Posts
413
Joined
4/1/2008
Location
CO
US
Edited Date/Time
4/9/2016 5:59pm
So my bike has been a dog to start from the day I bought it. I'm running VP U4E (I love in Colorado and we can't get the normal U4.4) with stock motor, pipe and air filter/cage and it's never started right away from a cold start. I live at 10,000ft and race at 5,500 ft and it doesn't like cold starting at either altitude.
Given that it's EFI I thought that it automatically adjusted for altitude and I didn't have to do anything like I used to reject my two-strokes for air temp and altitude (this is my first 4-stroke). I also called VP and they said I didn't need to do anything to run the U4E race gas. In any event, something's not right so I did some digging and thought adjusting the TPS voltage could be something to easily try. I measured the output voltage at 0.65v (right in the expected stock range I think) so I turned it up to 0.72v. I honestly have very little idea of what I’m doing other than seeing a load of stuff on the net saying most bikes benefit from turning it up to trick the ECU that you’re a bit more twisted on the throttle than you actually are.
So I cold start the bike with the new 0.72v TPS output voltage and it seemed to start a little easier (on the 4th try with the choke button pushed in – air temp was about 50F). I wanted to test throttle response so after warming it up for a minute I rolled the throttle on and it picks up well, but then when I crack the throttle hard from idle it dies (see video).
I’m obviously going to put the TPS output voltage back to 0.65 since the bike didn’t do this before I changed the voltage, but is there anything else I could try to make this bike start better? Would it be worth going the other way and leaning the TPS out a bit by dropping to, say 0.60v or lower? Is the altitude messing with it? Is my gas messing with it? Was I misinformed by the VP guys? If this was a two-stroke I’d be able to jet it for my temp, altitude and track conditions but this 4-stroke has me totally stumped. For example, I can’t even work out how to get the spark plug out to have a look at whether the cold start issue is too much or not enough fuel and the manual is totally useless.
Any ideas greatly appreciated!
Oh, and I’m racing tomorrow so it’d be great to fix this today
Cheers
Simon
Given that it's EFI I thought that it automatically adjusted for altitude and I didn't have to do anything like I used to reject my two-strokes for air temp and altitude (this is my first 4-stroke). I also called VP and they said I didn't need to do anything to run the U4E race gas. In any event, something's not right so I did some digging and thought adjusting the TPS voltage could be something to easily try. I measured the output voltage at 0.65v (right in the expected stock range I think) so I turned it up to 0.72v. I honestly have very little idea of what I’m doing other than seeing a load of stuff on the net saying most bikes benefit from turning it up to trick the ECU that you’re a bit more twisted on the throttle than you actually are.
So I cold start the bike with the new 0.72v TPS output voltage and it seemed to start a little easier (on the 4th try with the choke button pushed in – air temp was about 50F). I wanted to test throttle response so after warming it up for a minute I rolled the throttle on and it picks up well, but then when I crack the throttle hard from idle it dies (see video).
I’m obviously going to put the TPS output voltage back to 0.65 since the bike didn’t do this before I changed the voltage, but is there anything else I could try to make this bike start better? Would it be worth going the other way and leaning the TPS out a bit by dropping to, say 0.60v or lower? Is the altitude messing with it? Is my gas messing with it? Was I misinformed by the VP guys? If this was a two-stroke I’d be able to jet it for my temp, altitude and track conditions but this 4-stroke has me totally stumped. For example, I can’t even work out how to get the spark plug out to have a look at whether the cold start issue is too much or not enough fuel and the manual is totally useless.
Any ideas greatly appreciated!
Oh, and I’m racing tomorrow so it’d be great to fix this today
Cheers
Simon
Cheers
Simon
If it was a cold start issue, I would try unplugging the temp sender if it's handy. That should default the ecu to a richer setting and may help you initial cold start up. Although this is a little backwards for a high altitude scenario, it's an easy thing to try for a test to see if it needs more fuel or not.
Good luck....tonight and tomorrow as well.
The Shop
I'll mess with the temp sender after tomorrow when I have a bit more time to tool around with it. It may be that I just take it back to the dealer and say fix your shitty bike.
Thanks for the suggestions!
Cheers
Simon
Wish I could help. Only if it were a Honda. Plenty of KaTooM's will be there to help if you need. Bet a re-map would make it better.
Cheers
Simon
When I'm done messing with the idle and temp sender I'll look into the hotter plug idea.
Thanks again for all the ideas!
Cheers
Simon
Nick #64 Honda
Cheers
Simon
Cheers
Simon #375
Saw this pic.
http://www.7twophotography.com/Lakewood-CO-RMXA-Round-1/i-TbPQCh8/A
http://www.tylerjphoto.com/Motocross-Portfolio-/RMXA-Round-one-/250cc45…
Pit Row
Cheers
Simon
Yea, second motos, 3 laps, I'm barely warmed up.
Anyhow, there's a happy ending to this story. It wasn't seized. There was a KTM recall last week on the capacitor (condenser?) bracket which caused the capacitor to fail. My dealership, Motobreck, replaced bracket and capacitor under warranty and it was back running in a day. Now, the interesting thing is it has no problem starting from cold on the button, which is great of course. The bike also wouldn't pull a second gear start even going down a tooth on the front and rear, so it'll be interesting to see if it now has more power under starting load.
Cheers
Simon
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