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carb syncing problems

  • Thread starter Thread starter newbie851519
  • Start date Start date
N

newbie851519

Guest
I've been trying to tune this thing up to get it on the road in the next couple days for a 2200 mile trip. i set valve clearances, cleaned the airbox, etc..now i'm trying to do my first carb sync. the float heights were way off, but now they're set right. it's pretty clean inside, and the jets that I can get at are clear. here's the problem:
i can't seem to be able to turn the idle mixture screws to set proper idle mixture. #1 and #4 turn fine, and I set them at 2.5 turns out, where the idle sounds the best. #2 and #3 will not turn at all - it looks like the PO had stripped the heads on them pretty well. I've soaked them in liquid wrench overnight, with no success.
The current readings are:
#1: 40 cm Hg
#2: 11 cm Hg
#3: 9 cm Hg
#4: 17 cm Hg

Per my understanding (from bwringer's carb sync tutorial), #3 is supposed to be drawing about 25.5 cm Hg. Since I cannot turn the idle mixture screw on #3, how should I proceed?
I don't have the time before the trip to drill out the idle mixture screws and replace them. Should I set them all by #3 even though it isn't drawing enough? Will that make all of the cylinders rich?
Thanks for the help, as always.
 
I believe you have to turn the adjusting screw that controls the actual butterfly valve. Correct me if I am wrong but there are 3 or 4 small screws with lock nuts that you can turn to change the actual position of the butterfly valves
 
yea, you turn those to sync up the carbs, but you're supposed to set the correct idle mixture first, using the idle mixture screws...if you can get them to turn at all.
i played around with the #1 carb throttle screw (with the locknut) since it was way out of sync, but no matter how much i turned it, it didn't adjust the vacuum. any thoughts on this and the stuck idle screws?
 
Nick, if you're talking about the 4 brass screws just forward of each carb before the rubber boot. Yes, they need to be adjusted before you atempt to sync. Each screw should be adjusted to achieve the "best rpm" If you have a digital tach that you can install, that would be best. Otherwise you just have to use your ear & the bikes tach. That would be adequate.

If you cannot adjust any of these, you're screwed. Literally. It is essential to adjust this setting BEFORE attempting a carb sync. Trust me. You just won't get it right, and you'll be forever frustrated. Yes, it sounds like you may have to drill them out & replace. Not an encouraging comment, I know. But I speak from experience. On my '80 GS1100, I also had two screws so badly corroded they wouldn't turn. I took the bike to a local shop for the drill out. They did it while I waited.

Once you get over this hurdle, you can try the sync. On your bike you can only adjust #1, 2, and 4. Number 3 has no adjustment. Is this correct? Just checking to make sure I give you good advice. Some models are different. What type of sync gage are you using? Mercury stick? Dial gages? I like the dial gages because I don't have to worry about sucking mercury into my motor. The gages each need to be "calibrated" to a single cylinder, usually #1, before you attempt to sync the carbs.

Once you are ready to sync, I would not worry about an actual value on the gage. Instead, look for a pattern. With #1 & #4 equal, but higher than #2 & #3, which should be equal but a little lower.

If using a sync stick the pattern should look like this:

1....2....3....4
_..............._
_...._...._...._
_...._...._...._
_...._...._...._

I hope some of this advice helps. Good luck with the project & the trip!
 
thanks for the advice. i'll order the two screws and have them ready for me when I get home, where I can have the local shop drill out the stuck ones. i hope it'll be alright to ride it home. :-s
once i get there i can get all this in order, along with a few other repairs needed. you're advice was right for me, i'm using mercury sticks and i can adjust 1,2, and 4. #3 is not adjustable. and yes i was talking about the 4 brass screws just behind the intake boots.
if i am using mercury sticks, do i still need to calibrate them to one cylinder?
I'll pack up the mercury sticks and take 'em with me, it'll have to work for now, it runs decent anyway. [-o<
your advice helps a lot.
thanks.
 
NO, you do not calibrate mercury stix. Its not possible. :-) #3 cylinder is the control cylinder. All cylinders are to be matched to number 3.

E.


newbie851519 said:
thanks for the advice. i'll order the two screws and have them ready for me when I get home, where I can have the local shop drill out the stuck ones. i hope it'll be alright to ride it home. :-s
once i get there i can get all this in order, along with a few other repairs needed. you're advice was right for me, i'm using mercury sticks and i can adjust 1,2, and 4. #3 is not adjustable. and yes i was talking about the 4 brass screws just behind the intake boots.
if i am using mercury sticks, do i still need to calibrate them to one cylinder?
I'll pack up the mercury sticks and take 'em with me, it'll have to work for now, it runs decent anyway. [-o<
your advice helps a lot.
thanks.
Click to expand...
 
By the way Nick. Looking at the readings in your first post, #1 is clearly too high. If you adjust that one carb down, the others should come up. You may be able to achieve a good balance, in the pattern I have indicated, just but setting #1. Some fine tuning may be required.
 
With reading that different, it may be difficult to do a good mixture setting by speed.

I like to set the mixture, set the sync, re-check the mixture and re-check the sync.

Once you have the gauges hooked up, it only takes a couple extra minutes.


.
 
earlfor said:
NO, you do not calibrate mercury stix. Its not possible. :-) #3 cylinder is the control cylinder. All cylinders are to be matched to number 3.

E.
Click to expand...

I am having simular problems...do number #3 is the control cylinder, so depending on what I get on my Mercury stix I should set the other three simular, correct...I notice TOM MLC says to make the others higher and the two inter slightly lower which is :confused:

You would not happen to know where the fuel mixture screws are located on a 82 GS1100EZ (12 valve motor) would you? as these need to be adjust first for best idle after setting idle to approx 1700 rpms then, sync carbs, reset idle speed, reset idle mixture, Re-Sync Carbs, idle speed then idle mixture, correct? Right now it has not bottom end and runs bad until I get above 3500 rpms...I don't mean to hi-jack this thread but I posted one this evening and seems everyone is out of town 8-[ or something :)

Orginal post here: http://www.thegsresources.com/_forum/showthread.php?t=109391

Ken
 
From what I understand, with factory airbox and exhaust the inner two cylinders will have slightly less vacuum. With pods and aftermarket exhaust, it should be equal across the gauges.

I was a little :confused: myself before it was explained to me.
 
txironhead said:
From what I understand, with factory airbox and exhaust the inner two cylinders will have slightly less vacuum. With pods and aftermarket exhaust, it should be equal across the gauges.

I was a little :confused: myself before it was explained to me.
Click to expand...

My bike is stock except for a foam air filter in the stock air box...going to keep it stock too.

So translating this to a merury stik what are we looking at?

Thanks,
Ken
 
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