Carb / digisync question

[nogrey]

Helped a friend today with a desmog. Went very well and sure dressed up the engine. Put it all back together and as a finishing touch threw the digisync on. Now, I’ve done several bikes with the digisync and always had great luck. Usually made a noticable difference too. His bike was different. After making a few minor adjustments, carb 3 (right next to carb 5 which is the non-adjustable one) started acting very flakey. I got all the other carbs to read 187 +/- 1 except carb 3. It is stuck at 200. No matter what. Thought it might be the battery in the digisync so changed it. No appreciable difference. Never could get that carb to balance. It did have an impact on idle and the other carbs, just would not change the amount of vacuum it was pulling. Local Honda dealer said it was probably a torn diphragm. So I took the cap off and removed it and it was fine. Bike idles and runs good, just bothers me that I couldn’t adjust it like all the other ones I’ve done. Frankly, it defies reason to me. If you adjust the carb, which changes butterfly opening, vacuum HAS to change.....at least that’s what I thought.
Your thoughts?

[WintrSol]

The #3 carb is the non-adjustable reference for the other 5; its vacuum only changes when adjusting the main idle knob. The others have fine-tune screws to set the idle to match #3. BTW, #3 is the center carb of that set.

[Avanti]

Do not suppose you took a before reference reading. Do an exhausted search for any vacuum leak.  You can look inside that carburetor to see if the throttle butterfly is closing properly.   

[mark81]

Is it the carb stuck at 200 or the reading on the digisync?  Did you try swapping vacuum hoses to see if that chanel on the sync is bad? Just hook the one reading 200 to another cylinder and see if it still reads the same

[nogrey]

The #3 carb is the non-adjustable reference for the other 5; its vacuum only changes when adjusting the main idle knob. The others have fine-tune screws to set the idle to match #3. BTW, #3 is the center carb of that set.

You know how you “think you know” something, but you don’t? I think you have hit the nail on the head. I’ve done many carb syncs. Can’t really explain it, but always told those watching that #3 was tricky because it didn’t respond the same way as the others. That’s because I thought #5 was the “base” carb. Now where I got that idea is beyond me. Something to do with being 60???? Anyway, for some reason I had that in my head.
So, I’m now not sure I understand why this bike was different, I mean, #3 still interacts with the adjustment of the others and I never could get it to change or respond, and in my experience 200 is about 15 higher than what I normally see. Still think I’ve got an issue of some sort, but thank you for correcting me and reminding me that #3 is the base. That certainly solves part of the mystery.
Thank you.

[nogrey]

Is it the carb stuck at 200 or the reading on the digisync?  Did you try swapping vacuum hoses to see if that chanel on the sync is bad? Just hook the one reading 200 to another cylinder and see if it still reads the same

Asked myself the same question. Also, thought perhaps the 3 year old battery in the digisync might be going bad, so put a new one in. Then swapped the upper bank of sensors with the lower ones (swapped whole bank of tubes to other side of the bike). This had no impact on the problem. According to the instructions, a base value +/_ 10 is acceptable and this one is close enough that there was no issue with performance, so letting it go for now. If you read the first comment above, I also had the base carb #3 confused with #5 (thought base was #5) so that threw a curve ball into things, although has never kept me from getting them tuned. We’re going to giver her another try sometime soon. Thanks for your help.

[nogrey]

Do not suppose you took a before reference reading. Do an exhausted search for any vacuum leak.  You can look inside that carburetor to see if the throttle butterfly is closing properly.   

We had just finished de-smogging with Redeye’s kit. We did re-check everything and all was tight as a drum except the “drool tube”. We found it disconnected and thought we had it, but didn’t really change anything. We even checked all the plugs. Didn’t want to confuse the issue with that but we had noticed that the valves at #2 were tapping noticably. Owner said it had always been loud. Well, the spark plug in that cylinder was not even hand tight. 2 others were quite loose as well. After checking all 6 for gap and color, then retorquing, the valve noise went away, so we were hearing leakage from that cylinder. Still, did not impact the tuning issue.

[The emperor has no clothes]

The #3 carb is the non-adjustable reference for the other 5; its vacuum only changes when adjusting the main idle knob. The others have fine-tune screws to set the idle to match #3. BTW, #3 is the center carb of that set.

You know how you “think you know” something, but you don’t? I think you have hit the nail on the head. I’ve done many carb syncs. Can’t really explain it, but always told those watching that #3 was tricky because it didn’t respond the same way as the others. That’s because I thought #5 was the “base” carb. Now where I got that idea is beyond me. Something to do with being 60???? Anyway, for some reason I had that in my head.
So, I’m now not sure I understand why this bike was different, I mean, #3 still interacts with the adjustment of the others and I never could get it to change or respond, and in my experience 200 is about 15 higher than what I normally see. Still think I’ve got an issue of some sort, but thank you for correcting me and reminding me that #3 is the base. That certainly solves part of the mystery.
Thank you.

Maybe I'm misunderstanding what you are saying. But #3 doesn't really interact with the others. It is static and the value should stay the same except for the idle changing. At least that's how I understand it. As I remember doing mine the values were in the 192-195 range.

[Avanti]

Well, the spark plug in that cylinder was not even hand tight. 2 others were quite loose as well.

That is a catch that saved cylinder head spark plug thread problems.

[WintrSol]

Maybe I'm misunderstanding what you are saying. But #3 doesn't really interact with the others. It is static and the value should stay the same except for the idle changing. At least that's how I understand it. As I remember doing mine the values were in the 192-195 range.

There is some indirect change to #3, when adjusting the others causes a change in rpm; not much, though. Since #3 was reading ~15 higher, that means its throttle is more closed than the rest, so increasing the numbers on the rest to match will drop the rpm, possibly enough to lower the reading on #3 a few points, and requiring an increase to the main idle adjustment. Last time I did mine, it was also in that same range. Must mean the valves are still in spec.

[The emperor has no clothes]

Maybe I'm misunderstanding what you are saying. But #3 doesn't really interact with the others. It is static and the value should stay the same except for the idle changing. At least that's how I understand it. As I remember doing mine the values were in the 192-195 range.

There is some indirect change to #3, when adjusting the others causes a change in rpm; not much, though. Since #3 was reading ~15 higher, that means its throttle is more closed than the rest, so increasing the numbers on the rest to match will drop the rpm, possibly enough to lower the reading on #3 a few points, and requiring an increase to the main idle adjustment. Last time I did mine, it was also in that same range. Must mean the valves are still in spec.

[98valk]

all five get adjusted to the non-adjustable one.  if #3 is 200 or 185, doesn't matter all others get adjusted to that number which #3 is.

[nogrey]

Maybe I'm misunderstanding what you are saying. But #3 doesn't really interact with the others. It is static and the value should stay the same except for the idle changing. At least that's how I understand it. As I remember doing mine the values were in the 192-195 range.

There is some indirect change to #3, when adjusting the others causes a change in rpm; not much, though. Since #3 was reading ~15 higher, that means its throttle is more closed than the rest, so increasing the numbers on the rest to match will drop the rpm, possibly enough to lower the reading on #3 a few points, and requiring an increase to the main idle adjustment. Last time I did mine, it was also in that same range. Must mean the valves are still in spec.

Thanks again. That helps also. I just need to do it again and sort of start over.

[rug_burn]

I just re-synched my carbs on my 97 Valk, with what had to be the easiest, cheapest way ever,  took me about 1 hour or less. 
 
I got a regular dial type vacuum gauge from the local industrial hardware store, and put a 'Tee" on the bottom or outlet, with 2 brass 3/16" hose barbs.   I then put about 2 feet (same length) of silicone fuel line tubing on each, and hooked one line to the master carb, the other to the carb under test (CUT).   

I started the bike and let it idle at about 1000 rpm, without pinching off that vacuum line to the #6 like the book recommends.    Then I  just went through, and synched each carb by pinching off one carb line or the other, and adjusting the CUT adjusting screw  to match the swing of the needle in the master carb.   

 Actually a liquid filled gauge might have been a little better, but the carbs are without a doubt are well synched even with eyeballing the middle of the swing range.   I say this judging by the sound of the exhaust and smooth power pulling from about 400 rpm on up.   

The silicone fuel line tubing is a standard model airplane item, and is easy to pinch off by hand;  keeping the line length equal is also important.      My bike wouldn't idle when I pinched off that vacuum line to the #6 carb  as the book recommends, so I just left it open, and reconnected all vacuum lines to other carbs on cylinders that had them.   

-  For what it's worth, if someone else can use the info-