Odd Problem

[fatbiker]

Today I was checking the bike to see if I have a wrist pin problem by pulling the plug wires off the spark plugs while the bike is running. Didn't find a wrist pin problem but I did notice that when I pull the number 1 plug wire the bike idle did not change. If I pull the other three plug wires the bike runs rougher. Funny thing is that when I re-install the # 1 plug wire while the bike is running it makes a quick jump in rpm for less than a second then goes back to the previous idle. My first thought was that I have a bad spark plug, bad wire, or bad ignition coil. I replaced the spark plug with a brand new one; there was no change. Changed the plug wire with a known good one; no change. Then changed the ignition coil with a known good one; again no change. I know that the carbs are in perfect working order as Dannymax rebuilt them last month. Compression is 180 on all cylinders. When on the road the bike doesn't feel like it's running on three cylinders other than some excessive vibration. If I hit the throttle she takes off without any hesitation. Any idea why there is no change in RPM when I remove the number 1 plug wire?

Fatbiker

 

[alorio1]

Pull the plug wire out of the cap and start it, hold the wire close to the engine to see if there is spark. If you have an infrared heat gun check the temp on all exhaust pipes, if not spray some water on the exhaust pipes to see if it evaporates about the same on each header pipe. If you don't have fire to the plug wire your CDI probably went out on that channel, the CDI has 4 channels, one for each cylinder. Have you adjusted the A/F screw to see if it made a difference?

 

[one2dmax]

Probably just out of sync

 

[fatbiker]

Getting a big, fat spark from the spark plug when held against the engine. Air, fuel, and spark are all there. I will check the sync and see if that's the problem. Could it be stuck valves or valves that need adjusting? The bike has 73K miles and I have no idea if it's ever had a valve adjustment.

Fatbiker

 

[alorio1]

A stuck valve will give you a low compression reading, it's probably like Sean said, out of sync.....

 

[davesax36]

We're talking about carb sync, right?

 

[alorio1]

Right, carb sync..........

 

[fatbiker]

I checked the carb sync and all 4 carbs were dead on. Well, very close to dead on. Only the number 3 carb was a little off. The problem still persists. Good spark, new plug, new wires, air and fuel.

 

[alorio1]

Drain the carb on the cylinder and catch the fuel to check for contaminents. While the drain screw is open cycle the key on then off to get a good flush and see what you get. I hope you changed your fuel filter after the carb rebuild. Did you spray water on the exhaust pipes test?

 

[alorio1]

Did you raise the RPMs to do the sync?

 

[maleko89]

Make sure RPMS are 1000 minimum. Make sure boot for that carb/vboost are tight and in good condition.

 

[jfeagins]

Plugged idle circuit on that carb? You may need to do a shotgun proceedure to unplug it and then resync.

 

[dannymax]

While it's idling put your hand flat on the top of the #1 carb and see if the rpm's jump up. Certainly possible that a bit of schmutz that got in #1 and popping your hand on & off the top of the carb may pull it thru.

 

[fatbiker]

Yes, after every adjustment I'd rev the engine then let it settle back down to idle.

New fuel filter was installed when the rebuilt carbs went on. Clean fuel going into the carbs.

Will try spraying water on the pipes after the next ride.

 

[one2dmax]

You can also try turning the a/f mix screw on that one carb out a little. Plugged pilot can for sure cause the isse too. Even a valve adjustment as Damon noted on another thread.

 

[fatbiker]

I finally got a chance to work on her this weekend and here's what I did.

Took the airbox off and put my hand on top of the carb and gave it some throttle just as DannyMax said. Just about pulled my hand into the carb. Popped my hand on and off the carb a few times but no change.

Did the shotgun cleaning procedure, no change.

Took her around the block a few times to warm her up then sprayed a mist of water on the piped. Right side dissipated a little faster than the left side. Carb 1 is on the left side.

Backed out the idle fuel mixture screw a little. No change.

Same problem still persists. I'm going to have someone do a valve adjustment on her soon as I have no idea how long it's been since one has been done, if ever. Will update.

Fatbike