high/low jet setting on older scorpion

[opsirc]

knock the jets out of whack on the scorpion my kids used. at full throttle it back fires alot. been trying the 1 1/2 out starting point, but can not seen to find the right spot.

O

[eurolarva]

Cant help on the carb settings but a backfire tends to be a timing issue more then a fuel issue. I would check for reversed plug wires or sheared flywheel key. I dont know what a scorpion is but if the flywheel has magnets the magnet should be just clearing the ignition module around top dead center on the spark plug. Good luck

[hanson]

1 1/2 turns out should get you pretty darn close.

What kind of engine does that Scorpion have?

I'm guessing you have a single Tillotson HD carb on there as well?

Is it backfiring out the intake side, or exhaust side?

How is the compression?

One very common problem on older sleds that creates a lot of little problems is bad crank seals. That sled is over 30 years old and it would not surprise me one bit if the crank seals were leaking a little.

Replacing them is not a fun job but I have a 1973 Yamaha 440 engine that runs like a top now that I replaced the crank seals.

Just throwing a bunch of ideas out there.

[Surface Tension]

Its a Tillotson HR carb. I believe it L 3/4 and H 1.5

Thats just a starting point and when the engine is old you can bet it will be different.

If its running lean you will get a pop called a lean sneeze. I'm willing to bet thats whats going on. As Hanson said a bad seal can produce that symptom but a dirty carb will also.

I've owned many sleds with Tillotson carbs and your lucky to go a season without a a cleaning and new diaphragms. Your fuel pump is in the base of that carb so you get the whole shotting match in a carb kit. Stop by Willamns or Rice Lake Small Engine for the HR kit. If you need a hand give me a ring and I'll give you a hand.

[Macgyver55]

An easy rule of thumb is, if it backfires thru the carb its lean, out of the exhaust its rich.

[Hookmaster]

I can attest to the "out the exhaust, too rich". In the early 80's I had a 1972 pickup. After driving on wash-board roads (that I found out later loosened the wire to the points) I had trouble starting it. Finally one big bang. I looked under the truck and the muffler was smiling at me. I about laughed my a$$ off.