On the advice of a fellow forum member, I removed the vacuum advance for distributor several months ago and plugged off the ports on the rats nest.

A few weeks ago I heard a conflicting opinion; eliminating the vacuum advance will hurt your MPG, as well as low-end response around town.

Today I reconnected the advance. It's too early to tell and may be wistful thinking, but the car does seem more driveable. My mechanical secondaries don't hesitate as much, and throttle response is smoother.

What's the final word on this? Are the vacuum advances good for a mostly stock car, or should I go all? Block off the vacuum hoses and lock the mechanical weights?

 

id like to see what people have to say about this to, i just took off my rats nest and afterwards i reconnected the vacuum advance. does not having it hurt just mpg or does it affect power too?

 

my opinion is you should leave them on. the timing advance helps stops early detination by retarding the timeing as you reach higher rpm. people take them off on car that see only track because the are only at high rpm and wide open throtle. if they are at wide open throtle the intake vacum drops off. so if there won't be any vacum to control the timing advance, why have it? they set their timing based on where they're rpm will be. if you take it off on a street driven car, the car will drive like it's suposed to at high rpm, but at the low end you could have things happen like mis-fire and back fire. also if the trailing timing is off, you won't get a complete burn out of the fuel mixture at low rpm. that means less power. so if i were you i would leave it on if it's gona be driven on the street.

 

I ran without. True, the car does get better milage and the part throttle response was better with vacuum advance. But, I went pretty agressive with the base timing for more WOT power and didn't want the additional vac advance. It's up to you what is more important.

 

i don't see the benfit of taking it off. you don't gain power or really anything. and you can adjust for timed advance with it on there. so i just dont get why take it off unless its a car built for track racing

 

also you loose gas milage. big time. you don't have the throtle response so the common thing to do is to step on it. that puts more gas into the chamber. you still don't burn all of it. and your milage goes shitty. another thing, it's really not good on a exhast tip. it'll turn a blackish color on the tip after awhile. you're car will smell like gas out the back end. so by taking the timing advance off all you're really doing is making the car run rich at low rph. by running rich you're engine runs cooler. and this may be a bad thing come winter time.

i would definatly leave the timing advance on

 

The vacuum advance only works on deceleration or part throttle. Its purpose is to advance the spark to give a more complete combustion at these times when the mixture is lean.
This helps MPG and smooth engine operation under deceleration.
Leave it on.

 

ok im new to rx7's completely, i only know the little bit i do from the net basically (i only got my first rx last saturday) and i didnt wanna ask it cause i thought id sound like an idiot but what the hell is a rats nest??

 

Why don't you lock it at max advance? That is the only reason I would disconnect the vacuum advance.

 

b/c it would fire too soon at low rpm and could cause mis-fire and back fire.

 

The car has a better exhaust smell (no cats) and I have a feeling my MPG is going to jump dramatically. I got 16mpg on last tank so i though to hell with this the advance is going back on

 

Well....you need to lock it if you run a turbo on your engine like I do if you don't go to a different igntion setup such as a J-spec 12a turbo's distrubuter. Not all of us can locate and afford one when you run a blow-through on a budget and you just want it working adquately. Plus its a good thing because you can make a little more power also at low rpm, otherwise you loose all your vac advance below 4000rpm at full throttle.

It also helped my bridgeport make slightly more power below 4000rpm even though there isn't much down there to start with. Ran great this way. It rev's quicker with less bogging this way when you goose the throttle a idle. I wouldn't suggest lugging the engine at WOT up a hill below 2000rpm though if it could.

 

how does vacuum advance work?

 

For some reason you can't access this directly from the main site anymore. Anyway, rumour is that Yaw's total timing settings are a bit extreme and should only be used if you're confident with the proper operation of your carb, no leaning out etc.

http://personal.riverusers.com/~yawpower/pultime.html

I run a total timing of 20* and 10* and get between 21-24 mpg on city/highway/flogging it tanks.

 

Re-reading Yaws explanation and am confused. He says eliminating vacuum and mechanical advance results in better MPG and response. But only if you have your timing advanced all the way to begin with correct? Because what I and other owners experience is the opposite.

 

you have to understand how u get intake vacum. easily said, when your at idle or part throttle, the throttle valves are partialy closed. this creates a vacum b/c the engine is creating a sucksion. so if u put a pipe after the throtle body then there is a vacum created in the pipe. the timing advance runs on this type of vacum. when at partial throttle. there is a vacum created on the switches. when u open the throttle all the way, the vacum drops off. this causes the switches to loose vacum, when that happens the distributor cap is rotated by a few degrees. causing the firing to happen a few degrees sooner. hence advancing the timing.