sync problems!

[KEITH KRAUSE]

So My gas tank with a long fuel line will be fine?

Also what do the increments on the carb synce gauge mean?My book say's to set the outside carbs 2 1/2 to 3 cfm's higher than the middle.Are the numbers on the stick that start at 2- 4- 6 and so on marked in cfm?In other word's if # 3 reads 10 should I set the outside carbs at 12.5 to 13 on the gauge?It is stock exhaust.

Gas tank with a long fuel line is fine. Avoid big dips/loops in the line.
Most gauges use lines marked in centimeters. Most tuners agree you should get the levels to within 2cm of each other (2cm difference from the highest to lowest level). If you can do better, fine, but don't drive yourself crazy with it.
I don't know what tool you're using but I'd assume the "2,4,6" you mentioned are lines measured in cm, roughly 3/4" apart. Sounds like you are correct about how to set your levels for your stock exhaust, adding 2 1/2 to 3cm to what your middle levels are.

[earlfor]

When I do a synch using a long fuel line on the gas tank, I measure the distance from the bottom edge of the gas tank to the floor when the bike is on the centerstand. I then remove the gas tank and put it on a stool/bench or whatever at that same height. It may not make any actual difference that the fuel head is the exact same height as it would be if on the bike, but it makes me feel better. :-) Be sure to plug the vacuum nipple on the #3 carb when synching and running on the petcock prime setting. I just stick a piece of clear vinyl tubing over the #3 nipple and stick a pencil in the end to plug it. :-)

E.

Gas tank with a long fuel line is fine. Avoid big dips/loops in the line.
Most gauges use lines marked in centimeters. Most tuners agree you should get the levels to within 2cm of each other (2cm difference from the highest to lowest level). If you can do better, fine, but don't drive yourself crazy with it.
I don't know what tool you're using but I'd assume the "2,4,6" you mentioned are lines measured in cm, roughly 3/4" apart. Sounds like you are correct about how to set your levels for your stock exhaust, adding 2 1/2 to 3cm to what your middle levels are.

[tconroy]

Gas tank with a long fuel line is fine. Avoid big dips/loops in the line.
Most gauges use lines marked in centimeters. Most tuners agree you should get the levels to within 2cm of each other (2cm difference from the highest to lowest level). If you can do better, fine, but don't drive yourself crazy with it.
I don't know what tool you're using but I'd assume the "2,4,6" you mentioned are lines measured in cm, roughly 3/4" apart. Sounds like you are correct about how to set your levels for your stock exhaust, adding 2 1/2 to 3cm to what your middle levels are.

Your right Keith.This is just a mercury gauge with cm's marked 3/4" apart.2 cm's= 3/4"s. Thanks guy's for all the help.

[tconroy]

When I do a synch using a long fuel line on the gas tank, I measure the distance from the bottom edge of the gas tank to the floor when the bike is on the centerstand. I then remove the gas tank and put it on a stool/bench or whatever at that same height. It may not make any actual difference that the fuel head is the exact same height as it would be if on the bike, but it makes me feel better. :-) Be sure to plug the vacuum nipple on the #3 carb when synching and running on the petcock prime setting. I just stick a piece of clear vinyl tubing over the #3 nipple and stick a pencil in the end to plug it. :-)

E.

What do you mean the vacumn nipple on #3? I thought all you blocked was the vacumn line on #2,the one that goes to the tank.

[earlfor]

The vacuum line on the carb that is normally connected to the petcock is blocked off at the carb.

E.

What do you mean the vacumn nipple on #3? I thought all you blocked was the vacumn line on #2,the one that goes to the tank.

[ddominik]

So what is the recommended cm HG setting for a 77 GS750

I have just finished rebulding the carbs on my 77 GS750 and am ready to vacuum sync the carbs. ..... but my shop manual refers to a OEM Sukuki vacuum gage.

Question - what is the recommended cm HG setting? 12? 14?

I will be using a Carbtune Pro. Anyone else use a Carbtune Pro?

Comments/Suggestions?

Thanks

Dom

[t3rmin]

I have just finished rebulding the carbs on my 77 GS750 and am ready to vacuum sync the carbs. ..... but my shop manual refers to a OEM Sukuki vacuum gage.

Question - what is the recommended cm HG setting? 12? 14?

I will be using a Carbtune Pro. Anyone else use a Carbtune Pro?

Comments/Suggestions?

Thanks

Dom

There is no recommended vacuum setting except that they should all be equal (or inside-outside equal with CV carbs). The _amount_ of vacuum makes no difference; the _relation_ of vacuum between the cyls is the important thing. Make sense?

[Steve]

I just took the time to read through all the above posts and was amazed at all the misleading information. :shock:
The job can be intimidating enough without adding to the confusion.

Tconroy is apparently doing a carb sync on an '83 650L. \\/

Dave8338 says "About 4 feet of 5/16 should do the trick, make sure that the petcock is in the PRIME position..."
Length of hose is irrelevant, it only needs to be long enough to run from your temporary tank to the carbs. PRIME position is only necessary if you do not also run a vacuum line to operate the petcock. If you do NOT run a vacuum line, plug the port on carb #2.

Rustybronco - I am glad the gear lube bottle works for you, but I am concerned about an open hole that would leak if it fell. And, just how do you hang the bottle upside-down from the handlebars? My temporary tank is only slightly less dangerous. 8-[ I use a one-gallon oil container with a screw-on lid. I have drilled a hole in the lid so a fuel line is very snug going through it. By laying the jug on its side, fuel flows nicely, even without a vent. Simply turn it upright and fuel flow stops. Easy enough to drain back into the tank and store for next time.

Bradleymaynar - I have recently learned (by reading the factory manual) that carb sync is to be performed at 1750 rpm. I have always done it at idle, 1100 +/-100 rpm.

Tconroy - vacuum at 4 grand may not be enough to suck the mercury up the tubes, but be careful of sudden throttle changes. THAT is when strange things happen.

Bradleymaynar - Nice idea about leaving the adapters on and covering them with rubber caps. If that is your only bike. Some of us have more than one bike, so we have to remove them. If they fit snugly, the chance of losing them while riding should be minimal. After all, they are being sucked into place by vacuum.

Tconroy - Not sure what book you are using, but you are confusing measurement terms. The lines on your sync gauge are not cFm, they are just cm. That's centimeters. The lines are 2 cm apart. The actual value of the vacuum is not important, it might be 8 or it might be 12. What matters is that the outer two are .5 cm, that's one-half centimeter, or 1/4 the distance between the lines, higher than the inner two.

Earlfor - the vacuum vent on #3 is only on the earlier VM carbs. Tconroy is working on an '83 which should have BS carbs. Remember, carbs (and cylinders) are numbered from clutch hand to throttle hand.

Ddominik - Actual values are not important. Mercury gauges are actually more accurate than the factory gauge since there is no way for them to become uncalibrated. See my comment just above to Tconroy about values. Since you have the older VM carbs, note that your vacuum port to the petcock is on #3.


Not trying to sound "holier than thou", but there seems to be a lot of confusion out there. Just trying to keep it simple. 8-[

.

[Dave8338]

I just took the time to read through all the above posts and was amazed at all the misleading information.
The job can be intimidating enough without adding to the confusion.

Tconroy is apparently doing a carb sync on an '83 650L.

Dave8338 says "About 4 feet of 5/16 should do the trick, make sure that the petcock is in the PRIME position..."
Length of hose is irrelevant, it only needs to be long enough to run from your temporary tank to the carbs. PRIME position is only necessary if you do not also run a vacuum line to operate the petcock. If you do NOT run a vacuum line, plug the port on carb #2.

Rustybronco - I am glad the gear lube bottle works for you, but I am concerned about an open hole that would leak if it fell. And, just how do you hang the bottle upside-down from the handlebars? My temporary tank is only slightly less dangerous. 8-[ I use a one-gallon oil container with a screw-on lid. I have drilled a hole in the lid so a fuel line is very snug going through it. By laying the jug on its side, fuel flows nicely, even without a vent. Simply turn it upright and fuel flow stops. Easy enough to drain back into the tank and store for next time.

Bradleymaynar - I have recently learned (by reading the factory manual) that carb sync is to be performed at 1750 rpm. I have always done it at idle, 1100 +/-100 rpm.

Tconroy - vacuum at 4 grand may not be enough to suck the mercury up the tubes, but be careful of sudden throttle changes. THAT is when strange things happen.

Bradleymaynar - Nice idea about leaving the adapters on and covering them with rubber caps. If that is your only bike. Some of us have more than one bike, so we have to remove them. If they fit snugly, the chance of losing them while riding should be minimal. After all, they are being sucked into place by vacuum.

Tconroy - Not sure what book you are using, but you are confusing measurement terms. The lines on your sync gauge are not cFm, they are just cm. That's centimeters. The lines are 2 cm apart. The actual value of the vacuum is not important, it might be 8 or it might be 12. What matters is that the outer two are .5 cm, that's one-half centimeter, or 1/4 the distance between the lines, higher than the inner two.

Earlfor - the vacuum vent on #3 is only on the earlier VM carbs. Tconroy is working on an '83 which should have BS carbs. Remember, carbs (and cylinders) are numbered from clutch hand to throttle hand.

Ddominik - Actual values are not important. Mercury gauges are actually more accurate than the factory gauge since there is no way for them to become uncalibrated. See my comment just above to Tconroy about values. Since you have the older VM carbs, note that your vacuum port to the petcock is on #3.


Not trying to sound "holier than thou", but there seems to be a lot of confusion out there. Just trying to keep it simple. 8-[

.

...............................Ah,................ NO, I'll refrain. :-\"
Tim, any questions, you can PM me.

[rustybronco]

Rustybronco - I am glad the gear lube bottle works for you, but I am concerned about an open hole that would leak if it fell. And, just how do you hang the bottle upside-down from the handlebars? My temporary tank is only slightly less dangerous. 8-[ I use a one-gallon oil container with a screw-on lid. I have drilled a hole in the lid so a fuel line is very snug going through it. By laying the jug on its side, fuel flows nicely, even without a vent. Simply turn it upright and fuel flow stops. Easy enough to drain back into the tank and store for next time.
.

I have made a hook that goes around the neck and attaches to the side of the bottle with wraps of duct tape and then hangs over the bars.
Like every thing in life there is danger, and what if's. I guess it's no difference than carbs leaking on a bike and a hot exhaust, a shorted wire and the loom and bike go up in smoke, what if...

your tank idea sounds good.