RB55
Member
Hello All,
I am fairly experienced at working with small engines, both 2 stroke and 4 stroke, but for the life of me I can't understand what's going on with 212 I just built for a minibike. Below is a list of the mods I did:
Predator 212 Hemi, Stock Bore, Stock Stroke, Stock Valves, Stock Crank, Stock Flat-top Piston, Stock Rockers, Stock Head (no porting)
Governor and low oil sensor systems completely removed
Governor and low oil sensor holes plugged
ARC Billet Rod +0.020" over (torqued to spec, zero deck at TDC)
.009" Stock 212 Metal Head Gasket
PVL Flywheel with Coil Gap Set to Recommended Gap (.039")
26 lb valve springs, lash set to .003" for both exhaust and intake
Chromoly stock length pushrods
Dynocams CM camshaft
NR Racing GX390 carb billet adapter
Genuine Honda GX390 carb with adjustable main jet from EC carburetors (? pilot jet but is plenty rich at idle)
NGK BPR6ES spark plug
Using 10w-30 Royal Purple HPS oil
I originally bought this minibike used with a Predator 212 Hemi engine. I had plenty of fun with it for months and the engine never gave me any issues. Cut the low oil sensor and changed the oil a few days after I got it. A few weeks ago I bought an upgraded center-exit minibike exhaust with an RLV muffler and it ran fine in the warm weather but struggled in the cold. From experience I know it's because the cold air is denser and makes the carb run too lean. I didn't ride it for a few days since it was still cold and I got the upgraded parts before I got a chance to ride it again. I was extremely careful with the rebuild process and am almost certain I didn't mess up anything. Yesterday it started on the second pull and after messing with the adjustable main jet and idle screw it idled for 30 min with zero problems. Started back up again multiple times with no issue. I even took it for a quick ride and it was definitely making plenty of power. It was probably idling a bit too rich since black smoke was coming out the exhaust but it accelerated fine and idled stable so I figured it was fine. It was probably about 60 degrees yesterday. Today I wanted to do some top speed runs and finish tuning the main jet. It was 28 outside. I left it outside all night. It started up and idled just fine (was idling a bit fast but I corrected it) but then after about 15 seconds of hard running it COMPLETELY cuts out and dies. No warning, no sputtering, but also no nasty metal-on-metal sounds that would indicate some sort of internal failure. No white smoke or any signs of a blown head gasket either. I push it back home and try to start it again a few times, absolutely nothing. Not even a single fire. I spray some starting fluid and try again. Nothing. I pull the spark plug out and let it vent to check if maybe I flooded the engine. The spark plug was pretty black but had no oil or fluid on it. I used a blowtorch to heat it up well until the carbon buildup was gone and I install it back into the engine. Nothing, not a single fire. I pull the plug out again and check to see if maybe I blew the ignition coil. I see a very strong and consistent spark so obviously that can't be the cause. I searched online and read that too much oil may be fouling the plug. I know I probably added too much oil to the engine (definitely more than 16oz) so I drain it until the oil level is below the H mark on the dipstick. I clean the spark plug once more and try to start it again but get absolutely nothing. I open the gas tank to see if its a venting or gas feed issue (I just use an external breather filter) and there didn't seem to be any vacuum at all. I pop off the fuel line to the carb and plenty of gas flows out. I try to start it again without any success. It seems like the engine is just turning over. No way it can be a gas feed issue, especially considering that it idled for 30+ minutes yesterday without issue. I pulled apart the carb and cleaned everything except the pilot jet. It's a brand new genuine Honda carb so I'm pretty sure that it's not some gunk clogging up the jets and I also cleaned out the fuel tank and fuel line thoroughly before installing the carb. Anyway, if it was, I should have at least gotten a few fires from the starting fluid I sprayed into the intake. Assembled it and tried to start again without any success.
I have absolutely no idea what's wrong with this damn engine. Sorry for the language but I'm incredibly frustrated that after spending over $400 on parts and 30+ hours of work to build this thing properly I can't even get it to fire. I have no idea what's happening considering that I have spark but it won't even light off when spraying lighter fluid straight down the intake. The only two possibilities I can imagine right now are that the air/fuel mix at idle is way off or that the head is somehow cracked and leaking compression. Ignition seemed like the culprit but considering that I saw very good spark when I turned the engine over AND I cleaned the sparks plug to eliminate a fouled plug I really can't see it being a possibility anymore.
The first one (air/fuel off at idle) is probably more likely but, considering that:
1. It started up just fine and idled for about a minute before I got on the throttle
2. It was idling very rich yesterday without issue and the colder weather today could only make it run even leaner
3. It won't even fire when using starting fluid
I don't see how this could be the problem. I do have richer pilot jets I can try but am doubtful that it will fix the problem,
The second one (loss of compression) would be a real pain in the butt to fix. I don't understand how I could completely lose compression today after having excellent compression yesterday. I never even got the RPM high or put a lot of load on the engine. I calculated that it's about 9.3 : 1 so there's no way I'm putting excess stress on any parts. I hear people running 12:1 or higher compression on methanol or race gas as well.
ANY help would be greatly, greatly appreciated right now. I am on the verge of scrapping this engine for parts or selling it.
I am fairly experienced at working with small engines, both 2 stroke and 4 stroke, but for the life of me I can't understand what's going on with 212 I just built for a minibike. Below is a list of the mods I did:
Predator 212 Hemi, Stock Bore, Stock Stroke, Stock Valves, Stock Crank, Stock Flat-top Piston, Stock Rockers, Stock Head (no porting)
Governor and low oil sensor systems completely removed
Governor and low oil sensor holes plugged
ARC Billet Rod +0.020" over (torqued to spec, zero deck at TDC)
.009" Stock 212 Metal Head Gasket
PVL Flywheel with Coil Gap Set to Recommended Gap (.039")
26 lb valve springs, lash set to .003" for both exhaust and intake
Chromoly stock length pushrods
Dynocams CM camshaft
NR Racing GX390 carb billet adapter
Genuine Honda GX390 carb with adjustable main jet from EC carburetors (? pilot jet but is plenty rich at idle)
NGK BPR6ES spark plug
Using 10w-30 Royal Purple HPS oil
I originally bought this minibike used with a Predator 212 Hemi engine. I had plenty of fun with it for months and the engine never gave me any issues. Cut the low oil sensor and changed the oil a few days after I got it. A few weeks ago I bought an upgraded center-exit minibike exhaust with an RLV muffler and it ran fine in the warm weather but struggled in the cold. From experience I know it's because the cold air is denser and makes the carb run too lean. I didn't ride it for a few days since it was still cold and I got the upgraded parts before I got a chance to ride it again. I was extremely careful with the rebuild process and am almost certain I didn't mess up anything. Yesterday it started on the second pull and after messing with the adjustable main jet and idle screw it idled for 30 min with zero problems. Started back up again multiple times with no issue. I even took it for a quick ride and it was definitely making plenty of power. It was probably idling a bit too rich since black smoke was coming out the exhaust but it accelerated fine and idled stable so I figured it was fine. It was probably about 60 degrees yesterday. Today I wanted to do some top speed runs and finish tuning the main jet. It was 28 outside. I left it outside all night. It started up and idled just fine (was idling a bit fast but I corrected it) but then after about 15 seconds of hard running it COMPLETELY cuts out and dies. No warning, no sputtering, but also no nasty metal-on-metal sounds that would indicate some sort of internal failure. No white smoke or any signs of a blown head gasket either. I push it back home and try to start it again a few times, absolutely nothing. Not even a single fire. I spray some starting fluid and try again. Nothing. I pull the spark plug out and let it vent to check if maybe I flooded the engine. The spark plug was pretty black but had no oil or fluid on it. I used a blowtorch to heat it up well until the carbon buildup was gone and I install it back into the engine. Nothing, not a single fire. I pull the plug out again and check to see if maybe I blew the ignition coil. I see a very strong and consistent spark so obviously that can't be the cause. I searched online and read that too much oil may be fouling the plug. I know I probably added too much oil to the engine (definitely more than 16oz) so I drain it until the oil level is below the H mark on the dipstick. I clean the spark plug once more and try to start it again but get absolutely nothing. I open the gas tank to see if its a venting or gas feed issue (I just use an external breather filter) and there didn't seem to be any vacuum at all. I pop off the fuel line to the carb and plenty of gas flows out. I try to start it again without any success. It seems like the engine is just turning over. No way it can be a gas feed issue, especially considering that it idled for 30+ minutes yesterday without issue. I pulled apart the carb and cleaned everything except the pilot jet. It's a brand new genuine Honda carb so I'm pretty sure that it's not some gunk clogging up the jets and I also cleaned out the fuel tank and fuel line thoroughly before installing the carb. Anyway, if it was, I should have at least gotten a few fires from the starting fluid I sprayed into the intake. Assembled it and tried to start again without any success.
I have absolutely no idea what's wrong with this damn engine. Sorry for the language but I'm incredibly frustrated that after spending over $400 on parts and 30+ hours of work to build this thing properly I can't even get it to fire. I have no idea what's happening considering that I have spark but it won't even light off when spraying lighter fluid straight down the intake. The only two possibilities I can imagine right now are that the air/fuel mix at idle is way off or that the head is somehow cracked and leaking compression. Ignition seemed like the culprit but considering that I saw very good spark when I turned the engine over AND I cleaned the sparks plug to eliminate a fouled plug I really can't see it being a possibility anymore.
The first one (air/fuel off at idle) is probably more likely but, considering that:
1. It started up just fine and idled for about a minute before I got on the throttle
2. It was idling very rich yesterday without issue and the colder weather today could only make it run even leaner
3. It won't even fire when using starting fluid
I don't see how this could be the problem. I do have richer pilot jets I can try but am doubtful that it will fix the problem,
The second one (loss of compression) would be a real pain in the butt to fix. I don't understand how I could completely lose compression today after having excellent compression yesterday. I never even got the RPM high or put a lot of load on the engine. I calculated that it's about 9.3 : 1 so there's no way I'm putting excess stress on any parts. I hear people running 12:1 or higher compression on methanol or race gas as well.
ANY help would be greatly, greatly appreciated right now. I am on the verge of scrapping this engine for parts or selling it.
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