Predator 212 starting problems

#1
Having some starting problems...

Engine is modified

Have spark have fuel...
Carb is a stock appearing Bored ruixing carb came with a 0.22 pilot & 0.36 main jet .

Problem is engine only pops over with choke closed & a shot of starter fluid then stalls out 2 seconds later..

Changed spark plug, checked valve lash. Switched main jet to a 36, 38...still wont pop over & stay running....

Engine is brand new this is first attempts to start
 
#5
What was done to it? Was sidecover or head removed? Was flywheel removed?
Side cover & head both removed when I removed stock parts... Dyno cam, billet flywheel , billet rod , heavy spring , no oil sensor, no governor, walbro fuel pump..... timing is fine on cam, I checked valve lash .003 both sides @tdc .. ignition air gap is good I checked that. Fuel in the carb bowl & I sprayed it out with carb cleaner before I switched jets oh & I took out the low speed idle jet an blew threw it with cleaner....still no pop without the choke on & a shot of spray
 
#8
So if you have starting fluid you can leave choke open spray into carb with throttle open. Then open throttle a little and it should run out the prime. You should have gas turned off for that test. If it still pops and does not run out the prime then something else is wrong. Make sure plug isn’t fouled (black insulator)
 
#9
So if you have starting fluid you can leave choke open spray into carb with throttle open. Then open throttle a little and it should run out the prime. You should have gas turned off for that test. If it still pops and does not run out the prime then something else is wrong. Make sure plug isn’t fouled (black insulator)
With the choke off & throttle slightly open & a shot of spray it will pop but it dies as soon as it starts...it purrs real loud for 1 sec & pffft dead.... now I did foul a plug earlier & since then replaced it & have same issue
 
#10
Maybe, just maybe, double check your carb/adapter gaskets. It is possible to install them incorrectly. Also if you are using the plastic carb adapter, make sure it's not cracked. Either/or can cause a big vacuum leak. Don't ask how I know....
 
#11
With the choke off & throttle slightly open & a shot of spray it will pop but it dies as soon as it starts...it purrs real loud for 1 sec & pffft dead.... now I didnt foul a plug earlier & since then replaced it & have same issue
Maybe, just maybe, double check your carb/adapter gaskets. It is possible to install them incorrectly. Also if you are using the plastic carb adapter, make sure it's not cracked. Either/or can cause a big vacuum leak. Don't ask how I know....
I'm not even using a gasket between the carb & head...ordered parts & no gaskets... but you think that could be the underlined culprit? A vacuum leak at the carb would cause these symptoms? .... it wouldn't be Air/fuel mixture? I'm not sure besides I know it's all carb related I have to assume....I'm going to rig a gas can above the motor an use gravity to feed the bowl to see if im having same results...I'll load a picture up so you have an idea of what my situation looks like
 

chrisr

Active Member
#12
The vacuum leak will make for a lean mixture where it will only want to run with the choke on and gravity fed fuel will insure you get gas in the fuel bowl if the vacuum pump if installed was not pumping fuel.
 
#13
The vacuum leak will make for a lean mixture where it will only want to run with the choke on and gravity fed fuel will insure you get gas in the fuel bowl if the vacuum pump if installed was not pumping fuel.
I had a gasket laying around from the stock carb I'll throw it on an see what the pig does...if doesnt work I'm going to break the carb down an soak it in chem dip
 
#14
20190127_120318.jpg
Had to file down the choke butterfly didnt have enough clearance with the bolt you see wasnt allowing to fully close choke..
20190127_120335.jpg
Much better all the way closed..
20190127_120521.jpg
Gasket installed
20190127_121448.jpg
Put tank on just to see if this helps out.. as before I've had the motor mounted on a 15° engine mount on the chassis of my flat kart, fuel tank is on the floor board & has a little trouble feeding the carb..
 
#15
If you were able to foul a spark plug I think you should at least give the idle jet from the original carb a try in the new carb. 0.022" seems a little big for an idle jet.

Maybe try to play around with the air bleed screw: Duromax Air Bleed.png
 
#16
If you were able to foul a spark plug I think you should at least give the idle jet from the original carb a try in the new carb. 0.022" seems a little big for an idle jet.

Maybe try to play around with the air bleed screw: View attachment 239258
Yeh tried messing with mixture screw.... didnt do much good I screwed it all the way in an worked it out 1/4 turns... still did nothing I havnt tried to start the motor since i put gasket & relocated fuel tank.....in laws are over when they leave I'll head down to the garage
 
#20
On a modified engine? Wouldn't that Restrict the flow? Defeating the purpose on having a bored carb or any other aftermarket carb
Actually it would have better flow over bolting the carb directly to the head. The carb's outlet is a round hole and the head's intake port is a D-shape. The insulator provides a smoother transition from this round hole to the D-shape, therefore reducing turbulence and increasing flow capability.



The main reason for using the insulator in this case is to allow the bowl vent a passage to atmosphere. If you look at the face of the OUTLET on your carb, there is a tiny hole at the 10:00 position. This hole allows air to enter and escape the fuel bowl as it fills and emptys. Without this vent, an air bubble would get trapped in the bowl that would keep the float from rising and shutting off fuel flow.



If you look at the carburator side of the insulator, there is a little snail-like passage that goes around the intake port. This passage, along with the matching passage in the carburator face itself, and the little extra hole in the gasket between the carb and insulator, allow the bowl to vent.




Now your problem isn't that this vent is blocked because the snail passage in the face of the carb is sufficient enough to provide the venting. Your problem is that this vent is now not only open to atmosphere (like it should be), but that it is also open to intake vacuum. What is happening is that the intake port and the snail passage on the face of the carb are overlapping, causing this "short circuit." When you try to start the engine, the engine is drawing air through the snail passage instead of through the idle circuit, therefore it is not getting fuel hence the reason it starts on ether. Once it gets running on ether, it still has the intake leak through the snail passage but now it is sucking on that bowl vent. The vacuum on that vent is sucking massive amounts of fuel into the engine, fouling the spark plug and killing the engine in that two seconds that it ran.

The solution is to dig that insulator out of the garbage and reinstall it.

I also encourage you to look at these parts for yourself and figure out how they work. Maybe even disassemble an old carb and spend a day shooting carb cleaner through all the holes to see where they go. WEAR SAFETY GLASSES IF YOU USE CARB CLEANER!!!o_O
 
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