VM26SS sync questions

remember to do your voltage checks with everything connected (back pin) and the system switched on 

Wookie58 wrote:

remember to do your voltage checks with everything connected (back pin) and the system switched on 

Be carful here, switch on to test yes, but should limit the “on” to a couple minutes per test. Leaving the coils powered up for more than a few minutes without them firing (discharging) can cause them to fail. 

Primary coil connection is the battery positive connection. Yellow/red wire directly from the “off-run-off” of the right hand control. The coil secondary is black for 1-4, and green for 2-3. As Wookie mentioned ignition on, “off-run-off” to run. Black meter probe on battery ground post and red to yellow/red of 1-4, then move red to yellow/red of coil 2-3. Voltage needs to as close to battery voltage as possible. Test battery voltage on the lead block not the screws or wires. If you’re less than 1.5 below than battery you have resistance in the old harness, corrosion in the connectors, or switch contact point. Resting battery voltage needs to be 12.6. It wouldn’t hurt to test coil primary while cranking the engine when cold. Again low voltage will cause your hard start and sooty plugs til the dynamo increases the voltage. Which should be about 14.6-7 at around 2500 rpm. 

You also need to test coils resistance. And the HT (plug) wires.  

EDIT, Reading what is in the red square has a mistake, verified from other FSM’s. The Brown wire mentioned in the last sentence needs to yellow/red.


 

I run ethanol free fuel in all my carb machines, luckily here in AZ we still have that….I went and filled it up today with fresh 91 octane. You read things here and there about leaded, unleaded, 87, 91, 94 octane….enough to drive you mad but this particular engine loves the 91 ethanol free fuel. It’s starting on the first couple cranks now. Still popping back now and again on the number 1&4 carbs but I have the Dyna S ignition system coming and still have the carb syncing to do. Getting better every day and I have to think that there is a bit of breaking in to do with new valves and rings.

Did I mention this bike is very, very fast? Well, for a ‘76 bike anyway. It sure is a head turner. Love it

Thanks guys. Will be testing those voltages today.

motomisfit wrote:

 Getting better every day and I have to think that there is a bit of breaking in to do with new valves and rings.

 

Getting back to this what did you do with your rebuild. Your first post died with a mix up of number and measurements. Did I miss the rebuild comments. 

Moose1800 wrote:

Here's a pic I took while syncing my VM 28 carbs on my 76 LTD, high miles bike with freshly rebuilt carbs.

I bought a kit just like this. It had these little adjuster screws in the bottom of each gauge. I’m going along doing the syncing and all of a sudden one of  the gauges started going crazy. The adjuster screw came out and got sucked INTO the hose! Holy crap! I’m freakin out but luckily the screw was too big to get sucked into the carb holder port. Whew. Lesson learned, take these screws out before you hook up.

Actually, this kit from Amazon is garbage and it’s going back. One of the gauges is stuck on 5. I ended up just using a single vac gauge I’ve had forever. Made in USA…..yeah, it matters.

I think I’m pretty dialed in on the syncing. Those are some fine adjustments for sure to get them all even. Will double check them all tomorrow, put it back together and go for a ride. Thanks again for all the help

A good synchronizing tool is a must-have. I have read that mercury sticks are available again (outside Kalifornia). Some guys swear they are best. I use a Morgan Carbtune and am well pleased with it. A good set of vacuum gauges are great, but hard to find and surprisingly expensive. 

www.ocdmachine.com/carbtune-pro-4-column.html

TexasKZ wrote:

A good synchronizing tool is a must-have. I have read that mercury sticks are available again (outside Kalifornia). Some guys swear they are best. I use a Morgan Carbtune and am well pleased with it. A good set of vacuum gauges are great, but hard to find and surprisingly expensive. 

www.ocdmachine.com/carbtune-pro-4-column.html

I have a Carbtune and like it.  Before that, I had a container of mercury, and some glass tubes.  That worked fine, but despite care, the mercury would occasionally spill.    

I have a motion pro Carbtune that is currently at SWests place. If you’d like to borrow it we can request Swest to ship it to you. Just need to have it back

EDIT, How about posting pictures of the faulty set you bought to help guide new members away from junk. Thank you

As you can see, the first gauge is stuck on 6 vac and the third on 1 pressure. Those little white inline adjusters are a joke. You can see the adjustable screw in bottom of the second gauge. I thought that was going to very helpful to minimize needle bounce……….until I saw that it unscrewed itself and almost got sucked into my brand new engine!!

I ended up just doing it with a single, reliable gauge and golf tees. I had to pinch off the hose with my fingers to get the needle to stabilize, but it worked.

It was a pain doing it this way, but I am now even on all 4 carbs. It was 90 degrees here in the desert all weekend, so I had to let the engine cool off several times. They ended up at 9 inches vacuum, fwiw. I was only able to take it for a short ride up and down the block and it’s running pretty darn smooth. Will go for a long ride later today and post final thoughts and pics of the bike. Will also post what I did in my rebuild and why.

So here’s a pic of what she looks like today. I’m going to start a new thread in ‘projects’ with the history of the bike and what I’ve done to it over the years.

A good long ride today. Ran great but still a little pop out of the #1 carb every so often. Syncing the carbs, although I’m glad I did it, didn’t seen to make a whole lot difference. Spark plugs are still blacker than they should be. I have now the Dyna S ignition kit and it will be my next upgrade. I haven’t checked my voltages at the coils yet but battery voltage static is fine. It starts now cold with full choke instantly so that’s a good thing. I honestly don’t know why it was taking so long before but as I said in a previous post, it might have been the fuel. I’ll post again when I get the Dyna system in.