Fine tuning Carbs and Idle after installing a new/used set.

[John OoSTerhuis]

Huh? The meter only displays two digits? So what does 1,200 rpm look like on the meter's display? And 1,150 rpm?

I'm having a hard time visualizing the fluctuations you mention. I suspect having the air cleaner lid off would make the actual idle unstable. Looking at the Honda Service Manual I'm sure the procedure should be done with the air cleaner buttoned up. Adam...?

Was the meter set on 2, 4, or 8 cylinders? Each spark plug fires twice during the four stroke cycle (4 cylinders, 2 coils - 1 wasted spark/cyl/cycle).

This doesn't sound like a very accurate measurement...

John

 

[Bush]

The display will give you 2 digits.X 100,so 57 is 570 rpm.

Seems the basic math here is faulty. 57 X 100 = 5,700

 

[mznyc]

Huh? The meter only displays two digits? So what does 1,200 rpm look like on the meter's display? And 1,150 rpm?

I'm having a hard time visualizing the fluctuations you mention. I suspect having the air cleaner lid off would make the actual idle unstable. Looking at the Honda Service Manual I'm sure the procedure should be done with the air cleaner buttoned up. Adam...?

Was the meter set on 2, 4, or 8 cylinders? Each spark plug fires twice during the four stroke cycle (4 cylinders, 2 coils - 1 wasted spark/cyl/cycle).

This doesn't sound like a very accurate measurement...
I'll look at DMM settings may have hit a view setting by accident

John

It is a 4 cyl engine isn't it? Set at 4 cyl.
I'll see if I can get a pic or video.
I'll look at DMM settings may have hit a view setting by accident
Like I warned first time I did this so learning and as suggested several members have done the procedure multiple times so may have more info,...
Bike's running smoothly and holding idle steady.

Seems the basic math here is faulty. 57 X 100 = 5,700

5.7

 

[Don B]

OK, if I read the unit's manual correctly
http://manuals.harborfreight.com/manuals/95000-95999/95670.pdf
the 50 rpm drop will be shown during the idle drop procedure when the meter reading drops from 120 to 115. IOW, it reads in increments of 10 rpm. I'm very interested in the accuracy of the unit in actual use.



I wonder if the ST1100's wasted spark needs to be adjusted for...?

John

John, the answer to your last question is on page 13 in the manual. Multiply the meter reading by 20 to obtain the actual engine rpm (Compare step 4 in the lh column to step 3 in the rh column.). It stands to reason that the wasted spark is going to affect the meter response, as compared to the older automotive ignitions using a single coil and distributor. Note that in the latter case, the meter reading is multiplied by 40 for a 4-cylinder engine.

 

[John OoSTerhuis]

I saw page 13, Don. Wasn't sure it applied. Plus Michael didn't indicate that was the method he used. Still waiting for an answer to my question: what were the actual meter readings that he saw/used to do the idle drop procedure on his ST1100...

John

 

[John OoSTerhuis]

Hmmm...

If the drill is to multiply the meter reading by 20, then 1,200 rpm would read as 600 and the 50 rpm drop to 1,150 that the idle drop procedure calls for would be 575. However, Michael seems to say the meter displays ONLY TWO DIGITS in tach mode (NOT so described in the manual!). If so... then 6.0 = 1,200 rpm, and 5.7 = 1,140 rpm; increments of 20 rpm, versus the 10 rpm indicated on page 12.

Have I got the idea now, Michael? Sorry, the numbers you used in your example in an earlier post make sense now.

I don't think I'd be happy with this meter's accuracy. Adam, how does one of the expensive meters like a Fluke display the rpm reading? And did you experience fluctuations like Michael? TIA

John

 

[mznyc]

Ok.Lots of conflicting info here.I was wrong on the 100x on the reading,it's 10x on the front of the meter,20x in the instructions that Don pointed out,and checked the x20 and seems to be correct.Still looking into it,...
I also spoke to a tech at ES Products and he said these,http://www.esitest.com/328.html , read in increments of 1rpm,(not confirmed be me) can be had on Amazon for $54 and local NAPA has them on sale for same price,...

 

[afrymoyer]

Hey John... Sorry for the delay in response. I don't spend much time over here.... I occasionally have a look from time-to-time and try to help when I can. Usually by PM....

I always synch and idle drop with the air cleaner assy off and as much STuff out of the way. Gives me better access to everything. I once overheard that one MUST perform synch's, drops, settings, etc, with everything installed or the readings will be inaccurate. This may be so with another application, but not with the ST. Because of this, I've tried it both ways and found that it makes NO difference. We're not measuring air flow, but vacuum from a port that is under the carb and throttle plate, AND at idle. Remember that this can only be done with a freshly tuned engine(plugs, filters, oil, valve clearance, etc). Personally I use a carb stick / manometer. Others are starting to use those air flow meter things you stick into the rubber snorkel to synch. Never tried one, but curious about it's accuracy vs. a manometer....

As you know, I've been working with Tom on the AOW. I will be doing (hopefully a video) a ST carb synchronization and Idle Drop procedure. Don't hold your breath as to when it will be completed, but probably by spring time. I'm not taking in any more carb work, till I get my own Fall / Winter stuff done.

I brought home my shop multi-meter and took some pictures for you on how it works. It reads down to "1" rpm. It reads ACTUAL engine rpm. I even hooked it up to the ST on #1 cyl. and ran the engine for you! With this OTC meter, I have to put the setting on "2-stroke" to get the proper rpm reading (wasted spark thingy), or I get twice the rpm reading on 4-stroke.

I also took some pix of my idle mixture screw tool along with the piece of "custom" coat hanger, that I use to help manipulate the tool into the screws (can be tricky).

 

[John OoSTerhuis]

Thanks, Michael and Adam.

Adam, I have always used merc sticks but have done a comparo with the SK flowmeter and Motion Pro's new blue fluid manometer with individual reservoirs. Much prefer the merc sticks. However, I do now have a STOC loaner SK meter for those that want to use one.

John

 

[mznyc]

OK.Until we can prove the HB tester can work with the conflicting info,I figured I would try the ES 328 plus.$54 on Amazon and got it in about 36 hrs with Prime.
Can't get to my garage till Tuesday but checked the Guzzi and it seems to be accuate.4 characters, reading in the 1000ths.But has to be set at 4stroke/1 cylinder to get correct reading, apparently because of the wasted spark and referenced in their instructions ,won't know how that will work on the ST until I can get it hooked up,but assume playing with the settings I should find one that will give me an accurate reading.I also want to check CO level at the exhaust with a sniffer,yes it won't be accurate after midpipe,but just want to get a reference after I believe I have correct settings in the ID procedure.What has anyone who has taken a reading shoot for ? On my Ducati we shoot for 4.5% as a target +/- with a good running engine.

 

[afrymoyer]

Could be tricky with no known factory baseline specifications. I would estimate that it may be around 3-3.5%. Remember that the the exhaust is a 4-into-2, into-1, into-2 design. Also consider the PAIR system will really "dry out" the readings. You would have to pinch / block off the vacuum supply to the PAIR system before considering an estimated C0 reading.... I'm very curious to see what readings you get. This is why we have to look at engine rpm and manifold vacuum for tuning on the ST.

 

[mznyc]

Thanks Adam,but you may have missed my previous post.
PAIR system is removed and I understand the mixing of gasses at the back end doesn't give you an accurate reading as taking it off the cylinder or header,(my Ducati has a port on the headers),just interested what a good baseline CO% would be after getting what I believe to be correct ID done.Pretty easy to do later on if curious,stick probe in can,read meter.No removal of plastic.That way you would know if your if your mixture has changed.Not that you adjust your mixture on a regular basis but looking for that reference for the future.I'll post my results,...
Definitely the benefit of FI bikes.You can adjust idle trim via the software.Open a window in the program,hit +/- on idle trimmer till you get correct CO reading.Still have to balance TB's,Idle and airbleed screws,but a lot easier than trying to get a tiny heading specialty tool on a tiny odd shaped head screw that you cannot see.

 

[ST1100Y]

Remember that the the exhaust is a 4-into-2, into-1, into-2 design.

Far worse, the downpipes are already connected by a "compensation line" right underneath the exhaust ports on the heads, covered by the heat-shields...

As for CO readings, I recently had both STs at the MOT (but can't tell if the tech just wrote down fantasy-numbers):

'94, 195Tkm/120Kmiles, PAIR removed and lines blocked:
CO: 0,6%
HC: 510ppm

'00, 90Tkm/65Kmiles, PAIR installed and working:
CO: 0,37%
HC: 588ppm
(both at ~1200rpm)


The tech claimed that in his opinion both engines are set too lean...
Well, both carbs are in OEM setup, idle already set a tat richer as they come from the factory...

 

[mznyc]

*** UPDATE***!!
OK ID done.
I couldn't get a consistent reading on the ES on two of the cylinders.Used 4cylcle/2cylinder setting. Would jump around ,exp;1200ish to 995ish to 800ish.I knew the bike wasn't fluctuating that much in the RPM range as I always looked at the bikes tach as a reference and just tell by the sound if it goes up or down a 100prms.When it would show a number that I knew was close,which I believed to be accurate I would use that for reference ,when it cycled through again in that range I would see if that number changed and use it as a reference as to whether to adjust pilot screw.I am thinking the fluctuation to the probe and not the tester.Kinda cheap looking.I think a more robust clamp and cable couldn't hurt.Mystery is that the Guzzi would show a consistent reading.Maybe a difference in the electrical systems between the bikes.
The good news is that I had the bike out for about a 20-30 mile test ride.Ran like a BRAND NEW BIKE! No popping or backfired.Tried snapping the throttle on and off in different gears and rpms and couldn't get it to hiccup once.I'll get a couple hundred mile test on it this week and report how she does but with fingers crossed think she is back to life.
Thanks again to Adam for his great write up and help.And all the other members who offered advice and positive input.Much appreciated.
I'll post some pics this week,...

 

[mznyc]

***UPDATE***!!
Getting an inconsistent idle and some popping and backfiring.Pulled the bank several times looking for something obvious and finally pulled bowl covers.Floats were set to about 10mm,should have been 7mm.Reset,re-calibrated carbs and VOILA! Idle is holding steady and no popping or backfires.Idle mix screws set to 2 turns out with #40 pilot jets.Once I get a tach reader that I can trust I'll do an Idle Drop,but for now she's running as she should,once I get a few hundred miles on her I'll report back.Thanks again to all who offered help,especially afrymoyer who took the time to talk me through it and to write up the carb overhaul document.

 

[Brant]

Glad to hear you got it back 'happy' again......and yes, fuel levels ARE the most critical deciding factor for ALL sidedraft/downdraft 'scoot' carbs. It affects mixture settings, right on up through WOT. Regularly gets overlooked, or 'that's close enough' does NOT work if one expects to get all four carbs feeding cyls. equally. Those floats take away ALOT of volume of fuel in bowls, and I found from experimentation on the Mikunis on my other listed bike, 1mm of static float level settings equals 3mm of fuel level change.....That's a BUNCH folks, and has DRASTIC effects on tuning AND running of motor.....correctly. I've seen many a forum member(other listed bike forum) 'chase their tale' in 'denial' that being the issue . Unfortunately, the spring loaded float needles, having a varience in spring load pressures cause varying RUNNING fuel levels. Impoossible to know for sure with the Kiehns being buried on these bikes, but if not too drastic, is unknowingly compensated with idle mixture settings.

 

[ST1100Y]

...1mm of static float level settings equals 3mm of fuel level change...

Which reminds me to give some attention to the carbs of the old '94, which idle starts to flicker with an occasional silent "blob" emitted while on the side-stand... can't be off by much then...

But glad that the OP has a smooth running ST again.

 

[afrymoyer]

Glad to hear you got it back 'happy' again......and yes, fuel levels ARE the most critical deciding factor for ALL sidedraft/downdraft 'scoot' carbs. It affects mixture settings, right on up through WOT. Regularly gets overlooked, or 'that's close enough' does NOT work if one expects to get all four carbs feeding cyls. equally. Those floats take away ALOT of volume of fuel in bowls, and I found from experimentation on the Mikunis on my other listed bike, 1mm of static float level settings equals 3mm of fuel level change.....That's a BUNCH folks, and has DRASTIC effects on tuning AND running of motor.....correctly. I've seen many a forum member(other listed bike forum) 'chase their tale' in 'denial' that being the issue . Unfortunately, the spring loaded float needles, having a varience in spring load pressures cause varying RUNNING fuel levels. Impoossible to know for sure with the Kiehns being buried on these bikes, but if not too drastic, is unknowingly compensated with idle mixture settings.

Float needle springs have no effect on fuel level. Once the level is set correctly and the needle is seated, fuel is no longer allowed into the bowl. Closed is closed. The springs in a float needle are purposed to eliminate float needle bounce and prevent the needle tip from pounding the seat (hence the rubber tip also). If the spring wasn?t there to absorb road shock, the bowl could potentially overfill from a bouncing needle. If everything is in good working order and level is set properly, variance in spring pressure?s means nothing to drivability?.

 

[Brant]

Float needle springs have no effect on fuel level. Once the level is set correctly and the needle is seated, fuel is no longer allowed into the bowl. Closed is closed. The springs in a float needle are purposed to eliminate float needle bounce and prevent the needle tip from pounding the seat (hence the rubber tip also). If the spring wasn?t there to absorb road shock, the bowl could potentially overfill from a bouncing needle. If everything is in good working order and level is set properly, variance in spring pressure?s means nothing to drivability?.

Sorry....I've proved otherwise, many a time. True, that IS the tiny springs function, but also has an unwanted effect. Trust me, the viton on the needle ends do NOT seat and seal identically, resulting in a tiny bit more fuel pressure against float raising the level ever so slightly. With that, your referance AND mine is to STATIC fuel levels, not static float settings. The SAME thing takes place while running, fuel being used is relative to fuel flow back in carb bowl to keep that level constant. The problen is, fuel load pressure up against float and the slight varience of each of those tiny springs STILL cause a slight varience of RUNNING fuel levels.Not that that would cause any noticable difference associated with the Kiehns, but if DOES in fact exist.
BTW, not here to argue bout it, just stating a known fact, to which there IS no argument anyways. A basic mechanical and hydraulics function taking place.Considering testing it yourself before throwing out mis-leading 'urban myths', would IMO be the better option.

 

[afrymoyer]

^^^ NO....