problem in high rpm

[VMAX1260]

i took my ride for a spin. when i turned my throttle full, at about 8000 rpm the bike FELT like from 4 cylinders, working only 3 (by the noise and from the accelaration) when i slightly turn off my grip evrything works fine. i turned again full throttle again the same thing. different noise in the engine and the acceleration stacks. at about 8500. when i slightly turn off the grip the engine hears fine and accelrates over 8500 but not full speed since my i slightly close my throttle. if i accelarate at about 8000 rpm and close complitely the throttle i hear bam boum only in the left exhaust with flames. i already replace my sparks but with no effect... ? ?

any clues someone ?

 

[mattness]

check your plugs, and your battery, try it out with your headlight dimmed,

 

[VMAX1260]

i have new battery new plugs and my light are a Xenon HID kit with a switch whitch i turn them on and off.

 

[maleko89]

Sounds like your main jet is too rich if you have to back off the throttle like that.

 

[VMAX1260]

mine main jets are 150 from 152.5 there wasnt any problem . today it started . before everything worked perfectly

 

[maleko89]

I would check to make sure boots are tight and for a clean air filter. Maybe check fuel filter too.

 

[vmaxcruzer]

I might be stabbing in the dark here but check to see if the four tubes connected from the float bowl vents that mount to the side of the top section of the air box, make sure they aren't kinked or plugged.

 

[COP RUNNER]

IF YOU JUST HOLD IT AT 8500 RPM'S , DOES IT DO IT ? .. COULD BE A BROKEN EXHAUST VALVE SPRING .. :confused2:

 

[VMAX1260]

if i keep it steady .... it comes together and works fine. when i accelarate is the problem..over 8000 rpm

 

[COP RUNNER]

its so hard to guess , could be a coil going bad ! .. I don't want to steer you in the wrong direction ! .. If a cylinder starts loosing spark and then fires it will blow a flame and you will feel it start holding back !

 

[mattness]

only when youre accelerating at high rpm.. could be a fuel issue maybe... but it came just out of the blue like that?? something broke somewhere. if it was a kinked hose he woulda known when he first did it.

 

[mattness]

if you werent getting enough fuel somewhere wouldnt you hear the fuel pump running nonstop?

 

[VMAX1260]

the engine runs perfectly untill i reach 8000-8500. P E R F E C T L Y. then it feels like from 4 cylinders run only 3. if i decrease a little the throtle everything comes to normal untill i push the throttle all the way ..

 

[vmaxcruzer]

Stupid question. As I don't know what kind of mods you have or how long youve owned this bike...Does it have a Dyna 3000?

 

[VMAX1260]

no dyna. i have it 5 years. and it has loyt's of mod as you see and from the pic. i just made 3000km with my rebuild engine 1300cc from tts performance carrilo rods, je pistons... etc.

 

[naughtyG]

It sounds electrical to me. Are you running OEM coils/HT leads/spark plug caps, or COPs?

Maybe you're getting arcing at higher revs.. Do you know anyone else with a Max so you could just swap leads and spark plug caps to see if that's the problem?

 

[VMAX1260]

i have yes another max friend , i will just have to buy him a cup of coffee xexe while i am doing the swap

 

[COP RUNNER]

i have yes another max friend , i will just have to buy him a cup of coffee xexe while i am doing the swap

PLEASE , PLEASE , PLEASE , KEEP US UPDATED , SOME THINGS GET FIXED AROUND HERE AND WE NEVER HEAR WHAT IT TURNED OUT TO BE ! .. :confused2:

 

[RaWarrior]

While this is a totally different animal, I had that same issue with the old engine for my minibike. Ran great up until about 90% throttle. Put it WOT, it actually lost power and the bike slowed down. It was only a 150cc thumper too, the problem suddenly occurred one day. Turned out to be crap in the carb partially plugging a jet, too lean at WO. A quick cleaning fixed it.

But since you say it shoots flames out the exhaust on one side, that's definitely indicating it's dropping a cylinder, which then "loads up" with fuel, causing a flamethrower when it fires again. The only other "flamethrower" is if the ignition timing is waay messed up(like if you accidentally swap the coil leads for the front two cyl's.....) My vote would go to electrical rather than fuel. Possibly arcing, but I got an arcing wire on my Magna and it would intermittently run like crap at any RPM, not just WOT. Testing that is easy enough....run the bike in a dark place, and carefully advance the throttle up to the suspect 8000RPM range while watching the HT wires. If they're arcing, it'll be obvious, you might even hear the "snap" of it. If so, new wires. If not, maybe consider the COP mod, since a set of COP's can be had for significantly less than OE coil packs and they just plain work better.

 

[woodsman30]

PLEASE , PLEASE , PLEASE , KEEP US UPDATED , SOME THINGS GET FIXED AROUND HERE AND WE NEVER HEAR WHAT IT TURNED OUT TO BE ! .. :confused2:

+1 we need the feed back it helps all here for future reference :clapping: