Issues with sync'ing carbs

[mhobryan]

I have a 650GS that I am trying to sync the carbs. When I try to sync the tool to the number three carb all four levels want to go right to the top....i have the screws on the MotionPro sync tool all the way out to get the liquid level as low as possible.

I can sync the tool to one of the other carbs, but the number three has a lot more vacuum.

My first assumption is that the other three carbs were way out of sync...that the number three was much more open than the others. Therefore increased the other three until it was idling at 3k, and then turned the idle screw almost all the way out to get the idle back down to ~ 1200 RPM. After doing this, it still wants to suck the liquid into the engine.

I also sprayed starting fluid around the intake boots, and did not perceive any increase in idle, so assuming no vac leaks.

I did do the idle adjustment using the highest idle method, and all four screws are sitting at abt 2 3/4 turns out. Bike is completely stock. Carbs were dip cleaned and re O'ringed.

I used the very same tool to sync the carbs on my other 650 and was successful, so don't think it is the tool.

Any suggestions as to where to look next would be appreciated.

 

[Steve]

When you had the carbs off for cleaning, did you do a bench sync? That would have gotten them close enough to get it running for the vacuum sync.

If #3 has higher vacuum, it is virtually CLOSED, the engine is running on the other three carbs. Turn the adjuster between #3 and #2 to close them down a bit to match #3. The manual calls for matching #2 to #3 first, then setting #1 "half a ball" higher. Finally, set #4 to match #1.

Through experimentation with a factory gauge, I have found that "half a ball" is 2cm of Mercury. That would be TWO of the marks on the sides of your gauge. (Yes, I have one of them, too.)

.

 

[chuck hahn]

Isnt 3 preset and an unadjustable on that bike? You sync the other three to match number 3s vacuum...which will change as you balance the others??

 

[Killer2600]

I have a 650GS that I am trying to sync the carbs. When I try to sync the tool to the number three carb all four levels want to go right to the top....i have the screws on the MotionPro sync tool all the way out to get the liquid level as low as possible.

I used the very same tool to sync the carbs on my other 650 and was successful, so don't think it is the tool.

How long ago did you sync the carb on that other 650? It sounds like the fluid level is low on your syncpro. The fluid is water based and it evaporates.

 

[mhobryan]

Thanks Steve - This helps; I had assumed the opposite that it was mostly running on the #3. Yes, did bench sync, however, I got the nuts a bit tight, and had to use a socket to loosen; the set screw moved with the nut mucking up my bench sync.

I did my other 650 about 2 mos ago, and the tool has been sitting in my basement; don't think it evaporated that quickly.

 

[Killer2600]

I did my other 650 about 2 mos ago, and the tool has been sitting in my basement; don't think it evaporated that quickly.

Did you cap off the tool when you stored it? In any case check the reservoir and compare the level against new, the lower the level gets the less vacuum the syncpro can handle before sucking it into the engine. At a fast idle the syncpro shouldn't be full scale and sucking fluid into the engine. The last time I synced my 750 with my syncpro, I was at 1/3 to 1/2 of the scale with all the screws turned in some. The fluid has since evaporated into uselessness so next sync I do I'll have to refill it first.

 

[mhobryan]

Just wanted to provide some feedback:

Steve - Your suggestion worked; thanks. Was able to get the carb's mostly sync'd. However it seems to be really immune to idle speed adjustments. Think I'm going to have to pull, bench sync, and pull the carbs a part and make sure they are still clean....dipped them abt a year ago, but can't remember if I drained the carbs before storing.

Killer2600 - Do you just put a golf tee in the vacuum tubes to cap it? Think my levels are fine, as after i got the carbs quasi close, running out of tube length wasn't an issue, but as i don't use very often, would like for it to be usable next time.

 

[Steve]

Thanks for the feedback, but there are a couple of things that are raising red flags here.

Was able to get the carb's mostly sync'd.

How can you possibly have the gauges connected and only get them "mostly" synchronized?

However it seems to be really immune to idle speed adjustments.

You really mean that you turn the large idle speed adjustment knob and nothing happens?

Think I'm going to have to pull, bench sync, and pull the carbs a part and make sure they are still clean....dipped them abt a year ago, but can't remember if I drained the carbs before storing.

This one is REALLY puzzling. You already have them "mostly" vacuum synchronized, there is NOTHING to be gained by pulling them to do a bench sync. At least not until after you take them apart and dip them again. It is not necessary to drain carbs for storage, if you use a stabilizer in the fuel before parking the bike.

.

 

[Guest]

However it seems to be really immune to idle speed adjustments. Think I'm going to have to pull, bench sync, and pull the carbs a part and make sure they are still clean....dipped them abt a year ago, but can't remember if I drained the carbs before storing.

Try setting the mixture screws again using the highest RPM method (or whatever works for you), get the bike running as well as you can & drive it with a couple of tank fulls of seafoam ladden fuel...

Then re-assess your issues...

 

[Guest]

We took the carbs off my sons 850 last week to change out the starter. When we put back in we got the throttle cable all goofy and nuts tightened in the wrong place and had no idle knob adjustment at all. Put it back to where it needed to be and all was good again. Something to look at

 

[mhobryan]

Thanks for the feedback, but there are a couple of things that are raising red flags here.

How can you possibly have the gauges connected and only get them "mostly" synchronized?

Got all four gauges where they were supposed to be, however, because I couldn't get it to idle at 1500 RPM as the suggest best speed for sync'ing, qualified it with 'mostly'. Carbs were sync'd at about 1000 RPM

You really mean that you turn the large idle speed adjustment knob and nothing happens?

I turn the large idle speed adjustment a qtr turn, blip the throttle let it come back down, turn another quarter turn, etc, would do this about 4 times, nothing would happen, and then it would all of a sudden jump to 3k. It would either idle at about 800-1000 rpm or 3000.

This one is REALLY puzzling. You already have them "mostly" vacuum synchronized, there is NOTHING to be gained by pulling them to do a bench sync. At least not until after you take them apart and dip them again. It is not necessary to drain carbs for storage, if you use a stabilizer in the fuel before parking the bike.

I "think" I put gas stabilizer in it, but can't remember; it did have a full tank of gas, which makes me think that I did. If I have to dip, they are going to come off anyways. I was going to pull them off, check that they were still clean, validate all the little orifices will still flow with a shot of WD40, etc. If they passed this visual inspection was going to bench sync while I have them out, and ensure that the idle speed adjustment is 2 turns out per normal specs.

Will check throttle cable as suggested by others. If you feel I am chasing the wrong source of my idle gremlins, I am open to suggestions.

 

[Steve]

..., and ensure that the idle speed adjustment is 2 turns out per normal specs.

"The idle speed adjustment is 2 turns out" ... from WHAT???

You sure you have the right names for the right parts?

The idle SPEED adjustment is the large knob that hangs between the float bowls of carbs 2 and 3.
It gets turned IN until it opens the throttle enough for the engine to idle.
It does not get "2 turns out" from anything.

The idle MIXTURE screws are the little screws on top of the outlets of the carbs. They originally came from the factory with sealing plugs on them. In the course of a rebuild (or just getting it to run right), the plugs need to come off and the screws adjusted. "2 turns out" might be where they end up, but it might also be a bit too lean for it to run properly, which could be one source your your aggravation. Turn them out THREE turns (those are full 360-degree turns) to start with (pun itended). When the engine is warmed up enough to turn off the "choke", you can start adjusting the mixture.

With your sync gauges still connected (after the carb sync), turn a mixture screw in, to see if the vacuum level rises. Note that it will rise in ALL cylinders. The vacuum will rise because the engine is running faster on a 'happier' mixture, with no change in the throttle setting. Repeat on the other mixture screws until your vacuum level is the highest possible.

You should now find that your idle SPEED control now works just fine.

.

 

[silverhorse47]

You could also have a vacuum leak.

S.

 

[mhobryan]

Thanks for the detailed response Steve.

I meant two turns out, not in, on the idle speed adjustment screw. Yesterday I started the mixture screws at 3 turns out. Today, I started about 2.5 turns in, as it seemed like it was rich at idle, let off the throttle, and it would bog/die. went down to 1.5 turns in on each of the carbs, still doing the same thing. Figured that had to be too lean, then went back to 2.25 turns in, and then it couldn't make up it's mind whether to bog and die, or just hang at 2k RPM.


It simply won't hold an idle, which makes me think I have gunk in the carbs. I've adjusted valves, replaced all o rings including the ones behind the intake boots. The bike has been sitting for over a year since I did the dip and rebuild... probably didn't stabilize the gas.

Silverhorse - I may have an air leak, but it used to idle fine before...I'm placing my bet on the carbs based on the way it is acting...simply won't hold an idle.

Thanks again.

 

[cowboyup3371]

What made you think it was too rich at 3 turns out? Did you look at the plugs after the first start at that setting and were they very black? My bike is actually set to about 3 turns on each carb and I'm seeing it running fine.

 

[Steve]

You can't just arbitrarily set all the screws to a certain number of turns. Start rich (3 turns), slowly turn a mixture screw until the engine speeds up a bit. (If you have your vacuum gauges connected, you will see an increase in vacuum.) Repeat this for each cylinder. Please note that all the screws may not end up at the same setting. On my son's 650, if I remember correctly, one is about 2 1/4, one is about 2 1/2, one is about 2 5/8, the last one is at 3 1/2.

It does not matter that they are different, what matters is that they are set to the best setting for that carb.

Still puzzled by your idle speed setting at a certain number of turns in or out. I have never really counted turns on that screw, I just turn it until the engine runs.

.

 

[mhobryan]

Appreciate your patience Steve. I should have been more specific; I initially used 3 turns out on the mixture screws as a starting point, and would would go lean from there, It appeared to have symptoms of being too rich (pop the throttle, and idle would dip and engine wanted to stall). However, I had the needles all the way down to 1.5 turns out - which would be a really lean setting. All the while the idle would hunt. So I tried the setting it 2 turns, and 2.5 turns out to see if I could get the idle to be more stable, and start tweaking the mixture screws from there.

I could never get the idle to stabilize, wanted to hunt regardless of mixture setting. Figure best to take the carbs off again and clean.


It held an idle at 1500 RPM long enough for me to get the carb's sync'd though, and was also able to reconfirm it held the settings from my sync from yesterday.

Will pull carbs tonight and report back.