Runs rich on the rear cylinder and will start cutting out have ignition tester spark does not go away compression on both 120

Do you have compression guage and fittings?
How To Perform Compression Test EricTheCarGuy

Check fuel supply, proper plug (resistor) compression 120 to 145 lbs. If saw will not run have the ignition tested with a 3-point spark tester.

Misfires are caused by one of 3 things-gas, spark, or compression-one of those is the problem. For gas, check the fuel pressure and see if it is at the right pressure for your car. Low fuel pressure will cause misfires. If pressure is good, it could still be an injector problem, like a clogged injector. If low pressure, suspect the fuel pump or the fuel filter.
For an ignition spark problem, check your spark plugs. Pull them out and inspect them for broken or cracked plugs, check the spark plug gap, check for oil fouled plugs. You may be able to isolate the misfire to a cylinder or two by the plugs condition. A misfiring plug or cylinder should show more black, sooty deposits than the other plugs. A normal firing plug will have a tan or brown colored insulator on the end with very little deposits. If the plugs are okay, clean them a bit if needed, and check for spark on the spark plug wire ends with engine cranking. Buy an inexpensive spark tester, or hold each spark plug wire metal end terminal 1/4 inch from a ground on the engine block, while cranking the engine. Wear a heavy glove to avoid getting shocked. Check that every cylinder is getting a strong blue spark to eliminate ignition as a problem. A weak, yellow or orange spark is an ignition problem, possibly a bad coil, or other ignition part.

If spark and gas is good, you may need to check engine compression. Any cylinder that has significantly lower compression than the other cylinders will cause a misfire, and set a misfire code. You should check for any trouble codes in the engine computer. A code reader or scanner would have to be connected to the diagnostic connector under the dash. What is "significantly lower" compression? About 15-20% less compression. Say you checked and had 150 psi compression in most cylinders. If one had 20% lower compression ( 150 X 20%= 30 psi, 150 -30 =120 psi, or same as saying 150 X 80%= 120 psi.), a condition like that can cause a misfire. I hope I have made sense here. Good luck, and post back what you find, or if any questions.

Check for spark on cyl 2. Auto parts stores sell a spark tester.
Unplug the wire from the sparkplug, insert the tester into the wire, clamp onto metal somewhere nearby. Then, have someone crank the engine. You should see a spark. If not, then your ignition wire or coilpack is bad. If there is spark, check the fuel pressure with a tester, fuel injector by checking ohms on injector tabs, and then compression with a compression tester.

To test for a spark is fairly easy, start by removing the top cover, now remove the spark plug from the cylinder, i guess you do not have a spark tester, so connect a clean spark plug to the plug cap, now earth the threaded part of the spark plug against the alloy cylinder finns, make sure the plug is away from the plug hole in the cylinder, the reason for this is if any fuel escapes from the cylinder, you do not want a spark near that could ignite it, now make sure the ignition switch is on, and crank the engine, as if trying to start it, you should now see a spark at the plugs electrode. The earth cut out wire from the ignition unit should have a spade connection, this then pushes onto the terminal on the switch.

Hello,
Your bike needs three thing to run.

• Spark
• Compression
• Fuel

The first thing to check is the spark on the front cylinder. You should remove the front spark plug and then put it back in the plug wire. Make sure that the spark plug is grounded by placing the threaded portion on the cylinder head fins. Now you can crank the engine over and watch for spark. If it does not spark you have an ignition problem, replace the plug with a new one and try again.

The next step is to check the compression. You will need a compression tester with the proper adaptor to thread into the spark plug hole. Remove the rear spark plug wire. Once the compression tester is installed crank the motor over with the throttle all the way open. Your compression should read at least 150 psi. If the compression is very low you need to have the motor dissasembled for inspection.

The last and most common problem is the carburator. If the bike has been sitting the carburator can become gummed up and prevent fuel from getting to the cylinder. The only fix for this is to remove the carburator and clean or rebuild as needed. This is very detailed work and should be performed by a qualified technician.

Thanks and I hope that this helps.
Steve

No, Harley Sportster engine is the best engine Harley ever built in my opinion. If your engine is fuel injected, I'm afraid you'll have to take it to the dealer to find the problem. If it's carbureted, you may can fix it yourself if you can find the problem.

The engine needs three things to run, compression, fuel, and spark. Since it's a 2010 model, it's new and the compression should be good but just in case, a quick compression test should be done. Average compression should be about 120 pounds per square inch.

Next, you must have fuel. With a hydrocarbon reading of 1600, I'd suspect that your getting fuel to the cylinder. Matter of fact, it may be too rich. Check your intake manifold for vacuum leaks. If your bike is fuel injected, you'll have to take it back to the dealer for service. There is no way a carburetor can cause this, it's got to be a vacuum leak if it's too rich on one cylinder and correct on the other.

Finally, you need spark. I would guess this is your problem. If the fuel is not ignited, you get a "missfire". Try removing your spark plug wires and install another set of plugs in them. Leave your original spark plugs in the heads. Spin the engine with the starter and watch the spark. If the spark looks good, install the new set of plugs in your engine and try that. If not, you need to check the output of your coil.

Tools(1) A compression gauge (2) a spark gap tester.(3) A Clymer service manual for your engine. (you can purchase from your local dealer. I know all these are expensive but if your going to be a polaris tech you will always need them. Troubleshooting (1) check compression. Look at your Clymer manual for specific psi.all cylinders need to be over 100 lbs and equal each other within 5 lbs.(2) check spark. use a spark gap tester all cylinders should jump a half inch gap. if you have good compression and good spark, fuel is the problem nine
times out of ten.Ethanol gas is proven to stay stable in fuel systems for only 30 days in 90 + degree heat. Drain gas tank,clean fuel lines replace and replace all fuel filters. Polaris has a gravity filter under seat, clean it. Finally replace spark plugs, I know spark plugs probably don't look bad but this is a C.D.ignition. Fresh spark plugs means less resistance for the ignition system. The ignition system is week compared to automotive. Test drive polaris, if the problem is still there then there is further steps to take. If your polaris is fuel injected. Pull out your clymer manual. what is great about the Clymer Manual for Novice techs is it gives detailed info on your polaris. Troubleshooting tips and teaches you how your polaris works. If its carburetor then you should clean carburetors. Inside the carbs is another filter that needs to be cleaned. Its not difficult you just make sure you put everything back in proper order. take pictures if you need to.

FIRST OF ALL YOU NEED TO RUN ENGINE FEW MINUTES DONT GET IT TOO HOT. TURN OFF ENGINE. THEN PUT ON SAFETY GLASSES. USE COMPRESS AIR BLOW DEBRI AWAY FROM SPARKS PLUGS.TO KEEP FROM GETTING INTO CYLINDERS.DISABLE YOUR SPARK IGNITION.AND DISABLE FUEL PUMP.BY REMOVING FUSE.NUMBER AND TAG SPARK PLUG WIRES.REMOVE ALL PLUG WIRES AND SPARK PLUGS.BESURE YOU NUMBER THEM AND TAG THEM SO THEY GO BACK IN THE ORIGINAL PLACE.THEN GET COMPRESSION GAUGE TESTER SCREW IT IN SPARK PLUG HOLE TO CYLINDER 1 FIRST.TAKE YOUR FOOT PRESS ACCELERATOR PEDAL TO FLOOR.PUT KEY IN IGNITION SWITCH CRANK ENGINE AROUND A FIVE TURNS.THEN CHECK COMPRESSION ON GAUGE.IT SHOULD BE NO LOWER THAN 100 PSI.IF SO SQUIRT SOME OIL IN THAT CYLINDER. IF COMPRESSION INCREASES.THAT CYLINDER HAS BAD RINGS IF OIL SQUIRT DONT INCREASE COMPRESSION. VALVES IS LEAKING. YOU DO ALL CYLINDER THE SAME.SCREW COMPRESSION IN PLUG HOLES.TURN ENGINE OVER 5 ROUNDS. WRITE DOWN ALL READINGS.

3 things to check 1 / check for fuel at cylinder is spark plug wet with fuel if so go to 2 . if not check carbs butterfly / jets etc ?.
2/ compression .. remove spark plug and fit compression tester should attain between 120 t0 150 psi or be in green for none numbered meters .. if not suspect valve seatings or cylinder head gasket ?. or compresion rings . if ok
2 check for spark at plug place plug in cap and place on side of engine turn over and look for good spark ( some plugs spark when out of cylinder but break down under preassure I am sumising you tried a new plug first ) if no spark check ignition /distributor cap and rotor arm clean and refit or replace . if all fails then can only suggest that you take to garage and have a tune test performed .. hope this helps.. Regards vortash