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V-8 Engine Tech

383 Vacuum advance leaking

Mopar Big Block Talk

by Eddie » Wed May 29, 2019 4:51 pm

My vacuum advance diaphragm is leaking.

The car is running sweet as a nut, but I get a bit of a flat spot on acceleration and occasional spit back, only when cold.

So hoping the leaking advance will solve this problem, a look around Mopar forums does tend to suggest it will.

So my questions are.

1. Can you just replace the diaphragm. Or is it just worth replacing the whole unit?

2. Is there an uprated version I should be looking for, assume mine is fairly stock blue streak one?

3. My advance timing is set, assuming I get everything back in the same place will it need readjustment being new?

Thanks in advance (timing based pun :D )
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by Chris_R » Wed May 29, 2019 5:21 pm

Your best bet for such advice is to contact The Distributor Doctor. http://www.distributordoctor.com/
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by Eddie » Wed May 29, 2019 6:53 pm

Chris_R wrote:Your best bet for such advice is to contact The Distributor Doctor. http://www.distributordoctor.com/


Thanks Chris.

Yes looks like he will know.

Ta
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by Roh » Wed May 29, 2019 11:03 pm

I'm pretty certain that you can get NOS vacuum canisters.

You may be able to repair it yourself with a dab of silicone. See here: https://www.youtube.com/watch?v=pNsVY0mvoO0

Is your motor standard? If so a standard canister will be appropriate. If not you would want an adjustable canister (I understand that the standard hex shaped canister is adjustable). For more aggressive engine set ups you wouldn't use any vacuum advance at all.
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by Eddie » Thu May 30, 2019 5:36 am

Rohan Christmas wrote:I'm pretty certain that you can get NOS vacuum canisters.

You may be able to repair it yourself with a dab of silicone. See here: https://www.youtube.com/watch?v=pNsVY0mvoO0

Is your motor standard? If so a standard canister will be appropriate. If not you would want an adjustable canister (I understand that the standard hex shaped canister is adjustable). For more aggressive engine set ups you wouldn't use any vacuum advance at all.


Thanks Rohan.

I took the unit off last night and to be honest it’s probably just worth looking at either NOS or a refurbished one from the distributor doctor who Chris put me onto.

My car is pretty standard, the only real mod is an edlebrock performa intake manifold. I have read on Mopar forums that some people don’t bother with the advance on there higher powered motors. I will have a drive at the weekend with it disconnected to see the difference.

Ta
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by Roh » Thu May 30, 2019 7:42 am

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by slotcarone » Thu May 30, 2019 10:50 am

Eddie if your advance unit is leaking vacuum then it is not working. You will not feel any difference with it disconnected. Easy to check. Have someone hold the RPMs steady at maybe 2000 and pull off the hose. If you don't have any change in engine speed then it is not working. If the engine speed increases as you put the hose on then it is working. :)
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by Eddie » Thu May 30, 2019 6:41 pm

Rohan Christmas wrote:Have a look here: https://www.manciniracing.com/vaadme.html


Great stuff, thanks Rohan, at that price it’s not worth mucking about replacing the diaphragm.

Ta
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by Eddie » Thu May 30, 2019 6:46 pm

slotcarone wrote:Eddie if your advance unit is leaking vacuum then it is not working. You will not feel any difference with it disconnected. Easy to check. Have someone hold the RPMs steady at maybe 2000 and pull off the hose. If you don't have any change in engine speed then it is not working. If the engine speed increases as you put the hose on then it is working. :)


That’s a great bit of advice, thanks Slotcarone :D

I assume when the engine is warm, choke off.

Will give it a go, now thinking of looking at leaks from carb to intake. I have the out of the box 2x rubber gaskets with metal gasket between, but would I be better looking at a different gasket?
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by DaveV8 » Fri May 31, 2019 7:11 pm

Andy at appleyards sells the vacuum canister
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by slotcarone » Sat Jun 01, 2019 12:51 am

Eddie what is wrong with the wat your engine is running? Why are you looking for vacuum/carb leaks? :)
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by Eddie » Sat Jun 01, 2019 6:14 am

Thanks Dave V8 for the info.

I get spitback into the carb on acceleration while the engine is getting up to temperature.

When at temperature it is fine and runs perfectly.

The carb has been rebuilt by Dave Barnett so we can rule out any carb problems.

All other aspects of the vehicle running is perfect. Cold starting, hot starting, generally the best it has ever run.
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by Steve Payne » Sat Jun 01, 2019 7:46 am

You can buy the cannister ready to fit like this
https://www.manciniracing.com/vaadcabmopre.html

Probably easier to get one here in the UK with shipping costs and import duty.

Easy to fit and only takes a few mins, you don't even need to remove the distributor from the car to do it with a bit of practice.

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by slotcarone » Sat Jun 01, 2019 10:46 am

I would fix the advance unit if it is not working. Could possibly be the cause of your problem. Could also be a choke/carb adjustment issue. :)
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by Eddie » Mon Jun 03, 2019 6:28 pm

Thanks guys.

Will replace unit and go from there :D
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