Strange little problem for you all. Got a vx in, apparently he stopped at the lights, bike cut out, started it again, started backfiring, cant get over 30mph. I've changed the plug, beautiful strong spark, coil, ht lead, cap, stator and pickup, fuel pump, stripped and cleaned the carb, re-jetted up to 130 main from a 112, only get an occassional backfire now with the bigger jet. Bike is standard except a viper exhaust which has been on there a year now. Was running completely fine before. Question is: Why all of a sudden would it need a hugely bigger jet increase.????
I had a similar issue some years ago, it turned out to be the cdi, it had like a default and would only run at tickover like a "get you home" mode, give it some revs and it would die? might be worth a look?
Yeah, I was slowly coming to that conclusion myself. I've replaced or changed everything else, the only things left are the cdi, flywheel and carb. All of which I don't have in stock! Replacement cdi for a vx is expensive, need the ignition barrel as well unless you get the Malossi bypass one. And thats £155. The flywheel appears to be ok upon inspection. There is a carb on fleabay for £40 that I might get, just for the hell of it, and for testing purposes. The seller says it came off a good running bike. But what makes me think about those type of things is why would anybody break a good running bike instead of selling it? Unless of course, like some of my customers, the body work is really tatty.
if i recall, the CDI is also the indicator relay, if its on the fritz it will send the blinkers crazy and will also show fault codes on them? also worth checking the inlet manifold, mine just split one day, hairline split all the way round.
Indicators working fine, as is everything else, horn, brake lights, high/low beam. I have a customer who has a vx with the malossi cdi on it that i fitted earlier this year, or late last year, can't really be sure when. I'm going to see if I can get him to bring it down on saturday just for me to try it.
check the engine earth at the front of the transmission cover, i had a similar problem on mine once when it fuzzed up
new cdi fitted....................no change at all. Changed the carb for a known good one.....................no change Starting to suspect the head/valves/piston itself now, even though the compression reading is where it's supposed to be, 157psi. Getting fed up of this one now, can't do my own toys
Been playing with this one again. The owner bought me another carb off his mates vx. That bikes running perfectly. I'm still convinced that it's getting too much air somewhere, but i'm damned if i can find it. One thing i did find though, is that if i put my hand tight over the exhaust, stopping the gas getting out, normally the engine should stop; this one does slow down a little, but it doesn't stop running, keeps ticking over. So thats got me thinking that although the initial compression reading of 157psi could well be correct, when the engine is at initial acceleration and high revs, the compression is actually blowing past the rings, instead of combusting in the chamber. Only one way to find out i suppose...................I wonder if the owner will go for it, considering what its worth.
maybe a ring is on upside down? try doing a cold and warm compression reading, and try wet and dry too, would give you a better clue as to whats going on. 157psi is quite a lot, is that normal for a leader engine?
Rings are not orientated on these, so no problems there. 157psi is about right for the leader engines. Specs say 154psi. I'll try a leak down test tomorrow maybe, see if the pressure drops over time. Will have another look before the weekend maybe.
Didn't think I'd updated this one. Found the problem..................water in the fuel reservoir tank, the little one that sits on the frame above the main tank. He had filled up at a back street garage, not one of his normal places. My theory is that as the fuel became low, it sucked the excess water into the lines, but stayed in the reservoir tank and couldn't clear itself. It's the only way I can see that any water could have got into the system.
