AR Engine tuning

[Simonypvs]

I have recently acquired my AR and have already fitted some Supermoto wheels, big disks etc and now am planning to pep up the engine. I am going to have the work done by a good mate of mine who can work wonders on 350 yamaha engines and I have challenged him to get some more top end out of the engine.

If anyone has got this months Practical Bikes one of his bikes is in it (NSRD350)

Has anyone got any pointers as to what may be required, I am doing the usual DEP full exhaust system but I suspect we may end up making a front pipe to match the tune he does. I will do all the common sense stuff like bigger reed cage and working out how to get more air into the engine and no doubt some bigger jets in the carb (more fuel and air will hopefully lead to a bigger bang!)

Cheers

Simon

[knackeredMk1]

Hi Simon, sorry to say this as it is a bit like a 'Now show' sketch but if you wanted to tune it to produce peak power without screwing up other aspects of the power production you should have started with a Mk3.

Aftermarket expansion chamber and silencer are a good start togther with some dual stage reeds. Skimming the head will be an option as will matching the ports and flowing the cylinder. After that it all gets a bit costly and messy. A larger carb will get some top end but you then have loose/modify all the AR sensors (to the point whether the AR doesn't work), you will have to use premix (if bigger than 33mm) and you will start to loose bottom/mid. Then modified intake etc ............. Essentially you turn an AR into a modified Mk3 with a second rate top end.

[Simonypvs]

Knackered,

Thanks for the info, I am not going as far as fitting a bigger carb but we will tickle the ports and take about .5 mm off the head. I will modify the airbox so it can flow some more air through it, re jet and see where we go from there.

I am going to take the engine out in a month or so as I want to use it until the nights close in.

I will update when we have tickled the ports etc


All the best

[helisupp]

I always found with my other 2 strokes that whenever we gained power higher up in the rev range, we lost tractability or useability elsewhere, everytime.

Tune for topend, tune for mid range, tune for mudplugging, but never succeeded in having a 2 stoke do everything.

Got fed up holing pistons, plug chopping, changing jets all the time (I used to rejet for nearly every enduro depending on terrain and altitude / temperature) seizing on overun, seizing when flat out, I even ride pushbikes with my hand over the left hand brake as if the bike might nip up at any time.

The AR might not be the ideal bike for tuning....................................

[njhardy]

I'm not sure if the TRX piston fits the AR, but it made a ton of difference on my Mk 3 compared to the old one and I took the piston to +4 oversized for good measure for a couple more cc's. I also gas-flowed the castings on the inlet, transfer and outlet ports (but didn't go as far a port re-shaping & timing, as Mr Honda seem to know what he is doing and I don't want to lose power or reliability. I skimming the head a little perked up compression, plus Boyessen reeds and a polished reed cage, plus polishing up the exhaust port and power valve and new bearings all round. I use pre-mix now, as I found the oil pump too unreliable during running-in. I actually ended up reducing my main jet size (its hot here in Vietnam) down to a 135 main jet and a 40 idle jet, which have made it run sweeter with my Procircuit pipe & tail- probably this won't be tru for UK. If there is a baffle in the airbox, remove it. Anything else and the ecu will need adjusted and that gets messy. She now runs like a proverbial 'pocket rocket' but I have lost a little low-end power for the sake of mid and higher.....Shame about the fuel consumption though!