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Space Emperor
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Discussion Starter #1 (Edited)
Hi lads

I've made a carb sync setup, and is almost ready to go:

- tubes with some oil in.
- Fabricated the nipples to attach the tubes (can' get them here)
- Cleaned the K&N air filter.
- Located the sync screw, and fabricated an angle screwdriver

Now I see the idle mixture screws (?) on the carbs (clearly adjusted differently) and I'm wondering if and how I should adjust these?

Before or after the sync and how to do it?

Anything else I should look at while/after adjusting the sync?

If some kind soul could give an advice on this while I wait for the oil to distribute itself on the K&N, I'd be very thankful!

Looked at Haynes, but the pictures are awful, and don't really show anything. Tried the search also, but I must be a search-git, as nothing useful comes up
 

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Hi lads

I've made a carb sync setup, and is almost ready to go:

- tubes with some oil in.
- Fabricated the nipples to attach the tubes (can' get them here)
- Cleaned the K&N air filter.
- Located the sync screw, and fabricated an angle screwdriver

Now I see the idle mixture screws (?) on the carbs (clearly adjusted differently) and I'm wondering if and how I should adjust these?

Before or after the sync and how to do it?

Anything else I should look at while/after adjusting the sync?

If some kind soul could give an advice on this while I wait for the oil to distribute itself on the K&N, I'd be very thankful!

Looked at Haynes, but the pictures are awful, and don't really show anything. Tried the search also, but I must be a search-git, as nothing useful comes up
I have only ever used a manufactured balancer, but the homemade variety seem to work.

You may want to mount your balancer pipe on a board, with some sort of graduations on it to make it easier to read when the levels are the same. I haven't heard of oil being used: I hope it does not cling to the tube sides, making the levels harder to read. Finally, at the apex of the trough in you tube (it should be set-up in a deep U shape), try and partially occlude the pipe with something pressing on the tube: it means that the fluid flows through slower, allowing you to see changes in vacuum more gradually.

The balancing: it should be ideally done after valves have been set.
It should be done with the engine hot.
You may want to set the idle a little higher (1500rpm?) for the duration of the procedure.

Finally, I don't see why you want to fiddle with the mixture screws.
Unless you feel that you're lean or rich at idle (new can/hi-flow air filter), these should be left alone.

All you want is for your throttle cable action to elicit the same fuel/air supply to both cylinders, via the action of the carbs. The vacuum gauge tells you any difference in relative vacuum between the cylinders and there is a single screw that will either increase or decrease that difference in vacuum. That is the screw you want and is usually located near where the throttle cable attaches to the carbs. On my TA it is accessed via a hole through the airbox, under the tank.

I may be wrong on the above, but that is how I have always balanced carbs, with the exception of my Ural boxer engine. If others know better, please let us know (i'm happy to get new tricks!).

Good luck.
 

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Space Emperor
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613 Posts
Discussion Starter #3
I have only ever used a manufactured balancer, but the homemade variety seem to work.

You may want to mount your balancer pipe on a board, with some sort of graduations on it to make it easier to read when the levels are the same. I haven't heard of oil being used: I hope it does not cling to the tube sides, making the levels harder to read. Finally, at the apex of the trough in you tube (it should be set-up in a deep U shape), try and partially occlude the pipe with something pressing on the tube: it means that the fluid flows through slower, allowing you to see changes in vacuum more gradually.

The balancing: it should be ideally done after valves have been set.
It should be done with the engine hot.
You may want to set the idle a little higher (1500rpm?) for the duration of the procedure.

Finally, I don't see why you want to fiddle with the mixture screws.
Unless you feel that you're lean or rich at idle (new can/hi-flow air filter), these should be left alone.

All you want is for your throttle cable action to elicit the same fuel/air supply to both cylinders, via the action of the carbs. The vacuum gauge tells you any difference in relative vacuum between the cylinders and there is a single screw that will either increase or decrease that difference in vacuum. That is the screw you want and is usually located near where the throttle cable attaches to the carbs. On my TA it is accessed via a hole through the airbox, under the tank.

I may be wrong on the above, but that is how I have always balanced carbs, with the exception of my Ural boxer engine. If others know better, please let us know (i'm happy to get new tricks!).

Good luck.
Thanks, Warthog!! I left the mixture screws alone for now, and just balanced the carbs with the manometer. They were so far off, that the liquid (oil, low viscosity) rushed about a meter in the air, and started descending, heading for the cylinders. Had to shut off the machine, and yank out the cable to avoid a smoky incident... then wait 10 min for the oil to settle back at the bottom of the loop. I would say it took about a full turn of the screw to balance them ...

What should have taken 2 hours, ended up taking 6. Today wes about 34 degrees, so my clothes are soaked, and I'm heading for a shower before I do a test run. I could already feel a major difference. She's comfortable idling below 1500, which she didn't really like before, so that's a good sign :thumbright:
 

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Space Emperor
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613 Posts
Discussion Starter #4
Ok, so I just did a 30km test run, and I'm totally disappointed as the bike runs like cr*p ... Much better idle, but not much power, and when I reach 5000rpm, which is usually where the magic happens in 3rd gear, the bike almost stand still. No accelaration above 5000 until I reach 4th and 5th gear.

Also, when I let go of the gas, it's like the bike, while revving down, get's a little gas ... hard to explain, but it's not a smooth de-acceleration.

My theory, which is not based on any knowledge on the area what-so-ever, is that since the bike had a confirmaed sticky choke, the previous owner had adjusted the mixture on the front cylinder carb, as well as adjusted the sync to make up for the sticky choke.

Now that I have removed the choke, and balanced the carbs, I'm thinking that the front cylinder may be running lean ... not sure about the 5000rpm lack of power, though?

Anyone with some insight on this phenomenon?

My plan is to count the rotations of the mixture screw on the back cylinder carb, and adjust the front to the same number of rotations.

Would that be worth a try?

Ah, forgot to mention that the bike had an aftermarked exhaust with no baffle, and a K&N airfilter ...
 

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Mixture screws should not affect much above idle, especially not anywhere near 5000rpm.

Did you have a problem with a split diaphragm, or was it someone else? Sounds like that may have gone again!!
 

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Space Emperor
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613 Posts
Discussion Starter #6
Mixture screws should not affect much above idle, especially not anywhere near 5000rpm.Did you have a problem with a split diaphragm, or was it someone else? Sounds like that may have gone again!!
Nope, that wasn't me ... yet :)Not even sure what they are ... The rubber thing that connect carbs to the cylinders?Ah, one thing I noticed while syncing the carbs was that after they were in sync, they would be off sync at higher revs ... Is that normal, and does it have anyhting to do with whats going on now?
 

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Nope, that wasn't me ... yet :)Not even sure what they are ... The rubber thing that connect carbs to the cylinders?Ah, one thing I noticed while syncing the carbs was that after they were in sync, they would be off sync at higher revs ... Is that normal, and does it have anyhting to do with whats going on now?
OK. Forgive me if I am stating the obvious. Based on your comments, you may not know so I'm writing down the basics!

Your carbs work on three circuits. The idle circuit, which is the mixture screw and the idle jet (a brass tube with a controlled aperture). Then you have the needle circuit. This is a needle with a controlled profile that tapers off at the tip. It rises and falls depending on throttle opening. Its tip occludes a brass tube's internal opening. As the needle rises, more of that opening is clear, so more fuel can escape into the carb venturi or funnel. Finally, you have the main jet that actually sits at the bottom of the brass tube mentioned above. That is for when the throttle is wide open.

The diaphram I mentioned is a thin rubber membrane that is connected to a solid plastic tube at the base of which is fitted the needle mentioned above. As the engine speed increases, so does the vacuum. This vacuum, sucks up the diaphragm, which then raises the needle, allowing more fuel in which raise the engine speed and so on.

These diaphragms can split with time. If it has, it would mean that once you move out of the idle circuit's range (about 0-25% of your throttle) and into the needle circuit, the engine will suffer fuel starvation.

There was a thread about this about 3 weeks ago. Do a search on split diaphragms on the site. If I find it I will post you a link, too.
 
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