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Discussion Starter · #1 ·
I'm about done with a soak clean and rebuild of my carbs.

I can rebuild 'em no problem.. not my first rodeo...

I can balance them no problem... done it before..

The one place I'm sketchy.. is adjusting the idle mixture screws. The manual says to screw them in until they hit bottom, then back them out so many turns as starting point... OK.. I can do that.

The next part, about adjusting them from there I'm questioning. (I don't have the manual in front of me, so I'm going from memory, so please forgive errors).

The manual says to hook up a tach, (an accurate one, with digital readout) and turn the screws in/out accordingly looking for drops in idle speed.

My questions are:

1. Any recommendations for a tach to accomplish this task?
2. Any other tricks/tips I may have been missing?

thanks in advance,

VMSGUY
 

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Cannot stress enough the importance of a proper bench sync prior to doing any mixture screw settings. All throttle valves have to be closely timed with the same opening amount. Whether you do this with a feeler gage, business card or paper, or a small drill bit is up to you. They got to be in the same ballpark.

If it will not run half way decent with mixture screw settings at initial adjustment +/- 1 turn at its stated idle with all mixture screws moving as a crew you got problems and need to go back into carbs or engine and figure out why.

A common mistake is to start jacking with sync screws to make it run better and you just shot yourself in the foot. It might run better but it will never be right. Sync screws do not get touched again until the end of the process and at that time should only take a little bit of an adjustment and is the icing on the cake.

.
 

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1 to what DriverRider said.

For the idle drop/mix adjustment, I used my multi-tester connected to the first yellow wire from the left going into the CDI, the third wire from the left as I recall, connecting the black lead to a good ground. Found out my digital tach on the bike itself was remarkably accurate! I synch'd the carbs first, then did the idle drop adjustment and then checked the carb synch again, but not much additional adjustment needed. Good luck!
Kevin
 

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Discussion Starter · #5 ·
1 to what DriverRider said.

For the idle drop/mix adjustment, I used my multi-tester connected to the first yellow wire from the left going into the CDI, the third wire from the left as I recall, connecting the black lead to a good ground. Found out my digital tach on the bike itself was remarkably accurate! I synch'd the carbs first, then did the idle drop adjustment and then checked the carb synch again, but not much additional adjustment needed. Good luck!
Kevin
Just how did you use the multi-tester? Did it have a tach setting? or were you doing something else?
 

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I always like to add stuff later.

With regard to sync screws there is always room for experimentation.

I got no issue with turning a screw 1/4 turn one way or the other and if going past the 1/8 mark there is a night and day difference, sure leave it there. It is when you crank it down 1 1/2 turns raising the RPM of that carbs cylinder to carry another cylinder things get messed up. And if you are at that point something is wrong.

Always remember where your bench sync screw setting is to return to if no change.
 

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Discussion Starter · #7 ·
Cannot stress enough the importance of a proper bench sync prior to doing any mixture screw settings. All throttle valves have to be closely timed with the same opening amount. Whether you do this with a feeler gage, business card or paper, or a small drill bit is up to you. They got to be in the same ballpark.
Can you elaborate on this a little?

For the last few days, I have had the carbs soaking in carb cleaner (the spray cans are nice, but soaking is the best.

I just finished re-assembling the carbs, but haven't installed them yet.

I've read and re-read the Honda manual, but it doesn't mention the throttle valve bench syncing you have written about.

If I read your entire message correctly.. the order of business is:

1. Bench adjust the throttle valves so they are open the same amount.

2. Install carbs on bike.

3. Warm up engine and adjust mixture screws.

4. Sync carbs with vacuum guages.

5. Assemble rest of bike and ride.


Do I have that about right?
 

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At some point in the manufacture of the MC the rack or carbs would have to be synced.

Did they have a guy at the end of the assembly line put gas in start up and sync, most likely not.:) The rack before installation on the bike would be put on a jig and flow tested where your sync was adjusted along with idle screw adjustment. And likewise whoever made the carbs would have a similar jig or fixture to adjust pilot screw on each carb before it ever left their factory. Rack installed on MC, crated up and shipped all over the world.

Why does the shop manual not get into it, could be it is considered more of a tune up item than a repair. There is no reason why a MC coming back to a dealer for repair would have the sync out unless there was a broken linkage or somebody jacked the **** out of sync screws for no reason and that would be fixing stupid and doesn't warrant being in a shop manual. Sync might drift over time but again it is a tune up issue.
 

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Discussion Starter · #9 ·
Thank-you for your response....

I was looking for more of a technical how-to, on how you envisioned doing an initial setting of the trottle valves. As I was awaiting a response, I realized I had been doing that very thing whenever I had rebuilt the carbs in the past. I was doing it by eyeball. This time, I'll try to be more accurate.

Next thing I need to figure out is how to use a multimeter to accurately measure RPM. I see some tachometer/multimeters available at Harbor Freight and Amazon. I'll have to see if HF has one Monday.
 

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Use the upper flap portion of the throttle valve for your clearance check.

I would use a tiny drill bit simply because that is what I have, I got bits that go all the way down to smaller than a pin.

What your exact clearance you are looking for is unimportant just as long as it is consistent among the four. Are your throttle valves all over the place now. Find the one which is the master carb and set the others to it. Not familiar with the 1200 and cant tell you which one it is or what screw controls what carb.

Your idle screw adjustment will determine your eventual opening.
 

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This should work. Take a small straight pin to upper flap of master carb and adjust idle screw until there is a slight drag. Then with sync screws adjust the rest of rack with the pin in each carb for the same drag.

If a pin is way too small now for the current opening of master carb find something bigger.

If during the overhaul idle screw has not been touched and assuming it was running at a previous point the master carb opening should be close now for an idle speed assuming it wasn't jacked up to run at 1500 RPM.

Make sure you got a spring or rubber band attached somewhere holding throttles and linkages closed just like when it would be installed.
 

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Just how did you use the multi-tester? Did it have a tach setting? or were you doing something else?
Yes, mine has an RPMx10 function for 4,6, and 8 cylinders. Just cut enough of the wire cover to clip the positive probe on and wrapped it with electrical tape when done.
 

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When you get the engine started let us know what you used as a "feeler gage" and what the RPM was. And if you got a micrometer to measure your "gage" even better. I had my 15 carbs off a little while ago and should have checked them. I got another 15 showing up sometime and depending how deep in I get will try to check those. This is good info stuff, I like it. I sure as heck aint gonna drop a bit into an intake though.:coollep:
 

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For the idle drop/mix adjustment, I used my multi-tester connected to the first yellow wire from the left going into the CDI, the third wire from the left as I recall, connecting the black lead to a good ground.

Saw this is the being as said by "Cornpone". what I need to know is where is the CDI found on my '86 Interstate. I did the carbs last winter and balanced the carbs twice since putting it back together, but I am not getting great MPG (38-40). I just turned out the air screws one more than the stock setting. The bike does run good with no flat spots, but I am not real happy with the idle, it is smooth, but I think that it could be better. After reading what has been said I think I will try the air screws if I can find out where to hook up my multi meter that I have.
 

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Discussion Starter · #15 ·
I finished the initial throttle valve settings today. I did this on the bench before I installed the carbs on the bike.

To do the initial adjustment, I used drill bits. My bit set has two 5/64" bits. Pretty small. I started with the #4 carb. (Left rear). This is the master carb. All other carbs are synced/adjusted to match this one.

Anyway.. I put the first bit between the throttle valve, and the carb throat. And let the spring action hold it in place. (First picture). Then I put the second bit in the same way on #2 carb. (Left Front). And adjusted this carb to barely hold the bit. (Second picture). I then went to the other side and did carb #3 in the same manner. And finally #1.

Then I installed the carbs on the bike. I got is started, and the idle isn't too bad. But alas, I have a fuel leak. Looks like the carbs are coming back out. Argh!

I wasn't really happy with the fit of the o-rings for the fuel rail (felt too loose).. So I'll start there. Which means.. I get to start over!
 

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:claps:

But darn though.

I forgot to mention earlier you want to use the shank of the bit, not the twisty part. Hopefully you caught my error of omission.

Before adjusting idle screw what did it want to idle at with choke off.
 

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Discussion Starter · #17 ·
I used the shank part.... If you look at the pictures closely, you can see it.

For the few seconds. I saw 1300 rpm on the guage. As far as choke on vs off.. I don't remember. It was only running for about 15 seconds. Long enough to see gas leek on both pair of carbs. So I shut it down.

I have the carbs back out.. And tomorrow I'll hit the hardware store in search of new, better fitting o-rings.
 

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I forgot to ask, how far out was the pre-adjustment sync.
 

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Discussion Starter · #19 ·
I'm not sure what you're asking. I used a 5/64" bit. But I let the throttle springs hold it in place while I adjusted the other throttle valves. I didn't adjust the idle screw to match that position. Then once I was done, I let spring move it the throttle valve completely closed again.

Anyway.. I really wouldn't count on anything as scientific. The bike only ran for about 15 seconds before I shut it back down.
 

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For the idle drop/mix adjustment, I used my multi-tester connected to the first yellow wire from the left going into the CDI, the third wire from the left as I recall, connecting the black lead to a good ground.

Saw this is the being as said by "Cornpone". what I need to know is where is the CDI found on my '86 Interstate. I did the carbs last winter and balanced the carbs twice since putting it back together, but I am not getting great MPG (38-40). I just turned out the air screws one more than the stock setting. The bike does run good with no flat spots, but I am not real happy with the idle, it is smooth, but I think that it could be better. After reading what has been said I think I will try the air screws if I can find out where to hook up my multi meter that I have.
It's in front of the fuse block/box as you sit on the bike, at least on my '85. My Wing averages 39mpg and given the performance and how I ride I'm happy with that. I honestly believe you can get more mpg by how you ride than how the bike is tuned. And, if it's poorly tuned, then sportier riding REALLY takes a toll on your mpg. JMHO
 
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