Some problems with my bike I could use some help with. Also, what does a carb sync. do?

Question

Hello all,

Let me start off by saying I'm a newb. at the motorcycle game. About two weeks ago, I bought a 1993 Yamaha XJ600 Seca II. The bike ran well aside from the fact that it needed a new back tire and some other general maintenance. Anyhow, the bike runs fine after I have it idle with the choke for a while except it's not as quick as I would expect it to be. The bike idles fine (although it's a little low, supposed to be from 1200 to 1400 but it's about 900-1100) but when I pull the throttle real quick, it bogs and doesn't rev. Sometimes it turns off when I do that but most of the time it just goes back to idling. Is this something a carb syncing would fix? I called a place and he said 75 bucks/carb which is 300 which seems like a complete ripoff, right? Any help would be greatly appreciated, thanks in advance.

Answer 1

First off, carb syncing won't do any good because that isn't the problem.  Syncronizing the carbs just means that each carb is adjusted so that all carbs feed an equal amount of air-fuel mix into their respective cylinder.

If the mechanic knew what he was doing, he could use the same gauges to determine if a rubber diaphram in the constant velocity (being a '93, I'm assuming CV carbs) is leaking air.  One thing you might do is check for the air vent at the top of the carbs.  If they are CV carbs, they should have a round or square plate at the top of each carb approximately 3 inches across.  Each one should have a very small opening to the outside and if grease or goo is covering the hole, it could affect the throttle action.

If your bike does not have CV carbs, the top of the carb will not have the large cover and instead will have a small round or rectangular top appproximately 1-1.25" across or 1"X2".  These throttle slide carbs are affected by sudden increases in throttle opening at low rpms.  In other words, with this type of carb, whacking open the throttle at low rpms drops the vacuum and as a result, the engine bogs down.  The answer is to not do it.

I wouldn't worry about the idle speed, as long as it idles ok and the oil pressure light doesn't come on, don't worry about it.  Bike tachometers are not super accurate and can't always be trusted at very low rpms.

Answer 2

Well newb, I've been fiddling with bikes since 1957 and still don't know everything.

You have a good old bike.  Now you have to decide whether you are going to really get into bikes or just be a casual rider.  

Bike mechanics don't get paid a lot and the 300 bill is about right.  On the other hand you might want to get a shop manual and other reading material about bikes.  The bogging might be due to several reasons but the cheapest fix is to look for air leaks in the intake manifold.  My kid fixed a Harley intake manifold with Mikuni carbs with some inner tube and glue.

When the throttle is opened the air leak may cause the fuel-air mix to be too lean and cause the bike to bogg down.  You might try riding with the choke on to see if that richens up the mix when you open the throttle.  

It comes down to one issue: do you want to work on the bike yourself and really know the machines or just have someone else do the mechanical work.  

Keep in mind, the more you know, the more trouble you can get into.

Have fun.

Answer 3

it should be around 75 to a hundred dollars to synch the carbs. you could buy a set of murcury gauges and adopters to fit your carbs if needed for around 120. once they are hooked to your carbs simply start the bike and the synch s***w is in the niddle if your carbs. simply turn untill the murcury is level all the way across. blip the throtle LIGHTLY and the murcury should rise and fall together across the bord so to speak. you might just need to pull the carbs and clean them but then they should be synched when re installed. I would adjust the valves clean and synch the carbs if it were me.Find another shop that price is way to high.

Answer 4

I was charged £40 for a carb balance on a twin carb bike which is about $80, $300 sounds a h**l of a lot.

Answer 5

Get some carb syncers and do it your self.

But first set your idle speed up to what it ought to be.  Keep the idle speed within spec. Whenever it drops or speeds up adjust it back.

Sounds like it might be letting air into your carbs some where.  Below is an amazon link for carbsyncers, you can get a set of 4 for less than syncing 1 carb.

Answer 6

i'm not sure of the price, but it is very likely that carb synching is your problem.