Help with breaking up on top

[BigcrewDuramax]

A little help would be great. I have a 350 play ported by fast and it has been a great bike, however recently it has been breaking up on top bad. Badassbanshee479 and i have tried everything and we are stumped. ex: new coil and wires, cdi box, stator, flywheel, plugs and cant get it to go away. any other ideas? are next step is to leak test.

[banshdog]

A little help would be great. I have a 350 play ported by fast and it has been a great bike, however recently it has been breaking up on top bad. Badassbanshee479 and i have tried everything and we are stumped. ex: new coil and wires, cdi box, stator, flywheel, plugs and cant get it to go away. any other ideas? are next step is to leak test.

 

 

What is your compression? If you haven't checked it yet, that should be your next step.

[locogato11283]

is it sucking coolant in? check your radiator and see if your coolant level has gone down.

 

you check all your grounds to make sure you have them to bare metal? bad grounds will cause this.

 

on my old cr500 banshee it was breakin up on the top end. ended up being a fouled plug. it would run fine until i hit WOT and then it would break up bad.

 

just some ideas to add to your confusion. :biggrin:

[badassbanshee479]

comp is 165 in both holes, rad is full, and as far as we can tell all the grounds are good.

do ya have to clean off where the coil mounts? he is running a nology coil on it.

I made sure to scrape the pc off where the front engine mounts are also.

[majicmike]

comp is 165 in both holes, rad is full, and as far as we can tell all the grounds are good.

do ya have to clean off where the coil mounts? he is running a nology coil on it.

I made sure to scrape the pc off where the front engine mounts are also.

 

 

If its jetted right then check your plug gap and your pick up gap.

[J-Madd]

A little help would be great. I have a 350 play ported by fast and it has been a great bike, however recently it has been breaking up on top bad. Badassbanshee479 and i have tried everything and we are stumped. ex: new coil and wires, cdi box, stator, flywheel, plugs and cant get it to go away. any other ideas? are next step is to leak test.

 

 

Were the new electrical parts you tried all in known good working condition? This definitely sounds electrical, but you could try a different set of carbs just for the hell of it, if the pressure test checks out.

[locogato11283]

comp is 165 in both holes, rad is full, and as far as we can tell all the grounds are good.

do ya have to clean off where the coil mounts? he is running a nology coil on it.

I made sure to scrape the pc off where the front engine mounts are also.

 

yes most def grind the paint off where the coil mounts to. id say it def sounds electrical but you could clean the carbs for good measure. have you tried a stock coil on it to see if that makes a difference?

[Master of Faster]

I had that problem once and it turned out the be a bad spark plug cap. I don't know if you replaced the caps when you changed the coil or not but if you didn't deffinitely unscrew them and check them out. If I remember correctly there should be around 4.5 k-ohms through the caps.

 

Mine would run fine until I went WOT and one of my caps didn't even have continuity through it with a multi-meter.

 

Sometimes if you shake a bad cap you can even hear the inside connection rattling.

[badassbanshee479]

yeah we took all the electrical off of my drag bike, we even swapped out my nology and plug wires. plugs look good as far as jetting goes, may be alittle fat if anything. I have a stock coil I will try that for shits and giggles, and I will pull the carbs and clean um.

[BigcrewDuramax]

Thanks alot, sounds like badassbanshee beat me to the responses, we will try these ideas tonight

[Fastrat]

Think jetting as well, if it's lean on top it'll cut and backfire. Jetting is affected by temp and altitude so it could explain why it's just started. Just an idea, good luck.