I have finally got my sons DNA running again. After new piston/rings, skimmed head, new plug, changed stator, changed carb - it was running. Then for some reason it would not start. It would fire but not start. Looked at all sorts, turns out it was the dash - changed it and runs fine. As it stands it has a Hebo pipe, 68 main jet and malossi std air filter. I have been out on it and it gets to 31mph and thats about it (I do weigh 15st though). I have checked the variator and the washer has been removed. Not sure of the weight of the rollers but they are 19.5mm in diameter. Any idea how I can squeeze a few more mph's out - 35 - 40 would be nice.
Rollers are definitely something that's needs to be changed with a better pipe - worth a look. As well as the plug being a good colour and belt being ok(18mm or so) No reason it wouldn't do 40-50 when set up right
Try rollers at around 5 to 5.5 gm. Though to be fair the rollers will only affect acceleration and not top speed. My understanding is that roller weights wont affect top end. They will help on pull away and hills. Other changes could be with a performance variator which has different angled plates, changing the behaviour of the belt, or a performance clutch. These are useful but cost money and time. Less expensive would be a performance coil, ht lead and iridium spark plug which may improve power. The other main change will mean derestricting the bike at the exhaust. How will depend on your pipe, either you remove a part from the inlet or the outlet, depending. If its for your son then any derestriction will render the bike illegal in the uk unless he has the correct licence and his insurance have agreed. Police cant check for derestrictions on the roadside but if caught speeding over 30mph then he may be riding other than in accordance with his licence and will render his insurance null. If he crashes then the insurance team may check for derestrictions. If he is 17 or older and has a cbt then he can ride it derestricted but his insurance must be made aware. If thats the case then do the exhaust, ensure the variator spacer is out, lighten the rollers to 5 or so and play with jet sizes around what you have. A little leaner will improve performance but monitor the plug colours. Besides that, lose weight, head down, have the wind to your back and aim downhill. Wearing a wet suit will give you an extra 5 mph as wind resistance matters more than how you look.
I was under the impression that heavier rollers give a higher top end and the std ones seem to be 6.5gms. Was also under the impression that as it is a performance pipe it would already be derestricted. He is 17 and has passed his CBT so ok there. I thought about losing weight but my 1000cc v twin doesn't have any problems so I may leave that one. Wetsuits a good idea but don't want to chased by greenpeace thinking a whale has escaped............!!
Others may have different opinions but my understanding is that the roller weight does not affect top end. Its a common misconception. Basically the rollers have one function, to push out under enertia force and force the angled variator plate to move in towards its sister plate, thus forcing the drive belt up and out, pulling in on the clutch drive at the other end. Not well explained however the weight of the roller determines how quickly they move outwards, pushing the plates together. Heavier rollers move out quicker, under lower revs, forcing the clutch to engage at lower revs. Lighter rollers move out a little later allowing higher revs to build before engaging the clutch, hence a nippier acceleration. Top end speed is not affected bythe rollers, irrelevant of weight as top maxed out revs dont change. There are some good blogs on line to explain. I have read that sliders may assist though, being better than rollers but i havent tried so i dont know.
i would look at the pipe first, check to see if it still has the restrictor fitted, then go from there
I checked the plug and it was very rich (the jet was 77 not 68). I have put the original jet back in and will be trying that to see how it goes. Thanks so far.
yeah if its rich your top end will suffer, mt scoot has a waaay to big main jet, and if i ride on WOT it will stop at around 60kmh, but at about half throtttle it will hit maybe 70-80kmh.
Test ride today with the standard jet (57). Ticks over fine and revs to redline when not under load but when riding it will bog down at about 7k revs, I then have to hold steady to increase speed. Am I right in assuming a larger jet is needed.
Update. I have changed the jet to a 68 (not checked the plug yet after a run), I have put new rollers (7.2g) in, not sure of weight of old rollers, and a new drive belt. Had a little run and it accelerates ok to about 25 then moves slowly up to about 32/33 then thats about it. At standstill it revs to over 9k but when moving it seems to top out about 8k. Any thoughts
Did you resolve the jetting / speed issue. Im having a similar problem so wondering what you settled on in the end?
Currently have put a 66 jet in so just need a couple of runs to see how it is. I have also put lighter rollers back in (they are about 6.5g) to see if that makes a difference. No MOT or tax on it so am limited to a run round the block to try it out. I have got a Hebo variator kit that was on our donor bike. Tried fitting it but there seemed to be too much play in the variator when I torqued it up. Measured the shaft the on the donor bike and it is a 1/4 inch shorter than on the bike I am working on. Will possibly change the clutch unit as the donor has a red contra spring so that may make a diference.
Keep your posts updated so i can follow how you get on. As i say , my dna is having similar speed issues. Im currently on 62 jet and 5.5 rollers and it revs sweetly on the stand but no more than 6000rpm and 20 mph on the ground. I've ordered a 68 jet and am going to try moving the needle clip position as well. Good luck. If you solve the problem then post your settings up, might help others as well.
