Triumphrat

PieMan · 01-11-2009, 01:29 PM

Here is a graphical representation of how a shim effects the AFR. The only difference between the two runs was the second run (dotted line) had a shim added. The major difference a shim makes is below 4,500rpm, from then on the difference is subtle. This is using a NAGB needle, the differences will be roughly the same using other twin needles.

propforward · 01-11-2009, 05:11 PM

Cool pieman - is one of those lines the throttle position sensor? How is that hooked up?

B02S4 · 01-11-2009, 09:08 PM

Thanks Mike, I realize that the post is directed at showing the difference for that single variable (shim v. no shim), however how about a few more details of the motor & carb settings for those of us who know how to interpret the data.

PieMan · 01-12-2009, 01:25 PM

Quote:

Originally Posted by propforward

Cool pieman - is one of those lines the throttle position sensor? How is that hooked up?

The red is the TPS. The spikes are just interferance, I need to put a resistor in the wiring to stop that. The RPM and AFR are spikey as well, but I put a bit of smoothing on them both.

The variance shown on the RPM is just wind resistance, riding in to the wind on one run and with it on the other.

790, TP Megatons, TP air box cover, 140 mains, 40 pilot, 1.75 mix screw.

propforward · 01-12-2009, 01:37 PM

Very excellent, are you running the TPS into one of the inputs on the LM2 then?

PieMan · 01-12-2009, 02:07 PM

I have a permanent cable spliced in to the TPS wiring by the igniter connection leading to a waterproof plug so I can just connect the LM2 when testing, and the same for the RPM. It takes just 5 minutes to screw the lamda in to the bung and connect the wiring up ready to go. The LM2 is in a modified magnetic tank bag with specifically cut foam to protect it from the vibes.

propforward · 01-12-2009, 02:18 PM

What a great idea - it never even occurred to me to use the TPS.

I like your tank bag idea for holding the LM2. I'm really looking forward to giving it a go!

Derby Boy · 01-12-2009, 02:55 PM

I'm the first to admit that I'm worthless when it comes to interpreting the graph (showing my age). What I found was my 07 had a flat spot (hunting) around 2500 rpm when just putting around. What the shim did was make me a little richer on the bottom which in turn smoothed the transition from idle circuit to cruise circuit. This is what we used to do on old 4bbl carbs on high output motors. Go to a 4 step or tapered needle from the stock 2 step. Smooths out the transitions but does basically nothing for WOT or high rpm. I guess that would be seat of the pants verified by modern technology.
My $.02