Rotary-MG

iTrader: (1)

The engine is a totally stock 12A with a full RB short primary exhaust system.
The headers and presilencer really helped to open up the powerband down low.
Torque is great while climbing up the gears, but things fall flat once I'm up to hwy speeds.
Above 80 mph she feels like she's missing something.

The car was tuned up just prior to the installation of the exhaust.
I am noticing and uneven and low idle.

What things should I be looking at?
My uneducated guess would be that timing has something to do with it.

Thanks for any words of advice.

t_g_farrell

iTrader: (1)

When you say totally stock, is that a nikki carb and the rats nest as well?

Rotary-MG

iTrader: (1)

Yes, nikki and rats nest are still there.

The nikki was serviced about a month ago, and the nest was checked out getting me to pass the smog test. I removed the air-pump and AC and added a dual-pulley and cold-air intake.

That's pretty much for things under the hood.

The engine was running smooth before the exhaust upgrade.
I didn't want to start messing with the settings without consulting here first.

rx7lives

You're right, check your timing.
Check to make sure the mechanical advance isn't seized and the vacuum advance as well.

If you have experience at it, do the timing by ear, just go slow on advancing the advance because pinging is not good to apex seals. I always set my timing with a light for smog and then after passing, advance it by ear. More advance gives you better throttle response as well as more top end, just back off whenever you hear the slightest amount of pinging and it's not as noticeable in a rotary like it is in a boinger.

I've seen this before on boingers where the header and exhaust move the performance curve either up or down so you either get more bottom end or more top.

Does it seem to have less top end that before the header or does it seem like it now that you have more bottom end?

j9fd3s

iTrader: (3)

checking the timing is fine, stock timing should be about right, i like to set it on the advanced side of the mark.

if its flat on the top end the things to check are the spark plug wires and distributor cap, if these aren't in excellent shape you will loose power up top. the wires should be under 16K ohms per meter, new wires are about 4-5k.

the next thing to check is the fuel pump; assuming you've already changed the filter.

once you have made sure you have proper ignition, and the fuel system is working THEN you could play with the timing.

ray green

iTrader: (14)

I had a similar problem, good torque and acceleration on the low end but didn't have the usual punch when accelerating at speed (passing at 70 mph, for example).

It turned out the secondaries weren't engaging (I forgot to connect the linkage last time I installed the Nikki; did you say someone recently messed with your Nikki?).

It was an easy fix and it made a huge difference.

LizardFC

iTrader: (1)

Don't forget to check the teeter totter. I have to reset that thing just about every time a non-rotary person touches my carb.

Rotary-MG

iTrader: (1)

I haven't owned a timing light in years, so I guess I'm going shopping.

Before installing the headers, the engine's happy spot was above 5k rpm. After the headers, although the overall power has increased, things feel like they flatten out up top compared to down in the lower speeds.

The carb was worked on by a very experience rotary mechanic, so for now I'm ruling out that he did anything wrong. It wasn't until after the headers that I noticed this issue.

Fuel filter is new. Plugs are new.
But I can't say that about the plug wires, cap and rotor. I'll go check those items out and see if anything needs replacing.

Thanks for the info.
It gives me a good place to start.

At Sevenstock my top end speed was suffering around the Willowsprings big track. That probably kept a rookie driver like me from going off track.

Trying to get ready for Buttonwillow on Nov. 18!

theNeanderthol

iTrader: (1)

Lot's of good advice already. My first thought was that your stock fuel pump can't keep up. Mine couldn't keep up at the top of 3rd gear, sometimes second. If I hovered at say 5k for a sec or two after it felt slower, then nailed it again, I'd have all my power back. It gave the carb's float bowls a chance to fill again after being drained. That's how I diagnosed the weak fuel pump.

Also, adding a relay and a new ground to the fuel pump gives it proper voltage. The old stock wiring sometimes has enough resistance to lose a volt or more at the pump. A volt below makes a very big difference to any fuel pump.

Rotary-MG

iTrader: (1)

OMG, what you said there makes so much sense. In lower gears I do have power above 5k, but I'm only there for a moment as I kept shifting gears upward. So would give the fuel pump enough time to catch up, but at higher speeds like in a long straight the pump never has a chance to recover. That's exactly what I'm sensing.

I'm planning on a new fuel pump anyways when I upgrade the carburetor next year.
The fuel pump is original, so maybe it's time to replace it.

One improvement begets another.
Gotta love this hobby.
How else does one find the weakest link?

ray green

iTrader: (14)

The symptoms are consistent with a weak fuel pump, but they still could be caused by something else.

You should at least check the output on your current fuel pump before replacing it, only to find out you still have a problem.

For example, those mechanical and vacuum links to your secondaries, which you're assuming are OK, could in fact be the "missing link" that explains your symptoms.

Assumptions are hypotheses; observations are facts.

It only takes a couple minutes to do a visual inspection of the vacuum lines and carb link, just to be sure they are correctly hooked up.

The onset of your symptoms with the recent work on the Nikki and rat's nest and installation of a new header might have inadvertently caused a problem under the hood.

On the other hand, there is no reason to believe that doing any of that work would cause a fuel pump to coincidentally go bad.

LizardFC

iTrader: (1)

The stock pump is barely enough for the stock car, IMO. When I put a header on my car, it continued to eat pumps until I installed a Holley red on it.

ray green

iTrader: (14)

I've driven stock 12A's for years with a stock fuel pump, stock Nikki, rat's nest and a full RB system, including the RB header. So have several of my RX-7 friends.

Power and gas mileage are improved with the header over the stock exhaust system, as you would expect because you'ver removed the restrictive cats.

And I've never had a problem with inadequate fuel delivery by the stock fuel pump with the RB header (nor have my friends).

For the HP delivered, headers reduce fuel consumption, not increase fuel consumption, and the stock pump will work fine if it and the rest of your systems are in good shape.

On the other hand, lots of people replace fuel pumps in an effort to solve a fuel delivery problem (sometimes several times) only to finally discover the fuel pump wasn't the cause after all.

LizardFC

iTrader: (1)

I'm just not a fan because I haven't had much luck with it. It's good for daily driving but with constant WOT it can start to run dry and cause cuts on hard turns. With a good regulator and a rewire it's much better at keeping up. I'm still a lot happier with the Holley though.

Mostro218

definitely sounds like a pressure problem, would look into replacing wires acap and rotor if they are old, with good fuel delivery you must also have good spark to ignite that fuel. But i'd definitely check fuel delivery first cause it sounds like your pump isnt recovering fast enough

Rotary-MG

iTrader: (1)

What fuel psi is recommended for the Nikki?
I was thinking of adding a fuel pressure gauge to monitor things.

Jeff20B

iTrader: (13)

Really? Check out Sterling's site for all the Nikki info you could shake a stick at.

Edit oh it seems to be down. That is I couldn't find it with a quick search. Maybe he changed the domain name, or forgot to pay his bill.

Ok I'll tell you. The Nikki wants anywhere from 2.5 to 3psi, but it depends on the year. The older ones were ok with a little more pressure, but all the modern or late model ones like 2.5 or so.

Yes get a fuel pressure gauge. It needs to be decent though. The cheap ones are always inaccurate. However even an inaccurate one can still tell you differences in fuel pressure while adjusting.

What you can do is look into the site glass windows on each side of the carb (get a mirror for the throttle side). You can use the level in the bowl to set fuel pressure. You want it in the middle of the glass.

Is your carb deadheaded or does it still have a return line? One thing I noticed about dead heading, is the fuel pressure tends to only be accurate while the engine is off. So set it to 2.5psi before you start the engine. Then start and watch for the fuel level in the bowls. Most fuel pumps will tend to read less pressure at idle for some reason.

These are my observations. I'm not a carb expert. I just know enough to get them to run right for me, and this seems to be how they behave regarding fuel pressure when deadheaded.

Rotor_Venom08

iTrader: (3)

is it jsut me or does the title say trouble TURNing after header install? i guess you meant tuning. the spelling police are on alert

ray green

iTrader: (14)

Nikki's like the fuel pressure the stock unit puts out, not sure why. Like Jeff says, it's about 2.5-3 psi (2.84 ~ 3.55 psi according to the FSM)

The Mazda units are a bit precious, I'd recommend the Carter replacement, they're pretty much bullet proof. Rock Auto has them for about $42:

CARTER Part # P60504 Includes Filter One of our most popular parts
Electric Fuel Pump IN LINE - UNIV $41.79

But before you buy a new pump you might want to diagnose the one you have first. Here's a guide:

http://www.carterfueldelivery.com/fu...diag_chart.pdf

Siraniko

iTrader: (13)

LMK if you need help installing the pump and FPR. I'm free next Sunday.

PS: dont do a deadhead, having a return line prevents vapor lock despite some peeps have a different opinion.

Jeff20B

iTrader: (13)

I've never had vapor lock in a vehicle with an electric fuel pump. How does it happen?

Rotary-MG

iTrader: (1)

I love how Chart 1 begins:

Is there gas in the fuel tank? > No. > Add 2 gallons

Vehicle Runs > Yes.

Vehicle was out of gas.

Pump is OK

Sorry for the lack of updates. I've only been able to rule out the plug wires so far since I had a newer set of Magnecors that I swapped out in the car.

Been busy getting the VORTEX CANNON ready for Halloween.

Jeff20B

iTrader: (13)

I read on this forum magnecors aren't as good as people thought ther were. Karack and some others were discussing it. The best choice worked out to be tried and true OEM NGK wires. Who'da thunk it? I like NGK personally.

I've been busy carving a pumpkin myself. Is your cannon going to blow out candles in jack-o-lanterns?

LizardFC

iTrader: (1)

Those cannons are awesome... with a little fog and some trick lighting, you've got a rather convincing ghost charging at trick-or-treaters.

Rotary-MG

iTrader: (1)

Oh Yeah.
It's a big black 4 ft sq cube.
The front is made of clear Acrylic glassine.
The orifice is 18 inch diameter, framed in a round aluminum screen frame.
(They make the frames round so they can be cut to form arched window screens.)
4 thick rubber bungee cords pull on a 16 sq ft diaphragm made of synthetic roofing material.
Last year I used a handle to pull back the diaphragm, and my hand and arm were raw after a few hours.
I welded up a pivoting lever arm that gives me a mechanical advantage. Even a small child can operate it now.
Last year it was 8 feet deep and filled the bed of my pickup truck. Chopping it down to 4 ft has only improved it's performance.

From a distance the fog and strobe light inside the box make it look like some other dimension big screen TV.
The smoke rings are about 24 inches in diameter. There is a lot of control over how powerful to make the rings.
It's cool to make a second ring overpower the previously fired ring. At night the rings have to back light. I'm going to try red spot lights tonight.

I've been planning on putting this thing on YouTube.
The ones I've seen there seem to have been designed and made by MIT scientists.
Scrap plywood for about $20, excluding the fog machine and lights. It is every bit as powerful as the "Candle Cannon" but without all the equations and big budget. It's a misnomer thinking that the cannon has to be in the shape of a cannon, cylinder or cone. Cubes work great and are easier to build. Only the orifice must be round to make a stable ring.

The idea to make this thing has been with me for over 10 years. I worked at Disney Imagineering (in finance, lol) and they were doing R&D to fire smoke rings from the fire god's mouth for an Indiana Jones ride going up in Japan. They used massive air compressors and a large butterfly valve to release the air. This is not as powerful, but I didn't have to 2nd mortgage my house to build it either.

This thing would be great at parties and carnivals.
I don't know why we don't see more of these large vortex cannons.