Joe what year sled is the 800? It would interesring to see if there is a consistent gian when the DPM is yanked. Adding weight and adj. clickers makes me think some real noticeable gains have occured. Have any numbers or time gains to show the improvement? I have a 02 800 and I have been thinking about yanking the DPM.
if you got the race dept to unhook then ask them exactly how or what affects it. It does work off float bowl pressure..........but does that mean that its altitude or barometric pressure affecting more than temp or what about humidity. Maybe in the summer it over compensates. Doesn't help you but gives more questions to answer
The DPM system is only supposed to vary the fuel delivery to the carburetors based on changes in temperature and barometric pressure. The Doo specs are 3000+ rpm, -4°F+ and 1000mBar, or less, atmospheric pressure for DPM activation. DPM compensation only varies fuel delivery by applying a vacuum to the carburetor float bowls using carb venturi vacuum controlled through the DPM manifold with a solenoid. Since only a vacuum is involved (on ZX Doos) the DPM can only lean the fuel delivery. Removing the DPM should only allow the sled to run the baseline jetting that is currently installed.
Joe did you lean the jetting after DPM removal? or did the Doo race guys install leaner jets?
What did they disconnect to disable the DPM? Only vacuum lines or did they disconnect electronics? Maybe there is additional compensation in the DPM system that is not published? - timing advance curves?
The DPM is as Summitak says but on the 03 models in particular and maybe other models as well, there are 2 other wires that come from the temp sensor and join the dpm wires that go to the mpem. That tells me that the temperature of the engine must be effecting either the timing or the carbs or both.
DPM only effects the float bowl pressure but there are other things tied into the mpem that are effecting the dpm and timing, I am 99.9 % sure of that. AND THAT IS A CLUTCHING NIGHTMARE.
I'm not saying that it can't happen but I've played with the temp and baro sensors and saw no timing change on my strobe. Moved the temp sens from cold to hot water and sucked and blowed on the baro tube, no change. But engine wasn;t under load and maybe the mpem knew that. One little known feature of the mpem is a something that works like a throttle position sensor. By timing the acceleration of the crank it knows whether you are on or off the throttle. This feature does make timing changes. This MAY make it hard to do timing curve checks unless the engines is under load. As far as I can tell the dpm feature is independant of the timing. I can see where it would be possible to use the dpm to bring on a rich failsafe condition based on coolant temp? The wiring diagrams I've looked at show the temp sensor only tied to the idiot light, no mpem wiring. If you say there is another set of wires from the coolant sensor to the mpem I'd guess overheat protection using the dpm on dpm sleds, and possibly timing on non dpm? Since the move to DC on the new sleds I suspect doo has made some changes. I've found doo very tight lipped about the mpem, kind of a need to know basis. I'm not sure even the race shop guys really know alot about it? From what I've seen they just take some timing out of the midrange, extend advance a little on top, and turn off the rpm limiter.
Does anyone have a non dpm, 2003 600 or 800 that they can check? Look to see if there are 2 or 4 wires coming from the temp sensor.
Hillpounder, when you did your experiment did you have the sled on a stand so that you could get the rpm's up to 6000- 7000?