How to synch your carbs using the home made tool

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xArmstrongx

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Hi there,

I was wondering if anyone could post a detailed tech article on how to properly synch your carbs using the home made tool?

Also, one quick question, does the air screw just adjust the air ratio when it comes to the fuel/air ratio?

If so, why isn't there a fuel screw like most carbs?


Thanks in advance

RIDE ON!:thumbsup:
 
I made a simple manometer- clear tubing and auto transmission fluid. Get 20 feet of tubing (whatever fits the vaccum nipple on your bike) and find the exact center. Place the center at the bottom of a 4 foot piece of wood, then attach the tubing up the length of the board (exact length is not important, but longer give you more time to shou down if you have to). I used zip ties, but I had the thicker wall tubing- whatever you do, make sure the tubing is not collapsed. The most time consuming part of this was getting the fluid to settle in the center. To get the fluid in, I put one end in the ATF bottle and sucked the other end like a straw. I drew up about 2 feet worth of fluid, the exact amount is not important. I then hung the apparatus with the tubes in the air and waited for the fluid to settle- took 15-20 minutes. I hung mine from a ladder to use it, but I was also using that to hold the gas tank (has to come off to get to the sync screw).

After warming the bike up, hooked the tubing to the vacuum nipples on the carb holders, I started it up.....and the ATF nearly got sucked into the engine because the left cylinder was drawing much harder- way out of sync. Word to the wise, keep your thumb on the kill switch until you get it close to synced. Shut it down if one side starts to rise too fast. Longer tubing would also give more time to react...thicker fluid too. I adjusted it a couple times after having to shut it down, then it was close enough that the movement was very slow. I adjusted back and forth and got both sides of the fluid as even as possible. Perfect is near impossible, but I got it within about 1/2-3/4 inch. According to what I read, that's pretty good.

Do not use a thin fluid as it will foam and be hard to read. I used ATF because it is easy to see and a bit (if only a bit) sucked into the engine will not hurt it.

manosmall.jpg


What you adjust is the screw on the shaft between the throttle butterlies:

400carbs1.jpg


The idle mixture and the idle speed are different adjustments on the carb which, provided they are properly adjusted, do not need to be messed with to sync. You will probably have to adjust he idle speed after you are done.
 
Wow!

This is such a great response.


I can't wait to get out in the garage and make it happen.

Thanks so much. :D:thumbsup:
 
Water levels have been used for years to establish a level line for buildings,etc.Water in a tube always seeks a perfect level. This is the same concept,as the pressure at rest will be level,and with pressure equalized,it will be level as well. Be ready with a pair of pliers to pinch the line,as the tube will quickly suck up all the ATF if the carbs are out enough. lha
 
Most any fluid will work. If that small amount of even anti freeze gets sucked into the engine it will get blown out ther exhaust before you shut the engine down.
I have found it to be very sensitive.
A good bench sync helps get it close. I use a piece of paper cut about 1/4 inch wide. Use it like a feeler gauge to set the sync screw so it takes the same force to pull it out from between the butterfly and carb bore.
In HoughMade's second pic set the left carb with the idle speed screw to get a firm slip fit of the paper, use the sync screw to set the right carb.
Leo
 
I bought a plastic tank from a mx80 for temporary use on my bikes for occasions like this and for the fact that I'm not satisfied with the way my tank on the dirt bike turned out. It can be used for riding by putting a bungie strap around it.I got it off ebay for $10.00+ $6.00 shipping,so I have a good testing tank for cheap,and it can't rust. It would be good for a use like this,as it's way out of the way when in use and holds about 1+ gallons,and will run a bike for a while. lha
 
xArmstrongx said:
Hi there,


Also, one quick question, does the air screw just adjust the air ratio when it comes to the fuel/air ratio?

If so, why isn't there a fuel screw like most carbs?


Thanks in advance

RIDE ON!:thumbsup:
Click to expand...

The mix screw adjusts the fuel. Turning it in leans it, turning it out richens the mix.
Also it's critical to have the rubber O ring, washer and spring on the screw.
 
lhaolpa, good deal on the tank. I use a plastic tank from an old riding lawnmower as a test tank. Yours is proably easier to use. Slips over the frame and set good. Fine I have to zip tie to the handle bars and hope it stays put.
Leo
 
This worked so good and so simple. The hardest part is being diligent on the first start because the left side wanted to pull so hard when I first started the bike.I had to shut it off right away!
I adjusted toward the 'weak' side to even it out maybe 1/4 turn initially to get it closer. Restarted the bike. No go...was still way off so another 1/4 turn. Restarted and that was better.I could let it run now. Than it was tiny, minute adjustments.The pressure from the screwdriver would even effect the levels so I waited for a moment after every adjustment until the levels settled.Got it within 3/4 inch. I know from 'houghmade' that this is good. I reset the idle(tick-over) to about 1200? and re adjusted the synch screw because it had changed with the idle adjustment. Yeah she was idling!! wohoo!! I frickin love this forum!! Thanks guys!!
 
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I spliced in a valve at the bottom of the U, and slowly opened it while the bike was running. This prevents the fluid from getting sucked up and allows you to close it quickly if you need to. A breather valve at the top of each end allowed me to re-balance the fluid level without shutting her down too. I bought these fittings in an assorted set of fish tank stuff for $3 at Meijer. I used motor oil since I was worried about what ATF would do to the engine.
 
ThePsuedoMonkey said:
I spliced in a valve at the bottom of the U, and slowly opened it while the bike was running. This prevents the fluid from getting sucked up and allows you to close it quickly if you need to. A breather valve at the top of each end allowed me to re-balance the fluid level without shutting her down too. I bought these fittings in an assorted set of fish tank stuff for $3 at Meijer. I used motor oil since I was worried about what ATF would do to the engine.
Click to expand...
ATF won't do any harm,and will actually do some good! Have you ever heard of Marvel Mystery Oil? It's the same thing as ATF,and I use a half quart per tank in my '41 Ford tractor as an upper cylinder lube.Also,if a motor has been sitting long,putting ATF in the chambers is the best and safest way to free up the valves and rings. It won't hurt your motor!! lha
 
lhaolpa said:
ATF won't do any harm,and will actually do some good! Have you ever heard of Marvel Mystery Oil? It's the same thing as ATF,and I use a half quart per tank in my '41 Ford tractor as an upper cylinder lube.Also,if a motor has been sitting long,putting ATF in the chambers is the best and safest way to free up the valves and rings. It won't hurt your motor!! lha
Click to expand...

how much fluid do you put in?
 
To free up rings and lube valves,you'd put about 1 tbsp in each cylinder,then let it set overnight. To add to gas,about 1 oz per gallon....lha
 

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