Stock Carb Sync

ski4

ski4

gonzo
Location
cleveland
i was playing with my carbs for the past week trying to fix a jetting issue and realized the carbs are not easily getting in sync.
if i adjust the sync screw to get the throttle plates to be open equally then the back carb also does not close fully and vice versa

2 questions, is there a way to fix this and will this give my stuttering top end and loss of rpms ??

when the carbs are synced in the closed postion the back open mostly all the way just a millimeter or 2 shy of full opening
 
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douglee25

douglee25

m3booooy
Location
South Jersey
You need to sync both carbs to pull the same vaccuum at idle with a manometer. You can build them for a couple bucks and use 5W30 as the oil of choice.

Doug
 
douglee25

douglee25

m3booooy
Location
South Jersey
ski4 said:
sounds like a lot of work
Click to expand...

It takes 15 minutes to make one and you're set for life. See this post when I made one for my motorcycle.

Doug

Note: I used this on a 4 cylinder motorcycle, but you would only need to do two cylinders.

http://www.r6messagenet.com/forums/showthread.php?t=42890&highlight=manometer


They look like this when done.

IMG_1152.jpg


IMG_1151.jpg


IMG_1149.jpg
 
douglee25

douglee25

m3booooy
Location
South Jersey
Big Kahuna said:
OK, I am gonna ask it cause somebody will......... What is that?
Click to expand...

A Manometer is a device used to measure pressure differential. When you hook it up to two different carbs, they each pull a certain amount of vacuum. If one carb pulls more vacuum than the other, the the oil, water, mercury (whatever the fluid is inside the tube) will flow upwards to that side. The object is to get the water level equal in each side. This means the carb vacuum levels are equal and thus your engine will idle and run smoother. Since two stroke engines are rattle traps to begin with, this may not be as imperative as with a four stroke, four cylinder motorcycle engine. If one cylinder is pulling more vacuum on a four cylinder bike, you will know it. Your hands and a$$ will be sore as hell from vibration.

Hope this helps.

Doug
 
vomitspot

vomitspot

Location
mobile alabama
who in the hell is gonna drill holes in the carb to hook up a manometer?
vw makes a carb sync tool $30
fits into the top of the carb measures vaccume. then you adjust and remove
done! only have to remove the air box/flame arrestor
no holes to drill
 
douglee25

douglee25

m3booooy
Location
South Jersey
vomitspot said:
who in the hell is gonna drill holes in the carb to hook up a manometer?
vw makes a carb sync tool $30
fits into the top of the carb measures vaccume. then you adjust and remove
done! only have to remove the air box/flame arrestor
no holes to drill
Click to expand...

I didn't say drill holes into the carb. I said drill holes in the intake stream. That's down from the carbs last time I checked.

Doug
 
vomitspot

vomitspot

Location
mobile alabama
sorry ..who in the hell would drill holes in their intake manifold just to sync the carbs?
1 that can be done by sight:if carb 1 is open -carb 2 needs to open @ same time
2 if a tool is needed its extreamly easy to put a carb sync tool in the top of the carb again 1 moves 2 moves
 
matty180

matty180

X-
Location
Mahopac, NY
Dude you don't need any meters or anything. Depending on what kind of carbs you have. If you have stock 38 carbs. This is the procedure. That meter is used for carbs in motorcycles where the slides are operated by vaccum. These types of carbs do not require that. All you have to make sure of is that the butterflies are equal.

1. Back out your throttle screw all the way so it is not touching the stop.This is the carb that you use to match up to the other one. This carb has no adjustment and should be totally closed. If it is not then your butterflies are bent or worn.
2. Look at your other carb and see if it is opened or closed. If it is open than you have to adjust the screw that is in the middle of the carbs where they connect. By turning it in or out will adjust the butterfly. Once you have this one closed they are now in sync.

If you have any aftermarket carbs it is really simple. Depending on what type of coupler that you have that connect the carbs together. Loosen up the 4 or 2 allens on the coupler. Back out the idle adjutment screw so it is off the stop. Always start with the carb that has the spring on the throttle shaft that allows the butterfly to return. Tighten up the allens that are the side of this carb. Next take a pencil and flip it over and use the eraser to push down on the butterfly of the second carb gently. While holding the butterfly down tighten up the remaining allens. And now your carbs are all set. And that is it. There are no special tools required. That manometer is for different applications. Defenitley do not drill any holes. If you have any other probs, let me know. Done a ton of carb work on all brands and makes. Bikes, ATVs,watercraft and snowmobile.

Matt
 
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