Starter valve question

Does anyone know for sure if dropping the vaccum, as stated in the workshop manual for cylinder 3 (-20mmHg) and cylinder 4 (-10mmHg) from cylinder 1 is a lower or higher reading?
Example, I only have inHg gauge, and cylinder 1 is around 11inHg at 1200rpm.
If 20mmHg is around 0.8inHg, should I be looking for 11.8inHg, or 10.2inHg?
In my mind, dropping the pressure should be a higher vaccum, so I think 11.8inHg, and it's how I've always have done it.
Am I right?

 

The manual labels this as "vacuum pressure". Vacuum is pressure measuring less than atmospheric pressure. The term "vacuum pressure" is thus redundant and confusing.

A vacuum gauge measures vacuum and the specification is framed the same way so we should not be translating the spec. A cylinder with a lower vacuum spec should read lower numbers on the vacuum gauge. A cylinder with a higher vacuum spec should read higher numbers on a vacuum gauge.

The proof is always in the pudding. Pressure staggered correctly to compensate for the varied exhaust header lengths should produce the highest idle. So that is the goal, whatever the gauges state, that the idle is highest (before turning it back down) and the throttle response is the smoothest.

If you wanted to observe the effects, doing what you proposed should be a significant enough swing where it would produce a noticeable lowering of idle speed (bad). There would be your proof as to applying the spec correctly.

As an experiment: I read that one of the owners sets his vacuum at partial throttle. He states his idle is lumpier but the off/on throttle response is better. Doing so, to me, would compensate for any variation among the butterflies, such as due to age and wear. As long as starting is not adversely affected...Since we are never at idle, even giving throttle before starting out and slipping the clutch, perhaps this alternate approach has some merit...?

 

The manual helpfully says to adjust #3 "until the vacuum pressure is dropped 20mm Hg from #1".

Vacuum pressure is a great and confusing term because vacuum is only relative to atmospheric pressure, but I have always read the instruction to mean the vacuum gauge level is dropped, so if it was at 200mm Hg then you would take it to 180mm Hg. Visually that means the mercury level would be physically lowered in the gauge, and is what I assume Mr Honda wants us to do.

But you could easily interpret it the other way around because in absolute terms, more vacuum is a lower pressure, so that would mean the mm Hg should be increased.

I've never tried adjusting the SV's this way.

 

Thanks boys, it's what I started to think as I was doing it yesterday.
I had to take out the TB's to fix a small leak in the thermostat housing, so I thought I might as well get the injectors cleaned and flowed.
To my surprise, the injectors all had identical flow, and only increased by 3% after the clean, not bad for 100000kms.
The benefit of only using the best fuel I guess.
The other thing I noticed, was the build up of varnish on the downhill side of the butterflies on the throats, a soak of carby clean spray and a bit of a scrub with a rag got rid of that.
As far a wear on the butterflies, once closed, they still held a cap full of WD40 without any leak through whatsoever. So there goes the theory of wear in that section.
The other thing I should mention is the thermostat housing, there was a lot of crap on the top side for whatever reason, and onced cleaned and new thermostat installed, it cools a lot better and drops faster once heated up.
In fact, so much better that I wished I had done this a lot sooner.
Bact to the TB's and readjust.

 

If that setup is like carb synching, each screw adjustment slightly affects the other settings. A juggling act.

 

It's nowhere near as hard as carb balancing, fortunately. The SV's are completely independent of each other, so you can tweak the adjuster for one cylinder and the others don't waver much at all.

I just re-balanced my ST1100 carbs and that most certainly was a juggling act (with flaming chainsaws) as the other cylinders respond to the tiniest adjustment for the cylinder you are working with.

 

Once 1 and 2 are set up, they stay the same no matter what you do to the other two.
You just need to keep going back to 1 to see what the vaccum is once you adjust 3, 4, or idle speed.
20 minutes to get it spot on, idle is much more stable and quieter now.
Ahhh, the days of carbs and fork, nut and bolt valve adjustment as on my 86 VFR750F.
I know what it's like Cadbury, my wife has started to complain about not seeing me for days, and smelling of fuel when I go to bed.
I didn't find removing the throttle bodies that hard, just time consumming, the starter valve inlet hoses to the air box are a different story, who was the idiot that came up with that design?
It didn't help that once I put it all back together, the coolant bleed hose from the thermostst sprung a leak. Take 2, now all fixed.
Also delinked the brakes while there, installed braided lines and replaced all the hoses and O rings in the cooling system.

 

It's almost like we're married to the same woman.

I got a telling off for firing my ST up just outside the garage door, not considering the washing that was hung up to dry in there! Needless to say, we all smelled like were running a bit rich for a few days.

I have had my ST's carbs in bits four times, chasing an air/fuel problem that turned out to be a shortage of sparks under load. There's a trade off between lots of mechanical carb parts, vs miles of hoses and wires for FI.

One of these days I need to disassemble the VFR's injectors (95000km) and have them cleaned, I think one of them drips fuel into the crankcases as my oil level mysteriously rises very slowly. It's a nice balance for the oil level in my VTR which quietly drops away when I ride! A yin-yang sort of thing.

 

Easy fix mate. Remove the sump plugs from both bikes and replace with a valve and hose connection.
When you return from a ride, you park them next to each other on their centre stand, hook up a hose and open both valves. You should never have to add/remove oil from either bike again.

 

Genius. Pure genius.


Sent from my iPhone using Tapatalk

 

Question that follows along this. Should the valve clearances be checked first before the sync is done? On a carb sync, everything is supposed to be in perfect working order before you do the sync. Is this the same concept? Mine's a 98 with 22,400 miles. Been well cared for, but maintenance history unknown. Should I even bother checking? I have to replace the thermostat soon.

 

Hi Mustang and welcome. If you have not yet done so, introduce yourself and show us your bike in the introduction section.

Yes same concept. The synch sets the idle vacuum in each cylinder and an out of spec valve will alter the vacuum, so the valve adjustment would go first.

However, the question about inspecting, then potentially adjusting valves, a labor intensive job, is a religious one here. Many do not do it, or do not do it until far later in the engine's life. I rev my engine like I stole it, and also prior maintenance did not exist. The oil was a primordial soup when I bought it. That is the type of thing that affects the valve wear. I am OCD and given these factors, I am having mine inspected at roughly 18,000 miles.

Thermostat: You may wish to wipe the throttle body down, replace the coolant hoses, and replace the aging vacuum hoses. All of these will be exposed in order to get to the pesky thermostat.

I have great memories of my cousin refreshing his '66 Mustang and letting me drive it back in the 1980's. Love the fastback from Bullitt. I never know years, is that a '68? Whichever, it was a wicked dark green!

 

Thanks for the welcome. I've read on here and VFRD about valve checking. Honestly it doesn't scare me, just don't know if I'm feeling too lazy to do it or not. I'll be that deep in replacing the thermostat...


You're right Bullitt was a 68 fastback with a 390 and a 4 speed. I had a 68 coupe with a 302 that made around 350hp. Then I got into bikes and it got sold and I haven't missed it since. Bikes are way funner anyways, and a lot less maintenance. Ya'll might think the thermostat looks like a big job, I think back on my 68 and it's just a walk in the park compared to anything you perform on a car.

 

You don't have to remove the air box or TB's to do the valves.
I did mine at 65000kms, and three valves needed adjusting, they were still in spec but only just.
I plan to do them soon, when I have a bit of time.