Question of Idle on 1997 ST 1100

Hondafan

I noticed recently my idle seems to flunctuate.

When it is cold in the AM and comes off the choke, it seems to be a little low. If I adjust it higher to normal level of 1k rpm when it is hot, then it seems too high the next time I start it. If I turn it back down, then I need to start all over. Am I adjusting it too much?

Is there a vacuum hose or something that has come off?

The only thing I can possibly attribute this to is the fact the idle adjust screw in the gas cap recess will not stay in its U holder and I assume it bounces around or vibrates itself one way or another. However the screw is always tight so that may not be the case.

Any suggestions?
 
How big a difference in idle speed between cold and fully warmed up are we talking about? Unless the difference is huge, I think this is pretty normal. When it's cool out, a carbureted bike will tend to idle slower until fully warmed up. The adjuster not staying in it's holder is pretty normal, too. Both of my 1100's had that problem.
 
Hondafan said:
I noticed recently my idle seems to flunctuate.

When it is cold in the AM and comes off the choke, it seems to be a little low. If I adjust it higher to normal level of 1k rpm when it is hot, then it seems too high the next time I start it. If I turn it back down, then I need to start all over. Am I adjusting it too much?

Is there a vacuum hose or something that has come off?

The only thing I can possibly attribute this to is the fact the idle adjust screw in the gas cap recess will not stay in its U holder and I assume it bounces around or vibrates itself one way or another. However the screw is always tight so that may not be the case.

Any suggestions?
Click to expand...

4 stroke engines idle slower when cold. On carbed autos the chokes had step up idle cams. On newer fuel injected autos the computer idles the engine faster.

On your ST the choke isn't really a choke but an fuel enrichener which increases the engine speed. The specified idle speed for a US speced ST1100 is 1200 rpm +/- 100. Canada 1000 rpm +/- 100 rpm. this is set at normal operating temp. I have seen bikes idle from cold to hot engine differences of 700 rpm.

Set your bike when hot and leave it alone. My 91 is set for 1200 on it's tac hot and when cold with no choke idles around 700 rpm. If you set a 1000 rpm idle when cold I'll bet the bike dles 1300-1500 warmed up.

Ralph Sims
 
Good advice Ralph.

I tried to ride this morning but the motor was knocking and sputtering and would not maintain an idle (hovering 500 then dropped) when choke lever was reduced. I was afraid of causing more problems or even damage trying to ride it.

I ended up taking my gear off, opened fuel cap, and there was no vacuum in or out. I'm told that is no big deal as it was abt 60 degrees this AM.

i drove to work, called the local dealer I use when they opened. I have a lot respect for them. They gave a suggestion or two to try before bringing in to them for diagnosis and correction.

He felt my filling up last week with high octane was not good, as it is used by motorists so infrequently it may be old. That may make sense as things have deteriorated over the last week as I have run bike. he suggested filling up wiht low octane as it is fresh, then run it to see if it clears up. (I think I will add a little fuel system cleaner as well)

Anyway, my fingers are crossed. I'll let you know how things pan out.
 
I have found that high octane is not the best thing to use in the ST11. It acts far more cold blooded, like you describe. On mine on -2c mornings lately the bike will idle slow (500rpm)without the choke on, but will ride away normally after 30 seconds or so. The cheaper lower grade fuel is the best to use, as the bike goes better overall.
 
Update-I filled up STella with low test Unleaded mixed Techron fuel system cleaner, rode to work and back 60 miles. I noticed a dramatic improvement of about 80%. I needed to reduce the idle notably and it holds a steady idle now. So all is looking well!

I will fill her up again with more fresh low test at about 1/2 tank.

I cannot believe how bad the bike ran with old gas -I just happened pay top dollar for. I just might change stations now.
 
What I was told from a station owner is that the Premium fuel sits longer and is not as fresh as the regular. Most cars burn regular, so that does make sense.
 
Hondafan said:
I noticed recently my idle seems to flunctuate.

When it is cold in the AM and comes off the choke, it seems to be a little low. If I adjust it higher to normal level of 1k rpm when it is hot, then it seems too high the next time I start it. If I turn it back down, then I need to start all over. Am I adjusting it too much?

Is there a vacuum hose or something that has come off?

The only thing I can possibly attribute this to is the fact the idle adjust screw in the gas cap recess will not stay in its U holder and I assume it bounces around or vibrates itself one way or another. However the screw is always tight so that may not be the case.



Any suggestions?
Click to expand...

ANY fluxuation of idle IS first indication of carbs out of sync. With idle adjustments not finding a 'happy' place, confirms that would be the prime issue;). Carb boots, if never changed to your knowledge can cause the same snenario with a slight vacuum leak around base mount of them to cyl. head.

See in post #7 issue seems to be resolved.........and +1 using the lower octane fuel. The 85octane regular has the LEAST amount of alcohol, which returns the best burn and BTU's;)
 
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maybe one of our "really friendly guys that can talk to anybody" members out there can talk to a bulk truck driver someday and see if he will tell them how offen he fills the higher grade tanks as compared to regular fuel tanks at most filling stations.
 
Air temperature + humidity as well as fuel quality do impact the behaviour at startup and functionality of the choke.
If the idle also doesn't set/still alters with a fully warmed engine I too check sync and trace possible vacuum leaks.

On my two ST1100 I however do note quite some differences:
The choke on the '00 model basically knows only 3 settings: full, medium and off...
To start when cold I need full, but it doesn't like to run smoothly there, so I instantly need to set it back to 1/2 once it has fired.
But after like 500 meters I must turn the choke OFF, cause otherwise the engine will tend to stall while idling at the next intersection; with the enricher off that soon it'll of course idles at ~500rpm only, but steady.

The choke on the '94 model on the other hand can be set/used seamlessly from full to off, I can neatly adjust the idle during warm up, yet can leave it in for longer then the above 500 meters...

According to the fiche both have identical jetting, the '94 twice the mileage of the '00...
 
ST1100Y said:
Air temperature + humidity as well as fuel quality do impact the behaviour at startup and functionality of the choke.
If the idle also doesn't set/still alters with a fully warmed engine I too check sync and trace possible vacuum leaks.

On my two ST1100 I however do note quite some differences:
The choke on the '00 model basically knows only 3 settings: full, medium and off...
To start when cold I need full, but it doesn't like to run smoothly there, so I instantly need to set it back to 1/2 once it has fired.
But after like 500 meters I must turn the choke OFF, cause otherwise the engine will tend to stall while idling at the next intersection; with the enricher off that soon it'll of course idles at ~500rpm only, but steady.

The choke on the '94 model on the other hand can be set/used seamlessly from full to off, I can neatly adjust the idle during warm up, yet can leave it in for longer then the above 500 meters...

According to the fiche both have identical jetting, the '94 twice the mileage of the '00...
Click to expand...

Highly likely that operating difference is being affected by a slight difference of actual running fuel levels in bowls of each bike;).
 
Brant said:
Highly likely that operating difference is being affected by a slight difference of actual running fuel levels in bowls of each bike;).
Click to expand...
Either this and/or different shimming of the jet-needles...
At current moment am I not in the mood nor the position to break the carbs out of both bikes, place them on the bench and compare 1 to 1 and/or swap them between the engines to see the change on the engine run/performance... (currently still in desperate search of a nearby rental garage/workshop I can settle with all my tools and stuff in... :cry: )

Its interesting how different two identical engines in stock condition can perform...
After selling my first '92 ST I was a bit disappointed with the brand new '00... its engine never ran as smooth, the power curve not as linear as the '92... despite all carefully braking it in, nursing and syncing...
The '94 engine now has that "seamless punch" again, when unleashed it just screams through to the rev limiter, whilst the '00 still kinda "peaks" between ~3500 and ~6000 rpm, but giving a sense of being "puffed" near 7000... hard to grasp though, but they are different...
At first I'd blamed the redesigned silencers of post '96 models (altered noise emission regs), but during the refurb the '94 also received the "new" OEM cans... with no impact on performance...

So as you say, it must be some fine tuning of the carbs causing this...
 
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