Can I use dead cylinder method to sync barb-less carbs with a Pamco / Boyer ignition?

[larrynyc]

Hello,

I have a stock 1975 XS650B. The points are finally getting to me. I'm thinking about getting a Pamco electronic ignition.

According to the Pamco website, it says the ignition requires a special dual-output ignition coil. Here's a link to it.

So here's the issue. The BS38 carbs on the '75 DO NOT have vacuum barbs for syncing -- so I have to use the dead cylinder method. Also it has separate throttles (and thus, separate idles, I'll get to that in a minute).

I sync the carbs by yanking the right spark plug cable, sticking a very thin metal object (ie: a washer) between the idle adjuster screw and the throttle tab on the left side, the slight thickness of the washer gives about a 1K RPM boost. So I turn the left idle screw to make the idle to, say, 2.2K RPM. Then I'll switch off the engine, replace the right spark plug cable, yank the left cable, swap the washer to under the right-side idle adjuster screw, fire it up and match the right idle to 2.2K RPM. When I pull out the washer and replace the spark plug cable, the carbs are synced.

But I can't do this method because according to Mike's XS, the dual-output coil has a warning that says: "Caution! Do not operate or apply power to the ignition system with one or both spark plugs disconnected." Apparently, it fries the coil.

So if I get a Pamco (or Boyer), how do I sync my barb-less carbs if pulling a spark plug cable fries the dual-output coil? I've thought about swapping the '75 carbs with a '76 set (that has vacuum barbs), but the '76 DOES NOT have separate throttles/idles, which means it would require a whole entire process to convert my dual throttle to a single throttle, all of which seems like a big costly mess just to be able to use a Pamco. Does this mean if I use a Pamco, I have to "guess" my sync by ear? It seems ironic to get an electronic ignition to get precise timing, at a cost of precise carb sync. Could I use the stock coils that aren't so fragile?

Any advice appreciated, thanks!

 

[pamcopete]

larrynyc,

You can pull a wire from a spark plug with the engine stopped and the ignition off and connect the wire to a spare spark plug that is firmly grounded to the engine. Do this procedure for each cylinder, one at a time.

Or, skip the dead cylinder method and adjust the idle of the right carb while listening to the exhaust to obtain the same sound as the left exhaust.

 

[Brassneck]

Couldn't you also just get Intake carb boots with vacuum ports? Cap them during normal operation and use a manometer to sync?

 

[TwoManyXS1Bs]

Then there's "this" method:

http://www.xs650.com/forum/showthread.php?t=33791

 

[XSLeo]

On the 76 set of carbs the only thing you need to do to use them is remove one throttle cable from the throttle housing.
You install the 76 carbs either into your 75 holders or use holders with vacuum ports.
I have ran both the 76 BS38 carbs and BS34 carbs with the 75 throttle housing and just one cable.
I think the later one cable housings just left out the second cable hole.
Some have used a spoke nipple and a short section of spoke to build an adapter. With this adapter the nipple screws on the plug, the section of spoke screws into the nipple. The plug cap plugs onto the spoke. The section of spoke is long enough so there is about a 1/4 inch gap between the plug and cap. This gives you room enough to use a jumper cable.
Clip the jumper to an engine fin, to "kill" the plug just clip the jumper to the adapter.
I didn't have any extra spokes or nipples but I had some scrap aluminum to make the"nipple" I cut a section of aluminum, drilled a hole and threaded it to match the plug. I then found a nail the right size and threaded it to match. I then cut the nail as the spoke was cut.
They work fine for that.
Leo

 

[chizler62]

It'd be safest to modify your intake boots to accept a vacuum or mercury gauge. Its MUCH safer and much more accurate than "the dead cylinder" method. As far as tuning your sync by ear? I just played with this on another bike while I had it hooked up to an EGA machine and mercury gauges. You obviously can't have a cross over tube in your exhaust system and you can get it close but not as close as a gauge set (unless you have years of experience) IMO
I'd just drill and tap my intake boots(you can use tubeless valve stems off bicycles etc) and purchase a set of merc sticks or vacuum gauges.

 

[larrynyc]

I have just bought the Pamco system, it's in the mail. I'll use the dead cylinder method with a grounded spare spark plug for now.

The Dogbunny sync method "by feel" is interesting. I don't know how accurate my hands will be but I'll give it a shot.

I haven't found barbed intake-side boots. I did buy barbed rubber boots for the engine-side, however I found the rubber boots don't fit within the stock metal holders because the barbs don't fit. I wonder, would they fit within the '76 metal holders (which I assume have room for the barbs), and would those holders fit on the '75?

 

[Brassneck]

I haven't found barbed intake-side boots. I did buy barbed rubber boots for the engine-side, however I found the rubber boots don't fit within the stock metal holders because the barbs don't fit. I wonder, would they fit within the '76 metal holders (which I assume have room for the barbs), and would those holders fit on the '75?

Yep, those are the style of boots I was referring to when I said Intake-boots... I suppose you need to get a different clamp if the stock one's don't work with the vacuum barb/port....or perhaps off of a later bike as you suggest?

 

[XSLeo]

Those aren't very good carb holders. They often have a loose fit on the carbs and are not as flat as they should be where they mount to the head. They can work though. Your 75 metal cages you can cut a nitch in them for the vacuum barbs.
JBM Industries buiklds a better set. They are a bit larger on the out side and the metal cages won't fit them.
You can find better carb holders on Ebay. The last set I bought were Tour Max. Very good items, much more ethanol resistant than Mike's.
I don't recall the manufacturers name that makes the Tour Max ones but they sell them on Ebay too.
Once you get a set of barbed holders then building manometer is easy, here's a diagram with instructions.
Leo

 

[larrynyc]

Update: Installed the new dual-output coil, and the Pamco with E-advance, what a great product.

As for carb sync, I just found out about a product called the Edelbrock Uni-Syn. This is a video of a guy using it on a Suzuki: Video. Basically, it takes carb pressure readings on the intake side of the carbs by simply removing the airbox and placing the product over the opening. Another brand I found is the Empi Universal Carb Syncronizer. A video of a guy using the Empi is here. It seems to be of a better build than the Edelbrock, however it looks pretty big, I'm not sure if it would fit.

These seem to be a great way to sync because I don't have to do extensive physical mods to my bike. Has anyone tried anything like this?

 

[pamcopete]

Update: Installed the new dual-output coil, and the Pamco with E-advance, what a great product.

I'm running out of room on the wall to post these!

Ride. Enjoy. Life is simple.