What is factory idle knob adjustment?

81 xj750 SECA

So my #2 cyl wasn’t firing. Replaced faulty coil, got good spark, still not firing. Over the course of this i tweaked the idle adjust knob so it would stay running on 3 cyl to get home.

Cleaned carbs. Everything looks good, slides move freely, got gunk out of bowls, needles and jets clean and shiny. Reassemble.

Bike won’t stay lit. If I throw her some starter spray, she fires right up, and a couple times it even burned gas and revved for a few seconds, but the ratio is waaay off and it won’t stay running at all. Tried turning the screw all the way in and backing it out in 3-turn intervals to see if I could find the ballpark, no dice.

Anybody know the factory turn on that adjust knob? It’d be pretty helpful right now...

Or is there something obvious I’m missing here?

Thanks!

 

Stock air box, stock exhaust. Nothing weird.

 

There is no baseline in terms of number of turns. You’ll need to pull the carbs and perform a bench synch to get the throttle plates to their baseline setting.

 

Dammit, k-Moe, that’s not the answer I was hoping for at all!

 

:sigh: guess I’ll youtube bench syncing and pull the carb bank back out...

 

While they are out got ahead and double check the pilot jets and the fuel enrichment(choke) holes in the carb bowls are clenn and clear

 

YouTube is not the best source of info for the XJ. We have bench synch info here.

 

Apparently. Im finally learning what YICS means...



So I followed the excellent and detailed instructions on bench syncing here to the best of my ability. Still won’t stay lit. Fires up with starter spray, but won’t idle at all.

Carbs are full of gas. Air filter is clean. Bike ran fine on 3 cyl last week.

Any suggestions?

 

What happened prior to #2 not firing? We're they all playing nice together?

When was the last time you had a good clarb cleaning done... A complete one... Rack split, replace all the replaceables, etc???

 

Well, I was getting ignition current on the outside of the #2 wire, so I replaced the coil. Was getting good spark when I held the plug to the motor, but pipe was still dead cold when I put it together, and motor didn’t change tone at all when I pulled the boot while it was running.

Figured it had to be a carb issue. Didn’t break them off the rack, but I did pull all the jets and slides, clean everything out. Wasn’t too bad, a little gunk at the bottom of the bowls, but all the jets and everything looked really good. And like I said, she was running fine last week...

 

Did you clean the little passage in the float bowl? Able to get air and carb cleaner to pass though each one of of those holes in each bowl?

 

I sure did, and carb cleaner squirted right through each of em.

 

So I bought three cans of starter spray, and just worked the idle adjust screw back and forth in like 1/3rd turn increments this morning, firing the bike up on starter spray each time. Finally got it to stay lit. It idled fine in the driveway for a few min, then started revving up. Figured maybe it was just getting hot, so i shut it down.

Once it was cold, i started it again, fired right up. Took it for a spin. Died at idle, wouldn't start. tweaked the idle control some, got some starter spray, and it fired right up. Ran errands on it, didn't die at idle any more and seems to be running perfectly now. Starts right up, idles fine. Hopefully it will run tomorrow.

All of this is reinforcing my original perspective that carbs are not actually mechanical. They're purely spiritual. Tuning them is useless, attempting to adjust things logically is useless. The only thing that makes any difference is praying and offering sacrifice to the Gods of Jet and Needle. They seem to like multiple bottles of starter spray and nihilistic, soul-wrenching hopelessness.

Next time I have carb problems, I'll just throw 4 bottles of starter spray into a raging bonfire and cover myself in ash, at which point I fully expect my bike to run perfectly again.

Hopefully this 100% accurate assessment saves some other poor soul a little time in this process.

 

Nope.
Carbs don't work that way.
You're thinking of televisions and radios.

 

Hmm. So one little hitch in my boxers here.

Bike will not cold start, at all. Cranks and cranks, won't fire. Full choke, partial choke, no choke; bike doesn't care. Absolutely will not start.

If I give it a shot of starter spray, fires right up immediately. Once it's warmed up, fires up on the first crank, runs perfectly. Idles at 1k, everything is peachy.

What does this mean? Any suggestions?

 

What are the idle mixture screws set to?
2 1/2 turns out? 2 3/4? more ? less?
Did you make sure that the enrichment jets in the float bowls are clear?

 

Try to give it a HOT SHOT ...prop tank up and pull fuel line off of petcock. Drain all 4 float bowls, get a large meat baster or syringe fill with ( I use Berrymans b11 carb cleaner..not spray type) mix a 50/50 of B11 and acetone fill the fuel line several times , let soak for 1 hr and drain float bowls. Put fuel line back on petcock reposition tank back into place set petcock to PRI and try to see if bike will start .

 

Throttle stop screw I think this is also the name of the Idle adjustment knob