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All of the mechanical stuff you listed plus nut/bolt check, fluids, bleed brakes, etc. Bring a helper or two to the track so you can focus on driving once you are comfortable with the car.
for a new car you want to have fresh fluids, and torque everything on the chassis. i set the alignment to something simple basic (totally fine just to check what you have an write it down), and then set tire pressure to like 28 cold and just drive.
this last car we spent most of the first day adjusting seat/mirrors/belts.
do bring a notepad (or have a primer square on the hood and a sharpie) and write stuff down. once you get the bugs worked out you do want a little log of what changes you make to the car, and what it did, over time it'll be useful
You guys are awesome! Thanks for all the pointers. Tom set up the suspension so before I mess with anything I'm going to catalogue in great detail exactly the way he had it so I can have a good baseline. That way if i change something and it ruins the set-up I can fix it!
I have another question for y'all: how rich do you tune your engines to run? Mine is currently running so rich that at idle, it'll leave a pile of soot and stain the tarmac! I know rotary engines need slightly different set-ups than piston ones, but we don't set-up any of our carbureted V8s to run anything near that rich, so Im inclined to believe I need to adjust the mixture on my carb. Does the rotary need to run that rich? If so why? Is it because of the higher operating rev-range?
Based on personal experience with Tom's carbs, I know that he liked to tune the carb very rich through the primaries. Somewhere recently I noted that cars he prepped ran like crap at part throttle, but were fine when you get to WOT. I had him rebuild a carb for me quite a while ago. That was for a stock port 12A with RB short collected header. The jetting was 140/130 primary/secondary, with all other jets stock. After several trips to the dyno, I eventually found that 110/170 resulted in the same (or slightly better) HP without the part throttle deficiency. The A/F ratio is 12.5 to 13-ish. That seems to be where the best power is. Others may have different/better experience.
BTW, I was racing with Lucky Dog this last weekend and ended up with two broken front spindles. One on Saturday and the other on Sunday. I am pretty sure that both are original to my car (Spec7 to Pro7 to ITA to STL/Endurance) with about 20 years of racing use. It doesn't seem to happen too often, but it does. I am planning on doing a dye penetrant test (chemicals are available for about $100) on a regular basis to try and minimize the possibility of future on track failures. I am also smoothing out a sharp transition from parallel to tapered on the outboard end of the spindle to reduce the possibility of stress risers occurring at that point (which is where both failures occurred). I started a separate thread that shows the failed spindles.
Have fun when you get out on track. Your car will work great with Lucky Dog type groups. Before our spindle failure a little over 2/3 of the way through the Saturday race, we were in 1st place in class C (29 cars). You and your team can easily get there too. If you want to win/podium overall, you need a much different car. Maybe turboed Miata or E36/E46 BMW. Class C is where we want to be tho
. Does the rotary need to run that rich? If so why? Is it because of the higher operating rev-range?
at low speeds it does need to be richer than a piston engine, a lot of exhaust gas gets recycled into the intake stroke, its like having a huge EGR valve.
What I was trying to say about the standard "Tom tuning" was that at part throttle, when the secondaries are not yet opening, the A/F is very rich. Spewing black smoke rich. Once the secondaries open, everything evens out and the car runs fine. This super rich part throttle makes the engine unresponsive if you have turns requiring part throttle. The super rich primaries though may make a functioning accelerator pump less important, since there is already plenty of fuel when the secondaries start to open. That may have been his logic. If the accelerator pump is working fine though, it is not a concern.
I am interested to here what jetting is installed in your carb. Let us know after you have taken a look.
Also don't worry about changing it before getting out on track. It will work OK and there were plenty of Pro7's driving around for a long time with Tom's jetting. Rick drove the car like that for a long time. Not very quickly, but drove it.
Based on personal experience with Tom's carbs, I know that he liked to tune the carb very rich through the primaries. Somewhere recently I noted that cars he prepped ran like crap at part throttle, but were fine when you get to WOT. I had him rebuild a carb for me quite a while ago. That was for a stock port 12A with RB short collected header. The jetting was 140/130 primary/secondary, with all other jets stock. After several trips to the dyno, I eventually found that 110/170 resulted in the same (or slightly better) HP without the part throttle deficiency. The A/F ratio is 12.5 to 13-ish. That seems to be where the best power is. Others may have different/better experience.
Carl
I definitely recall you mentioning the Tom Tuning before, perhaps in our private messages or earlier in this thread. That would definitely be a plausible scenario for why my car runs so rich, but I'm not sure if or when Tom may have tuned the carb. I do have an invoice and some dyno sheets from when the engine that came with the car was rebuilt in 2011by Mazdatrix and it shows that they tuned the carb then. I'm not sure what they did to it or what jets are in it but I'll dig it out of the filing cabinet later and see if it has any info I can use. I'll post some pics of it here too. I'm not sure of Tom tuned the carb at any point after Mazdatrix, but considering the car was in his care its very possible.
Originally Posted by j9fd3s
at low speeds it does need to be richer than a piston engine, a lot of exhaust gas gets recycled into the intake stroke, its like having a huge EGR valve.
That does make sense. I assume that a little richer than a piston engine at idle and low RPM doesn't equate to clouds of black smoke and piles of soot at idle though XD
I think I may tweak the mixture screw a little and see if I can lean it just enough to stop the smoking and plug fouling I'm having and leave it at that. If I'm careful and only lean it out a little I don't believe that'll cause any problems. I also have stock carb on a motor I pulled form an 83 auto RX7 in a parts yard on the 2nd but I doubt swapping it over to the race car would be the right call.
Tell me, gentlemen do your rotary powered racers run so rich they smoke?
The super rich primaries though may make a functioning accelerator pump less important, since there is already plenty of fuel when the secondaries start to open. That may have been his logic. If the accelerator pump is working fine though, it is not a concern.
Carl
Tell me, gentlemen do your rotary powered racers run so rich they smoke?
a puff here and there is acceptable, but not really no.
if it was mine, i would adjust the idle mixture, same as any other engine, just turn it until it runs the best. if it starts stumbling driving around, you can always run it richer.
I had an ISC carb and a Paul Yaw carb on my car when I ran in IT7/ITA. As I recall both of them idled pretty clean and the car only smoked a little on start up at the beginning of the weekend because of an excess of premix in the fuel bowl. Nothing sooty ever.
As long as I kept the floats and fuel pressure adjusted correctly the car ran like it had EFI. Typically I had to set both once a weekend.
Both of those carbs were way better than the stock ones my competitors had. So, make your race prepped carb work.
No smoking issues here either other than sometimes a small amount on start-up. I believe that happens if I pump the throttle a little too much before starting the car. Idle is fine at ~1200 rpm after the coolant temp reaches about 120 degF. Before that I keep my foot on the throttle at >2000rpm. Starts easy cold and hot. If it is smoky while driving full throttle you probably have some problem other than running too rich. Interestingly I never have to reset the floats and fuel pressure after initially dialing them in. I am sure it must be just luck on my part, as I am no where near as skilled with carbs as Paul Yaw or ISC.
It is really easy to check the jet sizing, just so you know. With your background it should be really easy to figure out, but I will give a quick rundown. Remove the airhorn. It is held down by a 6 or 7 (or something) small screws (examples of which are circled in red below). Then remove the center bolt (also circled in red). You will also have to disconnect the throttle return spring. With the airhorn off, you can see the jets. You might even be able to read the jet sizes if you are lucky (they will be 3 digits). If you can't see the sizes, there are access plugs that need to be removed (circled in yellow). Once those are removed, you use a flat bladed screwdriver to unscrew the jets. You might have to modify a screwdriver or two, because of access interference. You should be able to do it the first time in less than 20 minutes. About 5 minutes once you know the drill and have the right screwdrivers. Of course you don't have to modify screw drivers if you just pull the carb off the engine, which is only 4 nuts which should be pretty accessible on your stripped carb.
Although you can probably find it on the internet pretty easily, I can forward you a copy of the Mazda carb manual if you PM me your email address.
I had an ISC carb and a Paul Yaw carb on my car when I ran in IT7/ITA. As I recall both of them idled pretty clean and the car only smoked a little on start up at the beginning of the weekend because of an excess of premix in the fuel bowl. Nothing sooty ever.
As long as I kept the floats and fuel pressure adjusted correctly the car ran like it had EFI. Typically I had to set both once a weekend.
Both of those carbs were way better than the stock ones my competitors had. So, make your race prepped carb work.
Now that's how I believed the cars to run and idle when properly set up! That's what we aim for when setting up our piston-powered racers and I couldn't imagine that it would be different for a rotary engine, but it never hurts to check with the experts. The 3 of you having the same experiences further shows me that something's amiss. Not only do I have the smoking problem;em but my plugs are constantly wet as well, at first I assumed that it was just a consequence of running pre-mix oil that burned differently that the petroleum fuel, but now I'm pretty certain that it's another symptom of the car running to rich. I've been too busy with work to be able to so much as uncover the car let alone work on it yet! Hopefully be the end of the week (maybe even today) I can make some time to begin messing with the mixture.
Originally Posted by Carl
No smoking issues here either other than sometimes a small amount on start-up. I believe that happens if I pump the throttle a little too much before starting the car. Idle is fine at ~1200 rpm after the coolant temp reaches about 120 degF. Before that I keep my foot on the throttle at >2000rpm. Starts easy cold and hot. If it is smoky while driving full throttle you probably have some problem other than running too rich. Interestingly I never have to reset the floats and fuel pressure after initially dialing them in. I am sure it must be just luck on my part, as I am no where near as skilled with carbs as Paul Yaw or ISC.
It is really easy to check the jet sizing, just so you know. With your background it should be really easy to figure out, but I will give a quick rundown. Remove the airhorn...
Although you can probably find it on the internet pretty easily, I can forward you a copy of the Mazda carb manual if you PM me your email address.
I figured that the process couldn't be too different from checking the jets on a Holly 4-bbl and it doesn't seem to be. It would be nice to know what size jets I have so I may have to check them, but for the short term I may just try to adjust the air/fuel ratio with the mixture screw until I have some more time on my hands. Finding time is the bane of anyone's car hobby!
I have a 1982 model year FSM and I believe that I also have a carb manual in my folder of car documents. If I don't have it I'l be sure to send you a PM, Carl and then I can go from there in regards to finding out the jetting sizes. I'll also try to post pics of the old dyno sheets as they're in the same folder so if I have to have them out I may as well! I'll let y'all know what happens when I start messing with the mix, hopefully later today.
Well I finally properly looked over the dyno paperwork, and Carl was right! It appears that Mazdatrix tuned my carb with 140 primary AND secondary jets. That may explain why my car is running so very rich! I haven't touches the idle mixture screw yet, but I'm not sure it'll be able to compensate for the big honkin' jets dumping fuel into the carb! I still may try to mess with it and see what I can do, but I may have found my problem. Here's all the dyno paperwork I have:
Carl I'll send you a PM with my email in the hope you can send me over that rebuild manual you mentioned earlier
I also have a big binder full of printed out copies of a whole bunch of stuff including a Yawpower guide to carb tuning and this Mazspeed book as well. It's a bummer about the Mazspeed thing though as it seems the printer was low on toner and stopped printing clearly about half-way through. I'll check online and see if I can find a .pdf copy somewhere
That's nice HP for stock port 12A engine. The torque will be useful on corner exist.
Regarding the carb, do the main jets come into play on a Niki when the car is idling? On a Holley or a Weber changing the main jets does not affect idle mixture.
I am not a Nikki expert, especially on the non-WOT operating modes. The fuel for the idle circuit is pulled through the primary main jets though, so the main jets do come into play somewhat at least. I would think that the mixture adjustment screw (basically only effective at idle) should be able to make up for a lot of the effects of the large primary jets.
That's nice HP for stock port 12A engine. The torque will be useful on corner exist.
Regarding the carb, do the main jets come into play on a Niki when the car is idling? On a Holley or a Weber changing the main jets does not affect idle mixture.
I wasn't aware either as to whether or not the main jets affected the idle mixture, but it seems given Carl's posted pic that it may. As I've said a bunch I'm used to dealing with Hollys so my first idea was to adjust the mixture screw to see if it would solve the rich idle problem. After talking to some buddies of mine who have seen me driving the car it doesn't smoke under operation, both driving normally and spiritedly, so idle mix is the issue.
Originally Posted by Carl
I am not a Nikki expert, especially on the non-WOT operating modes. The fuel for the idle circuit is pulled through the primary main jets though, so the main jets do come into play somewhat at least. I would think that the mixture adjustment screw (basically only effective at idle) should be able to make up for a lot of the effects of the large primary jets.
Well that diagram does yield some great insight! I guess at this point I'll revert to my original idea and I'll attempt to adjust the screw just until the smoking stops and I won't change anything else. If that doesn't fix the problem I'll consider Carl's jetting of 110/170 and see if that improves anything. That dyno sheet shows pretty good power and torque, which makes me hesitant t really mess with the carb, but at this point the motor that test represents is in the garage and needs a full rebuild anyway so it may not be too big a deal.
Carl are you making similar power with you 110/170 jetting? Also does anyone see any glaring issues with my mixture screw idea? Is that the right court of action of does it pose some danger on Nikki carbs I'm not aware of? I've been treating them like Hollys bit as I learn more it seems that they're substantially more different than I thought...
Alright y'all here's an update: I leaned out the idle as much as I could with the MAS and there's no change to the presence of smoke coming out of the tail pipe. The MAS was basically as lean as it could go anyway. At this point I'm not sure if I'll try Carl's preferred jet sizes or try and finally get a different carb set-up for this engine like I initially wanted. I'll figure it out as I go along.
Alright y'all here's an update: I leaned out the idle as much as I could with the MAS and there's no change to the presence of smoke coming out of the tail pipe. The MAS was basically as lean as it could go anyway. At this point I'm not sure if I'll try Carl's preferred jet sizes or try and finally get a different carb set-up for this engine like I initially wanted. I'll figure it out as I go along.
My Bridgeport 12A with a modified Nikki carb is currently set to idle at 1500rpm when at operating temperature. I asked Daniel at Garage Life and read all the forum posts I could about where a bridge should idle and that was the answer I kept getting.
In an email Carl sent me he explained that the stock jets on a Nikki were something like 92/160 so I may be unable to compensate with the MAS for the jet being basically 50% larger than stock. But of course, if this engine actually is bridgeported than it would be able to consume more air than a stock engine, but then again the stock carb may already be flowing all the air it can, regardless of the engine's ability to move more air. I'm stumped, gentlemen! I guess I'll look into jetting the carb more towards Carl's preference of 110/160 and see how that pans out! If i need to I can also through the stock 83 12A in the car and see what that does.
so the idle hole is in a fixed place, physically. and when you raise the idle speed it moves the throttle plate away from the idle hole, and the carb will start using the next circuit (on a weber its the progression holes).
this reduces the effect of the idle mixture screw, because basically you're not using that part of the carb as much. its one of the quirks with the IDA on a rotary
if you lower the idle speed, the mixture screw will work more. the P port/Weber will idle around 900rpm, although nikki/BP is a different thing
i'm not sure how the Nikki works enough, but on the Weber the progression holes are controlled by the idle jet, so if you wanted to idle at 1500rpm, all the tuning is the idle jetting. mixture screw would do almost nothing
04-27-21, 08:38 AM
