Author Topic: Before I pull the carbs again.....  (Read 344 times)

scott s

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Before I pull the carbs again.....
« on: September 01, 2017, 04:55:14 PM »
 I can't get the rear cylinder to idle. I suspect a plugged pilot jet circuit. The carbs were professionally rebuilt, but I did run the bike on an IV bottle for a while, so it's possible that there's trash in the slow jet.

 Front cylinder/pipe gets hot. Rear cylinder/pipe does not. I'm getting a fat purple spark that will jump a substantial gap. The outer plug WAS gas fouled today, but I've been messing with it and trying to get it to idle on both cylinders. Fresh plug made no difference.
 I poured SeaFoam into the carbs and let them sit for 4 hours. Drained it, added gas, no change. I tried to pull the mixture screw, but I can't get it out of the carb body. Wish it was magnetic. No change when turning the mixture screw on that cylinder.

 I suspect the slow jet because when I ride the bike there's a BIG rush of power just past 3,000 RPM, once it gets on the needle/main. That cylinder/pipe starts to get a little heat in it then. I'm only riding it on what's in the bowls until the new petcock gets here.

 The gas tank will be coming off in the next day or two for a new petcock, so I thought about pulling the plenum and the carb top on that cylinder and checking the diaphragm.

 Before I pull the carbs, is there ANYTHING else I should check first? Anything electrical?

scott s

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Re: Before I pull the carbs again.....
« Reply #1 on: September 02, 2017, 12:32:20 PM »
 Pulled the carbs today.. Pulled the main jet, emulsion tube, pilot jet and mixture screw and cleaned all of them and all associated passages. Did a bench sync. Didn't really find anything, to be honest.
  Still having the same problem. Checked choke operation. Checked fuel level in bowls using the clear tube method...both the same. Ran the bike with air box off and diaphragms/slides are working. If I put my hand over the rear carb, it wants to pick up and I get fuel on my hand. It just acts like it's not getting fuel to the slow circuit on that carb. Checked compression on that cylinder and got over 175 PSI. Fat purple/white spark. I'm stumped. Guess the carbs are coming off again.

scott s

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Re: Before I pull the carbs again.....
« Reply #2 on: September 03, 2017, 01:51:15 PM »
I pulled the carbs a second time this morning. Pulled every possible jet on that carb AND the diaphragm. Cleaned every single passage with carb cleaner, guitar string, compressed air, etc. Soaked the slow jet, main jet and emulsion tube in Seafoam and cleaned them again. At this point, I am very, very confident that everything is clean.

 Checked valve adjustment on that cylinder again. Had a "tight" .004 on the intake so re-adjusted them. The exhaust, which is a bit difficult to get to, was a loose .004 (call it a tight .005), so I left it alone. Turned the engine over and watched valve actuation. Swapped spark plugs around again.
 Started it up (starts instantly, BTW) and....same thing. It's simply not running on the rear cylinder at idle. At this point, I'm starting to suspect the ignitor. I'm getting good spark when grounding a plug, but who knows what's happening in that cylinder under compression? I was texting a buddy who owns a motorcycle repair shop and he says he's seen faulty ignitors cause similar issues. It may be firing, but not at the right time, or not under the compression of the cylinder.
 That's a clue, because there is fuel on the plugs when I pull them. They're not dry, like the carb isn't working. BUT....that cylinder will kick in under higher revs, so....who knows?
 I'm really stumped at this point.

 There are two ignitor boxes. I wonder if I can swap the plugs and see if the issue moves to the front cylinder?

scott s

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Re: Before I pull the carbs again.....
« Reply #3 on: September 03, 2017, 05:56:26 PM »
Got it guys! Third time's the charm!
I have to admit, it was a bit of a bonehead move on my part, but suggestions to go ahead and swap pilot jets and confirm jet sizes set me on the right path.
Turns out I was cleaning the FRONT cylinder carb every time! It's easy to get them confused when you pull them, flip them around and turn them upside down on the bench.
Found trash in the pilot jet. On the CORRECT REAR carb! LOL.
Running like it's supposed to now!
New petcock should be here tomorrow and I can (hopefully) wrap it up for good!