Diff'rent Strokers

[2TV owner]

Having never been satisfied with how my bike performs at the top end after fitting a '175' main jet which is the correct listing I decided to have another go at getting it sorted.

first time i stripped the carb i found a 125 jet in there and although the top end performance was much better than it is now i was concerened that it was running lean.

It idles fine and pulls all the way up until full throttle at which point it starts to splutter a bit. Putting the choke on makes it worse so i'm pretty sure my diagnosis is correct.

Off came the top of the carb and i decided to lower the needle, upon getting the needle out i found it was slightly bent! a new needle was ordered. I did notice though that i must have fitted the needle back last time i had it down on the second position down from the top so i only had one more groove to go. I also noticed that there was a plastic washer both above and below the circlip. I decided to have both washers above the circlip and circlip on the highest position (needle lowest).

This has made full throttle positions much better but not 100% so i will have to drop a needle size, i was thinking 160 main and then putting the needle back in the middle. Am i going too low with a 160

Has anyone else fiddled with their carb and if so what did you settle on. I realise that all are different and some of the SDR's on here are modified and therefore needles and jets will vary.

[2TV owner]

I decided to go with the 160 jet and whilst at it i'm gonna change the float jet as i just don't know how old it is. Will post some pics on here when i get round to doing it.

Justin

[2TV owner]

Ok, I removed the carb yet again and fitted a new float valve and then reset the float heights. Whilst the carb was off I had a look at the reeds and found that one of the petals was not fully seating. A new set of HYTech reeds were installed, carb back on and low and behold,,, still the same.

Carb came back off and for whatever reason I decided to put the #175 jet back in and put the needle at the mid position. I knew at this point that it wasn't going to fix it but I was growing very tired of taking the carb off to check what had been done. It had even got to the point of work mates advising me that perhaps a four stroke would be a much better option. These people obviously don't tinker with their bikes!.

I was quite confident that everything that I had done was justified and in it's own small way had helped improve how the bike would run but I had now run out of ideas as to how to get this bike to perform at wide open throttle speeds.

I had been tipped off about a Bike shop in Horsforth (Leeds) that had a dyno and did do two strokes and did know what they were doing. They have done some setting up for Mick Abbey of Mick Abbey tuning fame. This seemed a good enough reason to let someone else have a go.

I gave them a call and spoke to the owner, Gavin and talked him through what had been done etc etc etc. He said he would have a look and try to get to the bottom of it. He charges £35 to run up on the dyno and diagnose what the fault is. I left the bike with him for a few days as it was no good to me.

I got a call a couple of days later from him to tell me it was all done!!!! this was what I needed to hear, at last I had a bike that would actually go. I went to collect the SDR and again had a lengthy chat with Gavin who said his initial thoughts were that it was an electrical fault but he noticed on the dyno that at WOT the bike was massively over rich. He changed the jet for a smaller size, (sounds familiar) and had no luck. He thought that there may be some restriction in the air flow, I had advised him that it had a new air filter.

After taking the tank off he found that the SDR has a rubber 'snorkel' that collects the air from under the tank and sends it into the air filter box. For whatever reason he decided to remove this snorkel and once back on the dyno the bike performed as it should and he recorded 28.32bhp at 8763 rpm. Before he found the fault he only got 21.66bhp at 7985. What a result! it's a few hp off the claimed 34bhp Yamaha said it should have but that's life.

Just been out on it tonight for a quick blast round the same test route I used to try and diagnose the initial fault and yes it does go now and revs right out and passes traffic without fear of them pulling away from you

Don't have pictures at the moment but if I get chance i'll upload the dyno sheet. Cost? £72 inc VAT bargain!

Justin

[yanw]

A good result and hopefully there is still some of the year left to enjoy it to the full.

I am pretty sure that Yamaha quote BHP at the crank and not the back wheel so I would suggest it is "back to factory" in terms of power. Either way you have 30% more power for less than a hundred sheets