TIMING NOT ADVANCING WHEN VACUUM IS APPLIED TO THE DISTRIBUTOR VACUMM CAN

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d1970

d1970

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Hey guys this one has me baffled. I had a buddy over today with a 70 340 Swinger and he said his car is not working right. We found that his vacuum advance was not working properly. We checked his distributor vacuum can and it was working right when vacuum was applied and the plate moved like it should, but his timing did not advance. Any idea what is going on? He has a Mopar electronic distributor.
 
Well, its moving...? The plate the pickup is mounted on should pivot with the rod sucking into the diaphragm with vacuum. Is it connected? there is a little C-clip on the pot rod or its a 90 in a hole. What are you timing it off of? MSD?
 
If the plate is moving when vacuum is applied ithas to be advancing. I'm guessing the advance is locked out?
 
put on a new can and the rod is connected to the plate and the plate moves, but no vacuum advance. 17 degree of vacuum. I have never seen this before.
 
Then whatever you have as a measuring tool for timing is not working.
 
we had a hand held tach connected the the coil to and his tach in his car, but the rpms never increased when vacuum was applied, I have never seen this before
 
If everything is right, then why isn't it advancing? I'll clue you in. Everything AIN'T right.
 
d1970 said:
we had a hand held tach connected the the coil to and his tach in his car, but the rpms never increased when vacuum was applied, I have never seen this before
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Were you hooking it up to manifold vacuum or a ported vacuum source?
 
Either something is stuck in the distributor, or your "dial up" timing light is AFU. Try a "plain old" timing light. Beg borrow or steal a hand vacuum pump and or a vacuum gauge. Apply vacuum and LOOK inside and see what moves. Also be sure you have ENOUGH. Consult the specs section of section 8 of the service manual, which details how much vacuum give you so much advance
 
it is connected to manifold vacuum. We tried with a hand held vacuum pump to. We tried a different timing light to. We had a vacuum gauge connected to.
 
Its pretty simple: turn the distributor ..if it advances on the timing light, the advance plate is the same principle.
 
we moved the distributor and the timing advance liked it should, but nothing when the plate moved. We are going to put my distributor in his car tomorrow to see how it runs. We have never seen the problem before, we have worked on mopars for years and this has us baffled.
 
Maybe when you have his distributor out you can post a picture or video showing the plate moving with a vacuum source? I'm curious too.
 
d1970 said:
we moved the distributor and the timing advance liked it should, but nothing when the plate moved. We are going to put my distributor in his car tomorrow to see how it runs. We have never seen the problem before, we have worked on mopars for years and this has us baffled.
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My personal guess is the timing light is throwing you off
 
Does the mechanical advance work properly, as in advancing smoothly from it's idle degrees to it's all-in degrees?That is to say;does the timing light show it advancing smoothly with no dropped sparks or jumping backwards from time to time? This type of monkey business speaks of reversed polarity to the pick-up. I don't know how that would play out with the Vcan.
But as said above; if the plate is rotating around it's anchor-stud, then it has to advance the spark, unless the oil-pump driveshaft is simultaneously climbing up the cam drive gear. That, IMO, is extremely unlikely.
 
almost sounds like the advance cam is frozen in mechanical also, easy check with the engine off see if you can turn the rotor a bit by hand and if not the advance plate is rusted to the distridutor shaft, there is a felt under the rotor that should get a few drops of oil on occasion, I see so many distributors frozen up from lack of oil when I rebuild them, other than that if you see the plate moving no idea.
 
If the reluctor to pickup gap is too tight, the friction of reluctor teeth rubbing on pickup nub will retard mechanical timing, as the vacuum advance is applied. Hence no advance, check the gap ..... and the gap narrows some, as advance plate slides...
 
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update boys. We installed a brand new Mopar distributor that a friend had for a guys motor he was building before they left for a car show. We checked the timing and then checked the vacuum advance and it was working perfect. KitCarlson was close, the gap was good at .008, but the plate was lifting a bit for some reason and barely contacting the reluctor teeth. First time we have ever saw this and the distributor was new this year. He is sending it back to the company that sold it to him. Thanks everybody for all your help and time.
 
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