Recent Posts  By   (Read times)

Metal shavings are the least of his problems at this point.

Without the header and exhaust the motor runs lean and hot. Burns the edge of the exhaust valve and then it doesn't seal. No seal, no compression. Thumb over the hole test should push your thumb off, not suck it in. Also need to do that test with the throttle wide open allowing it to suck in as much air as possible.

Running with low or bad oil will damage the rings. Bad rings, low compression. If you're persistent you can force an engine to run with low compression but not well. A compression tester with a dial will give you a quantifiable number to work with. Only other way to tell for sure is to pull the head and the cylinder for a look see.

Those style fuel pumps run on vacuum pulses from the intake manifold. Poor compression, poor vacuum. Bad connections, poor vacuum. Split off a dozen different ways, poor vacuum. Alleyoop can square you away with what all can be disconnected and tossed in a box for later. The simpler it gets, the better.

A thousandth of a inch difference is a lot to a small motor. You can pick up a set of feeler gauges for less than $20 and do it right.

The solenoid is already a goner. Can't kill it if it's already dead.

If the spark plug is sparking then you've already got power. Don't spend your time in things that aren't broke. If it's trying to start on the ether then you're close. (Don't use too much. It strips the oil off the cylinder walls and can cause problems with the rings.)

Time to give the carb a good going over.

Look up Challenger Space Shuttle Disaster.

Venting exhaust out of what is essentially a leaky gasket isn't an ideal solution. The hot exhaust gasses flowing through the restricted opening will quickly burn up the gasket and the hole will be bigger than you intended.

At best is will sound like the exhaust is leaking. At worst the gasket will fail and you run the risk if overheating the engine from running too lean.

With that generic aluminum can muffler I would be more inclined to modify the guts of it.

The drain plug is relatively soft metal. A screwdriver (or more properly a cold chisel) and a judiciously applied hammer are likely the way to go, Work your way around the face of the plug, whacking it in the unscrew direction. Just don't go crazy with the hammer. You don't want to damage the engine case. Eventually it will come loose or you'll break off a chunk of the plug to where you can get more leverage on it.

Then buy yourself a new plug and keep your friend away from the garage.

Yup. What he said.

A few more years until fuel injection technology trickles down into the lower price points and becomes the norm instead of a luxury. All the collected wisdom of a hundred years of carburetor subtleties will be abandoned. We'll all become tuner boyz.

Better performance. Better fuel economy. No more chokes. You'll just open the app on your smartphone to connect to the engine management computer via bluetooth. Click an icon to change the fuel mapping from "economy" to "sport" or choose edit and adjust the fuel mapping curve just like you used to do with the stereo equalizer. Boop, done. Didn't even get my fingernails dirty.

The slide of a CV type carb is raised by vacuum which translates in to demand from the motor. Raising the needle in relation to the slide allows more fuel for the same amount of demand. Chopping the spring so that is weaker allows the slide (and the needle) to raise higher with the same amount of demand. Which accomplishes the same thing as raising the needle. Mostly this has an effect on the midrange as the needle is fully closed at idle, (all the fuel comes through the idle jet), and fully open at high speed, (all fuel is metered by the main jet).

Big displacement engines from Detroit don't care about minor nuances like a leaky exhaust. The smaller the motor gets, the more sensitive it is to everything, including ambient temperature and humidity. (Model airplane engines down to 0.049cc need to have the mixture screw adjusted a few degrees every time they run for optimum performance.) Changing the flow of air in or out of a scooter motor will effect the mixture. Yes, opening it up will allow it to breath better, affording potential gains in power, but you will need to compensate for the increased air flow by installing larger jets.

The actual size and length of the intake and exhaust runs are where you get in to voodoo science of tuning to resonant frequencies for induction boost and exhaust scavenging effieicency. Lots of trial and error there.

Milling for oversize: The cylinder sleeve needs to be able to fit down inside the engine block.



You would need to ream out the opening in the top of the block. No practical way to contain the mess without stripping it down.

+1 on getting a tach. Hard to judge by ear what's going on.
+1 on a free flow exhaust

Carbs are a fiddly business. More is not necessarily better. Too much available throughput and you lose intake velocity and vacuum. Consequently less fuel draw from the jets. Also intake stack length can have a big effect on how the motor behaves. Get it right and the resonant frequencies help give it some intake boost.

Aside from bore and stroke changes, most of your benefit is going to come from tuning the CVT properties.