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81 GS850GLX carb sync

  • Thread starter Thread starter DaveDanger
  • Start date Start date
D

DaveDanger

Guest
Alright guys, this seems to me to be a no-brainer, but lemme embarrass myself anyhow. I've dipped/cleaned/rebuilt my carb-set with no parts replacement other than seals and gaskets and have them back on the bike. I replaced all the intake o-rings and repaired all the seals in the airbox when I reinstalled it. It cranks instantly without choke and accelerates like a raped ape, but tends to shudder and pop when idling, it obviously needs to be sync'd at least to begin with. It may need more than that, but I have to start somewhere. I simply can't afford at this point to spring for a carb-tune? or any other decent brand of manometer to enable me to sync all 4 carbs at once. My question is... can I do a reasonably accurate job of syncronizing my carbs with a single vacuum gauge? I know it'd require having to jump back and forth from one carb to the next repeatedly, till they all match readings, but is this worth even atempting? I do have a very accurate large face vacuum gauge with a good flexible hose and I can easily fabricate the 5 mm port taps to slip the hoses over. I simply don't want to keep putting off riding the bike on the road because of badly sync'd carbs, but on the other side of the coin... I don't want to damage anything from running a too lean or too rich mismatched mixture.
 
One problem with that plan is that with CV carbs, you're synchronizing pairs of carbs, not one at a time. Each adjustment affects two carbs, and even has a smaller effect on the other two. And those furshlugginer adjustments are soooo incredibly sensitive...

I'm not saying it couldn't be done, but it would be very tedious. You're going to go back and forth a lot, so you'd definitely need some way of switching between the carbs that's much faster than removing and replacing vacuum lines. Maybe some sort of fish tank manifold valve?

Leaving the bike running for a long period while you're juggling hoses could lead to overheating. I like to sync above idle, about 2,000 rpm, and I have to work quickly and watch for overheating even with a full set of mercury gauges.
 
Ya threw me a curve there bwringer... I wasn't aware that I was doing a pair of carbs at the same time, I'll have to research that a bit. I did know that my adjustments would affect the other carbs as I went, and that I'd have to check them repeatedly, and that it would be very tedious. I had also thought of the idea of small t-valves in my hose connections. Also have a fairly large "squirrel-cage" fan that was originally mounted in an industrial air conditioning system that I could easily perch directly in front of the bike and have blowing cooling air towards the engine (and the exhaust out the back of the shop at the same time). Unless someone else posts in and tells me that I'm really wasting my time, I think I'll at least attempt this one day this week. Be alert for a post on my adventures :)
 
you could cheaply make a set using four vacuum gauges, just put restrictors of some type in the hoses so the needles don't bounce very much. its not the best way, but it works.

you can get them passably close by bench synching them , I used an itty bitty drill bit shaft, made for drilling R/C car shock pistons. use something like that to set the butterflies to where they are all at the same position, and it should be good enough to get an idle.

I noticed a world of difference after a valve adjustment and a carb synch using mercury sticks. rock solid idle and virtually no "buzz" in the pegs and bars. that after a suzuki trained tech looked at em with gauges and said they were fine lol. I guess he just didnt wanna mess with it.
 
carb synch

carb synch

You can make your own manometer. See http://www.powerchutes.com/manometer.asp

I haven't tried this myself, but will do it soon. Note that the model illustrated is for a two cylinder engine, but extending it to a 4 cylinder engine should be easy. The instructions for using the Suzuki synchronizers call for calibrating/zeroing them before use, so I think that it would be good to check each of the four parallel manometers on the same cylinder at the beginning to be sure that they all give the same reading.

Also, some bench work should be done prior to vacuum synchronization. See the Sudos tuning guide for Mikuni carbs, available at
http://www.sudco.com/

Tom
 
hey dave: do it the easy way:

plug your mightyvac (thats the vacuum gauge i have, also known as the swedish pen!s enlarger pump) into the vacuum nipples on your diaphragm caps (if you have slingshot carbs, dunno about stock) one at a time.
you can stop the needle from bouncing by pinching the hose.

from your desription though you need more than a synch....

being able to start it without a choke tells me you're way too rich on either the pilot or the fuel/air screws.

shudder is vague, but if you're talking pop, and if its when you close the throttle it means you're lean on the needle jets...

but what do i know, im stoned on fuel vapors, just spent the last 2 hours in the basement fixing my !@##@ carbs....
 
gsbert, I may well need more than a synch. I never considered that fuel mixture maybe being off because of starting with no choke... I was hoping that it means I'm spot on that adjustment.... considering the weather here where I am. It's only today that it's even beginning to feel cool in the early morning down here. We're still pushing 80's and 90's in the daytime here. I suspect that if it were to cool down some, I'd prolly need a tad of choke to start. "Pop" is prolly more accurate than "shudder" in describing my idle and very low RPM. Once It's above about 1600 rpm, it's the smoothest running thing I've been on in years. Below that, it does pop and "bust up" a bit instead of a smooth idle. If I try to ease out the clutch and roll away smoothly from a dead stop, the bike bucks like a horse with a hornet embedded in its rump. I have to sort of quick-blip the throttle up beyond that rough zone and then begin to ease the clutch out to begin rolling. Once I'm beyond that rough low end, it accelerates away like a heat-seeking moisture missile! I do NOT know the best specific steps to go through to set up these carbs. When I went through them in the clean and rebuild, I simply noted exactly where all screws, needles, orifice tubes, etc came from, laid them all out in order. Then cleaned all the carb bodies using a Methyl Ethyl Ketone dunk-bucket, probing all the tiny openings with a wire cut from a stainless wire brush, blowing out with forced air afterwards. I then reassembled all parts exactly back where they were with new o-rings and seals where needed and then set my float levels per M/M specs. I have done nothing else to them in the way of adjustments. I'm just thinking that a synch can't harm things, but like you say I may have other adjustments due first. Working on the assumption that things are prolly out of adjustment all the way through my carb-set... what are the exact steps (and in correct order) I should go through from start to finish to set these carbs up correctly? Is there a website reference I can follow, or a manual that I can use to tell me this info, step-by-step? The reference here on the GS site is great as far as it goes, for disassembly and cleaning, but it doesn't go into any detail on the exact setup of a carb-set from scratch. Is there something like that available?
 
start by making sure your float heights are correct.
then adjsut your idle screws with the highest rpm method, i can explain if you want, just ask...
then do a carb sycnh.

let me know if the problem persists, and we'll take it from there...
 
gsbert, the floats are set correctly. I did have someone give me the manual specs when I reassembled the carbs, so I got that right to start with. As for idle, are we talking the idle screw for the entire rack of carbs? or setting idle at individual carbs somehow? As for sync'ing, I have another post going here about trying to sync with a single vacuum gauge.
 
i told you a bit higher up how i synch with a single vacuum gauge, you might get more info in the other post, so im sure youll be able to do that...

no im not talking abotu the master idle knob... im talking about the idle screws/idle jets/mixture screws in the carbs...

normally those screws are covered at the factory so the end user doesnt play with them, but things beign what they are, people do.

in any case, you have some vertical screws near the bowls with some sort of needle taper a spring, a couple of washers and an o-ring to them...
there is one per carb. they might be air or fuel screws, but are adjusted the same way (near the airfilter side its an air screw, near the engine side its a fuel screw)
(im currently manufacturing extensions for my screws so i can turn them while the engine is running)

if your carbs have not been synched, set them up so all the butterflies are closed, use the synch screws on the butterflies so they all close and start to open at exactly the same time (visually, you'll fine tune it with the vacuum later if necessary)

here's how to adjust them (engine on and warmed up):
- adjust your master idle to 1000 rpm
- adjust carb 1 screw 1/4 turn at a time in one direction or another.
- the engine will either accelerate a bit or decelerate.
- you're looking to turn in the direction where the engine accelerates
- keep turnign 1/4 turn at a time until the engine decelerates, then back up 1/4 turn
- reset your idle to 1000 rpm with the master knob
- repeat for each other carb.

you should now have a rock steady 1000 rpm idle and perfect idle mixture, with no sputters of any kind.

you should also not be able to start the bike without the choke when the cylinder walls are cold, as the fuel droplets will just stick to them and not allow for combustion. (the choke enrichens the mixture until the cylinders warm up sufficiently).

hope this was useful
 
Thanks gsbert! Sounds like exactly what I need.... a specific set of steps to go through, and a specific goal that each step should accomplish. It may be a few days before I have the opportunity to begin... work has picked up dramatically, and as I'm self-employed... I have to make hay while the sun shines :).
 
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