Rotary Works Billet TB Question
 

Have a question on the rotary work TB. Yes I know of the quality issues with them, and the arguable improvement over stock. But my question is for anyone who is currently running one. Did you ever have your butterfly stick? My pedal seems to physically stick when the throttle is closed. It takes a bit of force to get it to unstick, then it makes it difficult to drive. So I was wondering if anyone else had this problem and what was your solution? Also, anyone have issues with cold starts and the IAC keeping up with the TB? Thanks for any help!

Sticking throttle is often the butterflies closing too much and wedging against the TB. I had that on my OE secondary and solved it with a 1/4 turn of the return limit screw which controls the closed throttle opening. Probably could do the same on your primary butterflies.

thanks I’ll give that a try! I’m assuming that would increase the idle rpm as well?

Take it in baby-steps. Dave mentioned a quarter-turn…just enough to help the sticking but not (meaningfully) increasing air-flow.

ahh gotcha, I will try it out this weekend! I appreciate the input

When I did that to mine it did increase idle speed ~150 RPM. I adjusted this back down to ~750 RPM with the air bleed screw on the bottom of the throttle body under where it connects to the elbow. Link: https://www.rx7club.com/3rd-generati...9/#post7326556

Hmm I don’t think the rotary works TB has an air bleed screw on it. I’m at work all day or id just run out and check lol but I will for sure keep that in mind

A mate used to make lots of various TBs, often times, a light polish with scotchbrite (light green or maroon might be best grades) around the edge of the brass plate was sufficient to improve any hang-up with the bore. In more extreme cases, if the butterfly wasn't very well fitted (and screws aren't staked), you might be able to loosen them and improve matters - loctite is your friend afterwards.

ah I didn’t think of that. I will definitely take that into consideration as well, thank you! Do you think it would be more beneficial to do that to the butterflies or TB bore around it?

IMO, since you're doing it just to get the TB and BF's to mate correctly, either would work. However I think doing it to the BF's would be easier (less material to remove). Looking inside the TB with a small flashlight you should be able to see where the BF's are hitting (there should be a scraped or clean area that stands out).

In any case, trying the close-stop screw adjustment will be way easier, and at least will tell you if that's the issue.

I tried turning the idle control screw a 1/4 turn and it seemed to help a little, but still sticks. It seems to stick closed when the rpm’s are >2k? Then once the rpm’s fall below that it seems fine. Not sure what this could mean.

So I’ve taken the throttle body off, rounded the leading edges of the butterfly with 1000 grit sand paper, adjusted it so that when I hold it up to the light I can see a small sliver of light all the way around. I’ve adjusted the idle/ butterfly screw from 850rpm idle up to 1400 rpm idle, and still the same thing. Over 2k rpm it sticks. Thinking of just throwing the stock TB on there and cutting my losses. I don’t think there are other billet TBs are there?

My rotary works TB does not do this! Ran it for over 10 years. I just recently switched to DBW for more control but it worked without issue.

If it's sticking, there will be rub marks where a butterfly is hitting some bump/roughness on the inner wall of the TB. You "should" be able to see those, or feel it stick as you open the throttle. Then mark that point with a marker and sand/grind the TB it until it doesn't stick. PITA, and tedious, but that should work.
The contact point could be anywhere on the edge of the butterfly.

I did color around the inside of it with a sharpie and I could see where the butterfly seems to scrap just a little bit top and bottom. Nothing on the sides. I sanded the butterfly with 1000 grit and adjusted the idle screw to alleviate this. It just seems weird to be the reason of it sticking when it ONLY sticks above 2k rpm. I cannot recreate it when the car is off or throttle body off. I’m running a Haltech elite 2500, could the IAC be tuned incorrectly causing almost a vacuum on it?

That's weird. The only mechanical logic to that is the BF's being pulled away from the TB inlet by vacuum and causing them to contact the TB wall a tiny bit inboard (or something else binding) that wouldn't be obvious w/o the vacuum. Maybe you can replicate that force by pressing on the BF's from the inlet side. I can't think of anything related to tuning that might cause that (not that I've had anything but the OE ECU).

The only other thing I can think of is the wax rod off-throttle cushion mechanism is binding.

i did try to gently force the butterfly closed as well, to try and recreate it binding up or getting stuck, and still could not. I have the same thought process as you do though lol I’m kinda stumped by it. One guy from the shop is gonna stop by my house and take a look at things as well, to see if im overlooking anything, but he can’t make it until next Thursday. So until then, I’m open to any ideas!

I suppose it's also possible the pedal or the throttle cable is sticking, have you tried working the throttle with your hand from the engine bay? If it always feels smooth in the engine bay even with the engine running, you might be misinterpreting an ECU calibration thing as a sticking throttle. Big changes to the Idle Air Control Valve position, or weird spots in the fuel map, might feel like a sticky throttle at 2000 RPM and light load.

I have not tried it by hand with the motor running. But I can do that this weekend and see if it does anything different! There were big changes to the IAC since there is no dash pot on the RW tb. Definitely trying to figure out mechanical vs tune. Thanks for the suggestion though, I’ll give it a try by hand this weekend

I might not have been clear about 'big changes to the IACV position', I mean if the ECU commands a significant change in IACV duty cycle that could affect how the engine behaves at 2000 RPM and low throttle. If the ECU changes the duty cycle from near 100% to near 0% it might be enough to make the engine temporarily stop accelerating which might feel like a sticky throttle. If you've got a wideband and it shows very rich or very lean AFR when this happens, that could be a fuel map tuning situation that needs to be fixed.

Not sure about rounding the edges of the butterfly, as they're cut at an angle, around 6/7 degrees usually - just basically polishing any tight spots is the intent.

Does it happen cold and hot and is the car RH or LH drive? You see quite a few sad looking cables on RH cars with singles when they don't heat shield them, but I'm hard pressed to imagine a melted one effecting just one throttle opening position even so!

ah I see what you mean now. As far as I know the AFR remains stable and appropriate, nothing too rich or lean. I’m not familiar with the type of “sticking” you’re describing, so I can’t tell you no that’s not it, but the gas pedal physically sticks at the top or “zero throttle”. As in it requires increased force to get it past the sticking point.

I didn’t round them much at all, my idea was to make them feel like the OEM butterfly edge. They just had the laser cut metal edge feel to them. If that makes sense. It does happen hot and cold. It’s RHD. The cable is a new USDM cable because I needed a little more length on it to reach. As far as I can see though it’s far enough away from any heat source that could melt it.

Any chance the inner cable (and maybe the sheath) got sharply bent during installation and the bend was severe enough to be permanent? I've seen that result in a cable that "hangs" at one position in its travel.

you should start to remove parts in that system then to find the one that is the trouble. i would start with the easiest part, and move the throttle by hand, if it sticks, then keep working on it. if it does not stick, then i would put the cable back and disconnect it from the pedal end, and then see if it works there.

IMO, that (USDM cable with RHD) makes it more likely that the issue is with the throttle cable since you may have some smaller radius bends than normal getting it in there.