Emulator

Actually, I'm pretty sure I know what's wrong. Turn up the deadzone to your controller. If it's inputting slight steering inputs while stopped, your acceleration goes to shit so you can turn.

Where do I get the latest development version?

From here: https://dolphin-emu.org/download/

Scroll down. Anyway, just increase the deadzone in the GCPad settings higher, and this issue should disappear even on Dolphin 4.0.

Actually, increasing the deadzone made it far worse... I did turn it up all the way- what should I set it to?

Can you set the deadzone to zero and give me a screenshot of your GCPad window. Upload it to imgur or something, because we can't have big attachments on the google code.

Basically, you want to make it so when you're not touching the joystick, it's gray rather than red. This issue is not happening for me on Windows except when I have zero deadzone.

http://i.imgur.com/e0uEiyE.png
Are you sure it's a joystick issue by the way? In this game, acceleration is not affected whatsoever by the joystick? The problem has also occurred with a ps3 controller, and keyboard.

You'd normally want to set the deadzone to 10 or 20, maybe 30 if your sticks are as wobbly as a heavily-used N64 joystick.

I'm not 100% sure; but that's the only way I was able to reproduce any kind of problem.

I can not really reproduce it.
In the big spiral in the Wario Colloseum the acceleration is a little delayed, but that is likely part of the physics.

Yea, unfortunately it didn't do much. I'm not incredibly tech savvy which is why I came here, but can you think of anything else that might be causing the issue? It wouldn't be with the iso itself would it?

Did you try using the latest versions of Dolphin? That's all else I can recommend.

Yes, and using the latest developer's version- still no fix. Would anybody be wiling to go so far as to humor me and record a video of the same spot at Peach Beach, without any issues?

Are you by chance no running full speed in that particular spot? Can you try running the game in single core, even if it is slower?

I don't really want to record/encode/upload a video, but I can if none of those suggestions work.

How does one adjust the speed?

I meant if you're not going full speed. IF you're not going full speed, there are potential control issues. I still say try to use Single Core.

How I run the game in single core I should ask?

Uncheck "Enable Dual-Core"?

Also:

I'm not incredibly tech savvy
which is why I came here
The forums are where you're supposed to go if you're not "incredibly tech-savvy"; this issue tracker is meant for legitimate, reproducible bugs.

Speaking of which, what the fuck is the actual issue? I don't see anything that actually looks weird, and the description is useless.

Alright, just forget it. Thanks for the help, JMC4789.

I don't know, it's either a physics quirk in the game that I'm not getting or something off in the Mac builds.

I'm not going to invalidate this issue because of something I found.

http://youtu.be/8BZOmTiAq48

This is probably related to your issue.

That video PERFECTLY displays my issue! Thanks so much for putting in this amount of effort to help me out here. I can't even begin to express my gratitude.

I'd like to thank you for putting up with my initial skepticism. This bug is a strange one, and likely is upsetting all of the physics in Mario Kart Double Dash. I may remake another issue with more information on how to reproduce (and then mark this as duplicate/closed/etc.) after I study it a bit more, so that people can more concisely see what's going on.

Excellent catch, and hopefully now that it's out in the open, we can have someone track it down and fix it.

Thank you SO much for further investigating my very questionable issue, and I apologize for being so brief in my description.

That last trick worked absolute wonders! It went from the problem occurring 99% of the time to practically never. Once again, I cannot thank you enough.

Glad we could temporarily alleviate the issue while the problem is looked for.

JITIL seems to have its own issues with accelerating even on flat ground and not steering. I honestly don't get what's going on. I can't find what build started this either; seems to go back a long way.

Yes, while switching to JITIL did seem to temporarily fix the problem I was experiencing on specifically that part of that map, I would still find myself having issues with acceleration in other aspects of the game that I I was previously experiencing. For example (and this is most likely only something somebody who plays the game as much I do would notice), when you are cruising at a normal speed, somewhere around 55mph, and are struck by any item that causes you to fully decelerate, it's far more difficult to reaccelerate to your previous speed, in that it takes way more time to gain back speed. This problem does not occur on the GameCube, and I can demonstrate this issue in a YouTube video if necessary.

I can already confirm everything you're saying, I'm 100% with ya. It's just that I have no idea what is wrong, and have no capabilities to investigate as I don't think there's a working combination in Dolphin whatsoever.

This is fixed in interpreter by using VERY_ACCURATE_FP. We just need to figure out why enabling it doesn't help JIT.