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Sputter under acceleration

7K views 9 replies 4 participants last post by  callmekb 
#1 · (Edited)
Just picked up a new to me 2007 Daytona and I've been doing a maintenance routine on it. Previous owner had moved and I wasn't able to inquire about previous mods or work so I don't have a good baseline. Here is the current condition:

- Valves checked and in tolerance
- Jardine RT1 slip-on
- EXUP disabled unplugged and verified open
- Using Wanyes Jardine map (also have tried 20400)
- Air filter cleaned
- New battery charged with solid voltage
- Throttle bodies balanced using TuneECU
- TPS adapted after every map change and voltage showing 0.59
- Brand new spark plugs
- No CEL

Problem --

Idle is perfect. No issues. Revs normally in neutral. Pulling away and at lower RPMs the bike works nicely. Initial acceleration from 3-4k to 5-8K is fine but after sustained higher RPM running opening the throttle up quickly causes what feels like fuel starvation (hesitation and coughing). At higher RPM 8-10k the bike really struggles with the same symptoms being amplified. Slower acceleration lessens this.

My suspicion is that the fuel pump is not meeting the fuel demand at prolonged and higher RPM. The fuel line itself doesn't LOOK to be kinked as far as I can tell. The injectors spray a nice mist after the line is primed. I've ordered a new fuel pump, but would like any further suggestions in the mean time if anyone can offer them.

Thanks! (I've spent a long time searching already and appreciate this resource. This is one of the better bike sites I've been on.)
KB
 
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#5 ·
Hmmm. It could be a vacume leak, but that would also mess up your idle. To check for this start the motor COLD and spray brake cleaner around the throttle bodies being careful not to get it into the air intake as that would give a false diagnosis. If the motor dies, you have a vacume leak to track down.

You can also clean your injectors using a 9v battery to open them, and by blowing compressed air through them backwards.

Are you using fresh 91 octane fuel? This really sounds like fuel starvation to me. I would make absolutely sure the fuel line is not kinked, or damaged from a crush too. I would make sure I had a good rectifier. Have you done a compression test, leak down? And have you checked the CPS?

Short of that I would try a different map, or an actual Dyno tune.

Good luck.
 
#6 ·
Thanks for the reply!

I did a vacuum leak check today with and didn't get any hits. I'm currently using fresh 89 octane as recommended by Triumph.

I've taken the fuel line off and checked it over it doesn't SEEM and restricted but I'll do another thorough check.

The rectifier is the newer replacement style but I can give it a look. I haven't found any electrical red flags so-to-speak yet.

CPS resistance resistance is OK.

I'm going to try to load the factory map because it occurred to me I've never tried the "default" setup. I should have really done that from the start.
 
#7 · (Edited)
Did more testing without luck. It seems like I can replicate the issue pretty easily above ~50% throttle by twisting it quickly. Above 7-8K (and consequently above 50% or so throttle) it sputters and surges randomly with small quick throttle openings (not so much with slow acceleration) and really gasps when I let off at 8K plus unless I upshift to lower the RPM.

New OEM air filter and new plugs didn't remedy anything. I'm looking to ignition/fuel management now.

I'm at the point of replacing the coils and a different TPS sensor. Could the slow to react issue be a faulty TPS? It seems reasonable. Could a failing coil cause these symptoms?
 
#8 ·
Issue resolved.

I tested the TPS in TuneECU watching the percentage gauge while slowly opening the throttle. I found a gap moving the throttle passed 20%. The needle would jump almost immediately to 45% and continue again normally after. I marked the actual throttle tube and was able to replicate the stumble right in the 20% to 45% gap while riding.

TLDR:
Worn out TPS. I replaced it with a new one and the issue was resolved.
 
#10 ·
Yes, the TPS is mounted on the right side of the throttle bodies. The only tricky part is tightening down the new sensor while keeping the voltage in range 0.58-0.62. It's really pretty simple. I only had to buy the sensor (I actually bought an entire complete throttle body for $40 on ebay!!) and a $6 tamper proof star bit set from harbor freight.

If you suspect yours is bad I would test it using TuneECU the way I described. The throttle should increase % very linear up to 100% while turning it very slow and steady. A new sensor will run you around $100 so it pays to be sure you need it.

KB
 
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