Content Wrapper

[STB]

I basically had the same experience: if the IAC and the TPS were adjusted, it was a miracle which could not be repeated. There was no rhyme or reason for how it would get in the sweet spot or how it got out of the sweet spot. I fiddled with it and fiddled with it until IT decided to hit the mark for the TPS and IAC. I had no real control or repeatability. And, opening the butterfly up to .006 caused it to "idle" at 2500 rpms.

Ultimately, by aggressively increasing the fuel mixture on the Alpha N so that when the engine switched to closed loop (single O2 setup) and the AFR in real time indicated 90 really helped, it seemed, to allow the IAC and TPS to adjust easier. Why? I have no idea since those are mechanical adjustments and not data adjustments.

The reality is that I had 45 IAC most of the time and sometimes it would hit 30 which was not relative to temperature since I might have 45 at 110 C and the next ride might have 30 IAC at 110 C. So, I decided to set it up on the very low side so that it might hit 22 when really hot which meant, in part, I was getting more air when it was hot. This was better than seeing 45 IAC when it was hot and it was only 10 points or so below nominal IAC which was better than 10 to 15 points above nominal IAC in my book. The proof was in the pudding since it ran really well set up like that. I have a 4.25" bore, so the engine needed more start up air when hot.

I don't know if you are running the 4 advance on a 95 CI or larger CI, but if you are you might consider upping your advance curve since the bike may perform better with a higher advance curve. I found that the DTT recommendation for 4 on a 95 CI is a bit low unless your compression is quite high, say, above 10.5 to 1. The larger the bore, the more advance is required on single plug heads. HOWEVER, there are other factors to consider than bore diameter when upping the advance such as piston shape, weight, load and gas quality not to mention cam profile. I run over 6 DTT advance map on a 4.25" bore at 10.2 to 1 compresssion ratio and a Redshift 577 cam in a heavy bagger with occassional two up riding, for example. I think the tuning was helped immensely by this advance "upping" since the dog was taken out of the bottom end with the higher advance. And, the tuning became easier, more stable and more repeatable.

Finally, turning off the Closed Loop helped a lot after I got it where I wanted the tune. I must admit, I don't look at the IAC and TPS that often since I prefer to avoid the inevitable consternation. When I starts to run doggy, I look at it and fiddle with it until the DTT gods decide to hit the mark.

Personally, I suspect that DTT gurus for pay have built in job security.

If I get my gaskets in this week, I will put the stock TB on and tune it this weekend, gods willing, and sooner or later report on stability and TPS/IAC adjustability. If it is unstable with the stock TB, I guess the SERT is on the horizon since at least a few local mechanics have immense experience with the SERT. I just hope the stock TB can handle a little bit of the engine demand since my cams don't turn on till 2700 rpms just when the stock TB might run out of air on a 4.25" bore. I ought to be able to make 110 hp with the stock TB, if so, it should work through midrange rpms. We shall see.

STB