Was out for a nice ride on the weekend but still think that the 640 is lacking in power, ie acceleration isn't that great but am assuming that this shouldn't be the case. It's pulling 'ok' but really nothing special and any kind of overtaking at speed is a struggle. My mechanic friend is still to do a compression test so will see what info that gives but curious to know what others think of the power delivery. My XR600 was good at pulling my arms out but this one is a more stately affair.

Checking the consumption, I filled up on 360kms and it took 24L so its getting 15km/L but would have thought this would be higher.

15 km/pl is quite poor, I average 20-23 km/pl over varied terrain at a decent pace... Your jetting is likely off, either the previous owner misjetted the bike or your carb slide, guide , jet needle and emulsion tube are showing wear...

Having owned an XR600 and XR650L and two 640's (Duke ll and dual sport) the KTM should be more powerful everywhere. I'd guess worn valve gear. :innocent:
A comp. test should tell the tale there. I doubt it's rings but the valve gear is suspect if last head/valve rebuild was not done correctly.

Could be jetting ...?? but I think you'd know if you were so far off that the bike lacked major power.

Good luck ... hope you don't end up with the only "slow" KTM on the planet!
(Most go like absolute stink!)

bier

It will touch 150kph but it's slow getting there. A lot of throttle is required for not much speed increase hence the high consumption perhaps so something isn't right for sure.

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So I went for a long (1,000km) ride this weekend. Here's my observations:

General lack of power - the throttle response is very poor, pretty flat really. Doesn't pull like I believe it should. On Saturday, it topped out at only 110kph and rpm was maxing at about 5k. The next day, after rev'ing the heck out of it, the revs got up to 7k max where it started coughing but at least the top speed improved again (150-160kph) but still very poor throttle response over the full range. The mechanic had said he'd only adjusted the air/fuel mix by 1/4 turn for slight fuel increase as apparently exhaust popping is due to lean mix?. At low speeds, its 'ok' but the problems are more noticeable at mid/higher speeds. It felt a bit like riding a 4 cylinder bike which was only running on 3 cylinders. (have since discovered a reason for this - tank had accidentally been left on 'reserve' by mechanic hence I suspect some crappy fuel got into the carb)

Fuel economy is bad - this weekends long run returned only around 14km/L. As mentioned below, this should be up around the 20 mark.

Aftermarket exhaust - very noisy and pops like hell on deceleration. My riding friends even experienced some 'spray' on their visors when riding behind me and saw a little smoke and actually a flame on deceleration which although quite cool, is not really desired..

Valves - have been adjusted

Oil/filters - have been changed

Battery - new

I've read about various elements that can wear out in the carb on these bikes and that the top end sometimes needs to be overhauled at this mileage however my mechanic doesn't believe these should be so worn at this stage. Unfortunately I don't have a proper work space here and my decent tools are all back in UK so can't do much personally.

You're going to have to start with a compression test..

Is there a diagnostic port in the 640 ? I can't remember..

Yup, I requested that be done...still waiting

From your description it almost sounds like whoever did the valves got them set at 180 degrees off. Or ... it also sounds like a throttle limiter or throttle stop/restricter has been installed. (they do this in countries where younger folk have HP limitations so throttle is limited to Half or less)

So ... recheck valves making sure clearances are correct when at TDC on compression stroke. Lots of guys on the DR650 forum get this 180 wrong. Bike runs ... but runs like poop.

Easy to check on throttle. Have someone operate throttle while you look in at Carb. Once its wide open, turn throttle actuator and see it it will go further or is it on the stop? (as it should be)

Something is most definitely WRONG with your engine or carb. I suppose it could be electronics but that would be weird indeed. (and rare)

Try to go through everything step by step. Get onto KTM 640 forum, maybe someone can help. Very strange goings on.

Good luck :D

Haha yes, I actually did that with my DR650, very quickly realised and sorted it lol. No restrictor, that was clearly from some crap in the bottom of the tank I think. First, we are going to check the timing and advance to see what's going on there.

Something is very off with that bike... First thing is to pull tank off and have a look at the carb... You can get at most carb wear items without removing the carb from the bike... First off pull the plastic cap off the top of the carb and remove the slide and inspect the diaphragm for defects... Have a look at your jet needle, make sure it has the metal washer on the bottom and the 2 plastic sandwich washers in place... The Jet needle sometimes will wear so much that it will break in 2... With a 17 mm wrench to unscrew the bowl plug you can then access the main jet with a right angle screwdriver and a bit of fiddling.. Take the main jet and the tube washer out and then you can pull the plastic slide guide up through the top of the carb... Inspect the slide guide for wear by looking at the wear indicator depressions on the slide running surface... Look at the needle jet{emulsion tube} to see if it has worn oval and check that the o-ring is in place on the bottom of the slide guide... All this can be done with the carb on the bike... also check the main jet #, it should be between 152.5 and 160, any larger than that usually causes an overly rich condition.. It has happened before where the pilot jet has rattled loose and found sitting in the bottom of the float bowl..

Like I mentioned before, issues with the fuel pump can also cause problems...

Thanks, good info there

Its a bit of detective work, I like to start with the easy stuff first and tick them off the check list before going more in depth and pulling the top end.

Once you get everything set up properly the 03 + 640s will go quite a while between top end service intervals...

Happy New Year :)

Well here's a quick update as I got the bike back:

Compression test - all good

Throttle Position Sensor - was apparently miles out, now adjusted (was showing that the throttle was wide open when in fact it was closed)

Timing - all ok

Carb - opened up and checked, very clean and nothing untoward noted, some minor adjustments made.

Air filter - despite claims from the previous KTM guy (see below) that this was cleaned, the filter was actually deteriorating and I suspect some of this had gotten into the carb earlier

SM Motech side stand fitted - damn that thing is fierce! But it works well and there's no danger of ever riding off with it down haha

Radiator - had used a little bit of fluid, guess this went out the overflow as no leaks noted

Backfiring/popping - apparently its doing this less now and only in low gears


Only got it back last night but my initial thoughts was it was going better so will try to get out on it over the next week to so see what has improved and will also check on the fuel economy.

Another issue that popped up recently (actually when I plugged in a USB adapter for charging my phone) was that the instrument cluster display got 'weaker' (now its hard to read) and the clock (time) disappeared - any thoughts?

Have you wired your USB into the clock loom ??

There's a standard accessory socket on the front panel

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