Let's Talk Troubleshooting
As Moped Army members had asked question, it does seem that some issues are covered over and over again. In response, this page was put together. This page is intended to cover the most-common issues, and is NOT the end-all of all troubleshooting instructions. Let's get to it.
No Start Issues
With a two stroke engine, if you've got fuel, spark and compression - it will run. So, this is a good starting point.
No Spark Issues
The absolute-simplest wiring for a (points) Hobbit is:
Run the black wire from the alternator (e.g. the black wire coming out of the engine) to the ignition coil (mounted to the pedal-chain side of the subframe). If the coil is grounded, you should have spark.
If you do not have spark, your spark plug boot might be loose, your coil might not be grounded, your points might not be opening, or one (or all) of these components might be faulty (in descending order of likelihood).
It is also worth checking your spark plug itself. If it's caked with a lot of carbon or the spark gap is too wide or narrow, it won't work properly. A spark plug that is caked with carbon may indicate that the carburetor's mixture is set too rich.
No Fuel Issues
Put gas in the fuel tank.
Once accomplished, check: 1) that your fuel hose is not crimped or pinched by it's torturous route across the top of the engine. 2) Remove fuel line from petcock, turn briefly to run and reserve, some fuel should come out for each, if not, your petcock is clogged (probably with rust from the gas tank). 3) If fuel is coming out of the petcock, reconnect your fuel line. If you have a fuel filter disconnect the fuel line after the fuel filter and see if fuel comes out when the petcock is turned to run. If not, replace it. 4) Remove the fuel line at the carburator, turn the petcock to run and see if fuel comes out, if it does you know fuel is making it to the carburator, but is it making it to the engine? Remove and clean the carburator, pay special attention to if there is gas in the float area, if there is you probalby just need to clean the carb, if there isn't, the needle valve that allows the fuel into the float area is probably stuck, remove and clean it very well, along with the rest of the carb.
You should now have fuel!
Low or no compression is not a good sign. Checking this can be a little tricky because there is no easy way to manually rotate the crank shaft. without taking stuff apart (a little bit)
1) With a cold engine, remove the spark plug.
2) Cover the hole that the spark plug once occupied with your finger. Make sure that you don't get dirt in there. That would be bad.
NOTE: The next step is easy if you have a kick start or a manual clutch. But the Hobbit doesn't...so you're going to have to remove the alternator cover and rotate the crank with your hand) The alternator cover is that round chrome thing on the right side of the crank case. There's a screw on the top and on the bottom.
3) With your finger securely covering the spark plug hole, rotate the engine's crank shaft. It'll only start creating a seal after it clears the ports. If you don't feel anything, keep turning.
4) An engine with good compression should create a vacuum or pressure against your finger when the crank is rotated. If there is weak pressure/vacuum, or the pressure/vacuum decreases over a few seconds...you may have some problems. Make sure that your finger is making a good seal against the hole. If you think that you have compression issues, move on to method 2.
1) Get yourself a metric socket and take the head and head gasket off. There are 4 long bolts on the front of it.
2) Push the piston down to bottom-dead-center and inspect the cylinder walls. Look for scratches. Scrape your fingernail against the inside and feel for scratches. It should be quite smooth and uniform. If all looks well, all is probably well. If not, you should probably do the rest of the steps, because it's messed up anyway.
NOTE: this next step may destroy your cylinder gasket.
3) If you tried method 1 and it seemed grim, you may want to pull off the cylinder and inspect the piston and piston rings. You may have to bang on it a little if the paper gasket is sticky. Be gentle. As noted before, you run the risk of tearing the gasket if it's stuck to the case and the cylinder. Get a new one, they're cheap.
4) Look at that piston and those piston rings. Are they shredded? Yes? I'm sorry. Now's a good time to get that performance head kit that you've been eye-balling, eh?
Why did this happen?
You got crap in your engine. Did you run it without an air filter? Did your filter element dry out, crumble, and get sucked into the cylinder? Is the inside of your muffler/expansion chamber rusted or covered with epic carbon? Were you tinkering with the engine/carb and got crap in there? All of these things suck and can ruin your engine. I'm sorry.
What can I do?
Well...if you're handy, you can get a new piston and rings. Then either buy a new cylinder or buy a brake cylinder honing kit and hone those scratches out. It depends on the damage, really. If it has anything other than fine, subtle scratches...you're better off buying some new big bore kit from 1977 Mopeds or treatland.tv or whoever. Remember to clean out your crank case first! It's probably full of metal flakes and sadness.
Low Power or Low Top Speed Issues
First off, identify your model. The PA50-i was only designed to go 20 mph, while the PA50-ii can do 27, bone stock. The specific differences include lots of things. In most cases, anything PA50-ii is superior, though the PA50-i rollers can be useful.
If you still lack power, follow this checklist:
Brake pads dragging? Test by disengaging the engine lever, and spinning wheels by hand. These should both freewheel like a bicycle wheel. Clean out brake drum with proper cleaner and adjust brake play.
Tires inflated (common problem)? Use a pump/air compressor with a proper gauge. Inflate to readings given ON THE TIRE.
Wheels aligned (common problem)? Align by looping a length of string around the front wheel, then pulling each end past the back wheel. You should be able to tell if they're not aligned. It's easy to get the back wheel out of whack if you've been trying to adjust the belt tension. Make sure the four bolts positioning the rear wheel are tight. If frame is bent, take it to a legitimate place to true it. Consider replacement frame or subframe--a bent frame often indicates past accidents and weakened welds.
Wheels trued? Align wheels first. Now spin the wheels. Any wobble suggests untrued wheels. Get a spoke adjuster and learn to true wheels, or take them to a bike shop.
Wheel bearings lubed? Adjust the race nut to tighten or loosen the bearings. If spinning isn't smooth, you might need new wheel bearings, or at least grease and repack them.
Other dragging? Stupid stuff like a bent fender dragging on the wheel or a faulty speedo sender means that much more resistance to power through.
Transmission lubed (common problem)? There's a hex bolt covering a fill hole. Squirt SAE90 in there until it oozes out the hole. Avoid laying the gearbox on its side or upside-down, as this oil will leak.
Transmission bearings OK? Tough to diagnose without cracking the tranny case. Problems here might be the previous owner not doing the previous check. Excessive heat on tranny case might be the only diagnosis. See the wiki article for transmission disassembly on how to replace them.
Belt adjusted correctly (common problem)? Belt should ride 2 mm below the edge of the lip of the rear pulley. Loosen the lower retaining bolts for the rear wheel assy to adjust this.
Rear pulley teeth worn? Might be the culprit if the variator doesn't completely open/close. Diagnose and treat with this wiki article.
Guide ribs worn? These wear out if you don't use plastic guides or have installed the variator and/or belt incorrectly. Make sure they're even. File them or replace the movable face if they aren't.
Weight endcaps broken (common problem)? Open up the variator and inspect. Teflon endcaps love to break.
Weights/ramps worn? Open up the variator and inspect. Make sure those bits get graphite lube, but not too much that it goes everywhere. Inspect for scratches and gouges caused by broken endcaps.
Belt installed correctly? Make sure you install the movable face and tighten the large nut WITHOUT the belt on the bike. Be sure to bend the washer beneath it so it doesn't go flying off while you're riding.
Bent rear pulley cheeks? Did you try to remove the rear pulley to disassemble it and clean up the inner teeth? Did the previous owner? Did you remember to use the real puller? (Found at 1977 or maybe Treats)
Gas cap vent hole clear? Ride around with the cap loosened and see if there's a difference in performance. Either meticulously clean the cap, or replace it.
Snorkel clear? The rubber airbox silencer has three intake holes in it. Spiders and other critters tend to make nests in them. The whole assembly is easily removed and cleaned.
Filter element lubed/existant (common problem)? Remove filter, which is hidden in the frame behind the belt. soak it in 2t oil, then really wring it out. Use paper towels to help. You'll be too rich and four-stroke if it's too oily, but you don't want it too dry or you'll lean out too much and it will crumble. Replace if it crumbles.
Float level correct? This might be the cause of an overflowing float bowl and super-rich mixture. Disassemble carb and hold it end-up so the rubber union to the airbox is facing up. Measure from the bowl mating surface to the middle of the float (which is a thin ridge). This should read 10 mm. Bend the plastic tab of the float if it doesn't.
Petcock clogged (common problem)? Remove all gas lines and open petcock. Fuel should freely flow. If not, drain the tank, unscrew the petcock, and really clean it out. Inspect tank for rust, and flush it out.
Fuel filter clogged? attach fuel line to your freshly-cleaned petcock, then an in-line fuel filter. Open petcock and examine fuel flow. Replace filter if flow is subpar. They're cheap.
PreMix correct? 50:1 is fine.
Every-single-last-speck cleaned out of carb (very very very common problem)? The most finicky thing on the bike, the stock keihin. Read the wiki article. Don't skimp here, just do it. I know it's a pain.
Reeds sticking? Inspect reed plate, which is hidden under the intake. The petals should open with a light press. Consider replacing with boyesen fiber reeds.
Air leaks around intake (common problem)? When reassembling carb/reeds/intake, make sure all surfaces get a liberal amount of 2t oil. USE A TORQUE WRENCH to torque down the intake bolts to 80-120 kg-cm (5.8-8.7 ft-lbs).
Spark plug fouled? Get another one! They're cheap and plentiful.
Correct spark plug/cap? NGK BP6HS or BPR6HS work and are readily available. Do not use a resistor plug (the second one) if you use a resistor cap. Use a multimeter to test your cap's resistance if you aren't sure. Any resistance over a couple ohms means it's a resistor cap.
Correct spark plug gap? Gap your plug between 0.6 and 0.7 mm (0.02 and 0.03 inch)
Timing correct (common problem)? See wiki page on timing. If you have a stock CDI Hobbit, you can not adjust this.
Point gap correct? Stock point gap is 0.3 to 0.4 mm. If you have any CDI Hobbit, you do not adjust this.
Points worn/fouled? Drag a piece of fine-grit sandpaper through your points to clean them off, then reset the gap and timing. This may need repeated. If they're too far gone, just replace them.
Condenser bad? While running, inspect your points and look for arcing. There will be no spark with a completely bad condenser, but a dying condenser will give you poor performance. Replace. If you have a CDI Hobbit, you do not adjust this.
Engine knocking? Make sure timing is correct. Inspect head and piston for carbon buildup, and clean. Do not use E-85 as gasoline.
Compression bad? Run compression test. See the procedures in the manual for the numbers you want. Clean up head gasket (use a lighter/torch to anneal it, or scrub with carb cleaner), and consider replacing base gasket. Inspect the decomp valve, and thoroughly decarbonize it or consider sealing it off. USE A TORQUE WRENCH when tightening head bolts to 90-120 kg-cm (5.8-8.7 ft-lbs).
Crank seals leaking? While engine runs, spray carb cleaner into the gap between the magneto and case, or between the drive face and case. Listen for a sudden change in RPMs. Replacement involves removing magneto or clutch, screwing a sheet metal screw into the seal, then yanking it.
Piston/Jug/rings out of spec? Get a good micrometer and measure them. Compare them to the tolerances in the manual. Inspect cylinder walls for scratches, etc. Consider honing cylinder.
Crank Bearings bad? Grasp the crankshaft and give it a wiggle. The shaft really should not have ANY wobble. Rotate it in your hand and feel for any resistance. Refer to specifications in the manual. Bad bearings can sap power and are very dangerous if they fail. Split the case and replace.
Cooling fins corroded? Get a good wire brush and really clean out old rust/oil/cobwebs/debris from in between your engine fins. This will help keep your temperatures down, as well.
Exhaust port decarbonized? Remove the exhaust and make sure the port is mostly free of carbon. Scratch it out with a screwdriver, but never scratch the piston or the interior of the cylinder wall.
Exhaust gasket sealing? When reattaching a mullfer/exhaust pipe, use a new copper crush washer. They're cheap, and ensure a good seal.
Pipe restriction-free? Blow through the pipe. If you have a hard time doing so, your engine does, too. Throw it on a charcoal fire and bake for a while. Let it cool, then knock out all the ash. Take off the bolt in the side and use a screwdriver to help get crud out. Strongly consider upgrading your pipe.
Pipe output hole bent? The stock pipe can easily have its out-hole bent or crimped. Make sure it's open. Strongly consider upgrading your pipe.
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