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what causes a 196cc clone to die under full throttle

M

MasonIsGreat35

Member
i built a 196cc with ss valves
14cc head 10.8-1CR
32 degree flywheel timing
jets are 038 main 020 pilot
runs on 94 octane

gov is removed and block vented to valve cover, then to catchcan

motor idles fine and runs half throttle but full throttle it will bog down it seems
im assuming this is due to too large of a main jet? but from what ive read 038 main is what is common to be used with open header and air filter kits
so i was thinking maybe its starving for fuel and i need a fuel pump?
maybe i have a compression leak somehow or its magneto gap related no clue

i tried cleaning the jets, and messing with air ratio screw
i cant recall if i tried running it with choke or not
im going to order smaller jets to try
but before i did i thought id make a post n see what others think
what are your thoughts what should i try and thanks for any info
 
you might want to take the pilot jet to between .028 and .032.
We have a lot of back yard guys and when they run the pilot jet that small and floor the throttle it falls on its face.
Hope that helps
Kent

Let me know either way what happens, hope it solves your problem!!!!!
 
Redfin10 said:
you might want to take the pilot jet to between .028 and .032.
We have a lot of back yard guys and when they run the pilot jet that small and floor the throttle it falls on its face.
Hope that helps
Kent

Let me know either way what happens, hope it solves your problem!!!!!
Click to expand...
hmm i did bring the pilot up a few size from stock but didnt think would have to that much, im new to building motors lot of info to learn

just ordered a pcv valve and fuel pump ill order some different main and pilot jets to try aswell

ill check the plug aswell at some point
 
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J'-remy said:
I had a motor that quit under full throttle two laps into a race. Builder sent me a new coil and a new fuel pump never happened again. I would also check that your fuel tank vent is working.
Click to expand...
good to know about 3910x plugs i got one currently,

i do have a brand new coil i havent put on yet i could try, just checked and the vent on tank cap isent clogged

another thing i forgot i did was change the etube that goes with main jet, the new one has a lot more holes in it i believe, could that contribute to the problem at all
 
gov is removed and block vented to valve cover, then to catchcan

I don’t see the need for that. Could be your problem
 
DynoDon said:
gov is removed and block vented to valve cover, then to catchcan

I don’t see the need for that. Could be your problem
Click to expand...
the idea was that at higher rpm it wouldn't build pressure in the crankcase
as well as its been spitting oil ontop of the rockers n springs and then draining back down into crankcase
the valve cover is then vented to a catchcan

how could it be the problem do i need some sort of pressure in the crankcase for it to run full throttle? or are you saying the problem is the gov is removed?
 
Redfin10 said:
you might want to take the pilot jet to between .028 and .032.
We have a lot of back yard guys and when they run the pilot jet that small and floor the throttle it falls on its face.
Hope that helps
Kent

Let me know either way what happens, hope it solves your problem!!!!!
Click to expand...
i havent been able to find pilot jets that large, largest i found was .022 on ombwarehouse
do you know any sites that have them in that size? its a stock carb aswell
 
Econosprint2 said:
If you do not have a fuel pump you may need to install one. If you are running an ARC flywheel make sure you have coil gap set correctly.
Click to expand...
i have a fuel pump i can put on but was told on another forum i wudnt need it and the gravity feed on my tank wud be enough is that correct or should i try the pump

heres a picture of the bike
 

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Ive tried a smaller main jet (.036) compared to the .038 i was runningand the problem got worse, instead of dieing after 3/4 throttle it now dies at 1/2 throttle with the smaller main, still running a .20 pilot jet

What is the usall turns out u guys end up at on the idle air screw? And what is the proper way to set those thanks
 
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turns out the issue was fuel supply

petcock was clogged up, i removed the two filters for main and reserve, aswell as cleaned it out pretty good, i put it back together so its switched to reserve since the handle broke flush and i cant switch it while put together

removed the inline filter on fuel line aswell as rerouted the fuel line straight from tank to carb nipple, with no twists n turns like how it was before

bike runs great tach read 8640rpm im not sure how accurate that is, when the bike was idling it was reading 800-1200 n bouncing around
i never saw it reach 8640rpm but thats what the max rpm recording was, as i passed under a streetlight i glanced n saw 7500 for sure so i know it was up there

i felt valve float im assuming around 7500-8600, not sure cudnt see what the rpm was as it was dark

the bike feels like it struggles as it climbs rpm for 1-3 seconds if u pin the throttle, then it feels like it comes alive and builds rpm quickly, i wonder if that is due to my small pilot jet any1 have any ideas on that?

thanks all for the help and suggestions sucks that it was something so simple but glad its figured out now.
 
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