Carb tuning sequence, AGAIN

[slamonte]

I know this forums has addressed this issue several times; but there has been contradicting info across threads. In setting up the idle circuit is the following the sequence correct for tuning carbs? I'm starting to doubt myself.

1. Bench sync
2. Adjust idle to about 2k
3. vacuum sync to lowest vacuum reading on all carbs
4. adjust each carbs air screw to best idle then back-off 1/8th
5. reduce main idle to 900-1200
6. adjust fuel mixture until carbs read clean

Thanks for your help. I'm having trouble with syncing mine and I want to take the human error out of the equation.

GS1000e, VM carbs, 4 into 1, pods, stage 3 jetting.

[mark]

3. vacuum sync to lowest vacuum reading on all carbs

This is incorrect, you want all your vacuum readings to be equal. The amount of vacuum is not as important as that they are all the same. I have guages and mine pull somewhere around 9 or 10 inches of vacuum just FYI. Remember that changing one carb changes the others as well.

Make sure that any vacuum lines are plugged. Make sure you have a constant fuel source.....don't try to synch them with just the gas in the carbs.......wont work.

You can synch your carbs at about any RPM you want. I usually do mine at about 3000 rpm, just because its closer to the rpm I'm running most of the time. Make sure you use a fan or two to keep things cool.

Your comment, "Adjust fuel mixture until carbs read clean" I don't understand.

[spdjunkie]

Invest in a Motion-Pro mercury manometer (about $40, last time I checked) and just follow the simple instructions. That's most likely your best bet. Look, I'm a very experienced aircraft mechanic, and one thing I've learned over the years is to go with the "KISS" principle wherever possible. That's "keep it simple, stupid" for those unfamiliar with the term. This kit makes things pretty simple. Just hook them up, preferrably with a temorary fuel source (to keep the gas tank out of the way so you can tune the carbs), and get the engine up to operating temp. Once that's done, just balance the #1 & #2 carbs, then the #3 & #4 carbs, then one side to the other. When you're within a half inch of mercury or so, you're getting great results! Make sure to blip the throttle a few times to ensure that they're all coming back to the same point on the scale. If not, simply repeat the proceedure.

Oh, and make sure not to cut the throttle too sharply to avoid getting mercury sucked into the intake! This could potentially damage some engine internals. BAD THING!

The fans(s) are a very good idea to keep things cool since the bike will be sitting still, and not have the benefit of any other source of cooling air over the fins.

[Nessism]

Invest in a Motion-Pro mercury manometer (about $40, last time I checked) and just follow the simple instructions.

Good suggestion except they don't sell them any more.

[slamonte]

Thanks for your suggestions, they are always appreciated. I still need to know the sequence of events for tuning my carbs. Can someone review the sequence I posted and provide feedback.

Thanks

[renobruce]

Bench synch
Adjust side air screws
Vacuum synch

If you can afford it, buy a Carbtune. MUCH more accurate and easy to use over mercury.

Don't forget you also have pilot air screws on those carbs. You need to do some chop tests at minimum throttle to see if they need adjusting. Or you can make your life REAL easy and buy a Colortune to go with your Carbtune.

[slamonte]

Bench synch
Adjust side air screws
Vacuum synch

If you can afford it, buy a Carbtune. MUCH more accurate and easy to use over mercury.

Don't forget you also have pilot air screws on those carbs. You need to do some chop tests at minimum throttle to see if they need adjusting. Or you can make your life REAL easy and buy a Colortune to go with your Carbtune.

Thanks Renobruce! I have a colortune and my #4 carb shows spark but no real explosion. Adjusting the slide screw at the top I can get some combustion but lean. The air screw and fuel mixture seems to have no effect. I originally had this problem on #3 and #4 was fine. For some reason they seemed to switch. I've been pulling my hair out. I have 4 vacuum gauges that I original sync'd on #1.

I've read that I should lower all carbs to the least vacuum reading. Is that your understanding or does it matter as long as they are the same?

They were chemdipped and cleaned thoroughly a couple of months back, then rebuilt. They seemed to work Ok but I hadn't had the equipment or time to sync them until recently. Kinda learning as I go along.

[hampshirehog]

Your colourtune only showing a spark and no explosion in No 4 makes me suspect that you've got a blocked pilot jet. (The small amount of explosion you can see is coming from fuel running through the 'higher part' of the carb circuit) I had the same on a 750 which wouldn't tune in for slow run and I wouldn't let myself consider that the jet could be blocked as the carbs had just been rebuilt meticulously. If I hadn't plugged in the colourtune and just seen the spark I'd still be convincing myself there was something else wrong.

In theory you should set the airscrews first as you are in effect opening or closing another air inlet alongside the slide, and adjusting the slide height and thus open carb bore is what you are balancing on. In practice I don't think it makes a lot of difference.

I always carb balance around the 2k mark but you can check your carbs are closely matched up and down from this by opening and closing the throttle. I've never found anything other than a tiny amount of drift through the lower throttle openings.

Wally

[Steve]

OK, I'll take a stab at answering your question directly. First, we have to assume a couple of things. It appears that you have a Stage 3 jet kit to go with your pods and pipe. Have you verified that they are, in fact, the correct jets? Let's hope they are. In a later post you mentioned syncing the gauges to #1, so I'll assume dial-type gauges. No problem. Sounds like you have the setup OK.

... is the following the sequence correct for tuning carbs?
1. Bench sync Good
2. Adjust idle to about 2k Book calls for 1500-2000, most settle for 1750. I do mine at 1100 idle speed, but check other speeds as well.
3. vacuum sync to lowest vacuum reading on all carbs Lowest vacuum means widest open (less restriction). Might be better to adjust the lowest reading UP to match the others. If you end up opening all the other carbs to match this one, you will not be able to back off the master idle screw to reduce idle speed.
4. adjust each carbs air screw to best idle then back-off 1/8th If you have your fuel screws on the bottom dialed in, adjust the air screws for best idle before syncing, then double-check after, then double-check the sync. It has been a long time since I heard anybody suggesting backing off 1/8. Might be best for emmisions, as long as driveability did not suffer.
5. reduce main idle to 900-1200 If you did the sync at 2000, this is a good idea. Again, I do my sync at 1100.
6. adjust fuel mixture until carbs read clean If you have dialed in your fuel screws for best plug color and your air screws for highest idle, this will already be done.

GS1000e, VM carbs, 4 into 1, pods, stage 3 jetting.

Once that's done, just balance the #1 & #2 carbs, then the #3 & #4 carbs, then one side to the other. When you're within a half inch of mercury or so, you're getting great results!

As mentioned above, the lowest vacuum reading is the throttle that is open the most. If you clese that one down first to match the others, you will retain more idle speed adjustment capability at the main idle speed screw. You say you are an experienced aircraft mechanic. In a horizontaly-opposed 4-cylinder, depending on how the carb linkage is connected, this may be correct. It is certainly correct for 4-cylinder GoldWings. In-line 4-cylinder Suzukis call for a different procedure.


Sequence: With the VM carbs, I raise the lowest vacuum first. With BS (CV) carbs, always start with #3. That is your 'master' carb. The Suzuki manual calls for adjusting #2 to #3, then #1, then #4. If your exhaust has a balance tube between #2 and #3, adjust carbs 1&4 to 1cm higher than 2&3.


.

[BassCliff]

What a bunch of great guys!

Wow. Great info Mr. Steve! Thanks for taking the time to share. I will copy and paste that into my carb sync tips collection.

I also wanted to point out that Mr. bwringer has some carb sync information on his site here: http://www.bwringer.com/gs/carbsync.html

Thank you for your indulgence,

BassCliff

[tconroy]

An interesting find when syncing today !!!

I made these little clear tubes with plugs in the end to put over my brass fittings that you screw into the boots to hook the sync tool lines to so I could warm the bike up and simply pull them off and slide the hoses on from the synchronizer. It makes the setup quicker so i can start syncing and not burn my hands off trying to screw those little brass tubes in the boots.I also made an aux. gas tank out of a weed eater fuel tank that I hang from a tripod.when I hooked the clear tubes up and started the bike I noticed gas started to fill up the ones on #1 and #2. but not #3 and #4. after warm up i put the merc synchronizer hoses on and found out that the ones that had filled halfway with gas were the ones that were off, #1 and #2. It took some time and a pint of gas but I was able to get them synced even all the way across the merc tool at 1750 rpm's like the clymer's manual say's to do. My curiosity got to me so i put the clear tubes with the plugs back on and none of them filled with gas which I guess means that all cylinders are pulling the exact same vacuum and fuel.the bike idles smoother and doesnt drop below 1000 rmp's at 4 way intersections when I throttle up and let off like it use to.there is absolutely no vibration and in 5th gear going 30mph I can roll the throttle wide open with no clattering at all like it use to do.My gas mileage has been dropping lately so I cant wait to see what it will be now.

[KEITH KRAUSE]

I know this forums has addressed this issue several times; but there has been contradicting info across threads. In setting up the idle circuit is the following the sequence correct for tuning carbs? I'm starting to doubt myself.

1. Bench sync
2. Adjust idle to about 2k
3. vacuum sync to lowest vacuum reading on all carbs
4. adjust each carbs air screw to best idle then back-off 1/8th
5. reduce main idle to 900-1200
6. adjust fuel mixture until carbs read clean

Thanks for your help. I'm having trouble with syncing mine and I want to take the human error out of the equation.

GS1000e, VM carbs, 4 into 1, pods, stage 3 jetting.

If you've re-jetted and preparing to road test...
BE SURE the valve clearances are set between .03mm and .08mm, and the ignition timing/advance is spot on.
Initially set the pilot fuel screws about 1 1/2 turns out.
Set the side air screws out 1 3/4.
Bench synch as best you can and be sure to set the idle adjuster knob high enough to allow the bike to start.
REMOVE the two floatbowl vent lines, leave the vent ports open.
Warm up bike fully and adjust idle closer to factory recommended 1,000 rpm's if the idle is too high upon initial start up/warming up.
Once fully warmed up, set idle to 1,000 with the idle adjuster knob and set the air screws using the highest rpm method.
Allow the bike to cool down some, not completely, in case you are slow to vacuum synch (to avoid over-heating).
Now hook up vacuum tool and vacuum synch.
Note the initial levels. It's much easier/quicker to adjust the higher level(s) down to meet the lower levels you initially see.
I synch at approx' 3,000/3,500 rpm's.
Get them close as possible, but if the difference is no more than about 3/4" from the highest to the lowest, you're good.
Always SLOWLY exercise the throttle a few times (to avoid sucking up mercury) and double check that the levels remain as you wanted.
Now road test the jetting, minimal throttle for the pilot circuit, 1/3 to 1/2 for the jet needle, and full throttle for the mains.
Once it's jetted well, try some more advance timing to get the most power. Many times another 5 degrees or so will improve performance WITHOUT creating pre-ignition (pinging). This can help you fine tune the jetting and get the most out of your bike.
Just curious, what jetting have you chosen? Jet needle position, main jet, pilot jet.

[slamonte]

Thanks Keith for reply to my post. I just wrote a long response and was knocked off the site prior to completion. Anyhow I have two sets of carbs. The original set I rebuilt (chem-dip, air pressure, new o'rings and gasket, hex nuts, etc.) They have the following items installed:

117.5 main jet
5DL36 jet needle in position 3 of 5
15 pilot jet

I have an unknown (not cleaned by me or tested) set of carbs that has:

122.5 main jets
5DL36 jet needle in position 3 of 5
17.5 pilot jet

The Pods are 3rd party (K&N look alikes)
The 4 to 1 pipes are not marked so I don't know manufacture.

I was getting ready to put the 122.5 main & 17.5 pilot into my original cleaned carbs. I was also going to set the jet needle to position 5 (raise the needle). Re bench sync, adjust air screw to highest RPM, vacuum sync and then take readings.

I also have new intake boots (the kaw ones with the vacuum valves).

Any and all help is greatly appreciated. My son and I took this on as a bonding project and we are learning a lot.

[slamonte]

I forgot to mention that this is a 1979 1000E

The valves were very tight (less than .03mm). I have adjusted them to within factory tolerances (.03mm - .08mm)

[KEITH KRAUSE]

Hi. Off to work and will have to help later if needed.
You sound familiar. Was I helping you at another time?
Needle in position 5 sounds good. I think a 122.5 main is a little small, based on previous experience. Something closer to 127.5, possibly 130 is usually better. Talk later.