WEIRD predator 212 issue

[nickengels]

Hey guys, I gotta weird one for ya. I recently started a mini bike build with a predator 212 hemi head model. I quickly noticed a problem when I first ran the motor. It stalls when you open the throttle over about 25 percent. I figured the carb was just gummed up and there wasn't enough fuel in the bowl. I cleaned it all out. And I checked and verified that the carb itself was getting good fuel flow. Same issue. This carb had a .38 jet, as the motor is stage 1. I next checked for vacuum leaks, there were none. I replaced every gasket to be sure. Problem persisted. So, I tried starting the motor at wide open throttle and shooting a bunch of starting fluid up the intake to see if it was a fuel problem and boom, it revs right up. So in anger, I changed the entire carb and the spark plug to be sure. Same problem. The entire fuel system from tank to intake port has been gone through. I'd consider myself a pretty experienced mechanic, but I'm at a loss here. It wouldn't make sense for it to be anything but a fuel problem, yet here we are. Does anybody have any suggestions or has heard of this before?? Thanks, Nick.

 

[itsid]

could you post a pic of the spark plug (business end)?

that could tell us if your spark plug's getting wet (not sparking because of too much fuel)
or it's white and crusted by now (too lean to run)

I think the "original" plug is a much better source, since you said you just installed a new one (and with that the pic might not be too telling on a lean mix..)

How's your air flow btw.. what air filter, exhaust are you running..
(a pic might help really )

'sid

 

[nickengels]

reply to sid

Hi, Sid! Thanks for the quick reply. I've attached some images to this reply that were all taken at different dates, but will hopefully provide the information that you seek. As you can see, the plug that came with the motor was pretty fouled, but didn't strike me as something that would limit the RPM of the motor like that, especially with the weird starting fluid results. The motor has an aftermarket airspeed air filter adapter and carb. I tried running an poem carb with no air filter as well and reached the same results. Hope this gives you something! Let me know if I didn't attach these images correctly or something, I'm new to the thread and still learning the ropes! -Nick

 

[itsid]

since it's a bit velvety it's indeed just carbon fouled ..
so way too much fuel over a loong period of time,
or a minor oil leak
maybe the next smaller main jet is indeed a better choice *shrugs*
if you can check the plug next time directly after it cuts out
can tell us more about it.

But true, that shouldn't really limit the rpms too much, more the ride time really..

talking about vacuum leaks..
you checked for an air lock already?
like running the engine w/o the valve cover in the garage for a bit?
to see if you can rev it up without it.
and checked there isn't too much oil in the engine..

since that would indeed limit the rpms
(and since air is compressable could possibly be overcome with a more violent combustion.. say with starter fluid )

check the oil level, and if that's okay, remove one of the dipsticks,
and cover that port with a rag instead
then check if it can be revved up any further
(should be less of a mess and hassle than running without valve cover)
if it can .. well you run into an air lock
and you need a crank case breather (valve cover or crank case directly doesn't matter much I'd say)

'sid

 

[nickengels]

I have a breather installed in the valve cover, but I should check to see if there is too much oil, a change wouldn't hurt anyways. I'll go ahead and run it without a dip stick and valve cover too just see. The bike is currently at my shop right now which is separate from where I live, and I probably won't be able to go out there until Friday or Saturday because of my work schedule... but I'l be sure to get back to you on that!
-Nick

 

[nickengels]

Hey, sorry it's been a while since I updated last. I ran the motor with the oil fill cap off and the valve cover off and achieved the same result. It also has the correct amount of oil, which I changed as well. I'm stumped on this one :/

 

[itsid]

Indeed odd.

So allow me to ask the stupid questions just to be sure
The governor is fully removed, right?
(since in case it's not.. it might just be improperly set)

would you mind to tell us exact gear ratio and wheelsize,
just so we can rule out any limiting factors there.

And lastly:
what happens if you (as in pic 4 for example)
disconnect the engine from the drivetrain and start it up?
does it rev up all the way or does it stay below 2500 rpms..

if by any chance you have a tachometer laying around,
maybe see if that's a hard limit or a squishy one
(hits 2400 rpm easily then stops, or has a hard time crawling up to 2500)

Oh one more thing I'm rather certain you checked but I want to make sure to have asked;
you skipped the throttle on the handlebar already and directly checked if the engine revs when you manually actuate the butterfly, right?
otherwise an incorrectly routed or cut throttle cable (sleeve) can swallow some of the movement
and thus the butterfly is just never fully open.

'sid

 

[nickengels]

Hey Sid, yes, the drivetrain has been disconnected from the motor this whole time. So the govorner gear is still in the motor, but the arm is not connected to anything. I have an aftermarket pull throttle lever setup that goes directly to the butterfly. So the governor is technically still installed, however it cannot adjust the butterfly.

 

[itsid]

Hey Sid, yes, the drivetrain has been disconnected from the motor this whole time.

Great!

HSo the govorner gear is still in the motor, but the arm is not connected to anything. I have an aftermarket pull throttle lever setup that goes directly to the butterfly. So the governor is technically still installed, however it cannot adjust the butterfly.

OUCH!
remove that governor gear while it's still in one piece and hasn't destroyed your engine!
everything else is waiting for a catastrophic failure!

DO IT!!

And lastly..
that doesn't tell me if you tried revving the engine
with nothing but the butterfly;
skipping all mechanical parts inbetween the twist throttle and the butterfly itself.
your fingers moving the butterfly lever and nothing else..
since if it revs nicely that way you have the throttleplate or cable setup incorrectly.
(and forgive me, but with the governor still in place, chances are not too slim for that to happen )

'sid

 

[nickengels]

Okay, I'll make sure to remove the gear! And yes, I have moved the butterfly with just my finger before, and same result...

 

[itsid]

And yes, I have moved the butterfly with just my finger before, and same result...

too bad, that'd been an easy fix

Has that been a 'fresh' predator?
I mean you got it from Horror Fraud
or second hand?

if it's a second hand engine, you might want to check the compression on the cylinder..
maybe it's flawed for some reason and that's why it cannot rev up as it should.

Is there any odd sound coming from the engine (stuttering, rattling, something that would suggest a mechanical issue)?

The next thing I would do is verify valve lash to be set correctly
(0.1-0.15mm intake and 0.15-0.20mm exhaust)
mm not inches mind you.

and hook up a compression gauge anyways just to check it's about right.
( roughly 125 psi [at sea level])

Oh and just to get it out of my mind..
when you opened the butterfly by hand, the opening angle was 80+some odd degrees (nearly 90° opening angle)
not just 45 or such, right?
So the butterfly itself isn't blocked by anything.

ideally just remove the airfilter with the engine off,
peek inside and see if the butterfly is perpendcular to the throttle body when fully opened.
that way you can also be sure to have the choke fully opened as it's supposed to be and not accidentally closed
since the choke butterfly sits in front of the actual throttle butterfly

'sid

 

[JTSpeedDemon]

Could you have accidentally hooked up the throttle cable to the CHOKE butterfly???