Seeking advise on leaning the mix

Hi guys.

Here's the deal. I ride at 8,300 ft ASL. Never got more than 30 miles per gallon. Used to change plugs every year or so because of sooting. Bike used to smoke quite a bit but after a carb synch and pilot screw adjustment, hasn't done so for almost 7 years now. Other than a flat spot at around 5k revs, rough cold idling and a max speed limited to 100mph, it runs fine. Last mandatory exhaust gas inspection showed a rich mixture. Passed on the upper limit.

I might add that when cold it will idle at under 800 rpm requiring constant throttle compensation (keep lubbing). However once it reaches op temp it will happily idle away at 1200 rpm. I seldom use the choke, once at most in the past year when it didn't start at first crank but for the most part, it does so without the choke despite the low ambient temps. When choke is applied revs don't rise.

Six months ago I bought my next set of Denso U24 plugs. Decided to replace one by one as they started failing due to sooting. Couple of weeks after replacing the first plug, the rest started going out in rapid succession and when I changed the last one, the first new one also failed. I'm thinking one sooted plug puts the other ones in higher risk of sooting. Still no smoke.

Now, since I've had the bike, 13 years to date (is there a trophy for persistence?) we've always suspected of at least a couple valve seals leaking. The bike spent five years in a garage. That's not going to change for now since seal replacement is a last resource. No parts or qualified labor in my neighborhood.

Any advise on leaning the mix? I already closed the pilots to 1.5 turns and set the floats at 8 to 9mm. I understand jetting is stock (never checked) and just found out that there's a needle clip which allows you to set needle height, the lower the leaner. Should I try that or should I bite the bullet and get a higher altitude jet kit. Any advise on jet sizes and a source? Thanks!

Constant soot clogging the plugs?
I have a 2 questions:
1) What air cleaner are you using. You might not be getting enough air through it.
2) What do you keep your rpm at when you're riding?

Mark

Hi Mark,

1.) Stock filter. I did use the Fram equivalent for some years but the last time I tried, it was way too restrictive and the bike ran like cr*p. Cleaned the stock filter and put it back.

2.) Not sure what you mean. When riding I use the throttle and revs rise with speed. When the engine is cold while standing still I open the throttle enough to keep revs from sinking. As soon as it warms up it will idle at 1200 throttle closed. My idle speed varies 50% from 800 when cold, to 1200 at op temp.

Thanks!

maubur said:

Hi guys.

Here's the deal. I ride at 8,300 ft ASL. Never got more than 30 miles per gallon. Used to change plugs every year or so because of sooting. Bike used to smoke quite a bit but after a carb synch and pilot screw adjustment, hasn't done so for almost 7 years now. Other than a flat spot at around 5k revs, rough cold idling and a max speed limited to 100mph, it runs fine. Last mandatory exhaust gas inspection showed a rich mixture. Passed on the upper limit.

I might add that when cold it will idle at under 800 rpm requiring constant throttle compensation (keep lubbing). However once it reaches op temp it will happily idle away at 1200 rpm. I seldom use the choke, once at most in the past year when it didn't start at first crank but for the most part, it does so without the choke despite the low ambient temps. When choke is applied revs don't rise.

Six months ago I bought my next set of Denso U24 plugs. Decided to replace one by one as they started failing due to sooting. Couple of weeks after replacing the first plug, the rest started going out in rapid succession and when I changed the last one, the first new one also failed. I'm thinking one sooted plug puts the other ones in higher risk of sooting. Still no smoke.

Now, since I've had the bike, 13 years to date (is there a trophy for persistence?) we've always suspected of at least a couple valve seals leaking. The bike spent five years in a garage. That's not going to change for now since seal replacement is a last resource. No parts or qualified labor in my neighborhood.

Any advise on leaning the mix? I already closed the pilots to 1.5 turns and set the floats at 8 to 9mm. I understand jetting is stock (never checked) and just found out that there's a needle clip which allows you to set needle height, the lower the leaner. Should I try that or should I bite the bullet and get a higher altitude jet kit. Any advise on jet sizes and a source? Thanks!

Click to expand...

Idle mixture setting is totally incorrect and WAY outa' whack. Your enricher/choke comment was my first clue. If idle mixture setting is correct, enricher/choke is ALWAYS needed starting cold, and of course no throttle is ever applied starting cold. BTW, stock jetting, pilot circuit and main circuit works perfect on these bikes since the vacuum diaphram carbs dictate vacuum draw which dictates metering rod movement and how much.Llots less vacumm at 14,000ft. than sea level. Approx. 6in.vacuum difference between the two previously stated, and have ridden both elevations and everthing in between with never an issue cept for the noticed power loss at higher elevations(3% horsepower loss for every 1,000ft. elev.) Also, I might add, if idle mixures are incorrect, a carb sync is a total waste of time, even though you may have all four showing even across. Remember too, that when cooling fan comes on while setting either mixures or a sync, that extra bit of current draw on alt. causes extra pull on motor changing fuel mixture ratios and also affects carb sync. In other words, when cooling fan comes on while tuning, shut bike off till it cools a bit. Running a 20" or so box fan in front of motor while tuning helps to prolong things a bit before cooling fan comes on. Just an FYI, I was taught all this by a mechanic who was factory trained on ST1100's. My bike constantly, depending on mother nature winds, got from 48-54mpg at 80-85mph on the slab for 300 mile runs at a time. 52mpg was its constant average m.p.g. over a long 300+mile run at a time. Notice too, that I say WAS, as I and bike were involed in a T-bone accident last June which totaled bike and I had metal plates added in several locations with a two month hospital stay. Fortunately ATGATT kept that incident from being worse than it was. Hope all that offers you some insight and help, and remember, ATGATT.

If by idle mixture setting you mean pilot screw setting, I wouldn't be so sure it's that much off. Remember, I'm at 8500 ft above sea level and plugs are indicative of a rich mixture. Besides, the fact that it starts sans choke with no throttle, would confirm a rich idle mixture. If anything I'd have to screw the pilots in even more, say under one turn out. Further out of spec according to Mr Honda. Don't know how much more I can turn these screws in without starving at idle but I'm betting I could seat them lightly and the bike would still start and idle.

I only use throttle after the bike has started and while still cold, just to keep it from idling at under 800 rpm as I've heard there may be lubrication issues at low revs. Once warm, idle speed rises above 1200 rpm. I find myself tweaking the idle screw near the gas cap to lower revs when hot or increasing them when cold. Definitely not normal.

Either way, I'm still focused on leaning out the mixture in the low and high speed circuits. My sister is coming over from the states in a couple of months and she could bring me smaller jets and even different needles but I need advise as to jet and needle sizes for high altitudes and possible sources to buy them from. Or would it be better to check the needle clip and see if I can lower the needles? Has anyone done this without removing carbs?

Thanks!

maubur said:

If by idle mixture setting you mean pilot screw setting, I wouldn't be so sure it's that much off. Remember, I'm at 8500 ft above sea level and plugs are indicative of a rich mixture. Besides, the fact that it starts sans choke with no throttle, would confirm a rich idle mixture. If anything I'd have to screw the pilots in even more, say under one turn out. Further out of spec according to Mr Honda. Don't know how much more I can turn these screws in without starving at idle but I'm betting I could seat them lightly and the bike would still start and idle.

I only use throttle after the bike has started and while still cold, just to keep it from idling at under 800 rpm as I've heard there may be lubrication issues at low revs. Once warm, idle speed rises above 1200 rpm. I find myself tweaking the idle screw near the gas cap to lower revs when hot or increasing them when cold. Definitely not normal.

Either way, I'm still focused on leaning out the mixture in the low and high speed circuits. My sister is coming over from the states in a couple of months and she could bring me smaller jets and even different needles but I need advise as to jet and needle sizes for high altitudes and possible sources to buy them from. Or would it be better to check the needle clip and see if I can lower the needles? Has anyone done this without removing carbs?

Thanks!

Click to expand...

lol.....can't be done without carb removal..........besides, a jet size change will be your second mistake. You actually need to re-read my prior post. Besides, I live at 5,000ft.elev. and ALL my riding, 30min. in three different directions puts me at or above 10,000ft. elev. Born and raised in the montains of Colo........so this ain't my 'first rodeo' by far.......goes the same for building and tuning high performance cars and bikes, with 50+ years 'under my belt'.

maubur, let me add a bit more CORRECT tuning procedure as far as idle mixture setting. The 'lean drop' method' IS the only correct way of setting idle mixtures BEFORE syncing carbs. First off this all HAS to be done with air cleaner assembly in place as it is normally while riding. Secondly, pick a carb to start with. Back out idle mixture screw a few turns for a start. Then gradually start in with it. When you hear the slightest idle drop, back screw out 1/8th of turn and no more than a 1/4 turn. Then re-adjust idle setting back to 800rpm. Go to next carb and repeat same thing, again re-setting idle speed to 800rpm. Do all four carbs same way, THEN hook up a manometer or four vacuum gauges and sync all four carbs together at 800rpm. Now you understand the use of a fan in front of motor as this all takes time, and don't forgt to shut bike off during tuning when cooling fan comes on so it can cool off a bit. When done setting idle mixtures and syncing carbs, re-set idle speed back to 1100rpm. Your done........go ride and enjoy.

Had you seen this page of the manual?

I doubt you can adjust the mixture screw out enough so the mixture will be so rich you don't need the choke to start. I think you have another problem besides the idle mixture screws being mis-adjusted.

Brant wrote:

, let me add a bit more CORRECT tuning procedure as far as idle mixture setting. The 'lean drop' method' IS the only correct way of setting idle mixtures BEFORE syncing carbs.

Click to expand...

Is this your (modified?) version of the Honda Service Manual's "Pilot Screw Adjustment/Idle Drop Procedure"...? Page 5-12 in mine.
If so, why not sync first, and use 1,200 rpm like the manual calls for? JuST curious...

JAT - would a clogged/dirty air filter, or the carbs' air cut-off valves possibly be Mauricio's issue?

John
via iPad Mini 2

Brant, impressive credentials you got there. Blessed to have you on my side. Somehow I missed much of your first post due to a glitch on my phone. All things aside, I'm sorry to hear of your accident but also glad it didn't go worse.

I hear you and everyone else on the idle drop procedure. I am familiar with the manual. Have had the carbs off at least 10 times. Even when some good soul loaned me the pilot screw tool, I never could get to the inner pilot screws without removing the carbs. I don't own a tachometer sensible enough for this procedure either. I'm ashamed to confess that I set the pilot screws on the bench and later synch by feel, not having the vacuum tool to do the job. Not available here either and I think it's an overkill to import a tool I'll be using once every couple of years at the most. To be continued...

Also, when your bike will idle anywhere from 800 to 1200 rpm, based solely on engine temp, detecting 50rpm drops becomes and exercise of futility. As for rejetting, I only mentioned it because it's all over the web. People rejet for higher altitudes all the time. Your explanation on how the diaphragm and vacuum system in the carbs will compensate for altitude, sounds very logical. However, my fouled plugs, high fuel consumption, and useless choke still point to a rich mixture which has been confirmed by a mandatory yearly exhaust gas analysis done less than six months ago at two different rpm ranges. Somehow, my specific carbs are not compensating for high altitude and this is not only at idle.

John, good to know you're still here for us. I'm not sure I know what the air cutoff valves are but I removed all the pair hardware almost 8yrs ago and the fuel cutoff valve on the right side has been sleeping in my drawer for 13 years now. About two years ago I had a persisting no start problem when hot which after many posts at the old My-MC forum (see Phoenix if interested) was traced to a pinched carb vent hose that went to the cannister. I ended up leaving the carbs venting to the atmosphere and the problem was definitely solved.

I'm also suspecting the air filter may be clogged. However, the bike starts fine and runs great until the plugs foul. I'm not so sure it would be safe to remove the filter for a couple of weeks and see how it runs. I mainly commute to and fro work in slow traffic about a mile each way, no dusty conditions at all. Should I remove it and see if the plugs hold up?


Jim, my choke is useless. The bike usually starts right up without choke. However, if it doesn't start first crank, it won't start at all unless I use the choke. This very seldom happens. And allow me to remind you that my pilot screws are almost all the way in.

Thanks guys and please keep the ideas coming.

maubur said:

I'm also suspecting the air filter may be clogged.

Click to expand...

If the air filter is clogged, light will not pass through the pleats, so hold a lamp inside the filter and see if you can see light coming through. If it is very dim, time to replace the filter.

You mentioned cleaning the filter earlier, so is it OEM or maybe a K&N? Did you oil it? Maybe too much oil has restricted the flow?

If in doubt, replace the air filter, regardless. The air cut valves are clearly shown in the service manual carb components schematic. Item 13 on the online microfiches:
http://www.servicehonda.com/parts/lookup#/Honda/ST1100A_(93)_MOTORCYCLE,_JPN,_VIN#_JH2SC260-PM300001/CARBURETOR_(COMPONENTS)/ST1100-93-JPN-A/2Y14MT3ME1AMT34E2101DE

Edit: pictures here in this article in the AOW by my friend Adam (scroll about half way down):
http://www.st-riders.net/index.php?topic=10249

I haven't looked but there's probably a troubleshooting guide in the manual also...

Yes, I remember your starting problem. What a conundrum that was.

John
via iPad Mini 2

John OoSTerhuis said:

Brant wrote:

Is this your (modified?) version of the Honda Service Manual's "Pilot Screw Adjustment/Idle Drop Procedure"...? Page 5-12 in mine.
If so, why not sync first, and use 1,200 rpm like the manual calls for? JuST curious...

JAT - would a clogged/dirty air filter, or the carbs' air cut-off valves possibly be Mauricio's issue?

John
via iPad Mini 2

Click to expand...

Guess you could call it that John. Never had any inclination of manual use for things as simple as that......only for possible needed torque specs. Would guess 50+yrs. of 'wrenching' on bout anything you can mention,(high performance muscle cars,diesel moters,hydraulic systems, certified welder and metallurgist,air brake systems, hydraulic brake systems,charging and conventionble 12v electrical systems, ect.) and majority of that was certified on has an influence. So, not really caring what manual states, it is ALWAYS idle mixture first before sync, no matter what the bike, or if it is multiple carb auto. I think you understand that fuel/air mixture affects vacuum draw and venturi velocity, therefore, mixture setting first......ALWAYS. The other thing I suggested was setting that idle mixture by listening closely, since majority here don't have a fancy low rpm reading gauge that can be hooked up. Just keeping it simple, and works well if your willing to be a bit particular like me. So again.......and this all comes from a factory trained mechanic on these ole' 1100's........setting idle mixtures and syncing carbs, in order to be correct HAS to be done with ALL air filter components in place, and shut down when cooling fan comes on to reduce additional load on motor which changes fuel/air mixture. Obviously there's something to that, otherwise show me someone else here that gets 54mpg at a constant 80-85mph for some 300+ miles non-stop. Worst I ever got running ALOT of high mountain twisties(10,000+ft. elev.) for a few hundred miles was 46mpg.......and that was pushing the bike really hard...and at times very fast! Sorry, can't argue with success.

Another possibility to consider maubur is the vacuum operated fuel cut-off valve. I don't know the internal workings of them, so this would be a guess. An internal leak combined with a pinhole in diaphram possibly could draw additional fuel through vacuum hose. Like I said, don't know internal configuration of them as to whether that is possible or not,but bypassing around it and temporarily plugging off vacuum hose may give the answer as to whether that be the issue or not. Just throwing out another thought.

Read your post #11........Those idle mixture screws HAVE to be set with bike running!...period. Borrow 4 vacuum gauges for setting carb sync......by ear or sound does NOT work nor even comes close for that matter. After reading that particular post, BOTH those issues as to how you proceeded IS why bike is having the issues you initially described.....OMG!......makes diagnosing way easier hearing what you had previously left out!

Fuel cutoff valve was removed 13 yrs ago (see post #12). The only way I'm going to set the pilot screws with the engine running is by somehow loaning the tool from someone in the states or welding a flexible extension to each screw. I had to dremel a slot on each pilot screw head the last time I was in there just to be able to set them on the bench with a common screwdriver. My (now late) uncle who was an engineer, copied the D tool for me from the loaner I sent him before returning it to its owner. That didn't go well either. The cloned tool never worked.

Regarding carb sync, back when my bike was a heavy smoker I detected a very obvious difference in air draw from one snorkel to the next. I've learned to sync by feel and not so much by ear. When someone sent me a vacuum tool from the US many years ago, the carbs weren't all that out of sync so I must be doing something right with my trusty palm in the snorkel intake method. Maybe many years tuning crappy guitars did yield some finesse? Who knows. You'd be amazed how good this bike runs until it fouls the plugs.

Will check the air filter and give it a blow. It's stock and very old but never really dirty. The Fram equivalent worked for some time but my last attempt, as I said before, was not successful. This may be a clue that I messed up something during that sync (pilots or floats?) which ended up making it rich. Previous gas analysis did not show as rich a mixture which should also be a clue. Well, looks like I'll be digging in the carbs again this weekend.

Brant, please bear with me. I'm out in the woods here as far as ST parts and tech resources are regarded. Only a handful of these bikes in the whole 45 million population country of Colombia. There are two shops that carry the works (dynos, vacuum sync tools, and everything in between). They quoted US$500 to change the fork seals. A pro carb sync will end up being more expensive than bringing a near new replacement set of carbs from the states.

cheers!

Brant said:

...Borrow 4 vacuum gauges for setting carb sync......by ear or sound does NOT work nor even comes close for that matter.

Click to expand...

+1...
Even a slight *touch* on the bolts changes the gauge readings... I work the extra long JIS Philips like a watchmaker with fingertips only...

And a Colourtune plug kit seems a convenient/efficient tool for idle mix setting... easier to work with then the idle-drop procedure (and setting by emission-tester won't do due to bypasses in downpipes and collector box...)

Thanks for the heads up on the colortune gadget! Never heard of that before. Do you have info on the plug size in mm for the ST? So, how exactly does it work? How can I relate flame color to mixture at idle and while synching carbs? Sounds promising.

Never mind. Saw a video on YT. Pretty cool. Still need to set screws while running and not useful to sync.