Author Topic: Carb sync (Read 49387 times)

csendker · « **Reply #125 on:** May 03, 2006, 08:52:54 am »

Would the snubber solve the bouncing gauge problem?

http://www.plumbersurplus.com/ProductDetail.aspx?Prod=12391&Cat=887

Of course, keep in mind the snubber costs more than the gauge.

Bob Wessner · « **Reply #126 on:** May 03, 2006, 08:56:47 am »

I'm lucky enough to have a Carbtune, love it. The "dampeners" on it are nothing more than a couple of plastic, cylindrical plugs that fit in the hose, which is cut so many inches from one end, forget which end, and in the center of the plug is a very small hole. That's it, just keeps up the vacuum without over reacting to fluctuations.

KB02 · « **Reply #127 on:** May 14, 2006, 05:11:25 am »

Does anyone have a good proceedure for bench synching carbs that they could post?

jdpas29 · « **Reply #128 on:** May 14, 2006, 06:01:00 am »

get a 1/8" drill bit. slide the drill bit into the gap where the carb slider(don't know the technical term) comes down to meet the floor inside the carb body. you want to make all the cylinders meet the floor with the same gap so use a couple of wrenches or a wrench and a socket to loosen the adjuster at the top of the carb to set this gap. you will have to remove the top covers on each individual carb. and from my experience, you can do this procedure with the carbs on the bike just as well as with them off. you will need a headlight or a good shop light. make sure that the "feel" of the drill bit is the same when retracting it from the groove/gap... and also make sure that you're not putting an angle or pitch on the bit itself which will throw off your measurement.

KB02 · « **Reply #129 on:** May 14, 2006, 01:10:40 pm »

Thanks!

Jonesy · « **Reply #130 on:** May 14, 2006, 03:45:18 pm »

Give this site a peek:

http://www.salocal.com/sohc/tech/carb/asmpg3/syncprep.htm

dgilling · « **Reply #131 on:** May 21, 2006, 08:53:31 pm »

This may be a dumb question...but how do you sync the carbs on a 77 cb750k? My clemer manuel doesn't explain this and I couldn't find it on the forums. Do I need a special tool, and does the gas tank need to be off the bike?

Thanks,
Dusty

ElCheapo · « **Reply #132 on:** May 21, 2006, 09:22:01 pm »

Yes the tank has to be off the bike.

I use a vacuum gauge set that has 4 separate gauges and a decent ketchup bottle )the restaurant style ones with the nipple) of fuel to run it on. First you must find the weak cylinder and adjust the rest to match.

Normally
1. Adjust Timing Chain tensioner
2. Adjust valves
3. Synch Carbs

If the first two are off you may get incorrect vacuum values.

Bob Wessner · « **Reply #133 on:** May 22, 2006, 03:21:21 am »

Engine should be warmed up also.

Paul · « **Reply #134 on:** May 22, 2006, 03:25:37 am »

As ElCheapo says..do all other adjustments first.
Then...

you will need some form of vacuum measuring apparatus such as
4 vacuum gauges or mercury pillars or Morgan carbtune(steel rods instead of vacuum)
Gauge -------Tube ------ Throttle / restrictor--------tube -------- fitting M5 Metric thread. (x4)
See photo example.

The throttle/restrictor is for vacuum gauges to stop the needles from flickering erraticly.
1. Start bike and run to op temp.
2. Remove tank and either raise it up out of the way or replace it with some resovoir to supply gas to the carbs.
3. remove cross head screws from the carb manifold and fit M5 fittings from your vacuum lines (x4)
4. Undo locknut on carb adj screw (image 1)
5. Run engine and adjust restrictors to dampen needle movement (if using vac gauges)
6. adjust slotted screw until all gauges are reading equal (doesn't matter what...just equal)

Some initially do the following:
If you can get at the carb throats, put something like a 10mm drill under the carb sleeve and adjust initially to that all sleeves are equal (This is just a starting point because it doesn't mean they will all draw the same vacuum)

Oh, and wait for confirmation of these steps...I'm not infallable (sometimes)

Bob Wessner · « **Reply #135 on:** May 22, 2006, 03:29:55 am »

This might help in visualising what is involved;;

http://www.salocal.com/sohc/tech/carb_sync/carbruetor_synchronizing.htm

eldar · « **Reply #136 on:** May 22, 2006, 08:31:43 am »

You may want to adjust you air or fuel mix after you do the sync also. A dwell/tach works best for this.

TwoTired · « **Reply #137 on:** May 22, 2006, 03:35:43 pm »

Each adjuster has a range of adjustment. Find one that looks like it is in the middle of the adjustment range, or where it was originally set, and lock it down. Run the bike and adjust the next carb to match the previous vacuum reading. Lock it down and readjust if the vacuum changes so that after it is locked down the two readings are the same or very close. Do the next in the same way, then do the fourth.

You want to do this with the lowest idle setting you can manage but not below 1000 RPM. You may have to fiddle with the idle adjust knob frequently. You may have to go back and readjust, a couple one at a time, if the slides don't return to the exact same position consistently after bliping the throttle.

Set up a window fan to keep the engine at an even temperature. Readings will change as the engine overheats. Fans as high a 40 MPH are not too big.

Cheers,

dgilling · « **Reply #138 on:** May 22, 2006, 05:33:23 pm »

All of this is excellent... After adjusting the timing chain will I need to adjust the timing?

eldar · « **Reply #139 on:** May 22, 2006, 06:01:32 pm »

You should check it. Just to make sure it is correct.

Gordon · « **Reply #140 on:** May 22, 2006, 07:25:35 pm »

Quote from: dgilling on May 22, 2006, 05:33:23 pm

All of this is excellent... After adjusting the timing chain will I need to adjust the timing?

Just to be completely clear, the cam chain has nothing to do with the ignition timing. Like Eldar said, you still should check the timing, but adjusting one does not affect the other.

eldar · « **Reply #141 on:** May 22, 2006, 07:28:16 pm »

It may a little since you are supposed to adjust cam chain before doing the valves and so that has a bit to do with timing but probably minimal. I could be wrong though, it just sounds good!

Gordon · « **Reply #142 on:** May 22, 2006, 09:47:35 pm »

Quote from: eldar, Master of the K8 Thunder! on May 22, 2006, 07:28:16 pm

It may a little since you are supposed to adjust cam chain before doing the valves and so that has a bit to do with timing but probably minimal. I could be wrong though, it just sounds good!

I think the confusion here is in the wording. Is he talking about adjusting the cam chain tensioner and then checking the valve clearances? When I hear someone mention adjusting the "timing" I automatically think ignition, since that's what it typically means. Or am I just the one causing the confusion.

dgilling · « **Reply #143 on:** May 22, 2006, 10:38:20 pm »

no confusion caused, your helping me figure all of this out.

csendker · « **Reply #144 on:** May 23, 2006, 12:18:47 pm »

I don't think the fuel lines are "main" & "reserve". I think the main/reserve thing ends internally to the petcock, and the lines are both main fuel to the carbs. It's just a 2 port petcock. Try running fuel through both lines.

my78k · « **Reply #145 on:** May 23, 2006, 12:41:56 pm »

I think you've hit the nail on the head with this one...although my petcock is a single line I believe from reading earlier posts that the 2 line type is exactly that...the fule is ditributed across 2 lines but the on/reserve is controlled at the petcock...

TwoTired · « **Reply #146 on:** May 23, 2006, 01:17:07 pm »

Quote from: Wykydtron on May 23, 2006, 12:52:04 pm

Thanks for the replys but I understand that the fuel's main and reserve is controlled at the petcock. When the the fuel is switched to ON it flows from the outermost port. The fuel line that is hooked to that port runs to the tube between 3 and 4. When switched to reserve it flows from the inner port whos fuel line runs the the tube between 1 and 2. I could be mistaken but Ill check on that tonight. But yes both lines end up being "main" because the tubing that runs between the carbs is all connected so all the carbs get fuel from either line...right? Pretty sure thats the case but Ill try getting fuel to both lines and see what happens. Anythings worth a shot at this point. Thanks men.

Both petcock outlets are fed at the same time. The petcock selector determines if it is from the stand pipe(normal or on) or the base of the tank (reserve).

One of the output lines feeds 1&2 cabs and the other feeds 3&4 carbs.

You carbs have no fuel connection between the 1&2 and 3&4 pairs other than that petcock. During your carb synch, you will have to supply both fuel lines to the carb bank.

When you run out of gas, the fuel level lowers below that of the slow jets which are about 1/2 inch higher in relation to the main jet. Unless you are cruising, the engine normally dies at this point, leaving some fuel still in the carb bowl.

Cheers,

my78k · « **Reply #147 on:** May 23, 2006, 01:25:03 pm »

One way to find out...connect 2 hoses...turn to on position and see if they both flow...

DaveInTexas · « **Reply #148 on:** June 12, 2006, 09:43:06 pm »

From reading the description in the manual it seems like it equalizes the mass* of air admitted to each cylinder. *not the volume, nor pressure
I say this because a) that is the important thing when it comes to stoichiometrics and equalizing the combustion forces between cylinders.
b) when you measure 'vacuum', you are measuring a pressure, but with equal displacements and vacuum, we end up with an equal mass of air.
c) I have started my evening drink and feel scientific and philosophical at the same time.
Is synching even a word?

DaveInTexas · « **Reply #149 on:** June 12, 2006, 09:43:27 pm »

Here is what started me thinking this:
After I set the throttle stops on mine by looking into the throat and measuring the gap, I got to thinking what you are adjusting when you set the cable tensions (this is a 4 into 1 cable).
And I think the answer is, 'the slide height'.....which in turn sets the volume of air (and fuel via the jet needle, btw). I checked all mine visually everywhere from closed to WOT and they all seem to be in the exact same posiition.
Now if it turns out they still need adjusting via the vacuum gauge test, does that mean they will not open by the same amount?
And if they need this adjustment, even though they all appear perfect right now, where is the error coming from? Differential leakage of air in or around the carb??

News:

Poll

What is the best method you have found to synch carbs on a 750?

Author Topic: Carb sync (Read 49387 times)

ElCheapo

eldar

eldar

eldar