What happened to my sync?

On my last ride my bike started to run rough about five mile out from my house. As I got closer my idle started to creep up an the bike started to get hot. After I got home I started looking at my carbs and proceeded to resync them this is when I found that the carbs would be in sync at one rpm setting but as soon as I blipped the throttle they would completely change. Any ideas?

 

Likely cause: Aluminum Oxidation of Diaphragm Piston Bores causing the Piston to Bind or Stick and Hesitate.

Scrub Bores with a 3/4 inch strip of ScotchBrite Pad (Gray).
May be done with Carbs in situ.
For maximized performance, ... Polish Bores.

••• Polished Bore <> Dremel <> #5 Jewelers Rogue.

 

I've polished them with 2000 grit paper followed by the polishing wheel. I'll go back and give it another go though.

 

If it's not that you may have air getting in somewhere.

 

Did you break the rack and replace the throttle shaft seals?

Sounds like a vac leak somewhere...

 

Carbs were rebuilt less than 400 mile ago. Same goes for the valve shim.

 

Did you align the rack using a surface plate when you rebuilt them? And as Fitz said, were the throttle shaft seals replaced (and the throttle shafts not loose in their holes, particularly carbs 2/3 where the cable pulls from?)

Also, did you use thread lock on the rack screws?

 

New shaft seals were used from xj4ever. I used a sheet of glass to align the carbs and used blue thread locker.

 

Cool, more likely a vacuum leak then as previously mentioned (I was wondering if maybe the rack screws had worked loose to start with). Another thing easy to check but unlikely IMO, it that the bolts holding the throttle "levers" on the end of shafts 2 & 3 haven't worked loose.

It's time to get the propane torch out & go leak hunting methinks.

 

Propane torch is out and leak is found. One of my clamps holding my boots tight cracked and was allowing air to leak.

 

Good stuff, just the clamp was cracked? that's even better news, no need to face the "made of cheese" intake stub bolts 8)

 

I've already dealt with the intake studs. Two heli coils later it all worked out.

 

Problems back again. I've tried the propane torch and carb cleaner to find the leak. Anyone have an opinion about trying to run the bike without the airbox to carburetor boots installed? Might be able to see which slide is rising the slowest to tell me which cylinder the air leak is on.

 

At idle, no slides should be rising. This is all about pilots and clean passages and orifices. Once the slides come up, we're not idling any more. And we don't sync at anything but idle.

The bike will not run properly with the carbs open (no boots,) and you won't be able to tell anything that way.

I have a question: what YICS blocking tool are you using when you do your sync?

 

I am using a tight fitting rag pulled through the yics tube. The problem that is happening is when I blip the throttle, the rpm jumps up and hangs. The carbs are synced right above 1k rpm. If I adjust the idle screw at all, the sync is back off. I just went back trough the valves and sprayed carb cleaner through each of the passageways in the carbs.

 

Before the bench sync did you check to see if all butterfly valves were closed all the way and seal properly with everything backed off?? I just went through that. I damaged one of them in disassembly. It was my ghost air leak.

 

You can see a little light around the edges when a flashlight is held on the back of each carb with the vacuum slide pulled up.

 

I asked chacal about this... These bikes r old and just a bit of wear is normal. But if you just stuck them in and tightened them without opening and closing them a few times to see if they were properly set then that might be the problem. If you loosen them a little they have a little play adjust them and make sure they close as best as possible. All of mine close completely now. Hope this helps.

 

I'll pull the carbs and take a peek in the morning.

 

Did you check the rubber diaphragms on the carb slides for holes?

 

As Fitz says, ... before you can begin any fine tuning ... the plant has to Idle.

Try scrubbing the bores with ScotchBrite (gray).

 

I re polished the bores yesterday, started it up and immediately lost cylinder one at idle. I pulled the carbs back out and am going back through them. After I get home from work they're going back on.