I already have a GPR powerjet that is doing the same thing as Kev's fuel mod, I think? Fooling the temp sensor to make the ECU Richten the fuel mix. (I think)

I have k&n open filter, bsm-slipon and the GPR PowerJet. I am planning to replace the powerjet with with a DynoJet Powercommander V.. Do I need a Kev fuel mod anyway?

I seem to recall (from one of your other posts - or maybe it was someone else?) that you weren't sure exactly what the two dials on the GPR Powerjet actually do - is it set up right for your filter and pipe? If you're going to get a PCV anyway, then I'd reserve judgement until you do. The 07/08 ECUs are pretty bad for surging, but an O2 controller/optimizer and a PCV can 99% sort it out.

http://www.xt660.com/showthread.php?t=8546

Your memory are good :) Yes, it was me that wasn't sure about the knobs on the powerjet. The previous owner had it installed and it was a mc company here in Sweden that set it up. I have still not found any instructions for the powerjet, so I have not touched the knobs. But I read that a powerjet or powercommander can't fix the fueling on low revs? (In the closed loop circuit)?

As somebody said earlier in this thread, I also think the bike is a bit stronger on low revs. And I have heard that the XT-bikes are set very lean from stock so I do think it is good to install this O2-controller either way to richen the fuel mix on low revs. Am I right?

You can't do any harm! The O2 controller will definitely have improved the closed loop fuelling. It is just that you are going to have to get the open loop fueling sorted to match the A/F ratio of the O2 controller (13.6:1). Any big difference between the closed loop and open loop fuelling will cause a "step", which contributes significantly to surging.

Without knowing what your GPR device is actually doing, and what A/F ratio it is giving, it's going to be tricky to setup without putting the bike on a dyno. As I said, if you're going to get a PCV, then you may as well get it all sorted at the same time: PC, dyno time and correct maps for your mods.

It will definitely make a difference with a PCV as it will bring the open loop fuelling much more in line with the closed loop. (The GPR unit should be able to do this to a degree - that's is if anyone new what the knobs did! ;) )

Aha, now I understand :) That can absolutely be the problem. As I don't know what the powerjet does, I will buy a Power commander V. I think it fools the ECU via the temp sensor in some way.. Says it is cooler than it's really is or something..

A question about the PCV... I don't think I can dyno bench the bike right away, can I find a suitable map for My bike anywhere? I know that it isn't the optimal solution, but maybe it works quite good until I can bench the bike?

Yes there are "ready made" maps available which will do the job very well. A dyno run and custom map will obviously be even better though. There are lots of maps available to download on XT660.com, tailored to all manner of mods. However, you do need to join the supporters scheme (�10) to gain access to them (and lots of other useful technical stuff and 1:1 support from Kev). To join click on the link in my signature.

I will be a supporter right away! :)
Is it for 1 year or for life? Does it cost 10 pound per year and do I have to Renew it in some way or does it just expire after a year?

It is a voluntary membership that only costs a tenner per year and there are no obligations to re-subscribe once the term expires, you get a reminder from the forum software a few days before the end of your year subscription, asking you if you wish to renew or not. If you ignore it or do nothing, your subs will naturally expire and you will not be bothered again by the software or anyone else, rest assured no money be taken from any account without your consent because this system only allows PayPal payments and as you know you always need to authorize these before PayPal pays anyone.

Cheers

Thank you for the information. I will be a supporter during the day today. Am on a train at the moment with bad mobile coverage. Don't wan't to deal with creditcard payments when I can get out of coverage :)

Other things that cause surging are worn chain & sprockets, chain to loose not adjusted correctly & the most common one is the rear sprocket holder damper rubber with free play.

1/ Make 100% there is no free play in your rear sprocket holder, grab the rear sprocket & try & move it forwards & backwards there should be no free play. If there is free play replace the rubbers or carry out my rear sprocket rubber mod.

2/ Make sure your chain does not have tight spots, lift the rear wheel in the air supporting the bike with a stand or box so you can spin the rear wheel freely, turn the rear wheel slowly while pushing the underside of the chain upwards towards the swinging arm the chain should not change it's length or try & push your hand downwards, if your hand is forced downwards & upwards when turning the rear wheel your chain has tight spots & can make the bike feel like it is surging.

3/ If your bike chain has no tight spots & is adjusted to loose the bike will feel like it is surging.