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CV Bench Sync

tas850g

tas850g

Forum Mentor
I just acquired a 1981 GS650GLX. I'm trying to bench sync the carbs. I've done this with success with the vm carbs but i'm not sure how much it varies from the cv carbs.

My slides will not go all the way down. There is a gap from the botton of the carb "throat" that is approx. 1/4"??? I know with the vm carbs the slide will go all the way down with no gap. When i start the bike it revs around 4-5k.

The butterfly's are closed.

I have turned the 4 sync screws all the way down and up and the slides do nothing. Is this supposed to happen with the cv carbs?

I just read Basscliff's tutorial on cv carb cleaning but there doesn't seem to be a well written tutorial like he has for the vm series carb on how to bench sync.


Maybe i missed it.
 
I'm by no means an expert but noone else has posted yet so here's my $.02 that may not be worth even that much.

The slides don't close all the way. they will stay open 1/4" or so. idle rpm is controlled by the butterfly. see if you can close them down more. I eyeballed mine when putting them back together on my 400 the first time going by the idle (? term) and transition ports. OR about 2 turns of the idle stop screw from completely closed, if even. I also eyeballed the synch of the butterflies. that being said the first time I got it fired up it idled about 1500 warm.
 
the butterflys really seem closed. I'll check again. Maybe since i backed off on the sync screws it will be better now. I just don't want to put it back together before i get more advice here.
 
Bench sync is not important really, just get them in the ball park using your eye and go straight to vacuum sync which is the important part. I trust you have replaced the intake boot O-rings since you have the carbs off. These o-rings often leak and lead to a high idle due to false air leakage.
 
True, the slides do not close all the way.

Some will use a small item like a 1/16" drill bit to make sure all the butterflies are open the same amount, I just use a sliver of light.
Hold the carbs in front of a light. Look from the engine side, adjust the master idle speed adjust screw so you see a sliver of light at the bottom of the butterfly in #3 carb. Keep in mind that the carbs are numbered from left to right, as you are sitting on the bike, so when looking through them from the engine side, #1 will be on your right, making #3 the second from the left. Once you see that sliver of light in #3, look at all the others, adjust them if necessary to have the same size sliver of light.

According to the Suzuki manual, the preferred order of adjustment is to match #2 to #3, then match #1 to #2. Finally, match #4 to #3. When you do your vacuum sync with the bike running, if you have stock exhaust, the vacuum levels on 1&4 will be just a little higher than the levels on 2&3. If you have a 4 into 1 header, they should all be the same.

.
 
I haven't gotten new intake o-rings yet. i'll get some. The boots seem good.

So now i just adjust the butterflies so they are even, by eye site, then i'll use my morgan to do the vacuum sync. The middle sync screw is sure gonna be a tuff one to get at with the carbs on.

I sure like syncing vm carbs better, at this point anyways. I'll get a better comparison after i sync the cv's.

thanks for the help guys.
 
tas850g said:
The middle sync screw is sure gonna be a tuff one to get at with the carbs on.
Click to expand...
Agreed. And I have found that many of them have either been over-torqued or rusted in place, making them even harder, so I like to loosen the locknut while it's accessible, then just barely snug it down before putting the carbs back on the bike. After using your Morgan, there is no need to use Gorilla-torque to lock the screws in place. Just makes it harder next time.

.
 
The o-rings are behind the boots. You can't tell by looking at the boots if they are good.
 
Hi,

To be clear, the carb cleaning guide on my website is just a copy of the fine work by John Bloemer that is hosted on the GSR homepage.

I do have some notes on bench syncing collected on my website from Mr. Steve and others...

Carb Sync Notes


Thank you for your indulgence,

BassCliff
 
Thanks Cliff, i meant to read that one yesterday but haven't yet.

I need to work on taking the screws off that secure the intake boots on. I used the hand impact for 4 of the screws but there is no room for the others. I have some ideas how to remove them and will try them today. I almost don't want to mess with the boot screws but i know i need to prob. replace the intake o-rings. The PO said he had $150 of carb work done on it over the last month. All they did was change the float gaskets and put in new jets. I have the old ones in a bag, torn gaskets too.

I was hoping by not tightening the sync locknuts much they would stay in place while riding. I was also thinking the same Steve about leaving all the locknuts loose until the vacuum sync. Nice to hear a +1 on that.

I also need to look at the start solenoid, right hand control, and clutch switch if it has one. I can only start it by arcing the solenoid.

Off to the garage.
 
Those intake boot screws are a pain. Some ideas to remove them include adding a long extenstion on your impact driver and/or removing the outer boot screws using vice grips and then spinning the entire boot to crack loose the innter screws.

Regarding those sync screws, Motion Pro makes a special tool to allow easy adjustment. I used to poo phoo such unnecessary tools but it's $20 well spent based on personal experience.
 
Got'em! Yesterday i was able to get the top screws off with the hand impact. Today i did just that, spin the boot and shoot some PB blaster and sure enough, OFF they came.

I have the model with that the clutch must be engage for it too spin the started. OR i just cleaned out the right hand control with contact cleaner. Someone was living in there. Regardless, pushing the starter button now spins the motor with clutch engage. I'll have to bypass that one.
 
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