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Discussion Starter #1
Hi guys, have not been able to find a match for some symptoms my ST2 is presently exhibiting.
Coming back from a 300km ride, on getting back to the crawling traffic, the ST2 kept stalling at the slow 1st gear traffic speeds when the clutch was pulled in.
At trailing or light throttles, the bike seems to hesitate or feels like it's stopping.
It doesn't seem to me to be a tuning issue since the problem came on suddenly. It even cleared on a brief ride a week later.
My first thought was some sort of fuel blockage.
Have cleaned fuel filter (use a K&N, external of tank), cleaned, replaced Jaeger Temperature senders with Bosch units, swapped out plugs, swapped relays 1 and 3 under seat.
Checked and cleaned CPS, looked OK. No fuel leaks. I'm out of ideas.
Do these symptoms ring a bell with anyone? Any solutions that worked?
Thanks!
 

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Even though it came on suddenly, I would still run through a tune. Check the throttle body walls, clean off any crud that may there. Keep us posted!
 

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It appears you've ruled out alot of fuel possibilities, as I once did with similar ST2 symptoms - until i discovered many frustrating months later the far less likely cause: random electrical breakdown, especially when moisture was in the air, via oxidized wiring joints. The main culprit was a large junction box right down in the belly of the bottom fairing: full of dry jointed powder. I cleaned and applied dielectric grease to every joint, and happy days! Worst that can happen is you'll rule that out for a very long time. Good luck.
 

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What Belter said. Having that external fuel filter is probably a nice convenience for replacement every year or two. It would unfortunately encourage you ignore the fuel pump's sump screen (pre filter) and noticing / cleaning out tank sediment.
 

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Discussion Starter #6
Thanks for all the quick replies guys!
Belter, I had to POR15 the tank some years ago after discovering my immaculate ST2 having a rust sludge filled tank. (after a blocked fuel filter that stopped the bike revving over 6.5K). SS904, wasn't aware of a fuel pump sump screen, worth a check - it feels like a fueling problem.
There goes next Saturday! Thanks again.
 

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Make sure the signal from the TPS is clean--no rashy "noise" spots. If there are any, replace the TPS.
 

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I vote for Fuel Pump screen (pre-filter) or even a leaking or partially split high pressure hose inside tank. Only a thorough inspection will clear up. Steve
 

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I vote for Fuel Pump screen (pre-filter) or even a leaking or partially split high pressure hose inside tank. Only a thorough inspection will clear up. Steve
I don't think so. If it were at big throttle settings, then maybe. But he's talking lower rpm, "slow" traffic.
And the bike runs great while giving it a fist-full of throttle, correct?

Maybe try some Chevron Techron. It's the best thing (fuel inj. cleaner) I've used on my Saab's with IMMEDIATE results in smooth running. I've used it on my FI Ducatis, but for no reason other than I know it's a great product for keeping the FI hardware clean.
 

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Did you double check the TPS signal? My buddie's ST2 had some lower speed running issues, and it turned out to be the TPS.

I was going to accuse the temp senders, but I see that you have already replaced them with Bosch senders...
 

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Discussion Starter #11
Hi guys. Finally got the bike running again. Took out the fuel pump, found a 25mm x 10mm sandy residue in the bottom of the fuel pump casting, under the fuel pump filter, but not in the filter. The filter had separated from the pump and the pump was not snugly fitted in the alloy casting but was a little loose. Thought the filter edge might have obstructed the pump inlet. Anyway, broke the O ring trying to re-install - have re-used it before. You have to really get that pump housing to slide EVENLY into the tank hole. Had to wait for some new O rings.
Anyway, back together, test rode it - no fix,symptoms remain. Sometimes she idles, sometimes not, tends to stall pulling up at an intersection with the clutch in. On trailing throttles,around 3000rpm feels like she's stalling, or wanting to.
How do you check the TPS signal Stick, in the ECU somewhere?
 

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Discussion Starter #12
Measured the TPS at 285 mV, 115mV with throttle stops backed off. 4.7V open throttle. Is it worth mucking around with the TPS setting trying to get 150 mV or is it new TPS time? Thanks! They're just little variable resistors aren't they?
 

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I'd say yes, it's worth going thru the entire setup. Usually also starting with the valve clearances. Make sure those are in spec, or bring them into spec, and then do the TPS 150mv, etc. The procedure is outlined here and there, Maybe in the H.O.W. area. Also, verify that the signal between closed throttle and open is nice and linear as you open the throttle SLOWLY. You're looking for no glitches in the progressive increase in readings.

Yes, it's a variable resistor. A potentiometer. Like an old fashioned volume control on a radio.
 

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Discussion Starter #14
Thanks Stick. Yeah, I made a little video of testing the TPS, it runs very smoothly, with a little dip at the end of it's stop. Can't post it here, video not apparently an attachment option on this forum. I'll try to set up the TPS to 150mV. I'm picking there's nothing wrong with it. I'm just puzzled what could have altered the set-up in 1 x 300km ride. The yellow paint was undisturbed on the the TPS mount screws. I checked the valves 6k ago, clearances were all in spec. Have you noticed how stable the clearances are after the first set-up? 66k on my bike, only had to change shims at 20k, but then all of them. Been rock stable ever since, checked on factory schedule.
 

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Many DESMOs seem to "bed in" after the first few checks. As long as you're not tracking the machine (always messing up near the red-line), these engines are great!
 

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Discussion Starter #16
Solved. The TPS appears to be fine as suspected. Just set it up to 153mV (close as I could get - she alters 30mV just tightening the screws!) 510mV for the idle stop screws. Idling properly again, and accelerating hard and cleanly (smile's back). Waiting for the throttle balancer nibs to arrive from Carbtune (Morgan Carbtune - carburetor synchronizer for balancing motorcycle carbs) before a balance and re-assembly. Thanks Stick and the guys!
 

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Sounds great! Thanks for writing back with your fix. And it's DIY !!! I love it.
 
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