These are the symptoms on my 996S (stock ECU - if not a termi supplied chip, balanced throttle bodies, reset TPS) 1. Air bypass screws all the way in, engine dies (as expected) 2. Air bypass screws out 1.5 turns or more, engine idles around 800rpm and no higher 3. Idle mixture is slightly rich (as measured with an O2 sensor, and Innovate LM-2) 4. To achieve an idle of around 1200rpm I have to screw in the throttle stop bolt, thus open the butterflies. But of course, doing this results in the rpm hanging when the throttle is blipped. 5. Adjusting the CO2 mix to be even richer does lift the idle, but of course I don't want the bike to run that rich. 6. Removing a vacuum port on the inlet manifold, thus introducing loads of air below the butterflies does indeed raise the idle substantially. 7. It might be worth mentioning that the tank is full of 100 RON fuel, which is the only high octane fuel available in the local village. So, maybe the idle is rich. But how could it be so rich that no amount of air introduced via the bypass screws lifts the idle? Or, how is it the bypass screws do not affect the idle speed? All sagely advise is welcome
Hi I have a 916sp that I have spent some time setting up. I found an excellent feature on the tinternet which I printed and laminated and use to set the bike up It states that you must work through methodically Before you start make sure valves clearances are all correct The bike needs to be at full operating temp TPS needs setting first. I remove the cover on the big ECU plug and back probe the terminals Wind the throttle stop off on the throttle body and remove the linkage to the rear throttle body Make sure the butterfly is fully closed and see what TPS reading is. (Typing this while suffering the flu. Will go out to the garage and get full details a bit later) I think it is 130mv but could be 150 Once that is set use the throttle stop screw to get 315mv. The throttle stop screw should not be touched again. You need to balance the throttle bodies now reconnect linkage to rear throttle body Fully close air bleed screws In this state is highly likely the bike won't tick over. I used the adjuster on the twist grip to set the bike running at a steady rate Adjust throttles as needed. Once balanced use bleed screws to set tick over
Thanks. It is indeed 150mV. I’ll give it another run through using your method (which I’m sure I followed, previously, but for the sake of sanity and arguments I’ll do it again). Then report back.
Mine doesn't tick over when cold. I use the adjuster on the handle bars while it warms up for a couple of minutes. Once warm tick over is perfect.
I should mention valve clearances were done as part of a full engine rebuild. Ok, I’ve been through another methodical TPS reset to 150mV, with linkage detached and throttle stop screw out. Then balanced the throttle bodies and adjusted the throttle stop to give me 315mV at closed. Throttle was snappier, as expected with less air flowing past the butterflies when closed. But no amount of air bleed screw would lift the idle sufficiently to stop stalling. Suffice to say, no change in the idle issue really. I’ve blown out the air bleed ports with compressed air. Some black slime came out. It might be worth running some carb cleaner through there next. Blocked or poorly flowing air bleed ports is the only reason I can think of now that would cause this issue. Off idle the bike is running very nicely. Quite strong under acceleration and very smooth running. I really don’t know what else this could be
What AFR are you reading for an idle mixture? If enriching the idle is helping to increase idle speed, then I'd suggest the idle mixture is still lean. Really the idle wants to be set with a CO (not CO2) meter.
I didn’t check the AFR after this last iteration. But it was reading around 11-13% previously. I’ll get another reading tomorrow.
Have you tried adjusting the trimmer in the ECU with minimal air bypass? You can adjust more coarsely to both cylinders, then fine tune the throttles with the bypasses.
Yes. Trimmer lifts the idle when in the middle of the range, where it is set now, but not enough to achieve an idle that can be affected by the bypass screws. The trimmer lowers the idle at both lean and rich ends of the adjustment, as it should. Gives me some ideas on how to test the efficacy of the idle circuit. I’ll give it another go tomorrow.
Can I just say you should have set the throttle screw before connecting the linkage and then balancing Also 315mv is for a 916 I believe it is 392mv for a 996
Ha! I now have 3 different throttle stop voltages. Very happy to try 392mV and bikerboy’s suggestion of 423mV. The bike could not idle at 315mV. I did set the throttle stop before connecting the linkage and made sure the voltage wasn’t affected after balancing.
Assuming same as 916? Set TPS voltage at fully closed to 150mv - but make sure the front TB is fully closed, I leave the connecting rod in place (for the spring tension) but back the rear TB off so that the front is definitely closed and consistently closing whilst setting. You then need vacuum gauges and CO meter to get everything balanced both at idle and through the rev range (as much as possible). I set CO to around 4-5%, use the ECU trimmer (if necessary) to get the value and the bleeds to fine tune/balance everything. I start out with the air bleeds closed and then open as necessary. Once all running nice and smooth and engine picks up smoothly and quickly, adjust the idle speed to suit your preference using the throttle stop, don't worry about the TPS voltage at idle.
The throttle stop voltage is somewhat academic... The critical setting is 150mV closed. The stop value can be anywhere across the figures you've read. They represent a "starting point". The idle can be affected by either the stop screw or the bypass screws/trimmer as both can alter the idle speed . Get the 150mV setting fixed. Set the bypass screws screwed all the way in and the trimmer mid point. Set the idle screw at a point that allows the bike to idle up to temp and then balance the throttles mechanically with a vacuum gauge and so you can check CO of each cylinder. Go for about 4% give or take a little. I set the front first, if its a way out, trim with the trimmer, if it's close use the bypass. Once you have that sorted, then measure the rear. They "usually" run richer so pull it down with the bypass. If the rear is weaker, then use the trimmer to bring it up, then go back to the front and bring it down with the bypass.
Ok, I checked the air and coolant sensors and both are fine. I didn’t get time to clean the air bleed circuit. But, alas, I made some progress. I connected my AFR meter and the whole thing was running hella rich (circa 10% AFR). That was with the CO trimmer at the mid point. So I leaned it out, via the trimmer, closed the butterflies, wound out the bleed screws out a turn and a bit and now have an idle around 1000 rpm, with a very nice throttle response on the blip (AFR now around 13.2% which might be a bit lean) at idle. It isn’t perfect, but it’s quite close (albeit with a low idle). Finally, I’ll be checking the AFR is ok from idle to WOT. Just need the replacement rectifier (FH020AA) to arrive so I can take her out for a decent ride and see if all this work has been worth it. PS. I don’t have an exhaust gas analyser. So I am relying on the AFR to give me a clue on what is happening
