ST1100 Gas Mileage Decreasing

Thread starter paulcb
Start date Nov 20, 2013

dwalby

#21

Re: ST11 Gas Mileage Decreasing

Brant, back in the mid-90s I was in a small town in Italy and came across a tire pressure gauge at a gas station that was a glass column of mercury about the diameter of your middle finger and about 4-5 feet high. Not sure what era that thing came from, but if that were to break in the US today they'd probably shut down a hundred mile radius for a year trying to clean it up.

Bush

#22

Re: ST11 Gas Mileage Decreasing

Brant said:
Factory fuel mixture settings are NOT real world applications. With that said, carb sync IS affected by fuel mixtures. That has to set to an overall best for your location..

I can agree with you on that Brant. Factory settings are based on mixtures needed for near sea level altitudes, where I happen to reside, as does the majority of the world's population. Where you live in Colorado, I'm sure your carbs need an altitude adjustment from the factory setting. Altitudes over approximately 600 feet will make for a richer mixture than the factory adjustment is set to provide and in cases where the machine is constantly operated at higher elevations, you probably cannot get the mixture correct unless you start changing out jets, or moving the needles.

Whatever sync method works for you is your choice, but you can't discount the success many have had using a Flowmeter to sync the carbs. Works fine for me and is dead easy and quick.

Last edited: Dec 14, 2013

Timothy1959

#23

Re: ST11 Gas Mileage Decreasing

Brant said:
figured a menmer that uses one would chime in. It's a flow meter set atop the velocity stack that measures vacuum Hg. Imagine no problem with the accuracy, but these bikes, and for the most part all multi-carbed bikes, the sync and idle mixtures are done like it is ridden, in other words with all intake in place. Now on the ST 11's, that makes it a real PITA accessing mixture screws and a bit more difficult accessing the sync screws. I watched a Honda tech friend of mine do my ST some eight years ago. He was specificly factory trained on the ST's, and he had his share of bad language through the sync/mixture adj. on mine. Aside from the frustration, he happens to be annal maticulate till he was satisfied. I personally use merc stixs on my other notorious classic muscle bike, but back then, was unfamiliar with the process on the Steed. Could not of learned the process from a better tech as he showed that during cool down wait(cannot have a proper idle mixture when cooling fan comes on as it creates electrical load on alt. pulling additional load on motor), to blip throttle several times to seat screw threads/stops on sync screws. Re-start and re-adjust sync. Repeat process a few times till merc. stabilizes across all four the same and stays that way.

On a related note, I just ordered the MorganCarbTune to take the place of my merc. stixs, as it uses stainless slides, so no spill't merc. as sources for mercury are becoming scarce.

Brant,
I still don't get what you mean by "flow meter." The Morgan Carb Tune tool works just like carb sticks to measure vacuum, except without liquids.
How about a manufacturer & model # for this "...flow meter set atop the velocity stack?"
Tim

Bush

#24

Re: ST11 Gas Mileage Decreasing

Timothy1959 said:
I still don't get what you mean by "flow meter." The Morgan Carb Tune tool works just like carb sticks to measure vacuum, except without liquids.
How about a manufacturer & model # for this "...flow meter set atop the velocity stack?"

Google is your friend.

Carburetor Flowmeter

Timothy1959

#25

Re: ST11 Gas Mileage Decreasing

Bush said:
Google is your friend. Carburetor Flowmeter

This is the wrong tool to use for synchronizing carbs on a Honda ST1100. Honda wants the relative NOT the absolute vacuum levels to be measured. You must see all FOUR carb vac levels simultaneously and compare them to each other. A multichannel manometer (such as by Motion Pro) is the correct tool to use for speed, accuracy and compliance with OEM (Honda) requirements.

ST1100Y

Site Supporter

#26

Re: ST11 Gas Mileage Decreasing

Timothy1959 said:
This is the wrong tool to use for synchronizing carbs on a Honda ST1100. Honda wants the relative NOT the absolute vacuum levels to be measured.

+1 on this one... IMHO you'll need to do the sync with the whole shebang, including air-filter, cover, fuel petcock, etc... installed.
Also ensure that there absolutely no leaks within the air circuit present; a small rupture in a tube, a not properly set carb boot/clamp or a small tear in the petcock diaphragm make any attempts quite useless...
We've a (quite sensitive) 4-channel digital carbmeter as well as a Carbtune (less sensitive, but also very accurate) avail, both excellent tools for this delicate adjustments.
Having two (big) ventilators in front of the bike to cool radiator and intake air at hand is very useful; you'll have to stop once the engine gets hot and starts a 'pounding' combustion in idle, at latest once the radiator fan starts to kick in, let the engine cool off and start adjustments again in medium engine temps.
Once flap settings appear close in idle, I slowly increase the RPM to ~2500 and let the throttle close again; this often slightly upsets/changes the settings again, so I need several cycles to get the best/proper 'average' thus ideal setting.
Once that's found the vac-meters show perfect scales from ~1100 up to ~5000rpm... that's a smooth engine then.

Doodaa

#27

Tried to stay out of this one, but the intent is to BALANCE each cylinder. Vacuum relative to each other. Try it on a V twin first, it'll make you a believer. YMMV

Timothy1959

#28

Doodaa said:
Tried to stay out of this one, but the intent is to BALANCE each cylinder. Vacuum relative to each other. Try it on a V twin first, it'll make you a believer. YMMV

Try what "on a V twin?"
It will make me a believer in what?

Doodaa

#29

Timothy1959 said:
Try what "on a V twin?"
It will make me a believer in what?

Carb "sync" on a V-twin. Can't recall the brand names of the tools (one homemade too), but having done the (intake vacuum balancing) sync with both mercury and lighter viscosity instruments, my experience is that having only two cylinders to work with shows the "out of balance" combustion levels much more drastically than having more cylinders to "hide" minute changes. JMHO

Timothy1959

#30

Doodaa said:
Carb "sync" on a V-twin. Can't recall the brand names of the tools (one homemade too), but having done the (intake vacuum balancing) sync with both mercury and lighter viscosity instruments, my experience is that having only two cylinders to work with shows the "out of balance" combustion levels much more drastically than having more cylinders to "hide" minute changes. JMHO

1. The factory service manual for the ST1100 specifies the "Carburetor vacuum difference" to be "Within 40 mmHg (1.6 inHg)." A standard multichannel manometer (such as from Motion Pro) has PLENTY of accuracy to satisfy this specification.
2. Air flow meter vs. vacuum gage (manometer): Honda wants the vacuum to be measured NOT the air flow through the carbs.
3. Carb sinc is not about "combustion levels" it's all about relative throttle valve position.
IMHO...

Brant

#31

True.....not about combustion levels, or lack of. But an incorrect or correct mixture setting DOES change vacuum on a particular cyl. which changes sync. It's all tied together and is why fuel mixtures and there settings is ALL related to a correct tune/sync

. Cant' have one without the other or your just fooling yourself........and correctly done includes ALL intake in place as it is normally ridden.

Doodaa

#32

Brant said:
True.....not about combustion levels, or lack of. But an incorrect or correct mixture setting DOES change vacuum on a particular cyl. which changes sync. It's all tied together and is why fuel mixtures and there settings is ALL related to a correct tune/sync. Cant' have one without the other or your just fooling yourself........and correctly done includes ALL intake in place as it is normally ridden.

That about sums it up. I stated the difference is more noticeable when you only have two to work with instead of four. All intake in place is a no brainer IMHO. Happy holidays

Slasher

#33

it would be interesting to see how far off a sync done with a flowmeter is from one done with via vacuum. Many guys swear by the flowmeter. I use it, not because I believe it is better than the tried and true method but mainly because I am lazy and I plumbed all my vacuum lines, except for the one for the petcock, to my vacuum resevoir for my cruise control. Digging them out and dividing them back up to use a traditional sync method isn't going to happen. Using a flowmeter, while not "correct" has to be better than no sync at all, no?

dwalby

#34

I've never noticed any real-world difference between a bike that was synched, and one that was considerably off. Always had the gauges, so I did it anyway, but for the most part figured it was some kind of theoretical exercise. Others will claim less vibration, better fuel economy, etc. but in my case I've never noticed any difference. Kicked my carb-stix over 10 years ago and spilled the mercury, haven't adjusted my ST since. Still purrs at idle, and delivers 50MPG @80mph.

Brant

#35

Bummer havin' the mercury spill. Did the same thing some 7yrs. ago but fortunately had another tube of mercury I had ordered from Motion-Pro at the time. We're SOL for getting replacement mercury now, least not on the commercial market.
Approx. a week ago I ordered the Morgan Carb-Tune, so won't have anything to spill since it uses 4 stainless sliders. Know several who use it and have compared its accuracy against mercury stixs, and find it matches perfectly. Ironicly, I personally haven't done the mix.adj/sync on my ST, but watched while it was all being hooked up and while all adjustments were being done. That was almost 9yrs. ago. My XS11 Venturer is the bike that tends to be 'needy' one in that department since the screw threads on sync screws are not coated on the Mikuni carbs like they are on the Honda's Kiehns. Threads being coated on the sync screws of the Kiehns seem to keep them stabil and in sync.

FWIW, Several I know who have and used the MotionPro blue fluid replacemet manometer dislike its functions. Apparently the fluid doesn't move in tubes properly and tends to 'hang' up.

Timothy1959

#36

dwalby said:
I've never noticed any real-world difference between a bike that was synched, and one that was considerably off. Always had the gauges, so I did it anyway, but for the most part figured it was some kind of theoretical exercise. Others will claim less vibration, better fuel economy, etc. but in my case I've never noticed any difference. Kicked my carb-stix over 10 years ago and spilled the mercury, haven't adjusted my ST since. Still purrs at idle, and delivers 50MPG @80mph.

Unless the throttle linkage is disturbed, relative changes in vacuum or fuel mixture (carb-to-carb), the sync will not change and the carbs will remain balanced. After a carb rebuild, sync in mandatory.

Timothy1959

#37

Brant said:
Bummer havin' the mercury spill. Did the same thing some 7yrs. ago but fortunately had another tube of mercury I had ordered from Motion-Pro at the time. We're SOL for getting replacement mercury now, least not on the commercial market.
Approx. a week ago I ordered the Morgan Carb-Tune, so won't have anything to spill since it uses 4 stainless sliders. Know several who use it and have compared its accuracy against mercury stixs, and find it matches perfectly. Ironicly, I personally haven't done the mix.adj/sync on my ST, but watched while it was all being hooked up and while all adjustments were being done. That was almost 9yrs. ago. My XS11 Venturer is the bike that tends to be 'needy' one in that department since the screw threads on sync screws are not coated on the Mikuni carbs like they are on the Honda's Kiehns. Threads being coated on the sync screws of the Kiehns seem to keep them stabil and in sync.

FWIW, Several I know who have and used the MotionPro blue fluid replacemet manometer dislike its functions. Apparently the fluid doesn't move in tubes properly and tends to 'hang' up.

I have had the same problem with the blue fluid "hang up" in the Motion Pro tool. I called Motion Pro and was told that this problem is caused by water evaporation, and viscosity increase of the fluid. They told me to prevent this, you must store the manometer with the tubes SEALED in a place with minimum temp change (such as an indoor closet). I will try, we will see. When the manometer works, it works GREAT, as a replacement for mercury carb sticks!

dwalby

#38

For my next sync I'm going to park the bike at the edge of a multi-story parking structure and make my own manometer using colored water.

Doodaa

#39

dwalby said:
For my next sync I'm going to park the bike at the edge of a multi-story parking structure and make my own manometer using colored water.

There's always the ATF substitute, then you only need a stepladder~!

dwalby

#40

Doodaa said:
There's always the ATF substitute, then you only need a stepladder~!

but ATF has a specific gravity lower than water, so the column would be even higher than if you used water.

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