Hi fellow adventurers.

I'm not sure where to post this, I don't do much forums, but I'm desperate for advice now.

My XT660Z just started giving me a strange problem. In 5th gear, it won't go past 5000rpm so my top speed is limited to 135 - 142ish km/h (around 87mph); and at the same time, I'm only getting about 14km/l (about 32mpg). This is breaking my brain. Usually, when I ride it hard on the highway at 150-160km/h (5500-6000rpm), I usually get around 18km/l. I can even get it to almost 21km/l, but I'm not that kind of rider

Have anyone experienced this with their XTZs?

Recently, the 3rd gear disintegrated, so I got that replaced by Yamaha, that came with new clutch plates. I got the valves done, cleaned the air filter, replaced the fuel pump and filters, new chain and sprockets and added more rubber to my cush rubbers, serviced the suspension, recalibrated the throttle and sensor, new tyres and got the injector cleaned. And still, this problem is still the same. The bike pulls as normal, everything below 5000rpm through all gears are awesome as usual, but not getting my usual top speed and consumption is frightening. Also, when I get a little side wind, the top speed will drop to 125km/h. There is something terribly wrong and going cross-country is going to cost me a lot more.

The history of the bike -
It's a 2014 model, I bought it brand brand new in 2015 with 0km on the clock. I put 87000km on it in the past 3 years. I won't lie, I wasn't easy on it. It was heavily loaded, did mostly offroad, I never missed an opportunity to take a jump. It has an after-market 2-1 exhaust with no other engine mods, except for the snorkel I removed. After everything I did to it after the gearbox went, it's practically a new bike. Only thing I haven't touched is pistons and rings. The mechanic gave up and said that the bike as had a great life, but it's getting tired now. That's not really good enough for me.

I will appreciate any advice.

The third gear issue is a common problem but usually linked to 2009 bikes and between a particular set of engine numbers, from memory, roughly 6200 to 9200. Sad to hear that gearbox issue can still be playing Russian roulette with newer bikes.

I read you changed the fuel pump.....I / we would like to know why that was done and was the replacement a genuine Yamaha part or a specifically recognised part?

It's great to hear that a bike has been 'used' and has done some battle mileage.

As for the valves, where they set on a cold engine and did you do them or where they done by someone else who said "they were done"?

Also the TPS, what angle did you set that to?

Your list of work done ....to me....sounds like the exact same list of, individual, possible causes that would bog an engine down at high revs, especially poor valve (may be too tight) gaps or a Chinese fuel pump not delivering or a TPS set incorrectly.

__________________
I have a lot of growing up to do. I realized that the other day inside my fort.

Chalk Two!!! Thank you for your reply. I really appreciate it. I love my bike and don't like to feel it so unhappy.

The gearbox was repaired by a Yamaha agent. After I got it back, I took it to a mechanic who I trust more than the local Yamaha agents and asked him to set the valve clearance for me as I had never done this since I started servicing the bike myself. After that, it was the first time I could properly test the bike again and I took a 1000km ride out for a weekend. This is when I noticed the top speed and fuel consumption was way off. I phoned him up when I returned and told him about the problem, and he suggested we look at the fuel pump filters as 86000km is a lot of time to collect dirt. When the bike is in neutral, and being reved, it sounds like it starts struggling from 6000rpm. Almost like the rev limiter is slowly kicking in earlier. I helped him to take the tank off and the pump out, and the filter was beyond dirty. He suggested that I just replace the pump and filter to make sure everything was new and clean. Yamaha wanted to charge me a ridiculous amount, so I googled a bit and found a company with aftermarket pumps.

I got this product -
http://www.fuelperformance.co.za/ind...product_id=653

We made sure the tank is clean on the inside. After he assembled everything, he started the bike and reved it up again, with the same problem from 6000rpm. He then took it to Yamaha to connect it up to the diagnostics system to see if it picked up anything. The throttle was a little bit out (think he said 3% or 3 degrees), they fixed that. Then the system also said the crank sensor was out, but the bike is not supposed to start in that case, so they reset the error. They also did a pressure test on the fuel pump and it was measuring 3.8bars which was apparently above the required pressure.

Now, I'm clearly no mechanic. I know the basic oil change and minor service, and fixed a loose crank nut once. That's it. But from what this mechanic explained to me about the valves and high revs, this problem also sounded to me like a valve problem, but I trusted him as that was the main reason I took the bike there (he only had to do the valves and fresh fork oil). Maybe he didn't set it correctly?

I don't know what TPS is I can ask him at what angle he had it set (if he touched it).

Do you think I should get someone to look and give a second opinion on the valves? Or maybe get in there myself and learn something new. I'm not scared of getting my hands dirty, just sometimes scared I do more damage than good. But I just bought a bigger bike now for the longer trips as I don't think this thumper is going to last me much longer if I carry on putting it through all this stress. So now I will have time to dig in there and explore new areas of the motor and learn new things.

hahaha sorry for this looong detailed reply. But I guess you can give better advice if you have more information Thanks again....

No worries about a lengthy reply. It's all good info.

TPS = Throttle position sensor.

As for your crank position sensor error code. I'm sure guys here have had the same fault code with a running bike. I maybe wrong but the fault code for the crank sensor may well be a number, 12. If the garage have cleared the fault code, it really needs to be seen if it is back. Clearing codes doesn't clear a fault. If it is back then it's a simple wiring checking process. The crank position sensor acts like the big drum in a marching band, everything else gets its timing from it, when and how often to inject fuel for example.

You mention your fuel delivery system was dirty. Have you cleaned and checked the integrity of the injector? Sorry if I've missed that.

As for valves. Mmmm? I think only you can answer that question. I know it's a pain but I'd do it myself. It's a simple bike to work on just a pain sometimes.

The XT Yamaha manual used to be downloadable from this site if you subscribed. It has all the tech spec and how-to's.

__________________
I have a lot of growing up to do. I realized that the other day inside my fort.