Okay got a SBO 350 with a 2BBL. I have Pertronix Ignitor III in the distributor and matching coil.

I plugged the vacuum advance and have it set at 32 degrees @ 2800 rpm. The weight springs in for the mechanical advance are the medium weight (all in by 2800 rpm). (initial timing was 12 degrees @ 1100 rpm)

Motor runs well, I peel the rubber off my tires simply by hitting the accelerator hard. I like it. Great throttle response. (best I can get for having 2.56 gears).

Now when I hook up the vacuum advance I lose all power and can't get even a little squawk out of the tires. After hitting the throttle it just kind of rolls into the increased rpm. Basically, no get up and go.

So, why the difference? I would leave the vacuum advance plugged, but it has erratic idle at low speed when I do that.

I am trying to get the best of both worlds, but no such luck.

Any suggestions?

d1

 

Is it on the timed or manifold vacuum? It's supposed to be in the timed port on the carb.

 

Yes, the vacuum advance is coming off the base of the carb.

d1

 

I'd check this again.

The vacuum advance should have NO effect on the idle if it is on the correct port. The mark should NOT move when you plug the hose back into the carb if you have it on the timed port, e.g. if you have 12* with the vacuum hose unhooked, when you hook it up, you should still have 12* unless there is vacuum being applied to the hose at idle.

sb

 

The vacuum is hooked to the carburetor. I tested it at idle and it is not "sucking" air at idle. When throttle is applied then it does "suck" air like it is supposed to.

Idle performance aside. This would not explain why I have no throttle response from idle like I do when I have the vacuum advance plugged.

d1

 

Are you removing the hose from the distributor or the carb? You could have a leaking hose.

 

I remove the hose from the distributor and plug it. I will double check my hoses just in case...

 

you are hooked to ported vacume (it has vacume as you open throttle and manifold vacume goes down). if the vacume advance is capable of adding say 15 degrees then at 2800 you would have 47 degrees of timing. if you hook it to manifold vacume then you will have 27 degrees at idle. when you hit the gas it would drop to 12 and start climbing with the mechanical vacume up to the 32 degrees at which time as manifold vacume comes back it would start climbing up to the 47. all this is based on 15 degrees of possible vacume advance so adjust the numbers based on what your really does. I personally just set my distributor up with the amount and time of advance I want and never use the vacume advance.

 

They don't compound. There is a maximum amount of movement in the advance plate and that's it. Once the mechanical advance is at it's limit it won't move any further.

 

?????

Maybe I'm misunderstanding you, but all three advance types (initial, mechanical/centrifugal, and vacuum) do add together. The vacuum advance doesn't allow the weights to swing out any further, but it does rotate the entire base plate that the weights are attached to. That's why you disconnect the vacuum aadvance when checking initial and mechanical advance.

 

Brian is correct, they do add up. that is why they use the vacume adv for the TCS system. the mechanical pivots the rotor on the shaft. when it is at full advance with the weights the vacume can move the points (or pickup) plate to advance it further. when you are cruising down the road at 3000 rpm the mechanical is at its full advance. in high gear the TCS then applies vacume to the can and moves the plate advancing it further.

 

Now see you (by that I mean me) learn something every day if you try hard enough. I had to go check the points dist I have and low and behold the vacuum plate rotates in the opposite direction to the mechanical advance. For some reason my mind was telling me they went the same direction and so once the mechanical topped out that was it.
I stand corrected and thank you for the information.

 

I think the mechanical advance is only for starting the engine as soon as the engine starts it goes all the way and stays there going back only when the engine is shut off.I'm pretty sure at idle you should lots of vacum,when you open the throttle vacum should drop advancing the time.If I'm wrong somebody tell me cause.........I'm about 180 degrees off if I'm wrong

 

Railguy, yes you are wrong. read my post a few up and it explains how it works. on some race engines there is no vacume advance and the timing is locked at full advance but that is not recommended on street motors. the mechanical advance can be changed with different weights and springs to make it start advancing at a different RPM. if you dont have an advancing timing light and do not understand the effect of timing on your motor you are best to leave the stock setup in the distributor.

 

Okay, I checked all my hoses and started from scratch with all my settings.

I went with 12* @1100 rpm.
I have the medium weight springs on mechanical advance (all in by 2800).
I plugged the V.A. and set the initial timing at 12* @ 1100.

I have an adjustable vacuum advance canister. I set that at 10*, based on the installation instructions.

Hooked up V.A. hose and drove the car and it did not have the same characteristics from low idle take off as it had previously. So, I was pretty happy with that.

I believe the only difference that I could tell from my original settings is that I changed the vacuum advance settings and backed it off a few turns. I based my initial setting on the manual's recommendation. Well, I guess that was too much (8-10 degrees too much). Not sure why it would affect hard throttle acceleration though as vacuum advance is not suppose to be in play

Problem: When I went to shut it down, it wanted to keep running (it's always something) So, I retarded the timing a hair.

I was not sure of the degrees as I was trying to make a car show last night and did not have enough time to throw a timing light on it. I just slightly rotated the distributor and called it good.

When I got to the car show (40 miles away) and shut it down it cut off normal. But when I went to crank it back over it is acting liking it is flooded and did not want to fire back up.

I think I have a boiling fuel problem in the carb. It is getting so hot that it is boiling up and over and leaking out the throttle shaft. I have adjusted the bowl float in the past so it can't fill the bowl completely. The PO had it set where it would leak out both sides of the throttle shaft.

The motor temp is 175* with A/C on while cruising at highway speed. Except when I pulled into town for the car show the temp shot up to 220*. Sooo, not sure what is going on and if this is part of my hot fuel problem.


So, I guess its back to the drawing board. And probably a new thread...