Dub's Personal Comments
Dub's Personal Comments
Sport-Jett 1.20
While we were designing and testing the Fan-Jett .95 it suddenly occurred to us that we had the makings of a really hot large size Sport-Jett. A little tweak there, a little stress analysis here, and we had it... almost. As it turned out, we were able to use only two or three parts and had to design the rest from scratch. Nevertheless, we were committed and excited about the prospect of building a big Jett.
What we got was better than we expected. Built primarily on the same size block as the Fan95, we had a really light and Jett-power-ful Sport-Jett. Our goal was to build an engine that would turn a 16 x 8 APC at 8500 to 9000, which would easily beat the competition. The first prototype turned 9600!! It turns out that the 120 is the most consistent engine we have ever built, with only 300 rpm total spread between all engines.
We test all the engines on a 15 x 8 APC (the recommended prop) and they all have to turn at least 10500. Most turn 10700-11000. Now, how about idle? When we first tested the prototype, we thought 1500 would be good. It is, but 1200 is about the norm. We have tried to get 1000, but it stalls after a few seconds, so I guess we can save the records for the next big Jett. On a side note, however, a single cylinder idling at 1200 is the same as your 6-cylinder car idling at 400, and we don't even have a flywheel. As always, the Sport-Jett 120 comes with a Red-Jett carburetor, tuned especially for this engine. You will find the same exiting responsiveness with this engine as you do other Jetts. It's a pleasure!
Some customers want to use an in-cowl muffler. We recommend that you run a full tuned pipe with the Sport-Jett 120, if you can make the installation with your cowling. The Mac 15cc quiet pipe will give you a slight increase in power over the stock muffler without hurting our famous user-friendliness. If you must, try the Bison Pitts-style muffler for the ST 75. It will fit the Jett and work well