slobanshee Posted April 28, 2014 Report Share Posted April 28, 2014 Went to dunes this weekend. Bike was doing fine. Pulled into camp, had lunch. Went back out and bike wouldn't run. Starts and idles normal, runs fine till 1/2 throttle. Over that it falls on it's face. Kinda fills like its crazy rich. Swapped over from another bike the coil, stator, flywheel, wiring harness.Tried new and old plugs. Swapped over the other bikes carbs. Pulled reeds and power valves and inspected them. Tried a buddies alky. Did a compression test. Swapped whole fuel tank and pingle...I'm baffled....Bikes a stock stroke 68mm PV cheetah. 38 alky lectrons. Tried going up and down on needle. And adjust pj, made no diff past 1/2 throttle. Redline port and domes. It's been fine and ran flawless many weekends till it sat literally an hour... Any help is appreciated!!! Quote Link to comment Share on other sites More sharing options...
J-Madd Posted April 28, 2014 Report Share Posted April 28, 2014 I didn't see you mention leak down test. Did a rat build a nest in your pipes while you had lunch? Did you pull the head? Is it sucking water? Quote Link to comment Share on other sites More sharing options...
slobanshee Posted April 28, 2014 Author Report Share Posted April 28, 2014 I'm headed home. Didn't have a leak down tester with me. Didn't pull head. Did look in the cyls with a bore scope. Didn't see anything unexpected. Quote Link to comment Share on other sites More sharing options...
LCW Posted April 28, 2014 Report Share Posted April 28, 2014 Try a different cdi? What did your plugs look like? Quote Link to comment Share on other sites More sharing options...
slobanshee Posted April 28, 2014 Author Report Share Posted April 28, 2014 Yes sir Quote Link to comment Share on other sites More sharing options...
WINDYCITYJOHN400 Posted April 28, 2014 Report Share Posted April 28, 2014 You have definitely done the leg work on trying to find this issue…. If would lean towards checking for an air leak. You already ruled out electrical and fuel. I had a machine once that lost a seal, but it only happened when it was under a hard load. (Like yours does above 1/2 throttle) Quote Link to comment Share on other sites More sharing options...
slobanshee Posted April 28, 2014 Author Report Share Posted April 28, 2014 Did a leak down find that seal leaking? Which seal was it? Quote Link to comment Share on other sites More sharing options...
LCW Posted April 28, 2014 Report Share Posted April 28, 2014 If you have an air leak your plugs should be showing it, unless it happened on cool down when you had lunch. What did your plugs look like before the issue? Still have plating on them? Quote Link to comment Share on other sites More sharing options...
slobanshee Posted April 28, 2014 Author Report Share Posted April 28, 2014 Plug chops earlier that day where about 1/3 of heat on the plug. Cyl temp on either side is was about 100-105*. When it started doing this the stator side stayed about 100* but clutch side was in the 80s Quote Link to comment Share on other sites More sharing options...
LCW Posted April 28, 2014 Report Share Posted April 28, 2014 Are you running 9 heat range with a tight gap? Seems like you could be blowing out the spark. How much change in ambient temperature? 1 Quote Link to comment Share on other sites More sharing options...
WINDYCITYJOHN400 Posted April 28, 2014 Report Share Posted April 28, 2014 Did a leak down find that seal leaking? Which seal was it? Chased jetting in the dunes. Would run fat for a while, then go crisp lean. Changed a ton of jets till I figured it must be something big. Put it on the dyno and the A/F readings would go wacky as the RPM climbed. So did a leak check. Turned out the cases were trashed. Bearing surfaces were letting crank move. The crank seals weregetting wobbled by the crank. Caused the seals to fail. The massive airleak would make it damn near die. In the sand it was hard to judge if it was rich or lean. But the dyno clued me into a bigger hidden issue. Leak test pinpointed it. Leaks can be odd. Sometimes heat causes them to get worse. Sometimes heat seals them up. Leak checks are just a cheap and easy first step in the diagnostic process. May not be a leak....but at least it would rule it out. Quote Link to comment Share on other sites More sharing options...
slobanshee Posted April 28, 2014 Author Report Share Posted April 28, 2014 Yes 9 heat range. And a 18-20 gap. Isn't a new build. It's ran well for a while. That's very so similar to what this is acting like. Sometimes it gets that lean 'crack' sound but blowing tons of fuel out. Quote Link to comment Share on other sites More sharing options...
WINDYCITYJOHN400 Posted April 28, 2014 Report Share Posted April 28, 2014 Yes 9 heat range. And a 18-20 gap. Isn't a new build. It's ran well for a while. That's very so similar to what this is acting like. Sometimes it gets that lean 'crack' sound but blowing tons of fuel out. Leak test. Also make sure your pipes are sealing to the cylinders well. Check those O-rings. Quote Link to comment Share on other sites More sharing options...
slobanshee Posted April 28, 2014 Author Report Share Posted April 28, 2014 Pipes where leaking some. Any insite on how that might affect it? Quote Link to comment Share on other sites More sharing options...
WINDYCITYJOHN400 Posted April 28, 2014 Report Share Posted April 28, 2014 Pipes where leaking some. Any insite on how that might affect it? When your motor is intaking Fuel/Air into the cylinder, the exhaust port is open. Fresh air and fuel flow out into the pipe behind the last exhaust pulse. As the piston moves up the cylinder, as it closes off the transfers, the exhaust port is still open. This compresses the cylinder and pipe. (At this point you can push fresh air and fuel out your pipe flange) The shape of the pipe causes the pressure wave to have a RAM effect and push the fresh intake charge that flowed into the pipe BACK into the cylinder. (This is that pipe hit feel) This boosts the cylinder pressure higher than it would be without a tuned pipe. If the pipe flange leaks at the cylinder, it can cause fluctuations in your final Air/Fuel mixture. It can cause one plug to read different than another, make finding the right jetting difficult, lower available power, not to mention make the front of your motor a mess. LOL I'm not saying a pipe leak will cause a problem as severe as what you have going on…..but if you had a pipe leak PLUS a small seal leak and or maybe in intake boot leaking….they can add up. Last season my buddy made a jetting change in the dunes to a good solid motor that had been together for 2 years. Soon after the motor suffered an RPM runaway. End of a drag race the motor just wanted to stay pinned to the moon! (Race gas motor. Not alky) In his efforts to do the jetting change, somehow a small intake gasket leak developed. That cause one cylinder to go lean. That cylinder then detonated hard enough that over the course of a few back to back dune drag runs, the cylinder lifted just enough to cause a base gasket leak. THAT was a BIG leak and caused his motor RPM runaway. So….point is….you can run for a while with ONE problem and not notice it till it causes a SECOND bigger problem. The trick to good diagnostics is not to find a problem…but to find ALL the problems. Ever heard of a top end letting loose and then 2 hours after the rebuild it goes again? That's a common knock on Banshee motors. But it's the result of people not solving ALL the problems. I use RTV sealant in addition to the O-rings to seal all my pipes to the motor. There have been a couple of threads about that in the past. Quote Link to comment Share on other sites More sharing options...
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