Carb sync, no reading on Carbtune

[hannibal]

Sorry in advance for the multiple threads in the last day.

I have float valve needles installed and that has fixed my fuel flowing into the motor problems. Got the bike warmed up and idling off choke. It took me a good 10 mins to hook up the carbtune and when I started it, it had a racing idle but no reading on the carbtune. Tightened up the brass adapters I got from Z1 and restarted.

I have a nice idle, but I can feel that the exhaust on 1 and 2 is far cooler than 3 and 4. Probably a sign that they need to be synced. My problem is that my carbtune doesn't move from 0 vacuum. I was trying to sync at 1500 rpm. I turned the idle up to 2000 rpm and still the carbtune didn't move from the lowest possible reading. I did see a flitch on one of the cylinders. I have the tubing from the ports to carbtune installed with the restrictors closest to the cylinder ports.

Do I need to tighten the adapters even more? The carbtune manual says not to overtighten their plastic adapters so I not sure how tight to go with the brass ones. Any ideas?

I'm planning to do the sync then adjust mixture/air screws for highest idle/vacuum, then recheck the sync. The fuel height in carb 3 did get a little high, so I drained it, tapped the bowl, and refilled it. Fuel height looks good when trying to sync

 

[chuck hahn]

On the two that are cooler try to turn the adjuster screws OUT. This will raise the slides and thus ( theoretically ) make them get more fuel. Youll have to fiddle with the adjuster screws some till they start to get reactions. And be ready to keep adjusting the idle to keep it around 2,000. As you change the slides the RPMs are gonna float around too.

 

[Steve]

Did you try turning the Carbtune over? :-k

In low-vacuum situations, you can turn it over so vacuum pulls the indicators down. Yes, it's in the manual.

When you get them closer to 'even', there should be enough vacuum to flip it back to right side up.

.

 

[hannibal]

Thanks guys. I opened up the cold cylinder 1 and got an increase in idle and a reading on the carbtune for that cylinder only. Turned idle back down to 2000 rpm. When I tried to open up cylinder 2 (also cold), I saw a small increase in idle, but no reading. The further I went the worse it sounded. Not sure how to describe it, but the idle got less smooth and sounded like it was sputtering or gasping. I kept opening it and I started to get smoke from the open breather hose (the bike came with pods and 110 mains in place of the stock 100; other jets are stock). I turned cylinder 2 back down and the idle sound improved but I continued to see smoke.

I thought if it wasn't happy opening up cylinder 2, I should close cylinders 3 and 4. Tried them both and made little to no difference in sound or idle, and didn't show a reading. Cylinder 1 continued to show a 'good' reading the whole time. I'm starting to think my bench sync was WAY off. I did consider flipping the carbtune upside down, but never heard of anyone having to do that on their GS. Since I messed with all 4 adjusters and I don't know where my baseline was, should I pull the pods off and do a visual sync to match 2,3 and 4 to cylinder 1? Or just flip the gauge over and start from there?

The battery came off the charger this morning and is showing 12.7-12.8 V (compared to 12.3 V last night). Getting spark from all four plug wires. I should mention that the highest idle I can get before the idle/throttle adjuster screw bottoms out is about 2500 rpm. Does this suggest my original slide openings are set way too small?

 

[chuck hahn]

I would redo the bench sync very carefully and get them at least back to a known start point again. When i bench them, i just touch the idle knob to the linkage and then go in about 1 1/2 turn..and then bench sync. Then i turn the idle knob out to be sure that the slides close all the way. This will at least get the idle knob somewhere in the middle of its adjustment range too.

Set the idle knob in the 1 1/2 turns and start the bike. Be ready to adjust a little to get it to idle and have some idle knob response as well.

General consensus from many here is to use a regular size paper clip wire to set the slides with as far as the gap goes.

 

[Big T]

You did put the restrictors in the lines to the Carbtune?

 

[gustovh]

You did put the restrictors in the lines to the Carbtune?

I have the tubing from the ports to carbtune installed with the restrictors closest to the cylinder ports.

Second paragraph, last sentence.

 

[Big T]

I have the tubing from the ports to carbtune installed with the restrictors closest to the cylinder ports.

Second paragraph, last sentence.

I guess I forgot how to read

Tightening? Once the O ring squishes, that's tight enough

 

[hannibal]

Yes on the restrictors. I definitely over tightened the adapters. My O rings were more than starting to flatten/squish. When I pulled the adapters off, 3 of the 4 had ripped in half. I'll steal the O rings from the plastic adapters from carbtune.

I pulled the carbs off and will bench sync. I should have time Friday afternoon to give it another try.

I feel like I'm so close. Thanks again guys.

 

[hannibal]

Perhaps this is a stupid question, but I had my fuel level hoses connected to the bowl drain ports while I was trying to sync. Should these be removed and replaced with the drain plugs when I'm syncing??

 

[chuck hahn]

Yes...they will suck air probably. I wouldnt sync unless the carbs are configures as if I was riding the bike.

 

[Steve]

Perhaps this is a stupid question, but I had my fuel level hoses connected to the bowl drain ports while I was trying to sync. Should these be removed and replaced with the drain plugs when I'm syncing??

Contrary to Chuck's answer, I don't see how that would affect anything, as long as there is fuel in the hoses. :-k

There would be no air flowing through there, it would, essentially, be the same as it would while riding.

.

 

[chuck hahn]

Yeah Steve..kinda rethinking it, the bowls do have vents. So maybe the fuel level hoses isnt a big deal.

 

[JTGS850GL]

Agreed with doing a complete bench sync again to start off with. Use #3 as the master carb and adjust it using the idle adjustment knob at around 1 1/2 to 2 turns in. Adjust the other three carbs to match the opening size of the #3 carb. I like to use thin feeler gauges to set them the same but a good visual check will help confirm opening size. Just make sure that all 4 carbs have the same amount of light coming through the throttle valve at the same angle. Make sure that all 4 fuel adjustment screws are set at 2 1/2 turns out from lightly seated.

Just to confirm, you are using the carb tune with it suspended vertically from the top. Do not lay it down on it's side to use it. It must be suspended vertically in order to be accurate. The restrictors do indeed need to be about 10cm from the engine side leaving about 90cm between the restrictor and the Carbtune body.

Like this:

 

[hannibal]

That's my setup JT. After I got a reading on cylinder 1, I swapped the hose to the 2nd channel on the carbtune and saw a reading there. I'm confident the carbtune is functional.

On the fuel level hoses, I don't think it should make a difference as long as the hoses have fuel, and they should if the bowls aren't empty. But I've left them on with the bike running and I no longer have fuel height issues so I'll pull them off and try to sync.

I reset the slides off the bike and put the carbs back on yesterday. Not gonna make it home before dark today so I'll have to wait til tomorrow to see if this improves readings on the carbtune.

Thanks guys.

 

[Steve]

Use #3 as the master carb and adjust it using the idle adjustment knob at around 1 1/2 to 2 turns in.

If he still has stock carbs on his '77 bike, they are VM carbs, so there is no "master" carb.

Also, when you make an adjustment on the VM carbs, the vacuum levels don't jump around as much as they do on the BS carbs. It's pretty much that one carb's vacuum level moves toward the others and they change a little bit (all together) to meet the one you are changing. Makes adjusting the VMs a bit easier and quicker. :encouragement:

.

 

[JTGS850GL]

Sorry, missed the year. Sometimes I get stuck on CV carbs in my mind. Thanks for the clarification.

 

[Gorminrider]

This might seem a stupid question, ignore if you have done this but do you have compression in the low cylinders? (per your mention of cold cylinders) No compression=no vacuum...and it's a good idea to check and set valves before sync.

 

[hannibal]

I've checked valve clearances and changed shims to bring it into spec. I have not done a compression test. The bike ran decently when I bought it so I assume compression is good.

 

[Gorminrider]

how is it going?.......thumb on a spark plug hole is a sort of test too...hand cranking