Dead cylinder Carb Sync

[azcafe]

Hey All,

I can not seem to wrap my head around syncing my carbs using the dead cylinder method. Ihave a 1971 with pamco, HHB PMA, BS38 carbs off a 72. My intake boots do not have the barbs so I cant do the fluid sync. Also I have no rpm guage.

main jet is 135, pilot jet is 45, running pods and pretty much straight pipes. The pipes have muffles but they are pretty much asstetics only. Needle jet is stock and the eclip is on the middle slot.

Is there a video of someone doing a dead cylinder carb sync.

My understanding of it is you ground out one plug wire to the engine and run the bike on one cylinder. Then adjust the idle to where it will stay idel but almost to the point where it will cut out. once your at that point then you turn the air fuel screw and quarter turn each way. Which ever way it runs better then you turn the air fuel screw a eight in that direction.

The problem i am running into is in order for me to get the bike to stay at an idle speed on one cylinder i have to set it up pretty high so when I am finished with the syncing and both plug wires are hooked up the idle is extremeley high.

Any info would really help.

 

[hard_y_rd]

Subscribed.

 

[DogBunny]

Your terminology is wrong. You are describing setting the idle air mix screw. And, you pretty much have it right. Maybe if you do a search of "air mix screw" or "idle mix screw" you will get a better sense of how to do it. There is also a good description of how to do it in the Carb Guide that 5twins and grizld1 wrote that is in the tech section of this Forum.
Synchronizing is completely different. In simplest terms, it is getting the two cylinders to fire with equal pressure while at idle. If you have dual exhausts, all you need to do is hold your hands a couple of inches away from the end of each exhaust. Adjust the idle stop screws until the exhaust pressure you feel from both pipes is equal and the idle RPM is correct. That's all there is to it. Of course, this is done after setting the idle mix screws.
I'm sure that there will be those who will disagree with me, but syncing the way I have described is completely adequate if you have dual exhausts. Syncing with manometers is necessary if you have a 2 into 1 exhaust, or 3 or 4 cylinders, but otherwise it is highly overrated in my opinion, and unnecessarily complicated.

 

[5twins]

For your carbs to be in sync, you want the butterfly plates to open the same amount and at exactly the same time. To achieve that, you need to exactly match the freeplay in the throttle cables to each other.

I set the left cable where I want it, with about 3/16" of freeplay. I loosen the right cable up more than that. I roll the throttle open slightly just enough to take up the freeplay in the left cable. While holding it there, I adjust all the extra play out of the right cable so it matches.

 

[azcafe]

Thanks guys for the response. I just wanted to make sure i was doing it right since it was my first time doing it. I will redo it since i messed around with teh mixture a little and see what happens.

 

[5twins]

Once you get both mix screws dialed in and have both plug wires hooked back up, yes, it's going to be running at too high an idle. You have to turn each carb's idle speed adjuster screw back down the exact same amount to maintain matched idle speeds between the two cylinders. Once that's done, you do the sync of the cables (match their freeplay). The sync of the cables matches the cylinder speeds at throttle openings above idle.