carb sychronization question

Just put new carb holders and some Emgo pods on my bike and it seems to have lost some power on the top end, so I'm guessing I need to go up in jet sizes. But before I do that, I want to make sure they're at least in sync first, so I just ordered four vacuum gauges w/orifices.
At what rpm should I check the sync?
And is there a thread on how to make a carb testing fuel tank on here anywhere?

del

Lawn mower gas tank! Excellent! I know just the guy to get one from too. Thanks!

that woulda been way easier than the way I did it

I siliconed two 700ml pop bottles together, and made a tap/fuel line thing using one of the caps.

It works nicely, but it woulda been way easier to use a mower tank

Balance has a big effect on these 4's. You balance at idle once engine is warm, but you can keep a fan running to avoid overheating, but if you'r quick should be ok.
Once synchronised you blip the throttle once or twice to see if it's all ok. I am a mega big fan of the morgan carbtune II, check the web, it's the easiest tool to use, just great...

I just stick the tank on my dustbin which is just higher than my bike and I use a long fueline to the bike, minimum investment...

For testing VM series carbs on our carb test bikes, I have two fuel lines; one has one inlet and the other two. Both use an inline fuel filter. The long fuel line section from the fuel filter to the tank is about 8" longer than normal. This way, we can put a prop under the tank when tuning and use the same hose to feed gas to the carbs when tuning as we do when driving the bikes in carb testing. For BS series carbs, this doesn't work well since the sync mechanisms require a much longer screwdriver to adjust so we use a K&L shop tank which is a small plastic bottle that holds about a quart of gas. This tank has a 5 foot length of hose and we use a barrel connector to connect it to the single inlet hose connected to the carbs. The barrel connect is a 1/4" vacuum fitting and we just clamp it in place using small radiator clamps.

You synchronize at normal idle speed. To set the idle speed, the engine must be fully warmed. Once fully warmed, set the idle speed using a remote shop tach OR by ear. Your bike's tach is often not real accurate in this rpm range. About 1200 - 1300 rpm is about right... You can get the bike to idle lower, but remember your oil pump is driven off your crank and if idled too low for too long, could starve your cam shafts of oil. Most folks make the mistake of setting their idle when the bike is cold which will end up being too high when the bike warms. Just allow your bike to warm so that you can take it off choke and not have to blip the throttle when setting synchronization.

Post edited by: wiredgeorge, at: 2007/09/24 11:14

Thanks George. I may just do it that way, with the longer hoses and propping the tank.
But right now I'm still waiting on my vacuum gauges. I got the email confirming he has my money, but nothing as far as a shipping notice. We'll see.
But to keep me busy, I tried to start my old '54 F100 yesterday, and found that the fuel in the float bowls has gone bad. Can't even light it with a match. And I swear I put Stabil in it last year.

OK, just now getting around to synching my carbs. Had to wait til the little orifices for my gauges to show up.
Checked sync last night, and the readings check as follows:
#1 carb= 9in @1300rpm
#2 carb= 12in @1300 rpm
#3 carb= 9in @1300rpm
#4 carb= 9in @1300 rpm

So should I try to make #'s 1, 3, and 4 match # 2?
Or just open up #2 to make it match the rest?
Does it matter?

Last time I checked compression, about a month ago, the cylinder pressures were all pretty even.

The actual reading number is not important. They are all relative to each other so you don't care if it's high or low. Therefore it's easiest to match #2 to the other 3.

However, have you checked the calibration on the sync tool? This needs to be done to make sure equal vacuum gives equal readings on all four channels.

If you're using a mercury manometer, I posted calibration details in this thread:
kzrider.com/component/option,com_joomlab...,3/id,154267/#154267

Oops, I see you ordered four vac gauges. You should still get the 4-to-1 plastic manifold at a parts store (Murray's or Autozone should have them) to make sure all four are calibrated.

Post edited by: loudhvx, at: 2007/10/06 13:14

Thanks loudhvx, I know I need a manifold to check how accurate they are, but in the mean time what I did was get the motor running warmed up at a constant rpm (1300) then I checked and recorded each gauge one at a time on one carb. For two dollar gauges, they all read within half of a single graduation which happened to be right at nine inches on the one carb. I figured close enough for government work and went with it.
So then I went ahead and hooked it all up and went for that #2 carb. Sure doesn't take much of a turn to make that needle move does it? Well I got that one synched real good, then I noticed #1 started running a little low, about 7 and 1/2 half inches. So I adjusted that one. Got them all running 9 inches.
So, I went for a ride. I seem to have lost some bottom end AND top end. So I guess now I need to start messing with the jets and needles. She's smooth as silk just cruising, but she prefers I stay a gear lower on certain hills at a certain speed or she'll cut out a little. Then there's the odd cough every once in a while.
But If I hit her hard from a stop and go on up through the gears I can feel some missing about midway on the tach. But then she'll scream right on up into the red.
Should I go up a size or two on the mains? They're #110's right now. Didn't see any #'s on the primaries, but then, I'm an old blind fart now.
Haven't looked to see where the needles are set.

Have to disagree a little on the comment that "it doesn't matter what level the mercury readings are at the same level"... have heard this before and it just doesn't work for me... I don't know what 9 inches means... my gauges do not use mercury and have numeric values and I just can't recall what the scale is. On my old mercury gauges they used cm over something... ANYWAY, I have found that when a bike is synchronized and if it isn't at at least 20 cm on my gauges, the idle mixture is wrong... either too lean or too rich. The levels will all equalize TOO LOW because the slides have to be opened up quite a bit farther to maintain an idle than if the idle mixture is correct. When this happens, I adjust the idle mixture for each cylinder by adjusting the mixture screw to max the idle speed, turning down the idle to the original speed after each adjustment. I almost always find that when the carbs are resync'd, the levels will be above the magic 20 cm mark. This is true for either mechanical slide or constant velocity carbs. Now the 20cm mark... not sure how well it holds across all types of gauges but it has been consistent for the past half dozen sets of mercury guages I have used and the current pro-grade dial type gauges... These gauges use a choke on each gauge with no fluids but the readings on good running carbs are almost always 22-24 cm.

I have mentioned in the past that adjusting one slide will effect the others to some degree. You did right to change the highest reading and then readjust the one that was affected by that adjustment. The reason they are all related is that the slides hang from the same rod. When one slide is down all the way it can go, it will force the others UP a bit... One issue I see frequently in customer carbs is worn slide actuator mechanism springs... there are little metal pads that push the ball on the end of the slide actuator that are spring loaded and these springs are frequently tired and won't allow the slide to lower as far as it should, making adjustment difficult.

Have to disagree a little on the comment that "it doesn't matter what level the mercury readings are at the same level"... have heard this before and it just doesn't work for me... I don't know what 9 inches means... my gauges do not use mercury and have numeric values and I just can't recall what the scale is. On my old mercury gauges they used cm over something... ANYWAY, I have found that when a bike is synchronized and if it isn't at at least 20 cm on my gauges, the idle mixture is wrong... either too lean or too rich. The levels will all equalize TOO LOW because the slides have to be opened up quite a bit farther to maintain an idle than if the idle mixture is correct. When this happens, I adjust the idle mixture for each cylinder by adjusting the mixture screw to max the idle speed, turning down the idle to the original speed after each adjustment. I almost always find that when the carbs are resync'd, the levels will be above the magic 20 cm mark. This is true for either mechanical slide or constant velocity carbs. Now the 20cm mark... not sure how well it holds across all types of gauges but it has been consistent for the past half dozen sets of mercury guages I have used and the current pro-grade dial type gauges... These gauges use a choke on each gauge with no fluids but the readings on good running carbs are almost always 22-24 cm.

I have mentioned in the past that adjusting one slide will effect the others to some degree. You did right to change the highest reading and then readjust the one that was affected by that adjustment. The reason they are all related is that the slides hang from the same rod. When one slide is down all the way it can go, it will force the others UP a bit... One issue I see frequently in customer carbs is worn slide actuator mechanism springs... there are little metal pads that push the ball on the end of the slide actuator that are spring loaded and these springs are frequently tired and won't allow the slide to lower as far as it should, making adjustment difficult.