Italika D150 Sputters and Dies - Please Help

[Nikibahama]

While I have an extensive background in Automotive maintenance/mechanics, I am new to scooters and know next to nothing about carburetors (other than them being a pain in the ass).

I have a D150 (150cc) Italika 4 stroke scooter. Months ago it began sputtering and dying. I'd go 100 feet and it would die. It would take forever to start again, go 500 feet and die, etc... I drained the gas tank, drained the fuel lines, replaced the fuel lines, replaced the fuel filter, blew out the carburetor with carb cleaner, re-assembled everything, filled with fresh gas and voila... she was back up and running like new. I hypothesized there must have been water in the gas somewhere, but here we are several months later and it's back to the same sputtering and dying garbage. I drained the gas, not a drop of water in it...


I drained gas from the drain tube that comes off the carb and hangs by the rear wheel. Once drained the moped started up and ran again for a few miles. Then it started sputtering again and I repeated... ran again for a couple miles. Every time I repeated this, it ran for less distance. Some guy passing by says "put it on the stand, it will start", so I put it on the rear stand (instead of kick stand) and it starts... No idea what the stupid stand has to do with anything, but thought I'd mention it. Put it back on the ground and it just turns and turns without starting (or starts after a minute of trying). So I put it back on the stand and it starts and begins sputtering. I disconnect the fuel feed line from the carburetor. Now it runs like a beast. Revs up, redlines, holds there, keeps going... runs for a minute straight without fuel connected. Re-connect the fuel line and the thing just sputters and dies. Spark plug is black so we're obviously running rich, but this is a stupid simple system... gravity drain fuel with a vacuum-controlled valve that then passes the gas through a filter and down to the carb. There is no fuel pump here where I could possibly be "pumping" too much fuel into this thing, nor have I made any adjustments to the carburetor (it's factory). Can someone please help me understand what the hell is going on here? I can rebuild an entire 8 cylinder motor in my garage but some stupid non-pumped, gravity fed factory carburetor with less than 1500 miles on it since new, is constantly giving problems and running rich without any excessive fuel pressure or force? I'm at my wits end with this stupid piece of s___.

[sc00ter]

Few things to try:

Try loosening the gas cap. You might be getting vapor lock.

Make sure the fuel line isn't being pinched somewhere.

If it has high miles or has been sitting for an extended amount of time you might have a clogged jet. I highly doubt that though.

The float height may need adjusting in the carb, or it could have gotten damaged. I've seen many people (including me) catch the float when pulling the float bowl off, knocking it out of adjustment.

Is the spark plug cap damaged or routed wrong, and/or pulling off the plug?

CDI failing. Also, highly doubt it.

Coil failing. Highly doubt it.

It does sound fuel related but it could also be:

Transmission issue. MANY variables....

Stator issue.

Bad earth ground, the ground can be in weird locations.

Nothing else is popping in my head right now.

I purposely picked a carburetor equipped scooter for the simplicity. I don't always like carbs but I've gotten pretty good at messing with them.

Keep us posted!

[sc00ter]

Oh, I've seen petcocks fail before but that is crazy rare. They work off a simple vacuum, on or off. You can pull a vacuum on the suction line (I use a shop vac) and see if the fuel flows and stops. The failure seems to be the little internal flap will warp and hang up. It's easier to replace it IF its bad. This problem rears its head on older scooters mostly. Again, very rare.

[sc00ter]

2 more things popped in my head last night:

Did you top off the fuel when filling it? Overfilling will flood the emissions system. I've done this twice on my scooter. Annoying but it will clear up after a few miles.

Plug gap set correctly? Usually the plug will be pre-set out of the box.

okay, 3 things. How many miles and has the valves been checked/set if needed to spec? That is the killer for most scooters, people not doing the valve checks. My exhaust valve will get a tad tight between check intervals

[Nikibahama]

Originally Posted by sc00ter

Try loosening the gas cap. You might be getting vapor lock.

Did try that, didn't make a difference.

Originally Posted by sc00ter

Make sure the fuel line isn't being pinched somewhere.

When disconnected from the carb and put into a clear plastic bottle, I would say there is a severe excess amount of fuel being drawn through the fuel line. Definitely no pinches.

Originally Posted by sc00ter

If it has high miles or has been sitting for an extended amount of time you might have a clogged jet. I highly doubt that though.

Scooter has 2500km on it (1562 miles). This is the second time this problem has happened in the past 500 miles.

Originally Posted by sc00ter

The float height may need adjusting in the carb, or it could have gotten damaged. I've seen many people (including me) catch the float when pulling the float bowl off, knocking it out of adjustment.

This issue began at random, meaning I hadn't taken anything apart or put anything back together, it just began happening out of the blue. This is only to say that I didn't catch a float or pull off a bowl or do any adjustments. I'm not even familiar enough with a carb yet to know what the float is, so I'm going to look up a diagram of one now to see what you mean.

Originally Posted by sc00ter

Is the spark plug cap damaged or routed wrong, and/or pulling off the plug?

The spark plug had not been modified in any way from the factory (from which it ran perfect). I simply removed it recently to inspect it, then cleaned it with a wire brush and put it back.

Originally Posted by sc00ter

It does sound fuel related but it could also be:

It's definitely fuel related. Without a doubt. Whether it's something to do with the carb or the fuel pressure regulator (vacuum valve), something isn't right.

Today I drained the carb after removing it, blew carb cleaner through all openings, drained the carb cleaner, let it dry, re-installed and now it runs like normal again. Undoubtedly this problem will pop up again in the near future and thus I'd still like to get a consensus of what's going on so I can figure out a long-term fix and not have to take my carb off to blow it out every 300-500 miles going forward.

I sincerely appreciate your response!

[Nikibahama]

Originally Posted by sc00ter

Oh, I've seen petcocks fail before but that is crazy rare. They work off a simple vacuum, on or off. You can pull a vacuum on the suction line (I use a shop vac) and see if the fuel flows and stops. The failure seems to be the little internal flap will warp and hang up. It's easier to replace it IF its bad. This problem rears its head on older scooters mostly. Again, very rare.

Ahh, so what looks like a fuel pressure regulator (vacuum valve) is referred to as a petcock in the moped/scooter world? It's a new term for me, but that would definitely help me identify what part people are talking about lol.

[Nikibahama]

Originally Posted by sc00ter

2 more things popped in my head last night:

Did you top off the fuel when filling it? Overfilling will flood the emissions system. I've done this twice on my scooter. Annoying but it will clear up after a few miles.

Plug gap set correctly? Usually the plug will be pre-set out of the box.

okay, 3 things. How many miles and has the valves been checked/set if needed to spec? That is the killer for most scooters, people not doing the valve checks. My exhaust valve will get a tad tight between check intervals

How often do you do a valve check? I ask because this is more or less my first scooter and it only has 1500 miles on it. Plug is gapped to factory spec from the factory (not changed). I have not overfilled recently, but may have done so at some point in the past. I do know this specific issue began after I had been gone for 3 weeks and there had been a hurricane here during that time.

One question as I'm looking at carburetor diagrams. I see a drain bowl set screw. I know on my drain hose there is a screw that allows you to drain fuel from this drain bowl, and when I've drained it there it will start and run again for a bit. What is the screw for? Could the adjustment of the drain bowl screw also be causing this issue?