I'm still in shock. I'm coming to work this morning, driving down the freeway and I have to change to a different one. I'm in the far left lane, and there is a bunch of cars to my right. I'm in 5th gear at around 75 mph, and I know that if I floor it the car will bog, as it has been doing it for the past month since the new carb with huge jets was installed. So I slowly floor it anyways to see if I can get any acceleration out of that and then, like in a dream, the car doesn't bog! at that speed in 5th it actually takes off, and before I know it I was doing 90 mph. Too shocked for words, I change lanes and get onto the next freeway. After the curvy on-ramp, there is a steep uphill for a mile or two, and with the bogging problem, top speed at that point is 80 mph. Won't go past that no matter what. Well, I gun it to some degree, and look at the speedometer. 90 mph! and I'm not even flooring it all the way. Once I get past the uphill part there is a short run on a flat section before I get off the freeway. Top speed there has been 90 mph. This time I gun it pedal to the metal, and look at the speedometer. 110 mph and still accelerating! and the engine sound is beautiful, secondaries fully open on a streetport with a PP muffler.

I have done no change at all on anything since I drove it last (yesterday), and I was having the usual problem then. Anybody care to explain wtf just happenned?

 

Always runs best before it dies. ):

 

shaddap you negative phucker

 

i dont know what happened to ur 7 maybe ur jets are wrong or its just actin up since ur drivin in steep hills on a carb....?? but i wouldnt push the motor like that since u only have a couple thousand miles on the rebuild..

 

Hmm yeah but I go the same route every day and it wasn't behaving like that before... same uphill.

You don't think 2k miles is enough to be able to push it like that? interesting. I was ready to do it after the first thousand miles, but couldn't because of the bog problem.

 

Sounds like a typical carb experience! Carbs are like women; they are hard to understand, subject to inexplicable personality swings, you can love and hate them simultaniously, and when you think you are playing them, they are really playing you! Air temperature, barameteric pressure, altitude...all play games with your setup. And no setup is uncompromised, as best peak power and best driveability always involve tradeoffs. Also like women, some guys have all the luck: they just know how to make them purr...most of the time. There are also high maintenance and low maintenance carbs, as well as ones that just seem to suit your personality better. For me, I like a nice simple, low-maintenance, sexy Weber 48/51 IDA. I have NO IDEA why some guys like Holleys on a rotary...but, hey, that's a *personal* decision!

Fuel injection is like having a robot girlfriend who is programmed to fulfill all your needs and desires. It might not be romantic or require nearly as much compromising skill, but at least you get results consistently.

 

how was the weather that day? carbs are moody like blake said. but i love them nonetheless!

 

Personally I don't like Holleys either. Anywho, I had the same experience when I first put in a Mikuni. The only thing I can come up with is there was some kind debri stuck in one of the tubes or jets and it finally blew itsealf out.

 

It was today. 9:20 am. So Cal, so warm. 75-78 degrees maybe. Low humidity.

 

Maybe, however this is a carb that was just rebuilt by rx7carl so I don't think it had any debri stuck there, but who knows. The funny thing is that the car aparently bogs out of being too rich. Fuel jets are 160s for the primaries (against 92 or so stock) and 190s for secondaries (against 160 stock). So if it was really bogging out of being too rich, something made it leaner. Fuel pump is relatively new and fuel filter is new. And the car still stutters and hesitates when I try to maintain speed at low and middle speeds, though maybe less now than before. It's just so weird. Oh well, banana boy is working on a Sterling carb for me and I just got my Carter pump and Holley FPR. That should be a pretty sweet setup for my sp once all installed. In the meantime, I'll enjoy this new gift from the rotary gods!

 

It's not uncommon to have a large carb bog at WOT from a lean condition caused from decreased velocity through the venturi. Part throttle can "solve" this by restricting the orifice enough to maximize velocity short of restricting flow. In other words, if your carb can't effectively meter air for the higher airflow (at lower velocity), you can get a WOT bog. If your setup suddenly works great at WOT and the environmental conditions have not changed radically, then check to see if the secondaries are working. If they aren't, that could explain your performance gain (the velocity throught the carb isn't sufficient to properly meter the fuel). And, it helps not to think of the throttle as a "go fast" linear potentiometer (i.e. more throttle = faster). Use your butt dyno to "tune" your right foot to maximize performance.

Obviously, this is only one possibility...and not even the most likely, given that it's a modified Nikki; not a 51 IDA.

 

maybe your jet got semi clogged and is now the original size

 

My bet is, you had something restricting your secondaries. I know that I have an issue with exactly that, and your symptoms prior to this miraculous recovery describes my car perfectly. Enjoy it!

 

FBII and Blake hit it on the nose. It's a difference in pressure, temperature, or humidity between the days that you've driven it. It will bog sometimes and sometimes not.

 

Oh the mech secondaries work, I assure you. It is obvious in the sound of the exhaust and the power of the car when the secondaries open. It's like this:

http://f2.pg.briefcase.yahoo.com/bc/...r=/rx7&.view=l

right click and save the obvious avi file. You can hear at around 5k rpm when the secondaries open.

 

First let me reitterate that those choices for jet sizes are yours, not Carls, and most certainly not mine.
They are far too large, and you've been dawgging it like a pig as it drowns in fuel.
You got "lucky" with the combination of being in a high gear and accelerating beyond 80 mph, which is a tremendous drag on the engine, thus calling for a very fat mixture.
You also did the one and only "correct" thing you possibly could have that too often too many refuse to see...and that was to "slowly press the accelerator.

But you are still jetted very poorly.
I have a stockport, and I can bring it up to 90 with the engine screaming going up a slight incline, shifting into fourth at about 85 mph.
I have .063s in the secondary main (the stock 1.92mm).

If I tried to accelerate the same speed and incline in fourth, I would have too much load for the mixture I can deliver at that carb velocity, and my mixture would prove too lean to get the job done.

What are you running for air bleeds?

 

Thanks for the reply Sterling, I always love to read your informative posts. Yes, your disclaimer is correct, those are my choices of jet sizes and venturi, based on the old RB formula for BP engines.

I'm running stock for air bleeds.

While I understand what you say about gear and load and all that, what puzzles me is the fact that I do that route 5 days a week, with the same shifting points and amount of pedal. For example, if I would try to go WOT on that uphill at 80 mph, the car would bog and start loosing speed. at 80 mph today, car didn't bog at all and started accelerating. It was beatiful to see the car taking off like that on a relatively steep uphill in 5th gear! but anyways the point being that up to last friday when I did it last, that was not the car's behaviour at all. Go figure.

 

fix the jetting....

 

OK CRAD51, when do we line up?

 

(in Doc Holiday's voice) Say when.

But regardless, we'll have to do it again after I get my Sterling carb and install my FPR and Carter pump. Do you have a 12a to line up against?

 

Yea no fair. That carb wont be near as good as what he's getting soon.

 

hey...i didnt think you had to break in a rotary...my understanding is that you need to break in a piston engine so you wear the piston sleves to mesh better with the rings...and that the engine was not 100% lubbed up till you did...i didnt think the was required for a rotary cuz your not trying to get oil between the apexes...and the housing...

am I wrong?

 

Thank you banana boy for your kind words of self-promotion

So back to the original subject, I just came back from a test run. The funny thing I found is that even though the car is not bogging from richness, it is now sometimes bogging from what seems to be fuel starvation! I would gun it on 2nd or 3rd, still being somewhat careful with the amount of acceleration to avoid opening the secondaries too suddenly, and it would all of a sudden, after a few seconds of wildy accelerating, loose power. This is the same symptoms I had experienced way earlier with stock carb and a clogged fuel filter. Fuel filter is now new, but the point is that it seems to be something in the fuel line that might be partially blocking it, or the fuel pump is partially failing, thus creating a leanness that allows me to take it to high rpms without bogging from running too rich, if that makes sense. That's my theory based on the data so far. Fortunately and with great timing, today I got my Carter fuel pump and Holley FPR. So those are going in this weekend, and we'll see if there is a difference. At least now I'll be able to adjust fuel pressure at will.

But as I said it was beautiful to watch the car taking off in 3rd and 4th. The streetport really has some high end power. I totally smoked couple of cars that tried to race me, including a Volvo station wagon from a stop

Love my car!

 

yup...this one.



bone stock...

just kidding...im just glad that you're getting urself familiarize with the carb. the more u play with it, the more you will understand how it works...

 

sounds like its running great to me man

at least your car runs good :P