Dial-A-Jet Update – Race & Rally Magazine


In the Fall ’94 issue of Race & Rally we ran an article on the Dial-A-Jet system from Thunder Products.


The Dial-A-Jet has been promoted as a way to “adjust” your jetting without having to change jets, so we wanted to find out for ourselves. After installing the Dial-A-Jet system supplied to us by Thunder Products on a ’95 ZR 700 and running it for over 1500 miles, we have learned some valuable information on how to get the most out of this system.


** It is critical to create a lean condition for the Dial-A-Jet to work. The Dial-A-Jet will only enrich a lean condition, it will not lean out a rich condition. (Even at the leanest setting, the total fuel delivered will be richer than the main jet operating alone. You cannot run leaner than what the main jet is by itself.) If you install it on a sled without installing leaner (smaller) jets, it isn’t going to work. You want to reduce the size of the main jets two or three sizes below the proper size for you conditions – which is usually two sizes lower than the factory jetting. We’re talking possibly four or five sizes lower than the original jets – really! You may also need to drop the needle (raise the e-clip) one notch. The Dial-A-Jet is working all the way from idle to full throttle.


** Reading plug color – the typical plug color that you learn to read is caused by the amount of unburned fuel in the combustion chamber. Since the Dial-A-Jet is supplying only the fuel needed, the amount of unburned fuel is less. Therefore, your plugs will look lighter than normal, and this takes some getting used to. If you use exhaust gas temperature gauges, trust your gauge. Gradually lean down until you reach your desired temperature – and when you get there, the plugs will LOOK very light.


** The Dial-A-Jet provides an “Insurance Policy” against lean burn downs. Many like the increased horsepower and better fuel economy when you jet down, but don’t like the worry of being too lean. The ability to adjust your jetting to one of five settings with the twist of a screwdriver is only part of it – the greater benefit is to be able to run leaner without worrying about damaging a motor. It is extremely difficult to have a lean burn down with a Dial-A-Jet installed. If the engine starts to detonate, the Dial-A-Jet responds be supplying enough fuel to keep you skirting this edge – where maximum power is produced.


** The Dial-A-Jet provides crisper throttle response – the typical hesitation when you rip open the carbs does not happen. When a normal carb is opened fast, the amount of air going in is greater than the amount of burnable (atomized) fuel being delivered. The Dial-A-Jet responds to the condition providing pre-atomized fuel during this period, resulting in crisp throttle response. (It fill in the gaps left by the various stages of jetting that carburetors have.) We felt this to be one of the most noticeable benefits – our ZR 700 really woke up coming out of the corners and had a nasty holeshot. It not only ran crisp all of the time, but the quicker throttle response was an advantage.


** The Dial-A-Jet constantly purges the carb of water. Since the Dial-A-Jet pulls its fuel from the bottom of the carb, it is constantly removing the water and alcohol that settle at the bottom of the float bowl.


** The Dial-A-Jet has no moving parts or electronics – it is nothing more than a siphon device with a mixing chamber. The black box that mounts on the carb is the mixing chamber that meters the air (according to dial setting) and mixes it with the fuel, injecting a pre-atomized spray of the fuel and oxygen mixture. The finer spray of fuel ignites faster and more completely, helping to burn the heavier, denser fuel being delivered by the other circuits of the carburetor.


** Fuel only flows up to the mixing chamber when the engine is under load and needs it. If you open the hood, rip the throttle and watch, you will not see fuel in the Dial-A-Jet lines. This is normal.


** How does the Dial-A-Jet differ from a power jet? A power jet merely supplies heavier raw fuel in the 7/8 to full throttle range, where the Dial-A-Jet supplies pre-atomized fuel across the whole throttle range.


** Two Dial-A-Jet systems work better than one. (See information on Dually system.) When you run two Dial-A-Jet nozzles on each carb, you can run even smaller mains. The dual system increases the amount of pre-atomized fuel being delivered. The entire system becomes less sensitive to changes in altitude or temperature. Instead of metering the fuel in a pre-determined amount (as with main jets), the fuel delivery is more of an “on demand” system.


Anyone who changes jets will benefit from installing a Dial-A-Jet. It is performance, convenience, and insurance in a single package. It could be the best money you will ever spend on your machine. The Dial-A-Jet is available through most major distributors or directly through Thunder Products, Inc.


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