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.

I think that’s a really good idea. I didn’t have much time today but I warmed it up it and controlled the throttle at the throttle body by hand, it did NOT get stuck when I did it that way. So I’m thinking it has to be within the cable/ pedal. I’ll dive into it more tomorrow, but still weird it doesn’t do it when it’s not running.

I’ve attached a few pics of the and highlighted the throttle cable route. What do you think? The tightest bend is the picture from the side.
https://cimg1.ibsrv.net/gimg/www.rx7...b65951ed2.jpeg
https://cimg3.ibsrv.net/gimg/www.rx7...2c3afe013.jpeg

In the last photo, the sharp angle change coming off the end of the metal tube is not good and I wouldn't be surprised if that is the bind point. I make it a rule that I never have a situation like that because even if it doesn't bind, it will wear the sheath lining and fatigue the inside cable.

noted….kind of my thoughts as well on it but I wasn’t sure how much of a binding point it would be. I’ll have to mess with it to see if I can get a little better of a route.

Prior to discs, on bicycles with v-brakes, the manufacturers used a steel tube for tight 90 degree turns at the end of the bowden. Dunno if anyone does a 180, something like that would be the only way to improve matters with that cable run.

Never paid any great attention, I've seen those rotary works TBs on yahoo recently, do they do a version specifically for RHD perhaps? Short of that, remaking the throttle wheel or adapting another one with some sort of cable stop above the plenum for a straight pull, would be the best way.

So I had the guy come from the shop that helped me finish up the car, he thinks it’s the vacuum on the engine during decel causing the butterfly to stick shut. He suggested drilling a small hole in the butterfly to help alleviate this. Any thoughts on that?

Drilling a hole will add airflow, which might raise the idle speed. It can also change how the car feels during deceleration, I think you might have less engine braking with your foot off the throttle.

no maybe, it will definitely raise the idle speed

which you could possibly do otherwise to see if it can be adjusted out of the “sticking” zone. I didn’t read the thread though to see if that had already been tried.
.

^He may be on to something... Different situation & TB, but way back in the early '90s I had similar issue with my '84 GSL-SE with the OEM TB. What was going on was after a quick decel (high vacuum) coast down to idle, sometimes the secondary plates would stay cracked open slightly & flutter, resulting in a high idle speed that would fluctuate. Stomping the throttle in neutral (to cause another rapid change in vacuum) would usually return the engine to a normal idle.

Turned out my TB just needed a very thorough cleaning - a combination of some carbon build up on the secondary plate shaft (I had over 100K miles on it by then) and the stronger vacuum during decel prevented the springs for the secondary plates from fully closing them upon return to idle

Similar thoughts in these 2 posts...

throttle body is brand new, I couldn’t see anything on it the could be cleaned. I maybe have 20miles on the tb? Basically shop-home-around the block a few times. So would the vacuum keep it shut or cause it to open? Mine is sticking shut.

I'm confused by what you said here. It can't be sticking closed at 2K RPM. Do you mean it doesn't want to open further once you get to 2K RPM, or what? When it's at 2k if you let off, does it close? Or just not want to open further?

If engine vacuum is actually pulling the throttle blade closed, the vacuum will usually be stronger when decelerating at 5000 RPM or 4000 RPM than when the engine is decelerating at 3000 RPM or 2000 RPM. Higher engine speed will pull stronger vacuum on a closed throttle, since it's trying to pump more air per minute.

i beleive it is stuck closed. opening it further is no issue. Example would be normal driving, shift around 2500-3000 rpm so you let off the gas, shift, then when I go to push the gas pedal after the shift, the pedal is stuck. It either requires excessive force to move past top position (zero throttle) or I have to wait until it gets down to about 1200-1300 for normal operation. There is no rpm hang at any level. I haven’t had it any higher rpm than 4500 due to my break in period, as far as I know it’s stuck as described through the rpm range >2500 which is why it leads me to believe it’s a vacuum/ iac issue. Which I could be completely wrong, it’s just my train of thought.

Yup - sure looks like vacuum is causing the issue. My guess is the butterflies must be hanging up on something when there is significant vacuum.

Back in the old days, some did drill the throttle blade (and add progression holes) when idle and emulsion circuits couldn't accommodate - that would be a hail mary on mixtures not vacuum.

Does your ecu log MAP? Looking at that cable run again, I'd wager you're under half a minimum bend radius on a bowden cable. I'd still fix that before acting.

I suppose you can silver solder the hole closed, so the mod is not irreversible. If you do proceed, I wouldn't start at your hardware store, 1/16th bit size either! Jet or wire gauge drills are probably what you're looking at. For best results, I'd be avoiding a wonky hand drill in situ - I'd probably resort to turning the pin vice by hand before that, although by rights, for the small sizes, you should be doing 10s of thousands of rpm to avoid breaking them endlessly.

on my P port i drilled the plates on my Weber, for just the reason Billyboy describes, the throttle plate needs to be in a certain place physically for the idle and transfer ports to work, but the engine wanted more air.
i started with the tiny drill bit set for like a dremel, similar to what your dentist uses. its been a long time, the old days, but i think i ended up at like 0.015" or something. you can solder it closed, or you can on a Weber, the plate is brass. i went up to like 0.030 or something and had to come back down, because the carb still needs some vacuum to actually carburate

or maybe you could just put a bigger spring in the TB, or use the Mazda throttle body which won't have this problem

Also, IIRC, usually butterflies are not always perfectly symmetrical in relation to their pivot axis. One side usually has a tiny bit more area than the other. If the side opening toward the TB inlet has more area, vacuum will help it close. If the side opening away from the TB inlet has more area, vacuum may prevent it from closing. Also, flow characteristics are different on the 2 sides because of the plate angle in relation to the TB, so even if the areas are exactly equal, high vacuum could be keeping the throttle open or closed and there may be no mechanical issue causing it. Once the vacuum decreases, throttle-plate motion then would be possible.

So:
If sticking open is the case, then j9fd3s' stronger spring suggestion may be the solution.

If it's sticking closed like I think ecurbd02 meant, then either some bleed holes or a longer radius (larger diameter pulley) to the throttle cable at closed throttle may enable opening. You may need a variable radius pulley like I see on some exercise machines to give more mechanical advantage coming off closed throttle. If the cable force is too high, then your circuitous large-angle-change cable routing could make the cable act like a capstan and cause it to bind.

Capstan ( https://en.wikipedia.org/wiki/Capstan_equation ):
The force gain increases exponentially with the coefficient of friction and the total angle of contact (around the cylinder or in this case, along the cable).

Capstan effect in throttle cable
 

So if there is even a small amount of force added to the cable tension, like what may be present in the butterfly pivot due to the vacuum pulling on it, or the sharp bend near the pulley, that multiplies exponentially through every curve of the cable and is, IMO, likely to be the issue making it stick closed.

totally understand the cable issue you guys are bringing up. My only thing that makes me think it’s not, is when it’s not sticking there’s no variance in amount of force required through the stroke of the pedal and that it’s rpm dependent. Please correct me if I’m wrong, it’s just the way my brain is working when I think of it lol once it gets above 20 deg where I’m at, I’m gonna drill a small hole in the butterfly. I was gonna check the duty of the iac at idle to make sure I have a little room to bring the idle down though

Well, what I mentioned and explained is only a possible cause, not 100% certain it's actually that. Good luck with it.

"When it's not sticking" - does that mean w/o vacuum on the intake, i.e., car not running?

The capstan reference only applies when there is some extra force to be overcome near and/or at the throttle plates, and that is only present when there is vacuum, i.e., car running. And that, IIRC, is when you said the issue occurs.

this is a good idea, the IAC adds air, and can change the cell of the map the engine is in, which can change fuel, which if its not right can do odd things to the RPM, its part of the bouncy PFC idle issues

BTW our solutions have basically been if the throttle is physically sticking, like the blade gets stuck somewhere, but it could easily be a map issue

yes when the car is not running. Ok I didnt realize the capstan reference was in reference to when there is an additional force to overcome. That does make sense though. If it is the throttle cable binding, do you have an idea where I could get a longer cable aside from custom? The USDM cable is longer than the JDM which is why I went with it. The jdm cable won’t reach.

all of the Mazda ones are basically the same, you might measure up the US Miata cable NA01-41-660A. the pedal is on the left, and the throttle body is on the right front, so its quite long.
you might also try to route yours more like that one

I only know custom cable suppliers - the best is "Control Cables." Website: controlcables.com (562) 949-0455
They are well known for supplying push-pull cables for aircraft. I use their cables for the throttle and for swaybar controls on my racecar.
They are VERY good and easy to work with AND THEY ANSWER THEIR PHONE. They can make almost anything you want, quickly and at a reasonable cost.