too much vacuum?!

[JOHN G]

Help-the vac advance on my D-II is fully activated at idle! Obviously, the lag off the line is the dead area until the weights kick in at rpm. Adjusting the vac advance doesn't help since there is less vac under load than at idle-oh and yes the advance has been replaced. Thanx too all!

 

[Anonymous]

Full vac advance at idle is to be expected when connected to a manifold vacuum source. Not always a bad thing. What is your initial timing set at with the vac advance disconnected and plugged?
You may need run a little more initial advance which should help acceleration, assuming you don't start pinging.
Doug

 

[JOHN G]

initial timing set at 12 degrees-pings under wot conditions,i am however using the vac port on the weber-not the manifold port on the log. I know that too much advance can cause excess vac so i'm going to try retarding it a bit and see what happens. a master tech friend of mine suggested using a solenoid from another application that can be used to shut vac off at idle and turn it on at a predermined pressure?

 

[Anonymous]

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[JOHN G]

is this to mean that the port on the carb is manifold vac and not port? The only problem i see with setting the timing with the vac in play is when the vac runs out under load-isn't there going to be a lag until the weights kick in? I am experiencing stumbling under light accel until rpms build or i stab the throttle and open up the other carbs. I do have to build some rpm before flooring it, otherwise it stumbles or stalls. I have tryed switching the carbs-same thing.

 

[66 Fastback]

If it is pinging at WOT, then the vac advance is not to blame. You have either too much Centrifugal or initial timing. Now if you mean it pings when ging from part throttle for a period before it gets to WOT, then vac advance may be contributing and could be partially to blame.

I am not familiar with the carbs you have, but depending on the carb, a port nipple may provide a "ported" source or a manifold source of vacuum. You should be able to tell if it is a manifold or a ported source using a guage comparing the difference between the two or using your finger over the end of the hose. True "ported" sources of vacuum do not peg the vac advance at idle.


For the off idle response, you might have to adjust centrifugal advance or I suspect your bog may be carb related, either accelerator circuit or a jetting problem.
Doug

 

[JOHN G]

I did order a jet kit and will install that this week. Is there any way to create a ported source if my carb doesn't provide one? The pinging got worse with the new coil-running out of juice at high rpm. I will rectify that with a bigger lead to the coil this weekend.

 

[Anonymous]

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[Lazy JW]

The pinging got worse with the new coil-running out of juice at high rpm. I will rectify that with a bigger lead to the coil this weekend.

Running out of spark at high rpm is a bad thing but it will result in a misfire which is quite different from pinging/detonation. If indeed you experienced pinging/detonation then I highly doubt that you had an ignition failure but much more likely either a lean condition or too much spark advance. Go ahead with the bigger lead to the coil, it certainly won't hurt anything.

Since you posted on the thread about "Vacuum Advance Tuning" I won't repeat myself but I advise that you treat this setup just like his. Get it to run right without vacuum advance, then add it back in.
Joe

 

[JOHN G]

car still pings with the advance plugged-too much initial timing i suppose-i am at 12 now-I'll back it to 10 and see what happens.I am also seeing that everyone with duraspark is running larger gap on the plugs than i(34 thous) versus other people running 50 on average. perhaps this is part of my problem with the hesitation?

 

[Lazy JW]

A bigger gap may help, try it and see but there is a practical limit. The bigger the gap the higher the voltage required to jump the gap, and when it is easier for the spark to go someplace else then you have a mis-fire. Keep experimenting until you find the best timing setting for maximum power. If this results in too little initial advance then you can re-curve the distributor to allow enough initial advance without too much on the top end. But before I limited the advance curve I would then try using full manifold vacuum advance. This may give enough response off the line to be satisfactory without doing the re-curving.
Joe

 

[Anonymous]

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[JOHN G]

it now pings at mid throttle-still stumbles under light accel at point where secondary carbs should come in. i opened up the gap to 50 with noticable power gains. base timing is set at 12 idling in neutral-should i back off to 10? i still have to try the manifold vac-i see that the port vac rise under light accel and disappears when i stomp it-maybe the rise is the pinging problem and manifold vac will be more linear.