Vacum draw

[mack]

has anyone ever put a guage on one of the carb boots with the motor running to see what the draw is on the intake cycle?

[crazy steve]

Sure, that's what you're doing when you do a carb sync. I'm seeing around 7-9 inches of mercury at idle after damping the vacuum signal so the gauge doesn't fluctuate too much. That's with my gauge, you may see something a bit different.

[motoman]

Here at 4,800ft. elev. I get the normal 18in. of vacuum that's expected at this elevation, mercury manometer AND MorganCarbTune. Sea level vacuum readings SHOULD be at near the the 22in. range at idle, auto or bike, as they are both just an air pump. Substantually lower than normal, with elevation figured in indicates several things besides valves not tottally sealing. A weak ignition spark dropped mine on the Bentley to 14in.to get it 'dialed' in evenly across all four cyls......which I didn't catch for couple yrs.. It was a gradual loss of a good spark, and I just kept tuning to THAT every so often.
Corrected with the common voltage drop areas on these ole'scoots, along with replacing gradual failing stock coils with VFR coils and new plug wires got vacuum reading back to where they're supposed to be at 18in. with mixtures and sync vacuums corrected.

[DiverRay]

+1 on 22" with my 4 gauge set-up. At sea level.

[3Phase]

Me too. 20" to 22" like any other IC engine or something is wrong. Most of items on the common vacuum troubleshooting charts apply to motorcycles too.

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[natemoen]

I can easily get 16+ inches here.

[BA80]

Guages usually vary though unless they are calibrated.

[DiverRay]

Guages usually vary though unless they are calibrated.

For the way we use them, just put in a "T" and set them all to the same port BEFORE starting a sync. If they are up or down a couple of inches, it doesn't matter, as they are all the same when you are done.

[BA80]

For the way we use them, just put in a "T" and set them all to the same port BEFORE starting a sync. If they are up or down a couple of inches, it doesn't matter, as they are all the same when you are done.

Exactly Ray, I have a hand vacuum pump I use. Could care less about inches of vacuum, just as long as they are all the same.

[mack]

Vacum

I was rolling my E over by hand and put my palm over the intake. I was surprised at how strong the suction was. Didn't know exactly how much it was and was curious if anyone had a number thanx.

[motoman]

I can easily get 16+ inches here.

Well, gonna 'pick' on ya' Nate. If the idle doesn't get you more than that at your location(should be about 20in.), there's an issue going on......BTDT. My bet is also, IIRC your bike having the later carbs(see yours has the earlier ones), if idle mixture screws are out that 3 1/2+ range(NEVER more than 2 1/2 out, even on the later carbs), the chances of a weak spark from coils, or prim. voltage TO coils being low IS fairly high.....BTDT also. Seem to remember you having installed Geezer's reg. also, but can't remember for sure. As you know, that's no guarentee that 13v exist at prim. side of coils at idle. Just for G/G you MAY wanna check that, key on should be same,same as batt. voltage with key on. If not, you know the fix routine. Whatever the case may be, your vacuum readings are what they are up here if I go up to 9-10,000ft. 16in. is maximan a vacuum pump specificly will draw at that elevation, and yes, you can AHIK.

[mack]

Ohh Lord

forgive me. I just wanted to ask a simple question. Brant, Greg, you guys need to get a secondary hobby. Normally I'd recommend fishing but on review I believe that would allow too much internalization. So I will instead recommend loud music and table dancers!!!!!

[motoman]

Exactly Ray, I have a hand vacuum pump I use. Could care less about inches of vacuum, just as long as they are all the same.

All good in theory, but those in. numbers ARE a tattle-tale of something a bit array if not within spec. realative to elevation location, same as if one or more have an erratic jump due to an occassional mis-fire.

[Rasputin]

I use the thing to equalize my draw on each carb no matter the number. That being said if the draw is too weak (eg 8 on the manometer) then I look at valve and cam timing issues. Too long since last used one but if the numbers are significantly lower than expected there are other things to check.

[motoman]

forgive me. I just wanted to ask a simple question. Brant, Greg, you guys need to get a secondary hobby. Normally I'd recommend fishing but on review I believe that would allow too much internalization. So I will instead recommend loud music and table dancers!!!!!

Sorry Mack, as a TOTAL gear head for 50+yrs., I hate fishing(loved elk hunting), and the poodle doesn't collect lint, so, your stuck with Greg and I's bantor back and forth.