 4200. 142 lbs starting at 2300 and climbed, then 140 until 5200. I'll try to post the print out in a few days
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R-Baja
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PostPosted: Sun May 13, 2012 12:35 am    Post subject: Reply with quote

You need to use a vacuum gauge and timing light and watch the vacuum gauge while you rev it. You will notice the gauge flickering back and forth due to the uneven pulses from cylinders 1 and 4. A vacuum damper or anti pulse valve smoothes this out. To see how your distributor advances, using the timing light compare it with and without vacuum. The vacuum can needs at least 10 inches of vacuum to pull it, 20 is better.

Are these anti pulse valves still available? Who sells them? I can't seem to find one.

Also, does anyone make larger knurled idle mixture screws for the 40IDFs? I have the hardest time turning those dinky screws by hand. My shortest screwdriver does not fit between the screw and the engine compartment. Mad
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Juanito84
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PostPosted: Sun May 13, 2012 8:08 am    Post subject: Reply with quote

WHY DOESN'T ANYONE UNDERSTAND HOW THE VACUUM ADVANCE WORKS ON AN SVDA?!?!


The vacuum advance mechanism is a device that compensates for LOAD CHANGES and has nothing to do with RPM. Even if your vacuum advance does not work, or is plugged off, the mechanical advance will be like using a 009 so there would be no advantage to switching to a 009.

Vacuum advance normally runs off of a "ported" vacuum signal that directs the intake manifold vacuum to the distributor vacuum advance whenever the throttle plate is open. When you close the throttle plate the ported vacuum is shut off so that at idle your engine produces less NOx emissions and so you have a little better engine braking. For a practical purposes, however, the ported vacuum can be easily bypassed by running your vacuum advance right off of manifold vacuum. You'll only see a difference at idle.

Even then the vacuum advance responds to manifold vacuum. It should produce up to about 10* advance at 10 in. Hg. or 33.9KPa or 4.9psi. If you have a high reving cam you will get a poor vacuum at low RPMs and therefore less, vacuum advnace. The Engle 120 has a duration of 294*, which is nearly 70* greater than stock (224.5*) making it produce less vacuum at idle.

Also a vacuum leak, especially in combination with a high reving cam, will produce less or no vacuum.

#1 Test your distributor with a vacuum pump and vacuum gauge first. If it doesn't give up to 10* advance at the numbers I said above then something is wrong with the distributor.

#2 Test your intake manifold vacuum with a gauge. If you have too low of vacuum at idle for your specific cam then find and repair 1) any vacuum leaks or 2) perhaps valves that are not adjusted properly.
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