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Carb Sync Going Wrong - Fluid keeps sucking into bike

Old 07-09-2013, 08:23 PM
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Carb Sync Going Wrong - Fluid keeps sucking into bike

Hey guys... A little background: I have the carb sync extenders installed (Honda nipple on front cylinder with piece of vacuum tubing run under the seat, TEE installed in rear vacuum hose, with piece of vacuum tubing run under the seat).

I have the vacuum line to the petcock removed, and plugged (I didn't plug the vacuum port on the petcock).


I have the home made carb sync gauge (yard stick with 20' of clear tubing, with a few inches of Stabil installed as fluid). Each side of the tubing is connected to one of the vacuum line extensions run under the seat.

When I first started the bike all the Stabil just ran into the bike through the hoses. After that I installed the original VTR size 45 pilot jets into each end of the clear tubing, then tried again.

The Stabil moved much slower this time, all the way into the bike through one of the tubes. I tried to adjust the sync screw on the rear carb back and forth, but I couldn't make the fluid stop.

#1 Question: Do you guys think the Stabil is too low of a viscosity to use for this? It seems really thin, and moves super easy.

#2 Question: Does any part of my process sound incorrect?

#3 Question: Can I get it close by listening to/watching idle speed

#4 Question: Any tips or pointers?

Thanks!
James
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Old 07-09-2013, 10:15 PM
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Is it going to the front cylinder or the rear? If it's the front then my suspicions that you placed the "T" in the wrong spot or the rear line is incorrectly installed.

If that's not the case and you're positive they're correctly hooked up, then one side is way off. But to be that far out of sync, I'd imagine it is running horribly? You're going to have to turn the screw in one direction out the other, and try again. Be ready to shut it down as soon as the fluid moves. Once you're sure you've got the right direction, turn it in small increments until you're close...

But something is telling me you're not hooked up correctly on one of those hoses, and my money's on the rear since the front is so easy and would be hard to do wrong...
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Old 07-10-2013, 01:10 AM
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One thing to note, you need to have the yardstick at ground level, ie uphill for the fluid going to the bike, not an easy downhill...
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Old 07-10-2013, 04:52 AM
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I never block off the petcock end of the hose. I just leave it on the tank. The idea is that you want the setup to be as similar as it would if the bike were running on the street. But that shouldn't affect your signal noticeably. Who knows- you could run it long enough to use all the fuel in the carbs and need that vacuum to open the petcock back up.

Search for a thread that Nath981 has contributed to... a few people have put vacuum restricters in the lines to slow down the signal.
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Old 07-10-2013, 06:59 AM
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I installed vacuum restrictors in the form of size 45 pilot jets originally from this VTR. That slowed the movement of fluid quite a bit.

I will check tonight on which cylinder the fluid is running to.


Thanks!
James
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Old 07-10-2013, 07:38 AM
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if you place a small valve between the two sides, at the top of the yard stick, you can control the sensitivity so you have the time to adjust the balance before it gets sucked into the engine. This is how I manage to make my manometer adjustable and also adjust the degree of sensitivity. A small valve can be found in the drip irrigation section of any large store selling irrigation for drip watering.
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Old 07-10-2013, 07:44 AM
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Use aquarium valves from a pet store. A set of them is like $3. This will slow the operation. I had the same problem but dont know if I did the tweety trick of downhill.

5 Pcs Aquarium Air Line Tubing Volume Flow Control Valves | eBay
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Old 07-10-2013, 07:46 AM
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Ahh.... Would another pilot jet work there? I have lots of those laying around for free....

James
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Old 07-10-2013, 07:52 AM
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I've never used one... if it's traveling that fast, I just turn the screw a bunch of times and try again. Only times I've ever had it do that, though, are when I swapped carb bodies and the first time I took them apart and thought the adjustment screw was an assembly screw so I turned it all the way in.

You have enough line to have it on for 2-3 seconds even with the fluid going real fast. After you make sure everything's hooked up properly and looks sealed, try turning it a bunch both directions so that the fluid travels too fast in the opposite tube, then at least you'll know whether or not adjusting it is going to work.

You never know... you could have something blocking the plate so it's out of balance or something.
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Old 07-10-2013, 08:16 AM
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There is no way that it is that far out of sync, of it is at a normal idle speed.
You need enough elevation of the tube and enough fluid in the tube that the vacuum can't lift the entire volume. I don't know how many inches of Stabil you have for vacuum. You need more inches than that in the tube and in vertical height of your gauge.

Don't disconnect the petcock vacuum. It is very important that your float level remain constant.
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Old 07-10-2013, 01:57 PM
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I think a lot of us probably scratch our heads over this one. I built one of those yardstick manometers last year but keep procrastinating using it for fear of exactly what this OP is struggling with. How about a photo or two from those who have rigged this up successfully with air valves?

I have this idea of centrally placing a three way aquarium valve between the 2 sides utilizing Tees so that the total vaccuum is equal and adjustable at the beginning until you get a sense which side draws harder and then can manage the adjustment before all the fluid sucks out one side.

But I'd rather know if someone else already tried it successfully.
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Old 07-10-2013, 03:02 PM
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I seriously use straight tubes with no problems. If they're way out of sync, I have to turn it off and then back on a few times, but that's after major carb changes and it hasn't been enough of a PITA for me to seek out alternatives.

If you use motor oil and suck it in, it's relatively harmless...
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Old 07-10-2013, 05:34 PM
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this is how I installed a valve. Turn it open and the vacuum is low, close it to increase the vacuum and increase sensitivity.
Attached Thumbnails Carb Sync Going Wrong - Fluid keeps sucking into bike-imag0292.jpg   Carb Sync Going Wrong - Fluid keeps sucking into bike-imag0293.jpg  
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Old 07-10-2013, 10:49 PM
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Originally Posted by 7moore7 View Post
I seriously use straight tubes with no problems. If they're way out of sync, I have to turn it off and then back on a few times, but that's after major carb changes and it hasn't been enough of a PITA for me to seek out alternatives.

If you use motor oil and suck it in, it's relatively harmless...

I've never had valves or restrictors of any type on my straight tubes either and I've never had a problem. I suspend my yardstick from the ceiling with fishing line and the weight of the two stroke oil I used keeps it hanging vertically.

I DO have the first 3 feet of tubing that comes off the top of the yardstick zip tied together every five inches, which might act a bit of a restriction on the system. I wove the fishing line through those zip ties to help it hang straight too, and to assist in keeping things running uphill as tweety mentions.

That three feet of line plus the three feet of yardstick allow me to hang the whole thing at eye level right next to me as I sit on my 5 gallon bucket and do the sync... Works out good.

Last edited by supermarto; 07-10-2013 at 10:53 PM.
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Old 07-11-2013, 07:47 AM
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Originally Posted by supermarto View Post
I've never had valves or restrictors of any type on my straight tubes either and I've never had a problem. I suspend my yardstick from the ceiling with fishing line and the weight of the two stroke oil I used keeps it hanging vertically.

I DO have the first 3 feet of tubing that comes off the top of the yardstick zip tied together every five inches, which might act a bit of a restriction on the system. I wove the fishing line through those zip ties to help it hang straight too, and to assist in keeping things running uphill as tweety mentions.

That three feet of line plus the three feet of yardstick allow me to hang the whole thing at eye level right next to me as I sit on my 5 gallon bucket and do the sync... Works out good.
the little valve was installed as a sensitivity adjustment/damper. I hang mine from above the bike, just next to it. I've only had fluid race to one side once, on a bike that was way out of balance because new carburetors were installed. I use ATF in my manometer because it's easy to see. This cheap tool has been very accurate and easy to use.
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Old 07-13-2013, 05:47 AM
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Originally Posted by twist View Post
this is how I installed a valve. Turn it open and the vacuum is low, close it to increase the vacuum and increase sensitivity.
THANK YOU!

This is exactly what I had in mind.
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Old 07-19-2013, 02:18 PM
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Originally Posted by twist View Post
this is how I installed a valve. Turn it open and the vacuum is low, close it to increase the vacuum and increase sensitivity.

I made one that functions exactly as yours does. Worked like a charm, movement is moderate enough at the beginning I had no problem managing the adjustment without sucking any 2 stroke oil into either cylinder. Thanks for sharing that pic.

Bike idles much smoother since synch.
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Old 07-19-2013, 04:25 PM
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I guess I cheated when I bought the guages and had no issues. They were not expensive.
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Old 07-19-2013, 04:50 PM
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Guess that depends on you definition of "expensive"
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Old 07-19-2013, 09:15 PM
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I gave about 30$ for the two-gauge set. No time wasted figuring out something that already exists.
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