From: "Terry" To: "BJW6632" Subject: Re: Carb Synchronization Tips, Please?????? Date: Monday, June 12, 2000 4:46 PM BJW6632 wrote: > > I have a Rotax 503 DCDI that recently would not come to full power (Up to about > 4500 RPM... that was the max).... when I took off the air cleaners I found that > one carb was at its' lowest setting at idle but the other carb was at about 1/4 > power (Maybe an exaggeration... but one was definitely at a higher setting)... > The dual carbs were recently added (Within the past 1.5 hours) and appeared to > be at the same settings at all throttle levels when they were installed.... the > engine ran fine with a slight midrange throttle problem... it ran fine from > idle (about 2400 RPM) up to about 5000... then it went from there to about 5800 > RPM up to a max of 6800.... > Okay, given that... here are my questions: > 1. The max of 6800 RPM..... was that okay?? According to what I've read in the > manual, 6800 with dual carbs is the absolute max safe speed for the motor but > that kinda concerned me. > 2. Carb Synchronization.... is there a easy, but good, way to do it? > 3. What other problems could cause the drop in max RPM??? I hadn't thought of > re-pitching the prop... should I have??? > I am new to the idea of dual carbs and unfortunately don't have someone around > that I can consult.... you folks are it!!!!! The reasons I went to dual carbs > is because of more uniform fuel delivery to the cylinders and more power. > I very much appreciate any tips and suggestions you all may have. > Thanks in advance, > Bill Hi Bill... Here's exactly how to do it..... and if you don't understand, please let me know and I will try to explain it a little better... Once you get it right, you will have no more problems... Step 1) Back off your slide cables "ones comming from the splitter to the top of the carb... do both and be sure there absolutely NO tension on the slides on either carb. Step 2) Back off your Slide stops to be sure both slides are completely in the bottom of the bore... these are the "big" screws located on each carb on the left side if looking directly into the venturi..... Step 3) Take (2) sharpened wood pencils, does not have to be "sharp", and insert into each carb under the slide... just resting in place... THEN adjust each carb slide stop screw IN until you see the pencil just BEGIN to move... ie: the slide begins to move up... do the same for the next carb. This puts both slides at the same position. Then screw each screw in about 2 complete turns and this will give you a decent idle speed to start. Then if you want to adjust idle speed up or down, adjust both screws EXACTLY the same number of turns and both will always be in step... Step 4) Now adjust both cables from the splitter to the top of the carbs.... using the pencils, hanging out of the carbs, adjust the cables so that there is about 1/32 inch movement in outer covering and top of carb, this makes sure there is no tension on one slide or the other.. Step 5) Using both pencils, the final adjustment of the cables from the splitter to carbs is to be sure both slides are being pulled at exactly the same time... while moving the throttle watch both "pencils" for movement.... adjust one or both cables to "fine tune" so that both pencils begin movement at EXACTLY the same time....very easy! When complete adjustment is made, be sure both cables have a very slight amount of free play between carb and splitter. Hope this helps.... Fly smart! Terry #782 Flightstar