webber vac port x2 passenger side?

[spdcrazy]

I feel silly even asking this but I can't find the answer via search so...

 

I have two vac lines on the passenger side near the base of my Chinese knock off 32/36. which one should go to my vac advance?

[Doctor510]

I feel silly even asking this but I can't find the answer via search so...

 

I have two vac lines on the passenger side near the base of my Chinese knock off 32/36. which one should go to my vac advance?

Plug them both and use just the mechanical advance in the distributor, set your timing near 34*-36* BTDC at 2,800 RPM, never mind where it is at idle, as long as it starts well, you should be good to go.

[spdcrazy]

Doc!!! long time, don't know if you remember me, but I lived in flagstaff, have a z32tt and at the time was working on either a 280z or my 510 wagon, spoke with ya multiple times! good to hear from you.

 

I have heard of this by some Toyota guys didn't know it applied to us Datsun folks as well

[Draker]

I remember you from tt.net

 

I don't frequent there that often, but still have the Z.

[spdcrazy]

ohhh man, my z32 is in long term hibernation. until I have a garage to be able to build it again. not gonna have a shop build the engine this time, spend to much for it to blow up to quickly with no help from them. if it blows up after I build it, it'll be no one's fault but my own.  

I don't frequent here or there very often. decided to stay away from z32 stuff all together. to depressing to be involved and not building one.

[datzenmike]

If you run part throttle you will want vacuum advance.

[spdcrazy]

I do a lot of that. its a daily.

[spdcrazy]

im not sure if it matters but, I am running an el dizzy and a 20b

[datzenmike]

EI or points have and need a vacuum advance. If you were racing there would be no vacuum to even use a vacuum advance and no need. If you drive WOT then you can leave it or run without.

 

Vacuum advance adds needed ignition advance relative to engine load. To get the most out of your engine and fuel, the advance must be tailored to the load on the engine. Light load... heavy advance, heavy load... light advance. For all part load driving your mileage and driveability will be much improved with vacuum advance working. 

[spdcrazy]

ok, any idea which port on my webber? I have two on the passenger side

[datzenmike]

Chinese knock off???  :rofl:  I would guess one is for advance and the other for EGR. Both are ported vacuum.

[Stoffregen Motorsports]

I'm with Doc...sort of. I don't like to run the vacuum advance, even on street cars, but I will take the time to set the mechanical advance curve by adjusting the slots in the distributor cam and removing one of the springs.

 

I've never felt that using a vacuum advance is advantageous on a street car.

 

Either way you go, make sure to check your total timing. Too much can really hurt.

[spdcrazy]

this is why i'm wondering if it I have it in the wrong port, I don't see any difference in the ports, but the option is there. I recently brought it to a Datsun friend to attempt to get it idling consistently (never succeeded on that) and he found that if we timed it to 12 or so at idle, it was about 8 degrees (I think that number is correct) to much at 3k rpms. So I took it to a Datsun mechanic that is knowledgeable at changing the weights and curve like you were talking. this mechanic just unplugged the dizzy and plugged the vac line, ran it up to 3k and timed it to max (don't recall that number off the top of my head). then checked it at idle and I think it was sitting at 8. with of course is a bit less than 12.

 

do you have a link or info on the slots and spring changes you speak of? I do have an el dizzy if that changes anything

[datzenmike]

Full throttle or race, there no need for a vacuum advance. Vacuum advance has been built into every distributor engine that will be driven on the street (which is almost all part throttle anyway) since cars were invented. There's a good reason for this. Part throttle means the cylinder is not full. A weakly filled cylinder even when compressed takes longer to burn than a wide open throttle and fully filled cylinder. When compression goes, up timing is always retarded, ask any turbo owner. A part filled cylinder needs more advance so the maximum pressure is reached above the piston as it has passed TDC and begins moving down.

 

Vacuum advance has a direct relation to engine load. Light throttle.. heavy vacuum..more advance. Heavy throttle... weak vacuum... little/no advance. As mentioned, max advance usually tops out at 32-36 degrees but this is full throttle. At light cruise speeds (again part filled cylinder) the max advance can be close to 50 degrees. If you are restricting your advance to 34 degrees then your maximum cylinder pressure is reached way past the best spot just after TDC and it is chasing a rapidly accelerating piston down an ever expanding cylinder. Starting the burn at the right time increases part throttle power and increases gas mileage. Period.

[spdcrazy]

this makes a lot of sense, and while I value the other idea, i'm leaning towards leaving it hooked up, just would like it to be correct.

 

Doc510 and stroffregen, what did you guys see as the benefit for not running vac advance?

[datzenmike]

It has no effect on full throttle performance. Some advantage of mileage and drive ability around town at low speed. The will run cooler and more efficient at part throttle.

[Stoffregen Motorsports]

You don't need to be at full throttle to realize the benefits of deleting the vacuum advance. Light throttle movements can change the vacuum load, which, if you arer using vacuum advance, changes the timing. Having the timing bouncing around at freeway speeds or mid RPM range, when the cylinders are building pressure and starting to "come into the cam" as they say, has its potential hazards.

 

If you set the mechanical advance properly, you can have the advantages offered by advanced timing, but eliminate those hazards associated with fluctuating timing.

 

It's one of the variables that you remove to have the best of both worlds - performance and long engine life.

[datzenmike]

It doesn't 'jump around'. It advances and retards the timing in response to engine load. It's not a concern for the billions of cars that were built with it. This is a 521 with a stock L16. It came with vacuum advance and runs best with it for the reasons stated.

[Stoffregen Motorsports]

50 million Americans can't be wrong argument. I love it.

[datzenmike]

50 million Americans can't be wrong argument. I love it.

 

This... is no argument.

 

Short of EFI or CAS equipped engines, probably safe to say all previous carb and distributor engines have vacuum advance and for good reason. Because you don't doesn't make it wrong.

[banzai510(hainz)]

So I took it to a Datsun mechanic that is knowledgeable at changing the weights and curve like you were talking. this mechanic just unplugged the dizzy and plugged the vac line, ran it up to 3k and timed it to max (don't recall that number off the top of my head). then checked it at idle and I think it was sitting at 8. with of course is a bit less than 12.

 

 

just leave it

[Lockleaf]

From personal experience I was happier with how my 32/36 carbed z24 720 drove after I hooked up the vacuum advance on it. I had set the advance as best I could before without it, but it ran better for me after I hooked up vacuum and reset it

[kelowg]

All right, so adv should b connected to vac before or after carb? (manifold or ported vac)

[datzenmike]

It should be connected to the carb ported vacuum. This just assures that there is no vacuum advance at idle but just above idle vacuum is applied. It's an emissions thing.

 

Prior to the mid late 60s vacuum advance was run directly from the intake. Distributors that are designed to wokl on ported vacuum won't tolerate this very well. 

[tr8er]

I say run it without the carb. That'll eliminate the advance issue too.