09 FE 450 Backfire and long cranking at start-up

Hello again!

So I have bought another 09 FE450 after few years break on a two stroke, as I liked the previous one so much and never had any issues with it.
This one has about 200hours on it and I have maybe done 15, but it always had taken a few more revolutions to start than the previous one, and is needing a bit of throuttle to fire-up, or if I do not touch the throttle I usually crank for a while, then stop and try again and on the second one it fires up but still needs a button pressed in for a little while.
This in itself would not be a big issue, but biggest problem is that it sometimes backfires on quick throttle from idle and dies. When I add the throttle slower it is fine, but when I need to open it up fast and a bit harder when jumping a log or something it backfires, splutters and thats it. I have to add that the problem happens often enough to piss me off, but sometimes it does not occur, but usually after 3-4 attempt it does.

It has been like that since I got it, and it doesent matter wether it is hot or cold, always the same issue. Apart from that it runs fine, pleanty of pull, and no problems when reving or idling.

It has a Devil Enduro End Can, but stock exhaust pipe.

I heard about the fuel pump issues and blocked injectors - so I got the injector out and professionaly cleaned and replaced the filter in the tank - which was actually quite clean in the end. I also changed the spark plug. But this has not changed it a tiny bit.

I have a map switch and it is the same on all mapping settings or with the switch unplugged.

I posted it in fuel, but not sure if it is not an ignition issue or what?

What should I check next? Rocker cover off and valve gaps? I remember on my 02 FE400 that was quite critical, but it was a hot start problem then.
Replace the fuel pump?

jon andersson said:

Valves are most probably fine but you can always check it. But I would start with the TPS. That is easily whacked out of position and will then read the wrong throttle position. Easy to check with a multimeter.

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Yes, Thanks. It seems like TPS is the problem (or rather a too lean mixture), I searched it round and people had the same symptoms. Found a link to KTM forum on TPS adjustment http://www.ktmforums.com/forums/offroad-4-strokes/9961-500-450exc-fuel-injected-tps-adjustment-richen-mixture-eliminate-flame-out.html and not having a multimiter in hand, I marked the original position and tried to move it clockwise and anticlockwise as well, it has quite a lot of influence on how it idles, starts and throttle stalls - but none of the adjustments made it run better unfortunately - so I reverted back to the original position, and rasied the idle rpm instead, which has cured the flameouts almost completely - on a short test - and it also seem to start better. It idles too fast to what I would normally have it, but for now this is the only cure, until I get hold of multimeter and actually figure out how to test it.

I am slightly dissapointed that none of the adjustemnts of TPS position made it run any better, even when I moved in the smallest increments possible from the original position - but always the starting point seemed the best.
Maybe it needs a bit more than only TPS adjustemnt, but why would it - hard to believe that a different Enduro End Can could make it so out of tune? Anyway I see if can test the TPS voltage at some point and take it form there.

jon andersson said:

If you have an open end can I think you need the euro/competition map.

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Yes, after reading a bit more, it seems that I might need remapping to run this exhaust.
Devil Exhaust

They do say it is without baffle, and it does sound nice
But until I find somebody to re-map, maybe switch back to stock End Can and see if that sorts it out.

V6II - not sure if your problem has the same cause, as mine was happening neither hot or cold, but if you think you are running too rich, you can always check your TPS sensor and lean it out to see if it helps.

So I have got hold of a meter, checked the voltage and it was at .564V - too lean, I set it to .605 and it is running and starting much better, and I could reduce now the idle rpms. Test ride tomorrow.

I found out that the tiny bit of a movement makes quite a big difference in voltage, so you have to be quite precise - I think it would be quite difficult to set it up without a meter. The counterclockwise turn - increases the voltage and in my case the maximum position was about .650V.

jon andersson - you were right, it is actually quite easy to check. I have stuck a paperclip into pin 5 from the left - top row of the ECU, yellow wire (only complete yellow wire in the loom) https://photos.app.goo.gl/H3Q8rleFg6v6Q7iI3 which is the feedback from the sensor, red pin to that and black to ground - I had to start the bike to get the voltage reading and off we go.

jdubb75 said:

I would definitely check your TPS. See the attached PDF for the procedure I created from a post on AdvRider. I actually just did mine today on my 390...very easy to do.

For mapping - If you can't get your ECU mapped the JD EFI tuner works great for being able to add/subtract fuel all throughout the throttle range.

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Thank for the write-up. Didn't know about the trick to put the ignition on.
What I noticed though is that when I check the TPS with engine off, the voltage is about .015 Volt higher than with the running engine. Also when engine is running the voltage fluctuates a bit by up to .005. Anybody has the same symptomps, is that normal?

So I have went up to .680V on ignition (.665V engine ON), it has improved but and still had a few flameouts, bad starts and a bit jerky throttle from idle. So I have put a stock pipe back on, set it to aggressive map, and left TPS at the same setting - throttle response it is alot smoother, better starting and minimal flameouts, and still lifts the wheel up well enough, and it is alot easier to control on tight track, so stock pipe stays for now - however still not perfect when hot - had 1 or 2 flameouts and starting is not perfect, so today I set it up to .700 (.688) and will have to test it out in a battle again.

By the way it turns out that if I push the TPS a bit harder the max setting is .835 so hopefully it will be enough for stck pipe. And until I figure out how to alter maps probably wont put the Devil pipe back on - bit too wild for me at the moment :devil:

Alan said:

When was the last time the injector was cleaned?

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Alan, It was professionaly cleaned 5 hours ago, as I thought that was the problem, I also changed the filter in the tank.
I am slowly starting to think that it might be something else than just the TPS position? I am already on what would seem like a rich setting comparing to the other bikes on the forum. I think the factory setting was supposed to be .604V? This is European bike.
However moving the TPS did help, but not completely solved - at the weekend another proper test on the track - cause when I test in the garage or round the house it seems OK.