2017 FC350 won't hold steady rpm at low throttle opening

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12/11/2018 9:48 AM

Bike only has 15 hours on it stock exhaust unmodified and still has the backfire screen in the air filter, no extra holes drilled in the air box. It has had this issue since I've owned it so I bought the vortex ecu from Tokyo mods but it hasn't solved this problem although the bike does run even better now in general. The bike starts good and I can wack the throttle open and it doesn't bog at all, runs good when winding it out. Issue is it won't hold a steady rpm mostly at low throttle like just going around the yard in 1st or 2nd gear or in the woods trying to negotiate a rocky trail. it wants to accelerate then decelerate like hunting I guess you could call it. I'm thinking a lean condition would cause this but maybe since I haven't opened the exhaust or unrestricted the air box it could be a rich condition? I don't think the tps adjustment is necessary with the Vortex since it has a procedure to learn the open and closed throttle positions but maybe that's not entirely true. I've changed the small inline fuel filter, didn't help. 66% 89 ethanol free mixed with 33% 110 race gas. Runs at 52psi fuel pressure without dropping. What should I check next or is this just the way this engine runs?


12/11/2018 10:02 AM

Your tps needs to be .6-.62v. Thats what the map is based on. Id try richening your lower rpm range


12/11/2018 10:27 AM

TPS setting is too lean.

Paw Paw


12/11/2018 11:11 AM

So I should turn up the idle until my tps reads .6 volts correct? The tps standard setting is .4 volts with the idle backed all the way out so the plate is closed. So what's the story with the vortex throttle position learn?


12/11/2018 11:56 AM

2000KTM200exc wrote:

So I should turn up the idle until my tps reads .6 volts correct? The tps standard setting is .4 volts with the idle backed ...more

No, you leave the throttle closed and adjust the sensor to be .6 at closed throttle. Essentially what youre doing when you increase voltage is richening the mixture.


12/13/2018 11:12 PM

I have a 13 YZ450F that has acted the exact same way since I got the bike 3 years ago. This is the first efi bike I have owned and assumed that was just how they acted. I'm curious to find out if adjusting the tps fixes your issue


12/14/2018 4:32 AM

I talked to Tokyo mods again about this issue, the tech guy told me as long as I do the tps endpoints learn procedure with the Vortex ecu that it doesn't matter where the tps is set initially. Pretty much told me that's how this engine runs. I'm a little skeptical, I will say that increasing the low fuel trim 2.5% helped but the engine still wants to accelerate under light load which makes technical riding problematic. I don't think the 450's have this issue at least not as pronounced.


12/27/2018 4:21 AM

Have you checked the clamps on both sides of the throttle body? If the motor side clamp is loose it might run lean. The air box side clamp was loose on mine from the dealer.