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Discussion Starter · #1 ·
I cant find anything on any forum after over a year of solid searching. Im hoping someone can help because Im desperate! 2007 BF650 SRA. Been chasing down a problem for nearly 2 years. Quad cranks, idles, revs, and runs good. Will randomly die under WOT, or when jumping or sliding sideways. I can putt around all day with no issues and ride wide open in a straight line. I have tried everything. Added an electric fuel pump, disabled the roll over switch, replaced belt and checked deflection, cleaned carbs and set float level to spec, checked and cleared all vent lines/removed check valve, ran it without the fuel cap, pulled the tank and checked the pick up, checked all electrical connections...everything I can think of. I have removed the crank case breather from the air box to rule out oil getting into the carbs and plugged the hole and added a breather filter to the line. I have killed the ignition as soon as it dies so it wont prime, and then drained the bowls one by one to see if there's fuel starvation but there's plenty of fuel in them. When it dies it will instantly shut off and coast to a stop with a flashing red light, but it’s not the belt light, it’s the oil light (which comes on when its not running so I dont think this is a symptom). It will crank back up after a few seconds if I hold the starter and give it full throttle. The really odd thing is it will run totally fine on pavement where there's grip....I can gun it and ride WOT and pop wheelies with no issue....as soon as im off road and get the wheels to spin it shuts off. Any solution or suggestion here?
 

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Besides the odd behavior between on and off pavement, those symptoms are indicative of a problem either in the carbs as in either the choke plungers loosing their seal or the float levels being too high for high RPMs ....or a failing pulse coil..which can be checked with a simple Ohm test. There is one other possibility...and that is a failing CDI. Some have been known to have a problem when hitting the rev limiter in that they stop pulsing and just kill the ignation. A key off then on resets it. If all else fails get a CDI from Dynatech and try it.
 

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Discussion Starter · #3 ·
Besides the odd behavior between on and off pavement, those symptoms are indicative of a problem either in the carbs as in either the choke plungers loosing their seal or the float levels being too high for high RPMs ....or a failing pulse coil..which can be checked with a simple Ohm test. There is one other possibility...and that is a failing CDI. Some have been known to have a problem when hitting the rev limiter in that they stop pulsing and just kill the ignation. A key off then on resets it. If all else fails get a CDI from Dynatech and try it.
Thank you for the reply! I know that the carbs are within spec because I went through them meticulously this weekend. Ive tried lower and higher float levels to no avail. Im at factory spec at the moment. The plunger seals are good, had to really work them to get them in, but made sure the actual plungers were sliding properly with the cable. Im leaning toward CDI, because it feels like an immediate ignition cut....makes sense that the reason for it dying at WOT and wheel spin is because the RPMs climb so quickly under load with all the fuel thrown at it, an ignition cut would cause a flood/blowout situation...and even more sense that I have to hold the throttle wide open while holding the starter for 10 seconds or so to clear it out before it will start. Being a stock bike, it takes a while to get to upper revs on the street where there's traction and load....not sure it will even hit the limiter under those conditions.
 

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Discussion Starter · #5 ·
Ok so Update: I installed a Dynatek CDI. More power, stalls quicker. haha. I decided to see whether this was motion related. I jacked the rear wheels off the ground and put it in gear. The bike does NOT stall in gear with the wheels off the ground under WOT. Wheels on the ground and WOT, instant stall. Took it to my friends motorcyle/atv repair shop and had him look at it. Spark is good all the way, not cutting out. Its getting BLOWN out by too much fuel, which is interesting since Im running stock jets. Plugs are wet/fuel soaked when pulled. Carbs have been cleaned and I have run various float heights with the factory recommended level, and above and below with no change in results. I am running a 3-5psi electric fuel pump, installed as part of the process of elimination when replacing the stock pulse pump yielded no change either. So this is a fueling issue somehow, but I dont understand how I would get so much fuel that it blows the spark out at WOT with stock jets. And this is not one, but BOTH cylinders, and not cutting out like it normally would with a rich condition, its an INSTANT and complete death, and you have to hold the starter and the throttle wide open for 10 seconds or so to clear it out and get it to start again. HELP PLEASE!
 

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I think if it is an over fuel problem that only happens when under the load of being on the ground, and if the floats are correct, then look at the choke plunger seals, springs and cable adjustment. Under load there will be increased vacuum between the CV slide and the intake valves before it starts opening which may be enough to pull straight fuel from the bowls to the choke port. Odd that it would be both though.. One other thought...and this comes from smaller engines with magnetos, they may start fine and run just off idle and just die..and this happens when the coil happens to touch the rotor killing the spark. The few rotations the engine makes when stopping fowls the plug and it becomes hard to start again. So..I think you said you tested the pulse coil...and it was OK. If not check it. Might see if you can get any movement out of the crank on that side. If so, pull that cover and test it and loon for any marks on the rotor where it may have touched. If any..it means a new main bearing which means a full rebuild. I also assume all your voltages are OK and the charging system is working fine.
 

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Discussion Starter · #7 ·
Yeah Its crazy. Both plungers and cables seem to be in working order and the o-rings are tight...had to kinda work them back and forth to get the choke plungers back in their seats after going through the carbs. There's a noticeable difference when the choke is on and off, and it doesnt run uneven in either case like it would if one carb were choked and the other wasnt. My friend (lifelong ATV/Motorcycle mechanic) hooked it up and tested all the electrical systems and spark and said he couldnt find an issue. He said it had good strong spark and then he would get it to stall and then immediately after he could hit the start button and it would have strong spark again...like the spark was never gone, it was just getting blown out by too much fuel. Its really odd that nobody has ever had this issue before. haha. Makes me want to put my head through a wall.
 

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Discussion Starter · #8 ·
Ok, so we have established that its NOT electrical in nature. The plugwires still fire during and after the stall. The plugs are getting wet fouled, so definitely getting a huge surge of fuel from somewhere. Guess Ill just do a full carb rebuild and see what happens.
 
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