Distributor vacuum advance

[craggle]

As part of my "fiddling with the engine" program I have now started looking at the distributor and advance system.
It is a standard HEI Distributor mounted on top of a 350 Chevy with the full Edelbrock performer RPM package.
I have just set the timing (car sounds awesome in the garage!) and did it by disconnecting the vacuum advance and plugging the pipe, then setting the timing to 15 degrees BTDC at about 900 rpm.

When I reconnected the vacuum pipe to the constant vacuum port on the Edelbrock carb, the timing goes round to about 20 - 25 degrees BTDC. It seems to run better with the vacuum connected but I have never seen so much advance at tick over before.

Is this normal?

Craig.

[Sidecarbod]

Originally Posted by craggle

As part of my "fiddling with the engine" program I have now started looking at the distributor and advance system.
It is a standard HEI Distributor mounted on top of a 350 Chevy with the full Edelbrock performer RPM package.
I have just set the timing (car sounds awesome in the garage!) and did it by disconnecting the vacuum advance and plugging the pipe, then setting the timing to 15 degrees BTDC at about 900 rpm.

When I reconnected the vacuum pipe to the constant vacuum port on the Edelbrock carb, the timing goes round to about 20 - 25 degrees BTDC. It seems to run better with the vacuum connected but I have never seen so much advance at tick over before.

Is this normal?

Craig.

Hi Craig,

It more normal to connect the vac advance to the timed port on the carb, that way the dizzy does not "see" any vaccum until you start to open the throttle. In fact on my motor when running at 1000 rpm tickover there is no difference in the timing with the pipe connected or not. RV8 but same thing really.

I also noticed that my motor runs better at tickover with a shed load of static ignition advance, the problem is that when you try drive the car it will hessitate badly as you pull away.

I guess the motor wants likes alot of advance at tickover because the cylinder pressure is very low. (The throttle being shut see's to that). Once the throttle starts to open the VE goes up and the engine does not like the massive static advance that has been dialed in and complains badly.

HTH,

Pete

[craggle]

Hi Pete

I did have the vacuum advance connected to the timed port but thought I would try the other one to see if it helps.
I am trying to get rid of a large flat spot thats come in when you accelerate gradually. I have tried some different carb needles and jets which did help but did not cure it completely. I have been trying to go richer with the carb but am now getting high fuel consumption, Sooty plugs and the engine doesn't feel as powerful. I have now returned to the stock needles and jets and am just trying other things as well.

I wanted to get some road time this weekend but the weather doesn't seem to be playing along.

Craig.

[Sidecarbod]

Originally Posted by craggle

Hi Pete

I did have the vacuum advance connected to the timed port but thought I would try the other one to see if it helps.
I am trying to get rid of a large flat spot thats come in when you accelerate gradually. I have tried some different carb needles and jets which did help but did not cure it completely. I have been trying to go richer with the carb but am now getting high fuel consumption, Sooty plugs and the engine doesn't feel as powerful. I have now returned to the stock needles and jets and am just trying other things as well.

I wanted to get some road time this weekend but the weather doesn't seem to be playing along.

Craig.

Hi Craig,

Unless your timing is miles out or there's something wrong with the advance mechanism then it is probably a carb issue. Its not just that the pilots need opening up a bit is it?

Regards,

Pete

[madjohnny]

Craig, this is one of the reasons I'm taking my engine to Tim Adams prior to it being put back in the car.

My car hesitates under hard acceleration (similar to bad turbo lag) which I think is down to the secondaries opening up to late. I'll let you know the outcome as it may give you some insight into your problem.

[craggle]

Cheers John

I fully intend to get my engine setup by some who knows what they are doing someday but I would like to get some more miles on it first. It won't be coming out the car again.

If you have to change jets, needles and springs in the carb try to make a note of what was used and maybe this will give me a starting point when I do mine.

Cheers.

Craig.

[Clarkson]

Originally Posted by craggle

Cheers John

I fully intend to get my engine setup by some who knows what they are doing someday but I would like to get some more miles on it first. It won't be coming out the car again.

If you have to change jets, needles and springs in the carb try to make a note of what was used and maybe this will give me a starting point when I do mine.

Cheers.

Craig.

It sounds like you 2 have the same engine,why don't you send your carb to Tim's and dyno it on the same engine on the same day and split the dyno costs between you?? That will give you a good starting point.

[craggle]

Now theres an idea....
They are both identical engines.

I'm up for it if John is willing to let his engine be run on the dyno twice. All I would need then is the base timing position.

Craig.

[madjohnny]

Fine by me Craig if that's what you want to do.

I can get Tim to sort the base timing settings for you.

[craggle]

Thinking about it some more I think there may be too many variables between the two engines. Distributor advance being one of them. No two engines are exactly alike and I'm not sure I want to risk running your engine twice. What happens if it goes wrong on my run? I couldn't live with myself

Are you supplying them with the Edelbrock callibration kit?

If you could ask them to note the parts used in the carb when they tune it I can then fit the same components and go from there.

I need to know.....

Colour of step up springs used.
Code on side of needles used.
Code on top of primary jets used.
Code on secondary jets used. (if changed)
Base timing position, With or without vacuum and how many revs?
What port to use for vacuum advance, Timed or constant?
Anything else I should know?

If you could try to get this information from them while they are doing the tuning it would be greatly appreciated.

Thanks.

Craig.