ALPHA-N or Map lag change.

[classic-indy]

I'm having a hell of a time tuning this motor. It's a ITB 2 stroke racing motor on a snowmobile. My Map signal is haywire, which I'm starting to believe is making this motor seemingly in-tunable.

Being a snowmobile it has a CVT (continuously varying transmission). The CVT automatically adjusts for load. I.e. going up hill or transitioning from trail to deep snow the clutches will gear down reducing load. I'm thinking that Alpha-N's inability to determine load will be minimized by the CVT.
Within the Alpha-N table 0-100 denotes load in %?

I guess my other option is to keep increasing MAP lag until it smooths out the MAP readings. How low can I set the lag before I'm going to run into other problems? At what point is it better to switch to Alpha-N, instead of increasing MAP lag.

[classic-indy]

Here are some datalogs and .msq

Autotune was creating crazy numbers and the engine was running worse the longer I used it. Note exhaust valves open @ 6700 rpm which you'll see in the VE table. I disabled the O2 sensor in these runs which helped, very seriously considering deleting it from the setup. You'll see this in the datalog. My main concern is that it drops the tach signal and MAP readings.

[gboezio]

For an engine like yours, I would use Alpha-N, the load is your TPS witch is a good indication of how much torque the engine outputs, I'm not a 2 strokes guru, but I think that the VE should be very constant in relation to throttle except for that exhaust valve that opens up and seem to have a huge effect on VE from your tables, most motorcycles use Alpha-N as primary algorithm. With your MAP signal pulsing like this and the little difference between all loads situations make it useless. Scale the TPS bins 0 2 5 9 14 or something like this, closer on the bottom and wider on the top, set your ve table with increasing VE from bottom to the top to get good AFR and you should see a big difference

[slingy88]

Hi,
i had similar problems on my GSXR turbo as the 750 is a very short stroke motor with not much vaccum and large cam overlaps.
it would swing viantly from its maximum 70kpa vaccum to 100kpa at idle.

I made a vaccum manifold to link all TB's vac points together using 0.6mm mig welding tips as restrictors to all connections . Then i added a cheap plastic fuel filter in line between the manifold and the MAP sensor to act as a buffer by both adding volume to the line and the paper element acts as a baffle to the air pulses as well.

This reduced my 30pka pulses to 0.5kpa with no delay noticed in logs.

worth a try if you want to stick with SD.

Cheers Slingy

[RotaxTriple2S]

Classic-Indy: Wow a 2 year project. I admire your skill and dedication. I have been searching for one successful snowmobile after-market carb to EFI conversion and you appear to be the only one. Clearly the market is ripe for an EFI conversion for our carbonated classic sleds, just read the snowmobile forums. I too have a snowmobile that gets 8.5 mpg, it is a 1998 Ski-Doo Grand Touring SE and it has been a great snowmobile now for 16 years and have fully restored it. Nothing like the Polaris and Ski-Doo triples smooth as butter arm pulling torque and almost no vibration. However reading your great posts and watching your well done videos I am reluctant to venture into this project, yet the factory OEM 2-strokes are in the 15-25 mpg range and the idle like and electric motor as well as through the entire rpm range. It looks like MicroSquirt is the best hope but based on your struggles to gain success I am not very encouraged. I am a retired electro-mechanical engineer and have rebuilt the electrical system from scratch based on an aircraft style buss system with a MOSFET 500 watt voltage regulator from Roadster Custom Cycles whom retro fits EFI to motorcycles of all types. This electrical project in preparation for an EFI conversion. What was the final result of your project, on your last video you seam to have it dialed in, did you see an improvement in mileage? Are there any other snowmobile EFI conversion projects in progress? Thanks very much for any advice you can add. Again I admire your tenacity and dedication. Thanks again.