new top end, running real hot, losing power

[espguitarist91]

I rebuilt the top end on my blaster because it seized up. it's now having the same problem again. it runs fine for the first 20 minutes, then it gets really hot and loses a lot of power. I stop when that happens to let it cool a little, because that's exactly how the top end blew before.
I have the air lid off, which makes me think it's running lean, but when the air lid is on, any throttle kills it right away, it's not even drivable.
what could this be? a jetting problem? any ideas will help, I drove 4 hours to ride it and would like to be able to tomorrow. everything on the quad is stock, including the jetting as far as I know. thanks for any help.

 

[scotj77]

if you remove the airlid with stock exhaust you should up your jet to atleast a 260 if not a 270. you also need to invest in a leakdown tester. an airleak will blow a top end faster than an bangkock hooker that you hand an hundred dollar bill. slickerthanyou makes a good tester for cheap

 

[NEONNIGHT34609]

i agree with what scotj77 says i think you need to rejet there is a reason why it seized up. did you find out why ?

 

[espguitarist91]

that makes sense, but why would it not even run with the air lid on and stock jetting then? it seems like there is more to it

 

[DirtDiggler]

First of all what mods are you running? What ratio are you mixing your fuel, exhaust , intake mods ?

 

[espguitarist91]

no mods, running 32:1, stock exhaust. when I did the top end i used a weiseco piston kit, .020 over stock.

 

[Luni]

When was the last time you cleaned your air filter?

Something has to be seriously wrong if putting the airbox lid on chokes it and it wont run. Considering youre stock and you havent done anything to jet away from that.

A way to tell if youre running too lean is to open the choke knob on the carb and see if it helps.

 

[espguitarist91]

well I changed the air filter today. the choke kills it right away. the only thing that made it better was the seat off, it ran great. so I tried using a 220 jet thinking its running rich, and it's just as bad if not worse. I give up for today.

 

[Luni]

Then something is starving the thing for air. This doesnt make much sense to me.

What Id do is Id pull the carb out, Id check the float levels (youll have to do a search, on how to do that for a stock carb, I have no experience with one), and youll want to just clean the hell out of everything. Put it back together, maybe blow up the airtube that connects to the back of the carb, with and without the seat on and see if you can "sense" a difference in airflow. Is it possible you over oiled the airfilter?

 

[Whitty21]

luni is speaking the truth, follow his advice, i can also vouche for slikerthanyou's testers, i personally have one and it works beautifully, now if only it could fix the leaks