This may not apply to cars however I suppose some car knowledge can be applied. I have an Aprilia SR50R Carburettor model and since I bought I was very happy with the performance. Since I have added a Leovince zx exhaust because the old exhaust was rusty and I hoped to get some additional power. However, after I installed the exhaust, I was advised to rejet to a 65-69 jet and I chose a 69, but to my amazement the jet that was in there was a 78. I tried to run the bike with a 78 jet and new exhaust however the bike just revved and would hardly go past 10mph. I am now running the 69 jet and getting a max speed of 65 kmh and the spark plug is dark brown. What should I do!
Yes, the back flow from the exhaust effects the needed jetting.
You may want a motorcylce shop to help you as they will change the jets as needed to get peak performance.
October, 3, 2012 AT 1:48 PM
Yes it does a tiny bit which I think is normal for 2 strokes, but I can tell the bike is running rich because the exhaust pipe is all oily. I think I have the correct jet in but it may be a case of getting the carb set up which I will do at a mechanics. I am also getting a new belt put in because the old one is worn, is there any chance that the lack of performance could be due to the belt being worn?