Vacum Advance

[TopCatGr58]

Hey Greg,

Just wanted to post a followup to this. Yesterday I needed to go back to my job location for a little repair on a piece of diagnostic equipment we use, and so I decided to take my bike instead of the cage. I grabbed a large file binder clip and folded and clamped my vac. adv. hose, left it connected to the carb but it was clamped shut! IT started just fine, and I then rode it the 25 miles to my work location, both city and highway. Revved perfectly fine all the way to redline, and had plenty of roll on power in 5th from 60mph to 80+ when I wanted to pass a herd of cages to get into clear traffic!

So this helps prove that the vac. adv. isn't ESSENTIAL for power and acceleration performance. I didn't ride it this way for a whole tank full of gas so I can't report how it would detrimentally affect the mileage, but my right wrist affects it enough anyways . The Vac. Adv. is nice to have but if I were putting on newer GSXR type carbs without a vac. port, I wouldn't be worried about it.

T.C.

[BA80]

So, take it off.

[IanDMacDonald]

Well, keeping in-mind my lack of knowledge regarding the workings of the vac advance, mech. adv., etc., I can tell you that locking out my advance at "full advance" and capping off the carb and advance nipples definitely makes the bike quicker in my opinion. I always felt there was a slow acceleration when I had the original advance on, almost like a locomotive steam engine gathering up speed.

[motoman]

Hey Greg,

Just wanted to post a followup to this. Yesterday I needed to go back to my job location for a little repair on a piece of diagnostic equipment we use, and so I decided to take my bike instead of the cage. I grabbed a large file binder clip and folded and clamped my vac. adv. hose, left it connected to the carb but it was clamped shut! IT started just fine, and I then rode it the 25 miles to my work location, both city and highway. Revved perfectly fine all the way to redline, and had plenty of roll on power in 5th from 60mph to 80+ when I wanted to pass a herd of cages to get into clear traffic!

So this helps prove that the vac. adv. isn't ESSENTIAL for power and acceleration performance. I didn't ride it this way for a whole tank full of gas so I can't report how it would detrimentally affect the mileage, but my right wrist affects it enough anyways . The Vac. Adv. is nice to have but if I were putting on newer GSXR type carbs without a vac. port, I wouldn't be worried about it.

T.C.

Since that's ported vacuum T.C., under throttle load you have zero ported vacuum. If you'll watch it on centerstand running, and as you gradually let off throttle as if cruising,the vacuum advance will start to rotate advancing firing time, just like old school vacuum advaces in automotive world.

[TopCatGr58]

Since that's ported vacuum T.C., under throttle load you have zero ported vacuum. If you'll watch it on centerstand running, and as you gradually let off throttle as if cruising,the vacuum advance will start to rotate advancing firing time, just like old school vacuum advaces in automotive world.

Hey Brant,

Yes, I understand that principle and action, I elluded to it in my previous posts that the vac. adv. kicks in during cruising rpms for increases timing to help with fuel economy providing more burning time!

As for the old cars? I remember doing the tuneup on my old 69 pontiac with a 350 V8 with points ignition. I would use an allen wrench and a dwell meter to set the gap. Then I would DISCONNECT the vac. adv. and set the timing with the timing light. Then I would CONNECT the vac. adv. and the timing would immediately increase some 5-10 degrees IIRC, and while in neutral I would rev the engine while monitoring it with the timing light, and it would advance more which was the cent. adv. engaging. But I do remember the timing advancing at idle once the vac. adv. hose was connected to the distributor. So...that's different in action a bit from our bikes. The vac. port on the intake manifold of the V-8 seemed to be just direct manifold vacuum, not ported/restricted aside from just the size of the hose nipple!?

T.C.

[BA80]

Your ol' Pontiac had the vacuum hooked to the wrong port TC.

[motoman]

Hey Brant,

Yes, I understand that principle and action, I elluded to it in my previous posts that the vac. adv. kicks in during cruising rpms for increases timing to help with fuel economy providing more burning time!

As for the old cars? I remember doing the tuneup on my old 69 pontiac with a 350 V8 with points ignition. I would use an allen wrench and a dwell meter to set the gap. Then I would DISCONNECT the vac. adv. and set the timing with the timing light. Then I would CONNECT the vac. adv. and the timing would immediately increase some 5-10 degrees IIRC, and while in neutral I would rev the engine while monitoring it with the timing light, and it would advance more which was the cent. adv. engaging. But I do remember the timing advancing at idle once the vac. adv. hose was connected to the distributor. So...that's different in action a bit from our bikes. The vac. port on the intake manifold of the V-8 seemed to be just direct manifold vacuum, not ported/restricted aside from just the size of the hose nipple!?

T.C.

Actually T.C. you had the manifold vacuum hooked up, not ported. The Q-Jet carb that came on that had two maifold vac. ports(on front right of carb and right side at rear. Tha carb base had manifold vac. port at rear for power brake booster and front side for PCV valve..........hows that for memory.

[TopCatGr58]

Well,

I got the car in '76 for HS grad. It was stock, but only had a 2 barrel, and the pathetic 2 speed automatic...Turbine 200 I think it was called? Trying to rack my brain cells for how it was hooked up...I remember the vac. adv. port on the distributor, small nipple, and I think there was a nipple on the front bottom of the carb....but while running, it seemed like it has direct manifold vacuum, but back then I was ignorant to ported vacuum vs. manifold.

Then I put an Edelbrock aluminum manifold and Holley 650 4 barrel on it, and now can't remember if I had the vac. adv. connected to the carb body, or to a nipple that I fitted to the manifold??

It's just that I remember FIRST learning how to do tuneups on it, when it was still stock with the 2 barrel and stock manifold, so "I" didn't change where the vac. adv. was connected to before doing the tuneups, but I could have gotten PO'd!? Nope, now that I'm thinking about it, I'm pretty sure I remember a small vac. port on the side of the carb because it fitted the vac. hose just right, same size. The only other vac. port was like you said, for the Power assist brakes....IF it even had power assist brakes?? The other hose was just the PVC to air filter.

I remember having my Chilton "Bible" guide, and so I think I would have noticed if the vac. adv. hose wasn't connected to the correct port!? But this was almost 40 years ago!

T.C.

[motoman]

Well,

I got the car in '76 for HS grad. It was stock, but only had a 2 barrel, and the pathetic 2 speed automatic...Turbine 200 I think it was called? Trying to rack my brain cells for how it was hooked up...I remember the vac. adv. port on the distributor, small nipple, and I think there was a nipple on the front bottom of the carb....but while running, it seemed like it has direct manifold vacuum, but back then I was ignorant to ported vacuum vs. manifold.

Then I put an Edelbrock aluminum manifold and Holley 650 4 barrel on it, and now can't remember if I had the vac. adv. connected to the carb body, or to a nipple that I fitted to the manifold??

It's just that I remember FIRST learning how to do tuneups on it, when it was still stock with the 2 barrel and stock manifold, so "I" didn't change where the vac. adv. was connected to before doing the tuneups, but I could have gotten PO'd!? Nope, now that I'm thinking about it, I'm pretty sure I remember a small vac. port on the side of the carb because it fitted the vac. hose just right, same size. The only other vac. port was like you said, for the Power assist brakes....IF it even had power assist brakes?? The other hose was just the PVC to air filter.

I remember having my Chilton "Bible" guide, and so I think I would have noticed if the vac. adv. hose wasn't connected to the correct port!? But this was almost 40 years ago!

T.C.

Aye......wait til it becomes "almost 50yrs. ago".