BIG POST! Carb syncing details?

[Phaseman]

I’m hoping to find someone with the time and patience to read through this and see where I am at. Thank you in advance if that is you.
I have completed a VM carb rebuild as per Paul Musser’s tutorial from BikeCliff’s website. I was pretty meticulous with the rebuild and am fairly confident that I have done it correctly. The bike is running now, but seems to lack the power that I would expect, though I lack experience with bikes this large. I have adjusted the carbs for high idle, again per instructions on Bike Cliff’s website and currently have the idle set at about 1000 rpm’s. Idle is smooth but the bike seems to me to need quite a bit of throttle to roll out in first gear, maybe a third to a half turn on the throttle.

Bike accelerates fairly smoothly through all gears I’ve had it up to 80 MPH or so. It seems that if I am tooling around at 2500-3500 RPM’s there is some fluctuation and muffled sputtering or popping unless I take it up to higher RPM’s. Also the bike generally returns to idle well but occasionally throttles down to about 1300-1400 rpm's then settles slowly down to 1000. Again it seems to me that throttle response and power should be greater than what I am seeing from a muscle bike. I have not yet had the carbs balanced with a sync machine of any sort, more on that later. Also I seem to be getting only about 20+ MPG and thought I would be getting much better economy than that.

Initial setup of the carbs was done with the pilot fuel screws lightly seated, then turned out to one and a half turns on the recommendation of a local shop. The side air screws were started at 2 turns out and then adjusted for high idle.

While rebuilding the carbs I found that the pilot fuel screw on carb #3 had the tip broken off and lodge into its orifice. After many hours with sewing needles and piano wire I finally dislodged that tip and replaced the needle. I am certain that the orifice was slightly enlarged during this procedure. This is evidenced by the fact that when seated and backed out 1 ½ turns that screw is visibly deeper set than those in the other 3 carbs.
Any suggestions based on what you have just read would be appreciated.

I am also looking for advice on my next steps.

Carbs have been rebuilt with all new ‘O’ rings, super well cleaned, new intake boots, new vacuum lines and vent hoses. Also rebuilt petcock and fuel lines. Lacking the funds for carb syncing at the local shop, I have decided to build my own sync tool, per some nifty instructions I found online. Assuming that it works, here are my questions:

Do the sync tubes connect to the ports just forward of the intake boots on the head? (I assume they are not connected to the vacuum ports on the carb bodies as only 3 of the carbs are so equipped.) Also, does anyone have any recommendations as to where I can find vacuum port nipples to replace the hex head screws that are currently plugging those holes?

Is my assumption correct that the pilot fuel screws which are adjusted under the float bowls will be used to adjust my low idle balance? Will the effect of adjusting those needles be shown on my sync tool?

Will the side air screw adjustment be reflected in my sync tool?

Is adjustment of the slides which is done from the top of the bodies with the lids removed reflected in the sync tool?

At what RPM’s should each of these adjustments be made?

I realize that these questions may show that my understanding of this process is way off base but I’m sure that someone here can straighten me out. I’ve done most of the reading that I can find through GS resources and other sites and I think I’m just not finding explanations written in a way that I need to hear it.

Thanks in advance for your suggestions, I’ll be sure and let you know how it goes.

P.S. I have also been considering attempting the plug chop method, but using a carb sync tool seems more straight forward to me.

[Nessism]

First off, the pilot fuel screw should be roughly 3/4 to 1 turn out from lightly seated for a starting point with a stock bike. Your bike must be rich with the screws set at 1.5 turns.

I had two pilot fuel screw tips broken off when rebuilding the VM's on one of my old 550's, the fuel screws set a little deeper into the carb body as you noted but the bike ran well regardless.

When syncing the carbs the only adjustment you should mess with is the one inside the carbs at the top of the slides. This is where you adjust and equalize the carbs. The vacuum port is as you noted, on the cylinder head. You can purchase vacuum port fittings or I've read about people drilling down into an allen head screw and then using epoxy glue to attach a piece of brass tubing into the socket head area of the screw. Hobby shops sell brass tubing like this for R/C usage. When syncing, set the idle stop to roughly 2500 rpm and make sure to set a large fan blowing on the engine to keep it cool.

I wouldn't pass judgement on the throttle response until you get the carbs properly tuned in. Of course, if you changed to an aftermarket exhaust or pod air filters, all bets are off regarding your jetting - which will have to change.

Good luck and hope this helps,

[Big T]

If you want to know if it's making power, you have to rev it up.Power starts at about 4,000rpm and kicks in at 6k.

Try running it up to redline in 1st and 2nd and see what power you have.

As for your carbs, you have a good start. Do a sync and go from there.

Or, you could bring it to the carb tuning party on April 11th

[Steve]

Do the sync tubes connect to the ports just forward of the intake boots on the head? (I assume they are not connected to the vacuum ports on the carb bodies as only 3 of the carbs are so equipped.) Also, does anyone have any recommendations as to where I can find vacuum port nipples to replace the hex head screws that are currently plugging those holes?

Yes, the ports in the head are the ports you use to sync the carbs.
Available from many places, one of them is Z1. (<- click the link)

Is my assumption correct that the pilot fuel screws which are adjusted under the float bowls will be used to adjust my low idle balance? Will the effect of adjusting those needles be shown on my sync tool?

NO, and probably not.
The pilot fuel screws are used to adjust the mixture, not idle speed or sync.
Even when carbs are properly synchronized, adjusting the pilot fuel mixture should have no effect on the vacuum readings.

Will the side air screw adjustment be reflected in my sync tool?

Probably not.
The side air screw adjustment is also to adjust the fuel mixtue. Like the pilot fuel screws, adjuting the pilot air screws should have no effect on vacuum readings.

Is adjustment of the slides which is done from the top of the bodies with the lids removed reflected in the sync tool?

YES.
This is where you do ALL the adjustment to synchronize the carbs.

At what RPM’s should each of these adjustments be made?

There is some discussion on this matter. Some like to do it at idle speed, some manuals actually specify 1500-2000 rpm. Since the purpose of synchronizing the carbs is to have them open the same amount at the same time, it is easiest to judge this when the carbs are open the least, meaning somewhere around idle speed.

Note that actual gauge readings are irrelevant. You are not looking for XX amount of vacuum. What you are looking for is that same amount in all four readings. Hopefully this "nifty little tool" that you made allows you to see all four carbs at the same time. While it is possible to use a single guage and a manifold to switch readings, or even two gauges for comparison, you will be chasing your tail for quite a while trying to get them all the same. If you ever see a four-gauge set in use, you will easily see how adjusting one carb affects the other three.

.

[Phaseman]

Nessism - First off, the pilot fuel screw should be roughly 3/4 to 1 turn out from lightly seated for a starting point with a stock bike. Your bike must be rich with the screws set at 1.5 turns.

Going to take em' in to 1 turn for now I guess, anyway to tell what's optimum?

I had two pilot fuel screw tips broken off when rebuilding the VM's on one of my old 550's, the fuel screws set a little deeper into the carb body as you noted but the bike ran well regardless.

Good to hear!

When syncing the carbs the only adjustment you should mess with is the one inside the carbs at the top of the slides. This is where you adjust and equalize the carbs. The vacuum port is as you noted, on the cylinder head. You can purchase vacuum port fittings or I've read about people drilling down into an allen head screw and then using epoxy glue to attach a piece of brass tubing into the socket head area of the screw. Hobby shops sell brass tubing like this for R/C usage. When syncing, set the idle stop to roughly 2500 rpm and make sure to set a large fan blowing on the engine to keep it cool.

Will do. Stock airbox and filter for now, unknown brand 4 into 1's.

I wouldn't pass judgement on the throttle response until you get the carbs properly tuned in. Of course, if you changed to an aftermarket exhaust or pod air filters, all bets are off regarding your jetting - which will have to change.

Good luck and hope this helps

Good to hear!

Big T - If you want to know if it's making power, you have to rev it up.Power starts at about 4,000rpm and kicks in at 6k. Try running it up to redline in 1st and 2nd and see what power you have.

I had no idea... Guess that means EVERYONE gets to know I'm speeding.

As for your carbs, you have a good start. Do a sync and go from there.

Looks like my new weekend project.

Or, you could bring it to the carb tuning party on April 11th

??? Carb tuning party? In the NW?

And Steve! To much to quote from, but thank you all. I have a busy weekend ahead of me now, if you think of anything else please let me know! I will let you know how it turns out and post pics of the syncing tool when I get it built.

[Big T]

??? Carb tuning party? In the NW?

Yeah, April 11th. I've sent you a couple of emails about it.

Carbtune, Colortune, a couple of knowledgable guys, food and drink, maybe a bit of a ride

BTW, what size jets do you have for the 4-1?

[Phaseman]

Yeah, April 11th. I've sent you a couple of emails about it.

Carbtune, Colortune, a couple of knowledgable guys, food and drink, maybe a bit of a ride

BTW, what size jets do you have for the 4-1?

Ah! Way behind on my emails, trying to catch up this weekend.

[Phaseman]

Carb Sync / Plug Chop

So I think I have all off the pieces in place to attempt the carb sync. I haven't hooked up my home made sync tool yet as I am waiting for a friends help later in the week. Don't know why but I feel like I should have a couple of extra hands/eyes/ears on the project.

The bike is running about as good as it has since I took ownership. Smooth through the gears, smooth idle, some popping and spitting since I located and fixed a couple of exhaust leaks. I figure that I need to re-adjust for high idle due to the change from fixing the exhaust leaks.

Should I do the carb sync before I start messing around with the plug chop method or after? My guess is before.


Maybe you guys can help firm up my understanding of Mr. tkent02's plug chop manual. I have questions on the following...

(For Fuel Screw Setting/Float Bowl Height) The low throttle chop: Just putt around a few minutes at about 20 or 30mph or so, keeping the throttle open, but just barely, in the correct gear for this speed. It takes a while to color the plug because there's not much going on inside the combustion chamber. This tells you about the mixture from the pilot circuit, the low-power stuff. Pay attention to how it runs and feels, you can tell rich from lean. If it runs well and the plug isn't black, it's probably doing OK. This one is probably the most important to get right, it sucks to have your engine screw up momentarily at the apex of a slippery corner.

I think maybe terminology is messing me up here. Does this section refer to the screw that passes through the float bowl and is adjusted from directly under the carb with the screwdriver held upside down? I have all of these set at 1 turn out based on your recommendations of 3/4 to 1 and 1/4 out. If my understanding is correct, this section of the "plug chop" instructions will address fine tuning of this screw for the individual carbs.

(For Best Needle Clip Position) Mid range: Go out on a highway and run it at about 1/4 to 1/3 throttle for a while, up a long grade is wonderful, but not required, as it doesn't take that long to get a good plug read. The plugs will color faster than the low power check. This tells you about your mixture from the position of the needle. If it spits and pops, that would be rich, if it surges, wanders or loses power for a while and comes back on, that would indicate lean. If it runs smooth and nice, it is close, looking at the plugs will tell you exactly. You need to see a little color here, a mixture resulting in lean, white insulators will run fine, but will eventually burn things up.

Does this refer to the "clip" inside the slide piston on the needle?

If so, which direction for richer and which for leaner? Also at rebuild time, these were in the same position on all four carbs, is that typical?

(For Best Main Jet size) Full power is done in one hard blast, full-throttle through the gears like a drag race. Does not take very long at all to get the plugs colored, you don't need to do insane speeds. You do need to find a place safe to go faster, where you can see any cops, and yet still be able to safely pull over to remove the plugs. The mixture at full throttle is controlled by the size of the main jet. You definitely need to see a color other than white; too lean here will burn things up in a hurry.

So would it be true that with all other adjustments in range, the only way to affect change here would be to increase or decrease the jet itself?

[Big T]

Clip - moving the clip higher on the needle (away from the taper) makes the mixture leaner - all 4 carbs should have the needles in the same position

As far as the inside of the float bowl, the float height can also affect performance also

You should sync 1st - if you make major jetting changes, resync