MPS rebuild, mission accomplished Options

[emerygt350]

I just used Chris Foley's excellent rebuild kit on my leaky MPS. After removing the spider webs and varnish it all went together nicely. Chris gave me some great tips on getting an initial set. I think it is there but I don't have any experience with how a well tuned djet 2.0 914 should run. I suspect there is probably 150k or so on this engine although it could be lower, I doubt higher unless it was cared for very very well. Impossible to know with the dead odometer. Compression is great on all cylinders with no variability.

I took a little video of a drive, start up, corners, and two pulls to 60 (of various quality). After the first 40 seconds I opened my sliding rear window so you can hear the engine sounds better.

https://youtu.be/Fi4vFCWhlCw

[ChrisFoley]

PB Anders did a great job of characterizing the d-jet system for us but the detailed MPS information tends to intimidate people rather than empower them.
The MPS is a simple mechanical device attached to a robust electronic sensor. Only the mechanical portion is serviceable so I ignore the electronic portion as soon as I know it's operational. I skip the bench tune and go straight to the operational tune.
I've come across some simple "seat of the pants" techniques that work well and don't require in-depth knowledge or specialized electronic instruments. The only requirement is that all the components are functioning properly. So far I haven't managed to organize my techniques into a set of tuning notes but it's only a matter of time.
For modified engines I always recommend an O2 sensor just after the collector, especially to be sure the engine doesn't go lean at WOT but I don't think it's essential on a stock engine.
I don't think spark plug appearance is a very reliable indicator of mixture except at the extremes.
A dyno run can verify WOT mixture is safe but the tailpipe sniffers used at most dyno shops aren't accurate for idle tuning. The exhaust gases get contaminated with backwash at very low flow rates.
Hot start issues are a good indicator of a lean tune. Properly tuned d-jet starts quickly, hot or cold. Imo most people chasing "vapor lock" issues with their stock injected engines are merely suffering with a lean mixture. I use this knowledge as a tuning tool: Take a drive to get the engine good and hot and then park it for 10 minutes. If it starts right up, the MPS adjustment is pretty good. However if you think it might be a little rich, screw in the small center screw by an eighth turn and try again, starting with a cold engine.

One very important thing to keep in mind though: the MPS should never be adjusted to compensate for other issues. Reliable tuning with the MPS can only be done on a properly functioning system.