oxygen fuel and the power jet

So, what's your altitude? And, what's your boost level?

What mountain are you going to bust, or which friendly competitor are you planning to teach a lesson?

This is one of those things in a snowmobiler tuner's life - bringing carb and motor into harmony. Grins stretch, motors sing and that snowmobile confirms it was well worth the investment you made.

More and more, western riders are finding the need to replace main jets an activity in their personal history books. Electronic fuel injection, mechanical altitude compensating systems and electro-mechanical compensating systems from the factories are all more plausible and affordable than ever before.

However, there are times when this is not enough. Especially when a turbo, such as an Aerocharger is mated to a two stroke motor, or that competitive hillclimb is in your face.

Jack Harris of Harris Autobody in Ogden, Utah, is Aerocharger's West coast distributor. His close work with turbo motors and thin air led him to create a fuel and oxygen adjusting system that gives owner and driver 12 on-the-fly settings. He calls his system the Power Jet.

The Power Jet units are supplied with either a screw or a small control knob that winds a valve in or out for fuel flow. Harris says, "Imagine a water valve, turn the valve to the right to slow or stop the water, turn to the left to increase the flow. The Power Valve works the same way." It is the purchaser's choice to go with either a notched screw head or control knob. I like the control knob.

The pre-atomizer extends about halfway down from the carb's horn to its center. Here, a vacuum pulls the fuel mist into the crankcase.

Harris engineered a way to mellow finicky altitude or temperature problems by bringing a full range of adjustments to round slide and flat slide carburetors, regardless of brand.

As a matter of fact, PSI believes in Harris' product- its Big Air Carbs come with the Power Jets. As of December 1999, Harris had sold 600 sets to PSI.

Harris' Power Jets make any snowmobile lacking high-altitude compensators equal to those sleds equipped with an OEM carb automatic adjustment system. However, the Power Jet owner must still make altitude adjustments himself, but the time to do so is, well, minimal. Open the hood, make adjustments to the fuel jet - up or down - and go. Oh, you might need to check the plugs now and then, but we all do that. With Harris' Power Jets, changing main jets for altitude is history, once the initial setup is complete.

Furthermore, if you run a mammoth big-bore (without OEM altitude compensators) or a turbo charger, Harris' Power Jets help knock out the weird peaks in the big-bores at high altitudes and the turbo lag from a boost induced motor.

Harris also says that when a turbo is bolted on to a mountain specific sled with an OEM altitude compensator, the compensator unit has to be removed; all to handle the new pressurized airbox and to handle the fuel demands the motor needs. Hence a call for another system - Harris' - with the same purpose, albeit with a wider range of adjustment.

The Power Jets atomize the fuel before it is sprayed into the carburetor intake to be pulled down into the crankcase. Normally, as fuel flows, it begins to break up into fine particles and then reaches its final atomization in the combustion chamber, a.k.a. the cylinder head. The Power Jets enhance this fuel atomization process.
Furthermore the Harris-designed adjust-as-you-go jets supply fuel to the motor only when under load, such as melting the lake, topping the mountain or snorkeling through the powder. Power Jets sense load increase and act accordingly by adjusting the fuel flow.

How to install the Power Jets on Mikuni or Keihin carbs.

1. Remove the carburetor air box. If removing the airbox from a snowmobile that uses a carburetor altitude compensation system, use caution to protect the hoses.
2. Detach the carburetor fuel lines and throttle pull cables.
3. If installing Power Jets on a motor equipped with a mechanical altitude compensating system, remove the compensating system. Note the hose routes.
4. Remove the carb from its boot.
5. Drain the fuel from the carbs by removing the main jets and float bowls.
6. Measure the carb horn's length - the 12 o'clock position to the 6 o'clock. Cut the Power Jet's dump tube to half the measured length.
7. Drill and tap the mounting hole for the adjustable jet on top of the carb horn at the 12 o'clock position, tap out the hole with a 1/4 inch by 28 bit.
8. Place blue Loctite on the adjustable jet's threads and screw in. Do not over tighten them.
9. Tighten down the Power Jet's valve to fully closed and re-open 1 1/2 turns.
10. On the float bowl, drill a 10/32-inch hole immediately in front of the main jet's mounting, half-way between the jet and the float bowl's upward curve. Smear blue Loctite on the threads and insert fuel line nipple.
11. Reduce main jet size from five to 10 sizes. For example, if the carb has a 300 main, replace it with a 250.
12. Reinstall carbs onto engine boot.
13. Reinstall fuel lines.
14. Reinstall altitude compensating lines if equipped.
15. Install air box and check fuel hose routes.

According to Harris, a snowmobile with a 250 main, should be adjusted as if it were throttling on 310 mains. Harris says for every one full turn out on the adjuster, the fuel enrichment concept is equal to an increase of four jet sizes. It is recommended to keep the adjuster within 1 1/2 to 2 1/2 turns.
Harris cautions that if the owner/driver starts screwing down the fuel adjusters, like turning off the hot water to a bathtub, the spark plugs should be checked- often. Choking off the fuel points to a lean burndown.
As mentioned, Harris' Power Jets help synchronize the fuel and air mixtures for changing altitudes and temperatures, regardless if the sled runs OEM altitude compensators. Also, if a motor is mated to a turbocharger, the Power Jets will keep the motor properly fed. More so, it offers peace of mind to protect your investment.

For more information, contact Jack Harris Autobody at 801/544-3653; fax, 801/544-3733.