erratic 2 stroke tacho

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    Hi Guys. I seem to have an issue getting a clean tacho signal from a 2 stroke engine. reving the engine causes the hp and torque to jump up and down and the tacho wont be accurate. some times it will pull the absorber on hard enough to blow the fuse – thats in neutral. I have an inductive clamp and also have tried the yellow wire directly to either the ht coil or pick up coil. 4 stroke bikes are not an issue and I have tried several different 2 strokes with different types of ignition systems. 1 bike (yz125 digital ignition) got a clean signal from clamping the stator loom – weird. most of the four strokes i do run wasted spark so I dont see what the difference could be. If i record from 0km the graph is so up the crap its really unbeilevable (300+ hp from a scooter) but if i record from about 15km on and take it easy to start it records fine. could there be a filter in the settings I can change?
    I have dynomax pro, sae 850 pro ec dyno

    This issue is on with a 2 stroke engine.

    After abit More playing – it seems to be the exhaust note??? block the muffler
    to make it quiet and it helps alot. What would I need to insulate on the dyno to stop this


    i had the same issue and once i put the laptop in another room it worked 100% ever since


    Here is a question, and our suggestions, regarding one user’s problem we received several months ago:
    “Sometimes my laptop’s screen freezes up in the middle of a long hard pull on our Harley motors. This only seems to happen when I am both recording and have the throttle wide open. As soon as I back off the power, the screen comes alive again. I believe it’s RFI, but why does this only happen while I am recording?”

    Your computer is probably sitting close to those engines. Laptops and newer PCs feature some of the lightest (per gigabyte) hard-disk drives ever made. This is great for reducing travel weight, but not so good for shielding their sensitive innards against the noise inside a working dyno cell. Under the extremely noisy conditions typical during a WOT pull, many new hard-disks refuse to transfer data – which, of course, is actually better than recording erroneous data.

    Some newer hard-disk drives even lock themselves up on purpose – especially if it is a laptop drive! Engine exhaust noise falls right into the frequency range that the latest drive’s “shock protection” accelerometers are tuned for. Each time the noise gets loud enough, the BIOS parks the disk-drive’s heads – in anticipation of a bigger bump onto the floor.

    So what happens to your real-time data? All personal computers provide solid-state (memory) buffers, where data queues up while waiting for the physical drive to respond (to Window’s write requests). Unfortunately, the buffers are small, intended to handle only short (one or two second) periods of drive unavailability. Once its buffers fill, Windows must sit and wait for the disk-drive heads to begin responding again.

    If your dyno pull is fairly short (e.g. a quick inertia only test), the drive buffers may be large enough to temporarily store all the real-time data. Once the noise subsides, the drive catches up and so there is no problem. However, during your longer full-throttle pulls, or if the disk-drive’s buffers are small, the buffers fill to capacity and Windows hangs – patiently waiting for more room on the disk drive’s “loading dock.” During that period the PC’s screen appears frozen.

    What can you do if your personal computer is a victim of this problem? Here are a few potential solutions:

    Solution #1) Upgrade to DYNO-MAX 10.09 (or later). It includes separate programming threads and data writing buffers that are able to deal with many extended drive-outage periods.

    Solution #2) Replace your old mechanical hard-disk with a modern 100% SSD (all solid-state drive) unit. These non-magnetic and non mechanical units rely on the latest flash-memory technology to store your data. Any new 100% SSD will be more robust when it comes to dealing with the conditions in a dynamometer bay compared to a mechanical disk-drive. For examples of top-notch SSD offerings, check out Intel, OCZ, Samsung or Toshiba units.
    IMPORTANT: Do not confuse Hybrid drives (a conventional mechanical/magnetic disk paired to an oversize solid-state buffer). Maybe the buffer will take longer to fill and lock up – but why risk the possibility of doing the upgrade and not fixing the problem. A genuine 100% SSD drive is just not that expensive these days. Be sure to read the drive’s box carefully – to avoid buying a hybrid drive when you go shopping for a 100% SSD models!

    Solution #3) A cheap/crude solution (while you wait for your 100% SSD drive) is using a Fast USB (2.0 specification) “thumb drive” to relocate your DYNO-MAX 2010 “TempRuns” folder into. Then set the Tools- Preferences tab to point DYNO-MAX 2010 to that Temp Runs folder location. Note: Your computer may not support the latest USB 2.0 specification. If it does not, skip trying to use the slower “1.1 specification” thumb drives – wait to buy a 100% SSD drive!

    Tip:For DYNO-MAX 2000 you would have to place/run the entire DYNO-MAX 2000 installation onto the USB thumb drive. Unfortunately, while these USB-interface devices are less expensive, they are much slower, than a genuine 100% SSD drive.

    Solution #4) Install “RAM disk” software to create a virtual disk drive in the PC’s memory. Then specify that drive as the location for DYNO-MAXs “TempRuns” folder. Note: Be sure to use a software package that provides “write caching” and includes automatic data synchronization with a physical copy on the PC. One, of many, such products can be found at and offers a free trial.

    Solution #5) Avoid the noise. Buy, or build, an industrial enclosure for the PC. Or, if practical, move the PC (hard disk) further away.

    Solution #6) If you have over $5,000 to spend on a noise-hardened military-grade laptop, check out Once you chose to go this route, be sure to specify their 100% solid-state drive and additional RFI/EMI hardening options!

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