I posted this as a reply in the Rotax forum, but thought this may be the more appropriate place for it:
We are seeing a huge delay, or lag between throttle application and engine response in my son’s Junior Max with the Evo upgrade kit installed.
If you basically “stand on it,” there’s almost a full second delay before the engine responds. Coming out of the corners, my son says he has to “roll” onto the throttle way more than even before the upgrade, and then there’s “a lot of popping” 3/4 down the main straight at his home track – like he’s topping out.
This is not how I understand the Evo is supposed to work (?). We have tried with the supplied 130 jet, 128, 122, 125 and 118, which is what’s in the carb now. The needle position was also changed, all trying to chase this lag.
His coach/mechanic is sure he grounded the ignition ground wire as per the instructions (correct bolt on top of cylinder head). I thought the problem might be a bad ignition coil, but some of the tuners I have spoken to say it’s carburation (faulty carburator?) – and some even battery voltage (we are using that “Yuasa” battery). Any thoughts?
Luis, have you guys played around with the throttle opening? I always assumed juniors ran with a throttle slide that opened fully, but a friend tells me that’s not necessarily true. Micros (I know, very different) have to run at about 3/4 max opening in order to function in Evo form. Before we limited the throttle opening, our Micro was behaving exactly as you describe. Rotax is now issuing new throttle stops for micros. I’d play with different throttle slide settings and see what happens. See you guys soon.
We haven’t – so that’s one of the things we’ll “put on the table” when we go testing it again on Saturday (will you guys be there?). I remember you telling me about Aidan’s issue, but did not make the connection, that it might be similar to ours. Thanks so much for the info and see you there soon.
I thought I’d give an update on this issue…it was all down to a defective carburetor. Maxspeed was kind enough to send us a replacement – as soon as we made the switch the issue was gone immediately. No other settings/changes were made. The old one will be a waranty return.
Thanks to all who read this and in particular those who provided suggestions!