Idle Tuning V-Twin with no IACV

[dudeman258]

Hello,

I am a student working on tuning an Aprilia sxv 550cc v-twin engine for a school project.

We are currently unable to use any iacv for idle, and I am very interested in your thoughts on the best way to maintain a stable idle as well as stall prevention after any sort of throttle input (un-loaded of course).

Currently we have created an ignition "trough" to hold the idle at 3000rpms (oem is around 2200). However we are having trouble going lower.

This trough also prevent the motor from stalling after throttle input as it was before the trough was created. However this is a little dodgy as sometimes it does stall and I would much prefer to get rid of that.

This is assuming the motor is at temperature, we are calculating load with TPS vs RPM only. Running a very small restrictor also.

I am curious if accel and decel enrichment can be used to help prevent stalling and perhaps allow us to not depend so much on the ignition trough we have thus far.

Any advice is greatly appreciated as we are taking this step by step but it is very difficult with no real detailed manual.

Thanks!

[RossB]

It sounds like you are idling the engine with too much advance, try running it with less advance and more air by-pass at idle and this should make it less prone to stalling and allow you to idle the engine at a lower RPM. Accel fuel is not a good way to fix this problem.

[dudeman258]

Thanks Ross,

We currently have our idle cell at 5deg btdc, and the cell adjacent to it is at 50deg to keep the idle stable. I will try to lower that and see if I can open the throttle body a little to keep the rpm the same.

Would decel compensations (fuel or ign) help at all with the motor "catching" itself when coming down from high rpm?

I aprechiate your help.

[RossB]

I have never used decel fuel to stop an engine from stalling. The stalling can be caused by the engine going rich on over-run but you should be able to tune this out. Make sure that you have a reasonable area on the map that has similar timing values as large steps in timing can make the idle unstable.