Starts but immediately backfires and stalls

[BlastrMastr240]

If you have any ideas please let me know, ive done EVERYTHING and ready every thread.... trust me, 200cc no mods. no tors. no parking brake, 32:1 premix, injection hose is blocked off.

(note how before it stalls it kind of "stepps down" in RPM and then stalls.)

I GREATLY appreciate anything you have that might help, ive done all the seals with a NEW top end, good compression.

https://www.facebook.com/video.php?v=950459068307071

 

[Awk08]

checklist....

piston in with arrow facing forward ?

reeds good ? no cracked or broken reed petals ?

flywheel woodruff key present ? unbroken ?
flywheel aligned with keyway notch on crankshaft end ?


new plug (they can foul instantly)
good blue spark ?
black ground wire at the coil to good bare frame gound ?
unhook the start and kill switches one at a time to eliminate them as the cause

restrictions to the air in and exhaust....rag left in there ? mouse nest in exhaust ?
you can unhook the airbox boot to the carb and the exhaust from the cylinder to see if that makes any difference ? do 1 at a a time, not both at the same time.
just 1 quick start then kill it if it starts/runs better with either of those unhooked !

carb cleaned properly and floats set to 20-21.5mm ?
good fuel flow to carb ?

answer some or all of those and report back.

 

[tbrooks]

Leaktest results?

 

[BlastrMastr240]

Piston is good

flywheel and key are perfect

reeds are good

good blue spark

ill check grounds again, loose kill switch could do that buuuuut when i can keep it running with almost quarter throttle it is powerless and will not move in gear it is like putting a brake on the engine when releasing the clutch.

plug is sometimes wet, not soaked but all symptoms show it running lean?

there dont appear to be any air restrictions at all but i can always double check exhaust, the intake is clean and in working order (results are same with no air intake)

carb is clean with good fuel flow. have a carbn from a running 06.... swapped carbs and the other 06 still ran, this one still wont so i cant imagine a carb issue.

 

[Awk08]

is your tors box under the hood unplugged ?
or the wires connected per the 03+ tors delete... if this has an 03+ harness/CDI/TORS box ?

 

[MURPH]

this probably isn't your problem but you should route that crank case vent tube up under the hood and not have it dangling at your legs also I see a bunch of orange stuff at the intake did you use rtv high temp silicon sealer for the intake to intake boot seal? you might have an airleak if you didn't use a real intake gasket

 

[BlastrMastr240]

thats what we thought, in the last hour we tore it apart (intake side) and that gasket was dry and tight. so i dont think it was that and it IS high temp as well as the gasket, we just cleaned it all up. all those hoses are for tests to try to get this thing running, and diagnostics, not permanent.

It is an 03+ with the CDI, the black and yellow wire is grounded. I looped the trottle and carb wires just in case im wrong but i will say this.... it "seems" that after i did that is was WAY more consistent with its symptoms.

my last ditch effort is the case half gasket that could be leaking. The bike got messed up (broke a piston) when the crank seal failed (clutch side) and was exhausting through that case vent. so we redid everything. like i said new seals ect ect cleaned the bottom end out spotless ect ect. put it back together and it fired right up and smoked a lot and it was powerless and would die on throttle movement. looped and removed tors garbage and parking brake cable and became more consistent but with the same more mild problem.

 

[MURPH]

your best bet is to get yourself a leak down tester( awk08 sells them) and a bottle of soapy water and look for the leak another thing I noticed is you used one of those crappy green base gaskets for the cylinder if u didn't torque it down properly they can suck in and create an air leak real quick. when I just rebuilt mine that gasket on the whole right side of the cylinder had sucked into the transfer ports

 

[BlastrMastr240]

Thanks, im going to check everything, splitting the halves in a few minutes here, already got it torn down.

Really appreciate your fast responses guys.

 

[Awk08]

Thanks, im going to check everything, splitting the halves in a few minutes here, already got it torn down.

Really appreciate your fast responses guys.

I'm still voting the tors delete was messed up.....
"Yellow wire is grounded "
??????
Black wire out of tors/cdi connected to yellow/black stripe wire. both directly as they exit the tors/cdi box.

Sorry I couldn't stick with you on this as I had to run out and am on my phone right now. It may have saved you a teardown, as I can assure you, there is nothing in the bottom end causing what I heard in the video, nor was that an airleak, or it would have started and revved to the moon.

Recheck your tors delete wiring, and all connections from stator to wiring harness

 

[BlastrMastr240]

your right about the bottom end... nothing wrong... but there is scoring on the piston and cylinder again.... probably not even 10 minutes of run time...

 

[Blaaster]

A pic of the piston may help to diagnose.

 

[speedyslyder]

show pics of your splicing job on tors wires.
show pics off piston.
and i want to see the handle bars lol.
did the crank seem ok and the case bearings when you took it apart?
was there any up n down play in the connecting rod?
also what year is it exactly?
adjustable stator plate? 4 or 5 wires?

 

[speedyslyder]

 

[Awk08]

View attachment 21530

good eye speedy !!!!!
it appears he has a drain line connected to the oil injection inlet nipple.
if thats not blocked off it would have caused a serious lean condition and score the piston as reported ?

that oil injection nipple needs blocked off, preferably with an 1/8" vaccuum cap right on the nipple itself.

 

[BlastrMastr240]

the blue hose is blocked off for the oil injection delete.

nothing has play but the cylinder is messed up, grooved up and down under the exhaust port.

Im ordering a new 66mm cylinder, the only thing that wont be replaced is the case, the gears, the frame, the head, and the ignition system so far. The stator is fine.

somehow something got in there and it is losing compression but only in that one spot.

 

[BlastrMastr240]

 

[BlastrMastr240]

 

[BlastrMastr240]

im sure somehow this is going to result in a flaming...

 

[Awk08]

im sure somehow this is going to result in a flaming...

I'll start the fire

1. please use an OEM or Cometic base gasket next time, that green construction paper is for kindergarden children to make paper angels, and known to cause major airleaks.

2. WTH...is there orange RTV sealing the case halves ?
you need to use yamabond to seal the cases.

from just those 2 items, I'll bet there was an airleak, and your next build must be leakdown tested before starting it, proper heat cycles done, leakdown tested again, then tuning