Derbi Senda 50cc tuning / hesitation

orac69 · Derestricted Danger Joined: 07 Mar 2013 Karma :

Hi guys, I wonder if I could get some advice please.

I have basic tuning experience, but I am by no means an expert...

My son has an '09 Derbi Senda X-Race 50cc.

Its de-restricted - the standard 17.5mm Dellorato carb now has a 105main jet, GA210 atomiser tube, A22 needle on middle notch.

It also has an after-market pipe, carb plate removed, and a 13T front sprocket.

It runs reasonably well, but I have a couple of minor problems.

1. There is a noticeable stutter / hesitation between 4.5 and 6k RPM - when it gets to 6000, it takes off nicely.

2. On wide open throttle it gets to about 10k, then again stutters a bit..

The plug looks healthy.

Im wondering what to do next to try and get rid of this hesitation ;

1. For the stuttering between 4.5-6k revs, should I move the notch on the needle? Up or down? Could it be something else?

2. Could the main jet be too big? The stuttering feels like its too rich perhaps..?

Thanks in advance.

nathan k · Spanner Monkey Joined: 28 Mar 2012 Karma :

What plug have you got?
Also if ypu haven't already, best value upgrade is the exhaust.

orac69 · Derestricted Danger Joined: 07 Mar 2013 Karma :

The plug is I think a standard B8ES - although I have one of the newer BR8EIX Iridium ones on order just to be sure.

It already has a aftermarket exhaust.

Its just the hesitation between 4 and 6k which is annoying.

P.addy · *Formerly known as* P. Joined: 14 Feb 2008 Karma :

Don't use the iridium in a 2 stroke.

Have you tried moving the needle up 1 notch?

cb1rocket · World Chat Champion Joined: 30 Jan 2010 Karma :

Plug will not make much different, but the fueling is wrong at the mid range point, so as paddy says take the carb needle up a notch and try again.

If you have money to spare get it dyno'ed with a gas analyser
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orac69 · Derestricted Danger Joined: 07 Mar 2013 Karma :

Thanks guys, will move the needle up a notch as suggested this evening.

Not to use an Iridium in a 2 stroke? Why not?

thx

SQL · World Chat Champion Joined: 08 Aug 2012 Karma :

The thinner electrode is also more prone to failure, and dropping off into your engine, not only causing a slight misfire, but normally a ruined cylinder

"Google"

nathan k · Spanner Monkey Joined: 28 Mar 2012 Karma :

Wrong plug mate, use a BR9ES if it's derestricted.
In fact someone on another forum had this exact problem a week or so ago and fixed it by putting in a BR9ES plug.

orac69 · Derestricted Danger Joined: 07 Mar 2013 Karma :

Thanks all / nathan k, changing the plug to the BR9ES fixed it..